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In keeping with the advancements in this sector, updates as and when found
necessary will be hosted in the Ministry website: http://moud.gov.in/ and the

reader is advised to refer to these also.
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No, portion of this document may be reproduced / printed for commercial purpose
without the prior permission of the Ministry of Urban Development, Government of India.
Copy Edited and Published under contract with JICA by

Creative Environmental Consultants, Chennai, www.cec.ind.in
in association with Water Today, Chennai, www.watertoday.org
Printed by : Advantage 4U, New Delhi

While the population of urban areas has increased from 19.9% to 31.2% between 1971 and
2011, the contribution of urban areas to GDP growth has shown a phenomenal increase from 38%
to 60% over the same period. Providing sanitation and hygiene to a growing population of more than
1.21 billion with higher aspiration levels is a major challenge. This increase in population has created
a significantly enhanced demand on water supply, health, hygiene and environmental sanitation.
To tackle this, the Government of India has initiated programs and given policy directions
to States and Cities through interventions like the launch of the Jawaharlal Nehru National Urban
Renewal Mission (JnNURM) and adoption of National Urban Sanitation Policy, 2008. JnNURM seeks
to promote cities as engines of economic growth through improvement in the quality of urban life
by facilitating the States for creation of quality urban infrastructure, with assured service levels and
efficient governance.
The National Urban Sanitation Policy (NUSP), 2008 pertains to management of human
excreta and associated public health and environmental impacts, including 100% sanitary and safe
disposal of human excreta and liquid wastes from all sanitation facilities like sewers and toilets.
I am confident that the revised and updated manual in three parts - Engineering,
Operation & Maintenance and Management will further enable the practicing professionals in
design and operation & maintenance of the sewerage and sewage treatment systems economically,
efficiently and effectively.
I would like to acknowledge the support extended by the Japan International Cooperation
Agency (JICA), Government of Japan and also the efforts of the officials of MoUD in this
endeavour. I am hopeful this effort would contribute towards achieving the Ministry’s vision of the
creation of economically vibrant, inclusive, efficient and sustainable urban habitats.
India is passing through a dynamic phase of development wherein the Government of India
is striving hard to provide all the necessary infrastructure facilities to urban population in order to
achieve sustainable economic growth. As per the 2011 census, the share of urban population is
31.2% as against 28% of 2001 census of the total population of the country which is expected to
be 50% by the mid of the century. Infrastructure facilities being provided for such an unprecedented
growth are unable to meet with the requirement due to various compelling circumstances. Water
supply and sanitation is one of the basic infrastructure facilities, which has a direct impact on the urban
population to meet the desired levels of quantity and quality.
Inadequate and unsafe water supply and sanitation services have a direct effect on the health
of the community and an indirect effect on the economy of the country.The report on “The Economic
Impact of Inadequate Sanitation in India” released by the Water and Sanitation Program (WSP),
World Bank states that inadequate sanitation costs India almost US$ 54 billion (about
Rs. 2.7 lakh crore) or 6.4% of country’s GDP in 2006. In view of this huge cost to be paid for
inadequate sanitation, it is really necessary on all the concerned agencies dealing with water supply
and sanitation sector in the country including the community to find ways for how best this loss to the
nation could be minimized.
I appreciate the cooperation extended by the Japan International Cooperation Agency (JICA)
and the Government of Japan through their financial and expert support in completing this task of
Revision and Updating of the Manual on Sewerage and Sewage Treatment Systems, which was last
published by the Ministry during 1993. Untiring efforts of the experts from JICA Study Team and India
culminated in bringing out such an exhaustive manual in three parts, is worthy of appreciation.
I am confident that the three parts of the manual will certainly achieve the program
objectives of the Government of India as stated in the “National Urban Sanitation Policy” adopted in
2008. I also sincerely hope that this Manual would serve as a guide to policy makers, planners, and all
practicing professionals in the field of sewerage and sewage treatment systems so as make the
systems economically viable to accrue benefits in the long term on a sustainable basis.
Finally, I would like to acknowledge the untiring efforts of all people who are associated with
the task of accomplishing the commendable job of formulation of this exhaustive manual for the
benefit and improvement of the sanitation sector.
Over the years, there has been continuous migration of people from rural and peri-urban
areas to cities and towns. The proportion of population residing in urban areas has increased from
28.0% in 2001 to 31.2% in 2011. The number of towns has increased from 5161 in 2001 to 7935
in 2011. The uncontrolled growth in urban areas has left many Indian cities and towns deficient in
infrastructural services such as water supply, sewerage & sanitation, storm water drainage and solid
waste management.
Sewerage and sewage treatment is a part of public health and sanitation, and according to the
Indian Constitution, falls within the purview of the State List. Since this is non-exclusive, non-rivalled
and essential, the responsibility for providing the services lies within the public domain. The activity
being local in nature, it is entrusted with the Urban Local Bodies. The Urban Local Body undertakes
the task of sewerage and sewage treatment service delivery, with its own staff, equipment and funds.
In few cases, part of the said work is contracted out to private enterprises.
Cities and towns which have sewerage and sewage treatment facilities are unable to
cope-up with the increased burden of providing such facilities efficiently to the desired level. Issues
and constraints that are encountered by the urban local bodies, responsible for providing sewerage
and sanitation facilities, are compounded due to various reasons. The main cause of water pollution
is the unintended disposal of untreated, partially treated and non-point sources of sewage and more
important is its effect on human health & environment.
While the conventional sewerage is an effective system for sewage collection, transportation
and treatment, it also remains as highly resource-inefficient in terms of technology. Consequently,
high capital and recurrent costs for the O&M of this system at a significant level, prohibits its
widespread adoption in all sizes of urban areas in the country.
As per the 2011 Census, only 32.7% of urban households are connected to a piped sewer
system whereas 38.2% dispose of their wastes into septic tanks and 8.8% households are having
pit latrines (single & double, etc.) and 1.7% of households are having other latrines (connected to
open drains, night soil removed by human etc.). About 18.6% of urban households still do not have
access to individual toilets – about 6.0% use public /community toilets and 12.6% are forced the
indignity of open defecation.
According to the report on the Status of Wastewater Generation and Treatment in Class-I
Cities and Class-II towns of India, December 2009 published by Central Pollution Control Board,
Continued
the estimated sewage generation from 498 Class-I cities and 410 Class-II towns (Population
estimated for 2008 based on 2001 census) together is 38,524 MLD, out of which only 11,787 MLD
(30.5%) is being treated with a capacity gap of 26,737 MLD.
The National Urban Sanitation Policy (NUSP) adopted by the Ministry of Urban Development
in 2008 envisions”All Indian Cities and towns become totally sanitised, healthy and liveable and
ensure and sustain good public health outcomes to all their citizens, with a special focus on hygienic
and affordable sanitation facilities for the urban poor and women”. With a view to promote sanitation
very rapidly in urban areas of the country and also to recognise the excellent performance in this
sector by the cities, the Government of India has instituted an annual award scheme for rating of the
cities on certain selected sanitation parameters. The overall goals of NUSP, is to transform the urban
sanitation into community driven, totally sanitized, healthy and liveable.
The Millennium Development Goals (MDGs) enjoins upon the signatory nations to extend
access to improved sanitation to at least half the urban population by 2015, and 100% access by
2025. This implies extending coverage to households without improved sanitation, and providing
proper sanitation facilities in public places to make cities and towns free of open defecation. The
Ministry proposed to shift the focus on infrastructure in urban water supply and sanitation (UWSS)
to improve the service delivery and formulated in 2008 a set of Standardized Service Level
Benchmarks for UWSS as per International Best Practice & brought out the “Handbook on Service
Level Benchmarking” on water supply and sanitation.
The Manual on Sewerage and Sewage Treatment (second edition) published in 1993 mainly
gave thrust to engineering aspects of the sewerage and sewage treatment systems. The topics
additionally covered in the current revised and updated revision are emphasis on O&M and
management of sewerage and sewage treatment systems, not dealt with in detail in the earlier
edition and are to create awareness amongst the practicing and field engineers on the importance of
sustainability of the systems in the long-term. The present Manual on Sewerage and Sewage
Treatment Systems has been divided into three parts, as Part – A on ‘Engineering’, Part – B on
‘Operation and Maintenance’, and Part – C on ‘Management’.
On behalf of the Ministry I would like to highly appreciate and acknowledge the financial and
physical support provided by the Japan International Cooperation Agency (JICA), Government of
Japan for the preparation of this exhaustive and informative manual.
The Ministry of Urban Development places on record its appreciation of the Expert
Committee for the revision and updating of the Manual on Sewerage and Sewage Treatment
Systems and the untiring services rendered by Dr. M. Dhinadhayalan, Joint Adviser (PHEE) &
Member Secretary of the Expert Committee who acted as the fulcrum between the Ministry of Urban
Development, GOI and the Japan International Cooperation Agency (JICA) to maintain an extremely
balanced relation throughout the period of preparation of the Manual so as to accomplish the task.
I also extend my thanks to all those people who were directly or indirectly instrumental in
giving such a praise-worthy shape to the manual
Ever since the publication of the Manual on Sewerage and Sewage Treatment in 1993
a number of new developments and changes have occurred in the range of technologies for
on-site and off-site sanitation systems, including collection, transportation, treatment and reuse of
treated sewage & sludge for various uses during the last two decades. While revising the Manual
a broad approach was adopted for the need for revision and updating of the manual on the three
important aspects, such as i) Engineering, ii) Operation & Maintenance, and iii) Management of
sewerage and sewage treatment systems. Additional topics on operation & maintenance and
management were added so as to create awareness amongst the practicing and field engineers
regarding the importance of these two topics for the long-term sustainability of the systems.
The revision and updating of the existing manual (1993), aims to meet the important
requirement of providing advice on the technology options for urban sanitation, for the new
infrastructure or upgrading of existing services. It is applicable both for small interventions in specific
locations and for larger programs that aim to improve sanitation on a citywide scale. The manual
would help the practitioners in the selection of technologies with various options for providing
techno-economic solutions keeping in view the health of the community and safeguarding the
environment so as to provide a wide range of options to the planners and designers.
The National Urban Sanitation Policy (NUSP) was adopted by the Ministry of Urban
Development (MoUD) in 2008. It envisions that “All Indian cities and towns become totally
sanitized, healthy and liveable and ensure and sustain good public health and environmental
outcomes for all their citizens with a special focus on hygienic and affordable sanitation facilities for
the urban poor and women”. With a view to promote sanitation very rapidly, in urban areas of the
country and also to recognise the excellent performance in this sector by the cities, the
Government of India (GOI) instituted an annual award scheme for rating of cities on certain
selected sanitation parameters. The overall goal is to transform Urban India into community driven,
totally sanitized, healthy and liveable cities and towns.
In view of the importance attached and impetus given to sanitation by the GOI in cities and
towns of the country, the MoUD decided to revise and update the existing Manual on Sewerage and
Sewage Treatment under the aegis of Japan International Cooperation Agency (JICA), who
appointed a JICA Study Team (JST) in July 2010 comprising of experts from Japan.
The JST visited about 40 Sewage Treatment Plants across 8 States during 2010-2011 and
gathered first-hand experience on planning, implementation and O & M of sewerage systems and
factual knowledge on the social, engineering, financial and management issues relevant to India.
The JST retained an Indian Study Team (IST) to assist in the preparation of the manual.
Continued
The MoUD constituted 3 Expert Committees (ECs) (Annex-1) (1st & 2nd in August 2010 and
the 3rd in November 2011) by nominating experts from Central Ministries / Departments, academic
& research institutions, senior engineers from State Departments & Utilities for reviewing and
finalizing the drafts of the JST. Two numbers of each one week long study tours were conducted in
November, 2011 and January 2012 by JST for the members of the EC to study the sewerage and
sewage treatment systems in Japan. This helped the members of the EC to get the first hand
information on the technologies adopted in sewerage and sewage treatment and how the sewerage
systems are being operated and maintained. The tours were facilitated by JICA.
The ECs, JST and IST interacted in 16 meetings at New Delhi to give a final shape to all the
three parts of the manual. The manuals prepared by the JST, ECs and IST address the following. :
Part – A on ‘Engineering’ addresses the core technologies and updated approaches towards
the incremental sanitation from on-site to decentralized or conventional sewerage systems including
collection, conveyance, treatment and reuse of the misplaced resource of sewage and sludge and
is simplified to the level of the practicing engineer for the day-to-day field guidance in understanding
the situation and coming out with a choice of approaches to remedy the situation.
Part – B on ‘Operation and Maintenance’ addresses the issues of standardizing the human
and financial resources. These are needed to sustain the sewerage and sanitation systems which are
created at huge costs without slipping into an edifice of dis-use for want of codified requirements for
O&M so that it would be possible to address the related issues. These financial and related issues
are to be addressed at the estimate stage itself, thus enabling to seek a comprehensive approval of
fund allocations and human resources. This would also usher in the era of public private partnership
to make the projects self-sustaining. This also covers aspects such as guidelines for cleaning of the
sewers and septic tanks besides addressing the occupational health hazards and safety measures
of the sanitation workers.
Part – C on ‘Management’ is a refreshing approach to modern methods of project delivery

and project validation and gives a continual model for the administration to foresee the deficits in
allocations and usher in newer mechanisms. It is a tool for justifying the chosen project delivery
mechanism and optimizing the investments on need based allocations instead of allocations in
budget that remain unutilized and get surrendered in the end of fiscal year with no use to anyone.
These draft manuals were discussed with an All India audience in the 2 National Workshops
held at New Delhi on 20th & 21st September 2012 for finalization of Part A: Engineering and on
21st & 22nd January 2013 for finalization of Part B: Operation & Maintenance and Part C:
Management, where in delegates from Central Ministries, State Government Departments, Urban
Local Bodies, Parastatal Agencies, and representatives from Technology Providers participated
and deliberated in detail regarding the contents of each part of the three manuals. These were
further reviewed and brought to completion by the Editorial committee constituted by the MoUD with
members as in (Annex-2). In all, 6 meetings of the Editorial committee were held at New Delhi.
The Editorial Committee while editing the Manual kept in view the TOR prescribed by the
Ministry and also comments, suggestions, views offered by the delegates who participated in
National Workshops and views received through e-mail were also accommodated suitably wherever
necessary in all the three parts of the manual.
Continued
The Expert Committee places on record its gratitude to:
• The MoUD for the necessary support & encouragement in the preparation of the manual
• The JICA for funding the meetings, study tours, workshops and publishing the manuals.
• The PHE Departments, Water & Sewerage Boards, Urban Local Bodies, and individuals for
their valuable suggestions on the draft of the manual.
The Expert Committee is highly indebted to Mr. Akira Takechi, JICA Study Team Leader for
his wonderful guidance, whole hearted support and encouragement of the members of the Expert
Committee during the entire period in fulfilling the task of preparation of the Manual.
The Expert Committee expresses its gratitude to Dr.S.Sundaramoorthy, Consultant, JST,

Team Leader IST & Member Secretary, Editorial Committee as the architect of the manual and his
team for giving final shape to all the three parts of the Manual.
I would like to extend my sincere thanks to Dr.S.R.Shukla, Former Adviser (PHEE), CPHEEO,
MoUD, Co-Chairman of the Expert Committees, for chairing all the Expert / Editorial Committee
meetings and for his continued involvement, guidance and support in preparation and finalization of
three parts of the manual.
I express my sincere thanks and gratitude to Ms.E.P.Nivedita, then Director (LSG), for
taking the initial efforts through coordination and chairing the deliberations of the EC meetings
in laying a broader framework for revision and updation of the Manual.
I am also privileged to express my sincere thanks on behalf of the Expert Committee to

Ms.Veena Kumari Meena, then Director (LSG) and Ms.Nandita Mishra, Director (PHE) for their
support in finalization of the Manual.
The contribution made by Mr.V.K.Chaurasia, Joint Adviser (PHEE), Mr.J.B.Ravinder, Deputy

Adviser (PHE), Mr. A.K. Saha, Assistant Adviser (PHE), and Dr.Ramakant, Assistant Adviser (PHE),
CPHEEO for enriching the contents of the Manual is very much appreciated. The painstaking efforts
taken by Dr.Ramakant, Assistant Adviser (PHE) and Member-Coordinator, during the entire process
of preparation of the Manual is stupendous and laudable.
A special mention and deep appreciation is due for the meticulous and diligent efforts of
Dr.S.Saktheeswaran, Editorial Consultant (JICA) & Copy-Editor to JICA for bringing out the manual
in a concise form, through several stages of editing and incorporating all the feedbacks.
The help and contribution by Mr. Takashi Sakakibara, JICA expert, CPHEEO and
Mr.C.Krishna Gopal, Consultant, NUSP Cell is highly appreciated.
The Committee also acknowledges the contribution and support of the representatives of
SMEC India Pty Ltd for the first phase of the study and CH2M HILL for the second phase of the study
for their excellent logistics support and facilitation throughout the period.
I would like to acknowledge all those connected individuals, organizations, institutions,

Bilateral and Multilateral agencies for their efforts directly and indirectly, through their valuable
contribution, suggestions and inputs.
The list of Editorial Committee members is in the next page
Part B: Operation and Maintenance
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CHAPTERS
Part B: Operation and Maintenance CHAPTER 1: INTRODUCTION
CHAPTER 1: INTRODUCTION
In engineering parlance, the term operation refers to the daily operation of the components of a
sewerage system such as collection system, sewage pumping stations (SPS), pumping mains,
sewage treatment plants (STP), machinery and equipment, etc., in an effective manner by various
technical personnel, and is a routine function. The term maintenance refers to the art of keeping
the structures, plants, machinery and equipment and other facilities in optimum working order
and includes preventive maintenance or corrective maintenance of mechanical adjustments,
repairs, and planned maintenance. However, replacements, correction of defects etc., are
considered as actions excluded from preventive maintenance. For replacements with regard to
sewerage and sewage treatment, the broad categories of infrastructure, which need to be
addressed are as follows:
1. Collection System including house service connections and manholes

2. SPS
3. Pumping Mains
4. STP
5. Utilities for biological sludge management and containment of chemical sludge
There are standard Operation and Maintenance (O&M) manuals for these in developed countries.
However, in India such a standard O&M manual has not yet been prepared in detail. Hence, the
following conditions prevail:
1. Most of the towns are only partially sewered.

2. Most of generated grey water continues to flow into road side drains.
3. Per Capita water supply is low in many cities for providing conventional sewerage system.
4. Water is used mainly from local groundwater with high TDS, sulphates etc.
5. The sulphates are an agent of corrosion of concrete in sewers.
6. Wash basins, kitchen sinks etc. do not have blenders below the sink.
7. Detergent powders have significant grit content.
8. Cattle are also housed inside the cities and their dung washed into sewers.
9. The cattle shed washing occurs during noon times after the peak sewage flow has passed.
10. The dung from the cattle shed settles, builds up and chokes the sewers.
11. The budgets of most ULBs are inadequate for purchasing sewer cleaning machines.
12. Though sewer divers are banned, still manual labour is used to “rod” and clean the sewers.
13. Pumping stations are not connected by website to know of flooding in the command area.
14. Removing sewer blocks take longer times due to problem of manual work.
15. Instrumentation based remote operation of STPs is a far away prospect.
16. Except a few metro cities, all records continue to be in handwritten hard formats only.
17. There are no newsletters aimed at operators sharing their experiences.
18. The above position is further complicated by many local languages.
19. Disposal of solid wastes by the public into sewer manholes.
1-1
These issues as in Indian conditions are directly in contrast to the situations in advanced countries
and makes it necessary to evolve an O&M manual specific to the Indian conditions.
1.1 NEED FOR O&M
According to the National Urban Sanitation Policy (NUSP), the proper operation & maintenance of all
sanitary installations requires:
a. Promoting proper usage, regular upkeep and maintenance of household, community and public
sanitation facilities

b. Strengthening ULBs to provide or cause to provide, sustainable sanitation services delivery
There is an O&M manual by CPHEEO for water supply systems, but there is no such manual
for sewerage systems. Moreover, unless there is an O&M manual, ULBs cannot justify budget
allocations to meet their obligations under such a manual. The net result is this lack of attention to
the important aspect of O&M of sewerage systems leads to deterioration of the useful life of the
systems necessitating premature replacement of many system components and also affecting
overall sanitation. As such, even after creating the assets by investing millions of rupees, they are
unable to provide the services effectively to the community for which they have been constructed, as
they remain defunct or underutilized most of the time.
Some of the key issues contributing to the poor O&M have been identified as follows:
1. Lack of finance and inadequate data on O&M.

2. Multiplicity of agencies, overlapping in their responsibilities.
3. Inadequate training of personnel.
4. Lesser attraction to maintenance jobs in career planning.
5. Lack of performance evaluation and regular monitoring.
6. Inadequate emphasis on preventive maintenance.
7. Lack of operation manuals.
8. Lack of appreciation of the importance of facilities by the community.
9. Lack of real time field information, etc.
10. O&M contractors not having permanent staff.
11. Connection of road gullies to sanitary sewer systems, which are major contributors of silt and
floating matter such as plastic bags, wood pieces, papers, etc.
12. Lack of storm sewer system.
13. Wastage of potable water, due to supply of unmetered water supply at cheap water tariff and
free water connections, which add to the load of domestic sewage.
14. The silting of sewer system is a common phenomenon and is compounded by low per capita
water supply.
Therefore, there is a need for clear-cut sector policies and legal framework and a clear
demarcation of responsibilities and mandates within the water supply sub-sector.
1-2
From the Indian experience, it has been observed largely that about 20 to 40% of the total annual
O&M cost goes towards the salary of the O&M staff, 30 to 50% of the cost is incurred on power
charges and the balance alone is utilized for consumables, repairs and replacement of parts and
machinery and miscellaneous charges. In most of the cities in India, the tariffs are so low
that they do not even cover the annual O&M cost. Hence, it is a felt need to bring out this O&M
Manual in sewerage systems encompassing various issues pertaining to an effective O&M such
as technical, managerial, administrative, personnel, financial and social aspects etc. At present,
there is no technical manual on this subject to benefit the field personnel and to help the O&M
authorities to prepare their own specific manuals suitable for their organizations. Therefore, CPHEEO
has under the aegis of the Japan International Cooperation Agency (JICA) made plans to publish the
O&M manual for Indian sewerage system.
1.2 BASIC CONSIDERATIONS OF O&M
1.2.1 Laws and Regulations related to O&M of Sewerage System
In fact, there are no laws directly related to O&M of sewerage systems. The laws which are
generally applicable are invariably the municipal bye-laws, that are of general nature. The GOA
Sewerage System and Sanitation Services Management Act, 2008 mentioned in Appendix C 2.2 of
part C of the manual may be suitably amended and adopted by the states to clearly mandate that not
taking sewer connection can be a cognizable offence so that the levy of penalties or disconnection of
other services will have the necessary legal validity to avail the central support.
1.2.2 Effluent Standards related to Sewage Treatment Plants
The effluent standards related to STPs are confined to BOD of less than 20 mg/L and SS of less than
30 mg/L and are more of historical nature.
1.2.3 Environmental Considerations
There are generally problems with industrial effluents which get into sewers and are difficult
to control. A conflict exists between the prevention and control of Water Pollution Act and the
Municipal Act or Jal Nigam Act or Water and Sewerage Board Act. The sewer system is to be
maintained by the municipality, Jal Board or Water Supply and Sewerage Boards. However, the power
to sanction a connection of the industrial effluent that is discharged in the sewers is not with these
agencies, but with the Pollution Control Board (PCB). The trouble is when industries are detected to
be discharging their effluents without the necessary treatment; the said local agencies do not have
legislative powers to put the industry on notice. They have to write to the PCB but the PCB are in no
hurry to immediately look into this specifically because for the entire metro city, the PCB may have
only a handful of engineers and they have many other situations like these to handle. Hence,
the backlog is high. Even if a legal process is initiated, getting the orders of the court to effect
disconnection of sewer connection is difficult. It looks that one simple way of getting over these is to
allow the industry to connect only their toilets, baths, canteen etc. But the real problem is the industries
may be surreptitiously using that connection to discharge their effluents also. The monitoring of these
is vested with the PCB. Thus, a very serious situation exists here. Hence, a joint subcommittee of
ULB and PCB has to be created with legal powers to recommended interim disconnections.
1-3
1.2.4 Budget
Appropriate budgetary provisions for the O&M of sewerage system need to be provided so that
O&M is carried out without any constraints such as human resources and finance. These are dealt
with in part C of the manual.
1.2.5 Preventive Maintenance
Preventive maintenance is a set procedure whereby each component of the system goes through
a systematic check and these components are brought into dependable use. An example can be,
checking the volume of oil and its consistency in the gearbox after a specified number of hours of
operation and correcting the situation either by topping up or by replacing fully as needed. The
preventive maintenance issues, checking parameters and timings are all given by every equipment
vendor as a manual. Carrying out these tasks is to be done by the respective equipment vendor
under a separate contract called preventive maintenance contract and should be delinked from the
O&M contract. Most often this is not fully recognized and what could have been saved by preventive
maintenance finally ends up as “breakdown repairs.” This situation needs the required importance
for improved efficiency.
1.2.6 Workmanship and Quality of Equipment
Workmanship is defined as the art or skill of a worker with which something is made or executed.
Materials and equipment shall be new and of a quality equal to or superior to that specified or
approved. Work shall be done and completed in a thorough and competent manner, in strict
conformity with the plans and specifications. In general, the work performed shall be in full
conformity and harmony with the intent to attain the best standards of construction and equipment of
the work as a whole or in part.
No material shall be used in the work until it has been found satisfactory by the Engineer. All
material and equipment are subject to test to determine their conformity with these specifications.
Certified factory and mill tests normally will be acceptable for standard manufactured items. Whenever
standard specifications are referred to, they shall be the latest revised edition. All work and materials
shall be subject to inspection by the engineer.
The engineer may assign such assistants as he may deem necessary to inspect the materials to be
furnished and the work to be done and to see that the same is strictly in conformity. The engineer
shall be notified of the time and place of preparation, manufacture or construction of material for
work or any part of the work, which he may wish to inspect, and of the time and place of making the
factory tests required under the contract. Such notification shall be given a sufficient length of time
in advance of the beginning of the work on such material or part or of the beginning of such test to
allow arrangements to be made for inspecting and testing or witnessing, as the case may be, if such
inspection and testing or witnessing are deemed practicable by the engineer.
All necessary machinery guards, railings and other protective devices shall be provided as specified
by the Industrial safety authority, which would be the Inspectorate of Factories (IoF). Before final
acceptance of the work, the contractor shall cause an inspection to be made by a representative of
the IoF and got certified that all safety requirements have been complied with.
1-4
1.3 OUTLINES OF O&M
1.3.1 Overview and Contents of O&M
Thus, an overview of O&M is taking note of the above issues and suggest appropriate remedies to
a given situation which includes finances and manpower and remote control.
1.3.2 Management of Facilities
Proper housekeeping, aesthetics and gardening are the requirement here. With the lifestyle in cities
changing to fast-forward, nobody is able to find time for these. In addition, getting labour to do these
is also difficult due to extra costs safety and security issues.
1.3.3 Schedule of O&M
A proper schedule shall have to specify what things are to be attended to at what intervals and to
whom it is to be reported to in case of faults. Clearly, this is not the case and it is all emergency
repairs all the way.
1.3.4 Response to Accidents
Mostly, the local staff may not even know how to do first aid. Hence, whenever an accident occurs, it
is the fire brigade that is called to the site. Thereafter, it is a standard procedure of getting the victim
to the hospital and thereafter the local agencies come into the picture only when defending the
compensation money payable to the victim.
1.3.5 Management of Buildings and Sites
There is the century old practice in Public Works Department (PWD) that the age of civil works is
30 years and for equipments is 15 years. Hence, civil works in sewerage will need strengthening
and renewal as the case may be. Similarly, equipments will need replacement in 15 years. However,
in actual practice, this is not the case. Only when a civil work shows up a crack or a leaky roof, the
position is reviewed as an ad hoc repair. Similar is the case of machineries.
1.4 ORGANIZATION OF O&M
1.4.1 Description of O&M Work
A simple understanding of O&M work is the relationship between human resources, equipment
availability, financing the O&M and career opportunities for the staff. These are within the local body.
The perception by the public and their payment of dues to the local body is the “other side of the coin”
as in Figure 1.1 overleaf.
This illustrates O&M of sewerage as responding to the four-sided compression of (a) limited budget,
(b) performance requirements, (c) less public acceptance and (d) higher legal requirements. If all
these act at the same time, the system may collapse and if one of them increases the pressure, the
ability of the other three needs to be resilient for the system to remain stable.
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Source: Ype C Wijnia, 2009
Figure 1.1 Combined Tasks and Challenges with the O&M
If this resilience is not there, the shape of the rectangle will be altered and the system may
respond without any control. Thus, the work of O&M involves the engineering, financing and
administrative interface with the public.
1.4.2 Deployment of Manpower
There are limited promotional avenues for people in the O&M sector. Non-engineers in the O&M
sector entering the service more often retire without any promotion if he has not advanced in
academic qualifications. This does not give them any drive to exhibit an involvement in the job all the
time as he will be doing a routine type of work.
Promotions by way of number of years of experience must be coupled with examination of his
experience and given weightage.
The staff may be rotated between sewerage and water supply sectors by providing suitable
training, so that he / she does not get into sickness from working in sewerage system throughout his
career. Incentives for career advancement of operators like, for example, timescale in ULB services
and additional allowances such as risk allowance or such other chances have to be explored to
ensure efficient O&M of sewerage systems.
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1.4.3 Outsourcing of O&M
Recent trend is to subcontract the O&M work. In this case, the contractor hires staff from local market
and deploys them on the O&M work. He will only place the staff and earn the money and after paying
to the staff earns his profit, but he may not have interest in O&M. If the contractor is also from the same
firm who has built this sewerage system, his interests may be more sincere. In the case of exclusive
O&M outsourcing not involving the potential O&M agency in the construction activity of the system
involved, the proper qualifications, experience, personnel, etc., are to be ensured.
Improvements to the existing system for better O&M can be identified by the O&M contractor,
but it has to be separately authorized by the ULB either to the O&M contractor himself or to
another O&M contractor.
1.4.4 Key criteria for selection of O&M contractor
The qualification for a contractor to be awarded an O&M contract by the ULB shall include not
only the qualification of the contractor firm itself in previous O&M works but also the CV and
qualification and adequate experience of key personnel in the O&M staff mentioned in the
document. The ULB should ensure that such personnel to be engaged for O&M shall be given training
during the O&M period through the existing training institutes of major utilities / ULB’s in the
region and this should be mandated in the tender document for outsourcing of the O&M work.
Incentives for career advancement of operators like, for example, timescale in ULB services and
additional allowances such as risk allowance or such other chances have to be explored to ensure
efficient O&M of sewerage systems.
1.4.5 Training
Development of operational skill is not taught in the schools, polytechnics or colleges. It has to be
learnt. This again must be verified once a year to understand whether the operator has understood
these correctly, and if not in order then he has to be put through a specific training. Thus, the training
is a continual system. The training institutes should orient the training of the operators with specific
reference to the O&M manual of the STP from which the operators are drafted for the training. In
addition some of the fundamental aspects shall also be included.
1.4.6 Monitoring through Information Control Technology
Extracting sewage treatment conditions from water quality information of the treated sewage is very
important for operating a STP effectively. An example of a Japanese STP implementing and using
monitoring using control technology is in Appendix B 1.1
1.4.7 Database for Effective O&M
It is also important to create a database of information obtained through monitoring, and to use this
database of past data for operation henceforth. Appendix B 1.2. contains such a database.
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1.4.8 Problems in Existing O&M
The problems faced by O&M sector in sewerage are a combination of engineering, finance, staff and
management. The engineering problems are absence of adequate innovations of economical design
and construction of infrastructure that will reduce the costs and will still render the project functional
to the stated goals in the required geographical coverage with lesser expenditure. Examples are
possible usage of decentralized systems, twin drain systems and incremental sewerage etc. The
finance problems are inadequate revenue as compared to expenditure and norms for budget
allocation, which is more of historical nature than based on time and motion evaluations as also the
symbiosis of the population, who are willing to pay only if they feel services are better on the one
side and the ULB, who cannot bring up improvements unless the population contributes increased
revenue upfront. The staff problems are the lack of promotional avenues for decades on end and
also absence of at least the time based scale of pay resulting in inordinate stagnations in posts and
staleness especially the field staff like operators, technicians, drivers and other such posts where
practically they enter and retire in the same post. The management problems are frequent transfers
from one headquarters to another resulting in disturbances to family establishment, education of
wards and care of elderly at home and lack of incentives for exceptional performers. These are very
easy to attribute but are very difficult to change given the service conditions, rules, regulations etc.
Yet another situation which prevails in democratic governance is to appraise the political governance
on the nuances of engineering projects while seeking funds and establishment by putting forth the
engineering components and need to explain to them convincingly by the chief executive of the
water and sewerage authority, depending on how equipped they are to comprehend the enveloping
issues. There seems to be a need to position the officers of these organizations who would possess
a basic qualification in related engineering whatever be their other attainments in management so
that they can effectively conceive and communicate both ways between the political governance who
are to deploy the necessary resources and the staff of these organizations who are to implement
and carry out the O&M, an aspect in which a country policy seems to be not in place. In addition,
please also refer to Appendix B 1.3, which is an extract from the Evaluation of O&M of STPs
in India – CUPS/68/2007.
1.5 COMMUNITY AWARENESS AND PARTICIPATION
1.5.1 Public Relations and Public Opinion related to Sewerage Works
Meeting the public and directly answering their questions on sewerage problems is the solid
foundation of goodwill. Mostly officials in charge of sewerage system feel hesitant to meet the public
because they do not have the funds to rectify the defects pointed out by the public. Reference to
Figure 1.1 is important. Only when the public are met directly, the system drawbacks will come to
light. Only then, a basis for calculating the budget allocations can be known. Only then engineers in
the field can carry out the remedies needed.
1.5.2 Complaint and Redressal
Most local bodies have launched the internet-based recording of complaints by the public. It will be
good to also publish on the web the actions to solve them. Otherwise the public will not know.
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1.5.3 Do’s and Don’ts for Community
The public are also responsible to help maintain the system and must not put solid wastes,
vegetable cut bits, meat, plastics, etc, into sewers. This is very well advertised by many ULB’s,
but the public continue to do so. Educating them continuously is needed.
1.6 POTENTIAL RISK WITH RESPECT TO SEWERAGE SYSTEM
1.6.1 Provision of Disaster Prevention Systems
Disaster by definition is something that occurs suddenly. For example, a corroded RCC sewer
not properly attended to on time, will collapse all of a sudden in the crown and all the sewage
upstream will get blocked. At the same time, if an earthquake occurs and the sewer collapses
by lateral movement, then also, it is the same problem. The former situation can be avoided by
monitoring the sewer condition once a year by an in-situ camera survey. The latter cannot be
avoided. The lesson is the need for programmed monitoring of sewerage system components.
1.7 SEWERAGE LEDGER
The NUSP & SLB are explained in Sections 1.5 and 1.7 of Part-A of the manual. In order to keep
track of their attainment, the upkeep of ledgers is necessary as explained below.
1.7.1 Preparation of Sewerage Ledger
A sewerage ledger can be either a simple ledger or a complicated ledger. The staff must receive
situation reports of such activities, which they can control. There is a tendency to insist on receiving
all sorts of data, whether that is meant for that person or not. This has to change. For example, an
administrator must be more concerned about complaint redressal than how much sewage is pumped
out. Similarly, the field engineer must know the sewage surface elevations in sewers and whether
sewage is overflowing the roads and document the case and put up for funds to solve the situation.
1.7.2 Management and Use of Sewerage Ledger
This has to be done by an independent team not connected with the O&M team. Only then, the real
problem will be known and remedies can be taken up. The sewer ledger for compliant redressal must
be put on the website to increase the consumer satisfaction in the ledger system.
1.8 BUDGET ESTIMATION FOR O&M
Budget estimation has been explained in Chapter 5 of part C of the manual. Revenue generation
to ensure self-sustainability is a political issue, and administrative will is needed to levy and collect
practicable costs and there is nothing to strategize in it.
1.9 SUMMARY
This manual has been prepared with the aim of offering guidelines to workers/operators of
sewerage systems on site for O&M and work performed by them, and to the field engineers for
passing on instructions and judgments to the workers and operators.
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In practice, a sewerage collection system or an STP requires its own proprietary O&M manual
suitable for the work done, the local conditions and the scale of its own facility. It is anticipated that
these facilities will refer to the contents of the present manual and prepare and make effective use
of its own proprietary manual.
1.10 RELATIONSHIP BETWEEN PART-A (ENGINEERING), PART-B (OPERATION AND

MAINTENANCE), AND PART-C (MANAGEMENT) OF MANUAL
The present manual is one of a set of three parts and which are interdependent as under:
i) Part – A on ‘Engineering’
ii) Part – B on ‘Operation and Maintenance’
iii) Part – C on ‘Management’
Part – A on ‘Engineering’ addresses the core technologies and updated approaches towards the
incremental sanitation from on-site to decentralized or conventional collection, conveyance,
treatment and reuse of the misplaced resource of sewage and is simplified to the level of the practicing
engineer for day to day guidance in the field in understanding the situation and coming out with a
choice of approaches to remedy the situation. In addition, it also includes recent advances in sewage
treatment and sludge & septage management to achieve betterment of receiving environment. It is
a simple guideline for the field engineer.
Part – B on ‘Operation and Maintenance’ addresses the issues of standardizing the human and
financial resources. These are needed to sustain the sewerage and sanitation systems which are
created at huge costs without slipping into an edifice of dis-use for want of codified requirements for
O&M so that it would be possible to address the related issues. These financial and related issues
are to be addressed at the estimate stage itself, thus enabling to seek a comprehensive approval of
fund allocations and human resources. This would also usher in the era of public private partnership
to make the projects self-sustaining. This also covers aspects such as guidelines for cleaning of the
sewers and septic tanks besides addressing the occupational health hazards and safety measures
of the sanitation workers.
Part – C on ‘Management’ addresses the modern methods of project delivery and project validation
and gives a continual model for the administration to foresee the deficits in allocations and usher in
newer mechanisms. It is a tool for justifying the chosen project delivery mechanism and optimizing
the investments on need based allocations instead of allocations in budget that remain unutilized and
get surrendered at the end of the fiscal year with no use of the funds to anyone in that whole year.
It is a straight forward refinement of a mundane approach over the decades.
It is important to mention here in the beginning of Part- B of the manual that trade names and
technology nomenclatures, etc., where cited, are only for familiarity of explanations and not a
stand alone endorsement of these.
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Part B: Operation and Maintenance CHAPTER 2: SEWER SYSTEMS
CHAPTER 2: SEWER SYSTEMS
2.1 INTRODUCTION
A sewerage system consists of the following:

• House Service Connections
They connect the house to sewers in the road.
• Sewers
These are pipes or conduits meant for carrying sewage and are laid along the roads and flow by gravity.
• Lift Stations
When sewers are at a deeper depth, lift stations are used which help to move sewage from lower
elevations below the ground to the required higher elevation.
• Pump Stations
They transfer the sewage from one location to another.
• Sewage Treatment Plants
They treat the sewage to meet the permitted discharge qualities.
• Safe disposal system of final effluent
The sewers are the most important part of a sewerage system.
They are laid below the ground and are difficult to repair. Hence, great care is needed in their O&M
and the following issues are addressed
• Objectives of maintenance
• Type of maintenance
• Necessity of maintenance
2.1.1 Objectives of Maintenance
Quality maintenance of sewerage system consists of the optimum use of labour, equipment, and
materials to keep the system in good condition, so that it can accomplish efficiently its intended
purpose of collection of sewage.
2.1.2 Type of Maintenance
There are three types of maintenance of a sewerage system – preventive, routine and emergency.
Preventive or routine maintenance should be carried out to prevent any breakdown of the system
and to avoid emergency operations to deal with clogged sewer lines or over flowing manholes or
backing up of sewage into a house or structural failure of the system.
Preventive maintenance is more economical and provides for reliability in operations of the sewer
facilities. Emergency repairs, which would be very rare if proper maintenance is carried out well, also,
have to be provided for. Proper inspection and preventive maintenance are necessary.
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2.1.3 Necessity of Maintenance
Sewer maintenance functions are most often neglected and given attention only as emergency
arises. Adequate budgets are seldom provided for supervision, manpower and equipment, unlike
the case for maintenance of other utilities like electric cables, telephone cables, gas and water
mains. Such attitude towards sewer maintenance is found even in large cities. Considering the health
hazards that the public at large has to face, it is appropriate to provide sufficient funds to take care of
men, material, equipment and machinery required for efficient maintenance.
All efforts should be made to see that there is no failure in the internal sewerage system of premises;
a serious health hazard results when sewage backs up through the plumbing fixtures or into the
basements. The householder is confronted with the unpleasant task of cleaning the premises after
the sewer line has been cleaned. Extensive property damage may also occur, particularly where
expensive appliances are located in the basements.
Maintenance helps to protect the capital investment and ensures an effective and economical
expenditure in operating and maintaining the sewerage facilities. It also helps to build up and
maintain cordial relations with the public, whose understanding and support are essential for the
success of the facility. The ULBs must ensure that sewerage systems are given their due importance
to improve the sanitation in the country.
2.2 INSPECTION AND EXAMINATION OF SEWER
2.2.1 Importance of Inspections and Examinations
Sewer collection systems are intended to be a reliable method of conveying sewage from
individual discharge to sewage treatment plants. Inspection and examination are the techniques
used to gather information to develop operation and maintenance programmes to ensure that new
and existing collection systems serve their intended purposes on a continuing basis. Inspection and
testing are necessary to do the following:
• Identify existing or potential problem areas in the collection system,

• Evaluate the seriousness of detected problems,
• Locate the position of problems, and
• Provide clear, concise, and meaningful reports to supervisors regarding problems.
Two major purposes of inspection and examination are to prevent leaks from developing in the
sewers and to identify existing leaks so they can be corrected.
A designer’s mistake and the failure in construction are directly responsible for many of the sewer
failures. Due to age, deterioration of the material of the sewer by attack of hydrogen sulphide or
other chemicals, settlement of foundations and leaking joints may result in the structural failure of the
sewer. It takes a very long time from the onset of the first initial defect to the collapse of the sewer.
A crack or a leaking joint will allow subsoil water and soil mixture to enter the sewer causing cavities
around it leading to slow settlement of foundation and the eventual collapse of the sewer.
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Very often soil with water is carried away below the bedding along the length of the sewer. The type
of failures often gives a clue to the cause. A shear failure due to faulty foundation or movement of
earth is a clean vertical break in the pipe or barrel. Excessive loading, either internally or externally,
causes horizontal breaks. Breaks caused by internal pressure leads to cracks in the sewer while
external overload causes the top of the pipe to be crushed. Regular inspection of the sewer can
pinpoint the sewer that needs to be attended to before there is a complete failure or collapse. For
preventing the above serious instances of damages to the sewer system, the maintenance engineer
should establish adequate inspection and examination programmes.
2.2.2 Guidelines for Inspections and Examinations
Documents and data that can give information on the status of sewer facilities are necessary for
operation and maintenance of the facilities. However, enormous time and costs are necessary for
examining and inspecting the overall information on sewer facilities that extend over a wide area.
It is recommended that a preliminary inspection be implemented to acquire with comparative ease

documents and data that can be used to decide the facilities to be examined/inspected and their
priority, and then decide the facilities to be finally examined and inspected for effective acquisition of
data. The methodology is to first acquire the basic information through preliminary inspection for the
examination and inspection of the facilities in a given length or area of the sewers as given below.
The detailed method for conducting a preliminary inspection is described in the following section
2.2.3 Preliminary Inspection
During the preliminary inspection of the sewerage system, subsidence, collapse, and overflows on
the roads on which sewers are laid, should be confirmed. Deformation or damage to facilities, and
deposits of sand and silt are to be confirmed during observation from the manhole. If damage or
possibility of damage to the facility or if any of the abnormalities listed below are confirmed during
the preliminary inspection, the facility manager should examine and inspect the relevant locations for
the following:
• Corrosion, wear, damage or crack in the facility

• Water infiltration
• Corrosion of steps, wear of covers, deformation of manhole, buried manhole
• Abnormal odours
• Clogging and overflowing
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The suggested period of preliminary inspection is based on the best professional judgment
prevailing in Indian conditions and shall be carried out as in Table 2.1, Table 2.2 and Table 2.3. In
addition, clause 3.10 of Part A manual also deals with tracer study.
Table 2.1 Preliminary inspection during Defect Liability Period (DLP)
Table 2.2 Preliminary inspection for Manholes & Sewers
Table 2.3 Preliminary inspection period for other facilities
Note: Remedial measures should be implemented immediately upon finding defects /

distress/dysfunction in the components of the sewerage system.
2.2.4 Type of Inspections and Examinations
In order to assess the condition of the sewers inspections and examinations are necessary.
There are two basic types of inspection and examination:
• Direct
• Indirect
2.2.4.1 Direct Inspection and Examination
This means a person walking through a sewer before it is commissioned and physically inspecting
the condition visually. This shall never be done once a sewer has been put into service.
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Even for new sewers, the inside diameter shall be more than 2 m. All safety precautions needed for
working in confined spaces shall be taken. Hitting at the sidewall with a hammer or other devise shall
be totally prohibited. The only purpose it will serve will be to get a visual idea of whether the pipe
joints are made fully. Once a sewer is put into service, this practice is to be banned forever.
2.2.4.2 Indirect Inspection and Examination
The indirect inspection and examination of the sewers is mentioned in Table 2.4.
Table 2.4 Methods of indirect inspection and examination of the sewers
Source: EPA/600/R-09/049 | May 2009
Even though there are so many technologies available as above, the technology to be chosen will
depend on the affordability by the user departments. A simpler and applicable technology compilation
is as shown in Table 2.5 overleaf.
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Table 2.5 Sewer System Inspection Technologies considered applicable to Indian conditions
The light and mirror is the oldest of known technologies is shown in Figure 2.1. Two successive
manholes are opened and vented sufficiently for about an hour. Thereafter, a long hand-held mirror
secured at 45 degrees to the handle is lowered into the bottom of the manhole and a torch light is
focussed on the mirror from the above so that the light beam is deflected by 90 degrees to travel
horizontally through the sewer pipe and the light is seen in the opposite manhole. This is easier at
dusk. This can tell whether the bore of the pipe is choked or clear or laid straight.
Source: http://www.sankyotrading.co.jp
Figure 2.1 Mirror Test and Mirror with rod
The closed circuit camera is propelled through the sewer by a remote controlled wired power supply
from a van and travels through the sewer and relays the picture of the inside to a TV in the van. The
sonar system is similar. A robot is sent through the sewer and it emits high frequency sound waves,
which impinge on the pipe surfaces and returns to the emitter as a reflection. By knowing the material
of construction of the sewer pipe walls, this can be programmed to verify the structural condition of
the wall of the sewers.
Indirect inspection is carried out by sending a camera through the sewer for taking photographs or
a closed circuit television equipment (CCTV) to send pictures, which can be seen on a TV screen or
recorded as video. The CCTV inspection can be used for sewer lines as small as 100 mm. Above
900 mm diameter there are limitations due to lighting problems and camera line angles.
Continuous advances are being made in the quality and range of TV cameras. The type of
camera selected should be robust so that it can be used in sewers and give good quality pictures.
The traction of the cameras is by pulling winches, by pushing or self-traction. The former two are not
used much at present. However, self-traction is suitable for use in sewers above 225 mm diameter.
Other constraints in the use of self-traction are the weight of the trolley and electricity requirements.
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Heavy silting of sewers precludes the use of self-traction. The cameras are attached to trolleys
or mounted on a pair of skids or single flat tray. Inspection of the sewer by CCTV is limited to the
top portion only. The objects under scrutiny are parallel to the camera and viewing is at 40 to 50
degrees. With radial scanning head, inspection normal to the sewer wall is also possible. A typical
arrangement is as shown in Figure 2.2.
Figure 2.2 Typical CCTV equipment in position
A classical problem encountered in stoneware sewers laid through light forest or heavy garden
areas is the roots of trees piercing through the joints and growing inside the sewers. These become
like a plug and choke the sewer. This is shown in Figure 2.3. On the right is the photo of the bunch of
roots inside the sewer taken by a CCTV camera.
Figure 2.3 Tree roots and sewers
Similarly, the structural condition of old sewers like brick arch sewers and concrete pipes can be
ascertained by sonar surveys, which can provide the frontal image of the wall on a 360-degree
vertical spiral around the horizontal axis. These images can be analysed carefully. The system can
also provide information on the deflection and sidewall breakages of the sewer as in Figure 2.4.
Figure 2.4 Photographs showing Structural Damage and Longitudinal cracked condition of the Sewer
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2.2.5 Sewer Inspection and Examination
If an abnormality is detected during preliminary internal inspection or externally noticed from outside,
the maintenance engineer should judge the urgency and the content of the abnormality, and then
make a proper inspection and study.
2.2.5.1 Visual Examination
Visual examination is an inspection through images or by sight to detect an abnormality and includes
direct visual inspection, and indirect visual inspection using pole-mounted inspection camera, and
closed-circuit TV equipment (CCTV).
2.2.5.1.1 Manhole Visual Inspection
The visual inspection of manhole is performed by visually checking the manhole cover and the
environment of the internal parts of the manhole. To inspect the internal parts of the manhole, the
inspector should enter the manhole with proper safety dress as in subsection 2.11.1.2 and check the
items listed below. However, refer to the sub-section 2.7.1.2 for details of the inspection items.
• Status of internal surface of manhole

• Status of sewer on the upstream and downstream sides viewed from the manhole
• Status of groundwater infiltration
To inspect the internal parts of the sewer from the manhole, either a mirror or a strong light should be
used for observation, or a TV camera meant for inspecting conduits should be used.
• Features of manhole visual inspection

• Inspection accuracy is high because the inspector actually observes the abnormality
personally.
• Economical compared to inspection using a TV camera.
• The inspected results become very useful O&M data.
• The procedure for manhole visual inspection is shown in Figure 2.5.
Figure 2.5 Manhole Visual Inspection Procedure
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2.2.5.1.2 Inspection Using a Pole-mounted TV Camera
A pole-mounted TV camera as in Figure 2.6 is used.
Source:JASCOMA,2007
Figure 2.6 Pole-mounted inspection camera
It consists of an extendable operating rod at the front of which a camera and light are fitted. This
arrangement is inserted in the manhole from the ground, and the inspector on the ground observes
a monitor and inspects the internal parts of the pipe through the camera.
The features of direct visual inspection are compared with those of inspection by TV camera and
shown below.
• Advantages
• The inspection is easy and observations can be made in a short period. Moreover, the data of
inspection can be recorded as images.
• Since the inspector works above ground, there is no chance of oxygen deficiency or accidents
by fall, and the work is safe.
• Disadvantages
• The scope of inspection is limited to the area around the mouth of the pipe.
• Offset in the horizontal direction or fine cracks cannot be detected.
• The condition of the side surfaces in the sewer pipe cannot be grasped (sides cannot be
viewed).
This check may also be used for pre-inspections.
The method of inspection is shown in Figure 2.7 overleaf.
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Figure 2.7 Illustration of pole-mounted TV camera inspection
2.2.5.1.3 Inspection using Closed-Circuit Television (CCTV)
Pipes that can be inspected by CCTV have inside diameters ranging from 150 mm to 900 mm, but
large diameter pipes may also be inspected by CCTV. The TV camera may be the traveling type or
the towed type. Either the direct method (taking panoramic shots of the overall scene) or the side
view method of taking local shots of only abnormal locations may be used. House connection TV is
described in a separate section (2.10.1). Figure 2.8 shows the TV camera and the vehicle on which
it is loaded. The illustration of the TV inspection work is shown in Figure 2.9 overleaf.
Source: EPA,2003
Figure 2.8 Step van CCTV system
The features of TV camera inspection are
i. By opening a manhole at one location, inspection using the traveling TV camera is enabled.
ii. Continuous inspection up to a maximum distance of 100 to 200 m (cable length) is possible.
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Figure 2.9 Illustration of CCTV camera inspection
iii. The connections of the lateral sewer and main sewer and defective locations should be photo
graphed by the side view method.
A typical TV camera inspection work procedure is shown in Figure 2.10.
Figure 2.10 Work Procedure for TV Camera Inspection
CCTV Camera Inspection Record
Abnormalities detected in the pipeline during the CCTV camera inspection should be recorded on
video tape or as photographs, according to the judgment criteria.
Figure 2.11 (overleaf) and Figure 2.12 (overleaf) show examples of the record.
The inspected results should be recorded in the inspection record.
Examples of forms of the inspection record are shown in Figure 2.13 (overleaf) and
Figure 2.14 (overleaf).
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Source: EPA,2003
Figure 2.11 CCTV data No.1
Source: EPA,2003
Figure 2.12 CCTV data No. 2
2 - 12
Figure 2.13 Forms of inspection record
2 - 13
Source: EPA,2003
Figure 2.14 Forms of inspection record
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2.2.5.2 Inspecting Infiltration of Water
If infiltration of water is more corresponding to the planned water flow in the sewerage plant, the
pipelines and treatment facilities will be adversely affected.
This also leads to an increase in the treatment costs of the STP. The cause of infiltration of water
is either the pipeline is inadequate or the drainage system is inadequate.
For this reason, inspection of cross connections, flow-rate inspection and waterproofing inspections
need to be combined and the route of infiltration water should be checked. Flow-rate inspections
help since useful data for improvements and modifications to the piping facilities can be collected.
2.2.5.2.1 Inspecting Cross Connections
Inspection has to be performed to check that storm water equipment is not connected to the
sewers in a separate sewer system. The scope of work is from the main pipe of the sewerage works
to the house drainage facility.
There are three typical methods for inspecting cross connections.
A. Smoke Test
The smoke test makes use of smoke emitters in a separate sewerage system pipeline. A cross
connection can be judged by checking for smoke rising from the house inlet or rain gutter.
This test identifies locations where storm water inlet or rain gutter drainage is directly connected to
sewer pipe house inlet and locations where storm water has permeated the ground from the ground
surface or gutter and has indirectly permeated the wastewater pipe or house inlet.
Figure 2.15 shows the materials to be used. Figure 2.16 shows illustrative sketches.
Manhole Smoke Blower Smoke Emitter Smoke Fluid
Source: EPA, 2003

Figure 2.15 Materials for smoke test
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Source: EPA,2003
Figure 2.16 Illustrative Sketches of Smoke Test
• Features of the smoke test

• The status of connection of drain pipes in each space can be checked in a short time.
• Inadequacies in the house drainage facility can be quickly detected.
• Smoke test procedure is shown in Figure 2.17.
Figure 2.17 Work Procedure of Smoke Test
2 - 16
B. Echo Sound Test
This is a method for confirming that piping facilities are correctly connected, and is also an effective
method for knowing the plumbing systems and the routes of sewers and lateral sewers. Ultrasonic
waves are used (transmitter and receiver). Figure 2.18 shows the test method.
Figure 2.18 Illustration of Echo Sound Test
• Features of the echo sound test

• Simple method to confirm that a pipe has been connected or not.
• Effective especially in the connections of lateral sewers.
• Cannot judge clogging or trap.
• Echo sound test procedure is shown in Figure 2.19.
Figure 2.19 Work Procedure of Echo Sound Test
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C. Dye Test
The dye test is carried out using water diluted with harmless fluorescent dye. This diluted water is
made to flow from the upstream side of the STP within the range of the sewer, lateral sewer and
drainage equipment. The water flow route, leakage route and reaching time are examined. Outflow
route should be checked quickly if notification of foul odour due to outflow of wastewater, particularly
from masonry or pump tank, is received. The method can also be used for checking the flow status
in the pipe and for measuring the flow velocity. The test method is shown in Figure 2.20. In addition,
clause 3.10 of Part A manual dealing with dye tracer study may be referred to.
Figure 2.20 Drawing of dye test
2.2.5.2.2 Flow Rate Inspection
• About important areas for inspecting flow rate
Inspection should be carried out at locations where possibility of infiltration is high, e.g. where
groundwater level is high, at a part of a river crossing, or at a location adjacent to rivers.
A. Flow Rate Measurement
Simple flow velocity meters (Palmer Bowlus flume, electromagnetic flow meter, water level
gauge, ultrasonic flow meter) should be installed tentatively at the mouth of the manhole for flow
measurements in the piping facilities and fixed period measurements carried out. For details of flow
meters, refer to Sec. 3.10 of Chapter 3 of Part A manual.
B. Pumping Test
This is a method for measuring the flow rate of water that has infiltrated the pipeline. The flow rate of
infiltrated water into the space or the system can be known within a short time. However, the flow rate
of infiltrated water varies with the variation in groundwater and thereafter, precipitation and weather
at the time of measurement should be confirmed.
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To drain out household wastewater from the test during inspection of each space, a cut-off plug
should be installed. This should preferably be implemented during the night time when the volume of
household sewage generated is small. Figure 2.21 shows the pumping test.
Figure 2.21 Pumping test

• Features of measurements during pumping test are
• The flow rate of infiltrated groundwater for each space or system can be measured within a
short time.
• The measured values differ widely depending on the variation in the groundwater level.
• During measurements of several spaces or each system, it is difficult to remove household

wastewater late at night.
• Work procedure for measurement of pumped water is shown in Figure 2.22.
Figure 2.22 Work procedure of pumping test
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2.2.5.3 Inspecting Corrosion and Deterioration
The status of deterioration or corrosion within the sewer should be judged by TV camera. The
materials in the piping facility are of various kinds: concrete pipe, ceramic pipe, hard UPVC, brick,
HDPE pipe, ductile pipe, and GRP pipe; and hence the corrosion and deterioration conditions vary.
Methods for inspecting corrosion and deterioration conditions of a sewer include the following:
• Inspection by TV camera of the wall surface condition

• Crack inspection
• Neutralization test
The causes of deterioration of structural concrete parts of the piping facilities are the following:
• Crack in concrete due to concentrated loads (live loads)

• Deterioration of structure due to changes with aging
• Deterioration of concrete structures (concrete corrosion) due to sulphuric acid from the generation
of hydrogen sulphide
2.2.5.3.1 Concrete Corrosion
In a facility where sewage resides for a long period, sewage is likely to become anaerobic and
dissolved sulphide will be generated, which leads to concrete corrosion because of its formation to
sulphuric acid. Locations where concrete corrosion is likely to occur in sewage
• Piping facilities at the discharge destination of pressure pipe (including manhole pump)
• Upstream and downstream ends of locations where sump discharge occurs
• Upstream and downstream ends of locations where discharges containing sulphide occurs
• Locations downstream of inverted siphon
For details of the corrosion mechanism, refer to chapter 3 of Part-A manual.
A. pH Measurement of Concrete Surfaces

For sulphuric acid corrosion of concrete, the pH on the surface of concrete is measured by pH test
paper or pH meter, which is placed on concrete surface directly, and the generation of sulphuric acid
in the concrete structure can be confirmed. When sulphuric acid is generated in a manhole, the pH
of the concrete surface may indicate strong acidity of as low as 1 to 2.
B. Neutralization test (neutralization depth test by phenolphthalein)

One of the indices for judging durability of reinforced concrete structures is the “neutralization
depth”. This is the method of judging alkalinity with pH of 10 and above as non-neutralized part and
non-coloured parts as neutralized parts, enabling quantitative information to be obtained easily by
simple measurements in Figure 2.23 overleaf.
When neutralization reaches the vicinity of the reinforcement, the reinforcement is likely to be
corroded easily. When corrosion of reinforcement progresses, volume expansion of corrosive
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Source:JASCOMA, 2007
Figure 2.23 Neutralization test
products causes crack or delamination in concrete, leading to excessive loss in the durability of the
structure. For the procedure, refer to BS-103: “Guidelines on Non-destructive Testing of Bridges.”
2.2.5.4 Other Examinations
Special examinations to study in detail the conditions of a facility are as given below. For more details,
please refer to relevant documents for each item. Various kinds of information relevant to analysis for
studying gas exploration are given.
• Sewer invert elevation examinations: Understanding pipeline conditions and collating with
sewerage facility records.
• Sediment examination: Check sediment material, such as sand and silt, which may have
entered damaged sewer or through loose joints from outside the sewer. This sand and silt may
accumulate around the sewer and form voids.
• Dangerous gas detection examination: Confirming gases generated in the piping facilities.
Water quality and gases encountered in a piping facility are closely related. Table 2.6 shows the gas
analysis items in a piping facility.
Table 2.6 Gas analysis
Source: JASCOMA, 2007
In Japan the accidents caused due to gases generated from sewerage system are shown in
Figure 2.24 overleaf. Accidents and casualties should be properly recorded mentioning all the
relevant details.
2 - 21

Figure 2.24 Fatal accidents due to gases from sewerage system between 2002 and 2012
The causes of the gas-related accidents were hydrogen sulphide, carbon monoxide and oxygen
deficiency. There is no data on accidental death in India and there should be such monitoring in India
at least hereafter.
2.2.5.5 Precautions
Cleaning equipment and machinery for sewers are shown in the following sections:
When entering manholes, safety measures during the work should be to ensure traffic safety, prevent
oxygen deficiency, precautions against hydrogen sulphide and so on. For securing workers’ safety,
manual sewer/septic tank cleaning should be avoided because persons are likely to come in direct
contact with sludge and sewage.
Therefore, cleaning machinery and equipment are needed. Furthermore, necessary safety
measures before entering manholes for cleaning should be taken. “Machinery and equipment for
sewer pipes” are explained in section 2.3 of this manual. The explanations on “Cleaning of on-site
systems” are in Chapter 10 of this manual.
The contamination of drinking water with sewage may occur when water supply pipe passes through
sewer manholes, generally in narrow streets, especially when water supply pipe joints are enclosed
in sewer manholes and whenever water supply pipe joints leak, contamination of drinking water
supply occurs.
As such, water supply pipelines should never be enclosed in a sewer manhole. If any such
situation is observed, water supply pipe be made non-functional immediately by stopping flow of
drinking water and affected public be supplied clean drinking water by other temporary means, such
as water tankers or laying separate pipe over the ground / road surface and portion of water supply
lines lying in sewer manholes be shifted out of manholes.
Special attention should be paid to decentralized sewer system, particularly when small-bore sewer
system or shallow sewer system is adopted.
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2.2.6 Judgment of Inspection and Examination Results
It is necessary to judge whether urgent repairs or modifications are necessary, or normal operation
and maintenance are sufficient to ensure that the functions of piping facilities are maintained when
an abnormality is detected by studies and analyses. The facility manager should make the judgment
considering material of the pipe, age of the pipe, location where buried, quality of wastewater, status
of groundwater, regional environment, and so on.
The criteria given below may be used as judgment criteria.
• Emergency response criteria

• Judgment based on results of inspection or examination
• Testing criteria
2.2.6.1 Emergency Response Criteria
Abnormalities related to piping facilities are generally detected from inspections or from
outside reports.
Prompt action should be taken when an accident has already occurred. Moreover, when the events
below are confirmed, action should be taken immediately.
• Road surface: Irregularity exists that can cause level difference leading to subsidence or
obstruction to operation.
• Manhole: Level difference exists that can lead to obstruction of operation.
• Inverted siphon: Water level on the upstream side is excessively high.
2.2.6.2 Judgment based on the Results of Inspection and Examination
Testing of the overall span and by each pipe should be carried out based on the results of visual
inspection. Table 2.7 and Table 2.8 (overleaf) show examples of testing criteria.
Table 2.7 Testing criteria for overall sewer span
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Table 2.8 Testing criteria for each pipe of sewer
The testing of the overall span is divided into the three categories (A, B and C)
• Functional degradation,
• Deterioration and
• Abnormalities
clarified by inspection and examination should be assessed as shown in Figure 2.25 overleaf.
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Figure 2.25 Illustration of testing criteria for sewer
2 - 25
2.2.6.3 Testing Criteria
A maintenance engineer should judge what counter measure are applied for inspected sewers
in accordance with Table 2.9, e.g., by usual operation and maintenance or by emergency repairs
and modifications.
Based on the criteria shown in Table 2.7 and Table 2.8, emergency level I is a state where immediate
response is necessary.
Emergency level II indicates that simple response may be adopted and radical measures
implemented within the next five years.
Furthermore, emergency level III indicates response adopted by operation and maintenance, and
implementation of simple response partially.
Table 2.9 Testing criteria for sewer
A’s, B’s, and C’s are judgement results of Table 2.7,

a’s, b’s and c’s are judgment results of Table 2.8.
2.2.7 Maintenance of Records and Follow up Action
To reflect the inspection and testing results in appropriate O&M of piping facilities, the test results
should be recorded and stored in the format shown here.
A. Inspection Sheet
When inspections and examinations are implemented, an inspection sheet should be prepared and
recorded as shown in Table 2.10.
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Table 2.10 Inspection sheet
B. Log
The log should be used to record daily work results, which can be used in the O&M of piping facilities.
The format is shown in Table 2.11 overleaf.
C. Monthly Reports
The daily record should be summarized in monthly reports. The format of the monthly report is
shown in Table 2.12 overleaf.
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Table 2.11 Daily report
2 - 28
Table 2.12 Monthly report
2 - 29
2.3 SEWER CLEANING
To operate and maintain a sewer collection system to function as intended, the maintenance
engineer should try to strive towards the following objectives:
• Minimize the number of blockages per unit length of sewer, and
• Minimize the number of odour complaints.
For this purpose, sewer-cleaning using hydraulic or mechanical cleaning methods needs to be done
on a scheduled basis to remove accumulated debris in the pipe such as sand, silt, grease, roots
and rocks. If debris is allowed to accumulate, it reduces the capacity of the pipe and blockage can
eventually occur resulting in overflows from the system onto streets, yards and into surface waters.
Roots and corrosion also can cause physical damage to sewers.
2.3.1 Cleaning Equipment and Procedures
Sewer cleaning works require usual implements like pick axes, manhole guards, tripod stands,
danger flags, lanterns, batteries, safety lamps, lead acetate paper, silt drums, ropes, iron hooks, hand
carts, plunger rods, observation rods, shovels etc.
In addition, sewer cleaning work calls for the following special equipment and devices like a portable
pump-set running on either diesel or petrol engine, rope and cloth balls, sectional sewer rods, a
sewer cleaning bucket machine, a dredger, a rodding machine with flexible sewer rods and cleaning
tool attachments such as augers, corkscrews, hedgehogs and sand cups, scraper, and hydraulically
propelled devices such as flush hags, sewer balls, wooden bail and sewer scooters, sewer jetting
machine, gully emptiers and pneumatic plugs. The kraite type of flexible rods in a portable reel is
useful in attending to house sewers.
2.3.1.1 Manila Rope and Cloth Ball
The most common way of cleaning small diameter sewers up to 300mm diameter is by the use of a
manila rope and cloth ball. Flexible bamboo strips tied together are inserted in the sewer line by a
person on top. If necessary, another person inside the manhole with full safety gears, precautionary
measures and safety equipments help in pushing the rod through the sewer line. When the front end
of the bamboo strip reaches the next manhole, a thick manila rope, with cloth ball at one end, is tied
to the rear end of the bamboo splits. The bamboo splits are then pulled by another person in the
downstream manhole and pushed through the sewer line. As the rope is pulled, the ball sweeps the
sewer line and the accumulated grit is carried to the next manhole where it is removed out by means
of buckets. This operation is repeated between the next manholes until the stretch of sewer line is
cleaned. This action requires a careful supervision.
2.3.1.2 Sectional Sewer Rods
These rods are used for cleaning small sewers. The sewer rods may be of bamboo or teak wood or
light metal usually about one meter long at the end of which is a coupling, which remains intact in the
sewer but can be easily disjointed in the manhole. Sections of the rods are pushed down the sewer.
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The front or the advancing end of the sewer rod is generally fitted with a brush, a rubber ring for
cleaning or a cutting edge to cut and dislodge the obstructions. These rods are also useful to locate
the obstruction from either manhole in case a particular portion of the sewer has to be exposed for
attending to the problem.
2.3.1.3 Sewer Cleaning Bucket Machine
The bucket machine consists of two powered winches with cables in between. For cleaning a section
of sewer; the winches are centred over two adjacent manholes. To get the cable from one winch to
the other, it is necessary to thread the cable through the sewer line by means of sewer rods or flexible
split-bamboo rods. The cable from the drum of each winch is fastened to the barrel on each end of an
expansion sewer bucket fitted with closing device, so that the bucket can be pulled in either direction
by the machine on the appropriate end. The bucket is pulled into the loosened material in the sewer
until the operator feels that it is loaded with debris. The winch is then thrown out of gear and the
opposing winch is put into action. When the reverse pull starts, the bucket automatically closes and
the dirt is deposited in a truck or a trailer. This operation is repeated until the sewer is cleared. Various
bucket sizes are available for sewers of 150 mm to 900 mm in size. The machine is also used along
with other scraping instruments for loosening sludge banks of detritus or cutting roots and dislodging
obstructions as in Figure 2.26.
Source: EPA, 2003

Figure 2.26 Power bucket machine setup
2.3.1.4 Dredger (Clam-shell)
It consists of a grab bucket on a wire rope, which is lowered into the manhole in the open condition
with the help of a crane and pulley. On reaching the bottom of the manhole, the segments are closed,
and the accumulated silt is picked up. The bucket is then raised above ground level where the bucket
opens and the silt is automatically dropped into a truck or a trailer. The bucket can be closed by wire
ropes or by a pneumatically operated cylinder. The disadvantage in this system is that it cannot clean
the corners of the catch pits of manholes. Sometimes the deposits at the corners may become so
hard that the same may be required to be chiselled out.
2.3.1.5 Rodding Machine with Flexible Sewer Rods
This consists of a machine, which rotates a flexible rod to which is attached a cleaning tool such as
auger, corkscrew or hedgehog and sand cups (Figure 2.27 overleaf).
2 - 31
Source: EPA, 2003

Figure 2.27 Power rodding operation
The flexible rod consists of a series of steel rods with screw couplings. It is guided through the
manhole by a bent pipe. The machine propels the rod with the tool attached to one end,
the other end being fixed to the machine. The rotating rod is thrust into the bent pipe manually with
clamps with long handles for holding the rod near the couplings. As the rod is thrust inside, the
machine also is drawn towards the manhole. The rod is pulled in and out in quick succession
when the tool is engaging the obstruction, so as to dislodge or loosen it. When the obstruction
is cleared, the rod is pulled out by means of clamps keeping the rod propelled to facilitate quick and
easy removal. The various tools are shown in Figure 2.28.
Source: EPA, 2003

Figure 2.28 Rodding heads
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2.3.1.6 Scraper
This method is used for sewers of diameter larger than 750 mm. The scraper is an assembly of
wooden planks of slightly smaller size than the sewer to be cleaned. If the scraper cannot be lowered
through the opening of manhole, it has to be assembled inside the manhole. The scraper chains,
attached to a control chain in the manhole into which it is lowered, are then connected to a winch in
the next downstream manhole by means of chains. The winch is then operated to push the debris
ahead of the scraper. The upward flow behind the scraper and the water dropping from the top of
the scraper will also assist in pushing it in the forward direction. This ensures that the bottom and the
sides of the sewer are cleaned thoroughly. The scraped debris is removed manually.
Circular scrapers are used on small sewers below 350 mm diameter for cleaning the body of the line.
They are commonly known as discs and these discs are both collapsible and made of metal or a
wooden pair separated by about 200 mm by steel rods.
2.3.1.7 Hydraulically Propelled Devices
The hydraulically propelled devices take advantage of the force of impounded water to effectively
clear sewers. The efficiency depends on the hydraulic principle that an increase in velocity in a
moving stream is accompanied by a greatly increased ability to move entrained material. The
transporting capacity of water varies as the sixth power of its velocity.
A. Flush Bags
A very effective tool for cleaning portions of sewers where rods cannot be used is the sewer flusher
or flush bag. The flusher is a canvas bag or rubber bag equipped with a fire hose coupler at one
end and a reducer at the other end. The flusher is connected to the fire hose and placed in the
downstream end, from the point where a choke is located. The bag is allowed to fill up until it
expands and seals the sewer. The upstream pressure built up due to this damming effect breaks
loose the obstructions.
B. Sewer Balls
These are simple elastic pneumatic type rubber balls, which can be blown up to varying degrees of
inflation. They are manufactured in sizes from 150 mm to 750 mm diameter when fully inflated. When
used in cleaning a sewer, the ball is first inflated and then wrapped in a canvas cloth, the edges
of which are sewed together. A trial line, little longer than the distance between the manholes, is
attached securely to the covering. The size of the ball and the covering shall be such as to fit fairly
snugly into the sewer. Immediately after the ball is thrust into the sewer, sewage commences to
back up in the manhole and continues to rise until such time as its pressure is great enough to force
sewage under the ball and move it downstream through the pipe. Acting as a compressible floating
plug, it affords enough obstruction, so that a continuous high velocity jet spurts under and to some
extent around the ball, thereby sluicing all the movable material ahead to the next manhole. If the ball
encounters an obstruction, which is immovable, the ball merely indents to the necessary degree and
moves forward. The only fixed obstruction, which will stop the forward progress of the ball is a root
mass or some similar obstruction tightly wedged into the pipe.
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Bricks, stones, bottles, loose metal parts, broken pieces of pipes, sand, gravel and settled sludge are
easily moved ahead. If the ball stops momentarily, a pull on the trial line is usually sufficient to set it
in motion again. If the pipe is very dirty, the trial line can be tied to a step in the upper manhole and
the ball’s progress can be retarded to the required degree as the lower manhole is reached, thus
giving time for complete removal of accumulated silt and debris, which has piled up ahead of the ball.
Equipment arrangement is shown in Figure 2.29 and Figure 2.30.
Figure 2.29 Typical setup for Hydraulic cleaning using Sewer Ball
Source: EPA, 2003

Figure 2.30 Balling equipment
A wooden ball, also called a sewer pile, can also be used for this purpose, particularly for cleaning
large outfall sewers. It is dropped into the sewer and owing to its buoyant action rolls along the invert
of the sewer. The obstructions caused by it to the flow produce a vigorous scouring action along the
invert and the sides, which has the effect of removing tree growths and the deposits from the sewers.
This method is economical and hence can be used at frequent intervals.
C. Sewer Scooters
This arrangement is an improved version of the scraper and consists of two jacks, a controlling
rope and the scooter with a tight fitting shield. In contrast to the scraper, the scooter completely
stops any flow of sewage. The scooter, attached to the control rope, is lowered into the manhole
and then into the downstream sewer line. The downstream manhole jack is lowered into place
from the road and the upper manhole jack set across the top of the manhole. When the scooter is
introduced in the line, it stops the flow of sewage thus building up a head behind the shield.
The resulting pressure causes the scooter to move through the sewer until it accumulates enough
debris to stop its movement.
2 - 34
The head is then allowed to build up approximately one meter before the control rope is pulled,
causing the shield to fold back, thus allowing the accumulated sewage to gush into the sewer
downstream, flushing the debris ahead to the next manhole from where it is removed. The control
rope is released, clearing the shield against the sewage and causing the scooter to advance again
until the debris stops its movement. This process is repeated until the scooter reaches the
downstream manhole where it may be removed or allowed to continue through the next section. The
operation of the sewer scooter is shown in Figure 2.31.
Source: EPA, 2003

Figure 2.31 Sewer Scooter operation
2.3.1.8 Velocity Cleaners (Jetting Machines)
The high velocity sewer-cleaner makes use of high velocity water-jets to remove and dislodge
obstructions, soluble grease, grit and other materials from sanitary, storm and combined sewerage
systems. It combines the functions of a rodding machine and gully emptier machine. It includes a
high-pressure hydraulic pump capable of delivering water at variable pressure up to about 8 MPa
through a flexible hose to a sewer cleaning nozzle. The nozzle has one forward facing jet and a
number of peripheral rearward facing jets. The high-pressure water coming out of the holes with a high
velocity, breaks up, dislodges the obstructions and flushes the materials down the sewer. Moreover,
by varying the pressure suitably, the nozzle itself acts as a jack-hammer and breaks up stubborn
obstructions. A separate suction pump or airflow device may also be used to suck the dislodged
material. The entire equipment is usually mounted on a heavy truck chassis with either a
separate prime mover or a power take off for the suction device. The high-pressure hose reel is also
hydraulically driven. The truck carries secondary treated sewage, if available, and if not untreated fresh
water for the hydraulic jet. The truck also has a tank for the removed sludge and the various controls
grouped together for easy operation during sewer cleaning. The manufacturer’s operating and
servicing manuals should be carefully followed for best results in the use of the machine.
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2.3.1.9 Suction Units (Gully Emptier)
Suction units create the vacuum required for siphoning of mud, slurry, grit and other materials from
sanitary, storm and combined sewerage systems. The vacuum elevated is such as to siphon the
materials from the deep manholes catch-pits etc., having depth ranging from 1m to 8m in normal
cases with an option to suck an additional 4m with the help of special accessories for the purpose.
The unit can be vehicle or trolley mounted.
Silt and heavy particles settled at the bottom can be agitated and loosened by pressurized air with
the help of the pump and then sucked in a tank. Once the silt tank is full, the effluent is discharged in
the nearby storm water drain or manhole and the operation is repeated until the silt is cleared off the
manhole. The silt deposited in the tank is then emptied at the predetermined dumping spot.
2.3.2 Notification to STP
Before clearing a large septic stoppage, be sure to notify the operator on duty at the downstream
STP. Septic stoppages develop when the sewer has been blocked for considerable time and/or the
air temperature is hot. Under these conditions, the wastewater and organic solids turn black and
smell like rotten eggs. If a large diameter sewer is blocked and a large volume of sewage backs
up in the pipes, there might not be sufficient fresh water arriving at the treatment plant to dilute the
septic sewage. When a large volume of septic sewage reaches the STP, the treatment
processes may fail to do their intended job. By notifying the operator in advance of the location of the
stoppage and approximate volume of septic sewage flowing towards the STP, the operator can be
alerted and can prepare to minimize the impact on the treatment processes.
2.3.3 Disposal of Silt and Sludge
Sludge from sewers can be disposed of along with grit and sludge of the STP (if available)
or the sludge and silt can be co-disposed in an eco-friendly manner with MSW.
2.3.4 Cleaning Records and their Utilization
Records of all cleaning operations should be entered and filed for future reference. These
records should include the data, street name or number, line size, distance and manhole numbers or
identification. Also the kind and amount of materials removed, wastewater flow, and auxiliary water
used should be noted. If particular problems were encountered, these too should be noted, especially
the exact location of obstructions. A record-form sample is shown in Figure 2.32 overleaf.
During the routine cleaning operations discussed in this chapter, many manholes should be opened
and used for high-velocity cleaning or flushing of sewer. Manhole Inspection form detailing its
location, condition, and any problems observed should be completed. If this is done each time a
manhole is opened during cleaning operations, over a time the database for these structures will
include up-to-date information on a high percentage of them and allow better decisions to be made
in regard to routine maintenance, repair, or rehabilitation.
If pieces of broken sewer are removed, a TV inspection may be needed and repairs may need to be
made on the broken sections of pipe.
2 - 36
Where S = pipe size, V = Ventilation, OTO = Operator to operator (communication methods:

walkie-talkie), NL = New lateral (New house connection), DOCK = Docking, Bk = Block number,
Pg = Peg number, SR/CR = Scraper Crane, PM/TV = Pole mounted TV, Gr = Grease, Rt = Roots
Source: EPA, 2003
Figure 2.32 Sewer cleaning records
Recording traffic patterns at a site can be very helpful next time the equipment is set up at the
location. Car park (such as over manholes), traffic volume during rush hours, and whether police
traffic control should be called for help before going to the site, should be indicated.
Computers are being used in many aspects of operation, maintenance and record keeping of
collection system.
Computer software packages are available for scheduling preventive maintenance activities,
issuing work orders for repairs, keeping track of where work is done, who did the work, when, and
the labour and materials required. With the correct software, any information in the computer’s
records can be recalled for future use.
Computers are also used to keep spare parts inventories and to order spare parts when the
supply runs low and before they are needed for scheduled maintenance and repairs.
When marking records, remember that someone else will be referring to them. The more
complete the record, the easier the next operation becomes since there is a history of this sewer.
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2.4 SEWER REHABILITATION
2.4.1 Introduction
Deterioration of sewers proceeds over the surface as a whole, and repair takes considerable time,
therefore, it is necessary to implement renewal and repair according to a plan on the basis of the
results of inspection and examinations. This practice will prevent accidents.
In older cities, most sewers have already exceeded the service life. In such cities, adequate renewal
and repair may resolve urgent problems and help extend the service life of the facilities, reducing
O&M expenses. The two terms renewal and repair are clearly segregated as follows. Renewal is not
included in O&M duties but in construction because the time of implementation is the starting point of
the new service life and changes must be made to fixed assets
A. Renewal.
This means improvement and replacement of facilities not caused by expansion of

drainage area. It includes improvement, which is reconstruction or replacement of the facility that has
not yet reached the specified service life and replacement which is reconstruction or replacement of
the facility that has reached the specified service life.
B. Repair
This refers to partial replacement or repair of damage to the facility. Repair provides utility, but not
an increase in functions, so it does not contribute to extension of the service life of the facility. Repair
simply maintains the capacity and life and does not cause a change in fixed assets.
However, making a clear distinction between O&M and construction duties is often difficult for
implementation of renewal and repair according to the plan. In certain cases, it is therefore desirable
to plan these duties as one package. Improvement of functions of existing sewers while incorporating
elements related to planning and construction projects is generally called rehabilitation. The definition
of terms related to rehabilitation is given in Table 2.13 overleaf.
2.4.2 Rehabilitation Method
Under the traditional method of sewer relief, a replacement is made or additional parallel sewer
line is constructed by digging along the entire length of the existing pipeline, while these traditional
methods of sewer rehabilitation requires digging and replacing the deficient pipe with
(the dig-and-replace method), trenchless methods of rehabilitation use the existing pipe as a host
for a new pipe or liner. Trenchless sewer-rehabilitation techniques correct pipe deficiencies that
require less restoration and cause less disturbance and environmental degradation than the
traditional dig-and-replace method. Trenchless sewer-rehabilitation methods include:
1. Pipe bursting or in-line expansion

2. Slip lining
3. Cured-in-place pipe
4. Modified cross-section liner
2 - 38
Table 2.13 Definition of terms
Source: JICA, 2011
These alternative techniques must be fully understood before they are applied. These four sewer
rehabilitation methods are described in detail in the following sections.
2.4.2.1 Pipe Bursting or In-line Expansion
Pipe bursting or in-line expansion is a method by which the existing pipe is forced outward and
opened by a bursting tool. During in-line expansion, the existing pipe is used as a guide for
inserting the expansion head (part of the bursting tool). The expansion head, typically pulled by
a cable rod and winch, increases the area available for the new pipe by pushing the existing pipe
radically outward until it cracks. The bursting device pulls the new pipeline behind itself. The pipe
bursting process is illustrated in Figure 2.33.
Source: JICA, 2011

Figure 2.33 Pipe bursting process
2 - 39
2.4.2.2 Slip Lining
Slip lining is a well-established method of trenchless rehabilitation. During the slip lining process, a
new liner of smaller diameter is placed inside the existing pipe. The annular space, or area between
the existing pipe and the new pipe, is typically grouted to prevent leaks and to provide structural
integrity. If the annulus between the sections is not grouted, the liner is not considered a structural
liner. Continuous grouting of the annular space provides the seal. Grouting only the end-of-pipe
sections can cause failures and leaks. In most slip lining applications, manholes cannot function
as proper access points to perform the rehabilitation. In these situations, an insertion pit must be
dug for each pipeline segment. Due to this requirement in most applications, slip lining is not a
completely trenchless technique. However, the excavation required is considerably less than that
for the traditional dig-and-replace method. System and site conditions will dictate the amount of
excavation. Methods of slip lining include continuous, segmental and spiral wound methods. All three
methods require laterals to be re-connected by excavation or by a remote cutter. In continuous slip
lining, the new pipe, jointed to form a continuous segment, is inserted into the host pipe at strategic
locations. The installation access point, such as a manhole or insertion pit, must be able to handle the
bending of the continuous pipe section. Installation by the segmental method involves assembling
pipe segment at the access point. Slip lining by the segment method can be accomplished without
rerouting the existing flow. In many applications, the existing flow reduces frictional resistance and
thereby aids in the installation process. Spiral-wound slip lining is performed within a manhole or
access point by using interlocking edges on the ends of the pipe segments to connect the segments.
The spiral wound pipe is then inserted into the existing pipe as illustrated in Figure 2.34.
Source: JICA, 2011

Figure 2.34 Spiral wound Slip Lining Process
2.4.2.3 Cured-in-place Pipe
A typical cured-in-place pipe (CIPP) process by the water-inversion method is illustrated in

Figure 2.35 overleaf. During the CIPP renewal process, a flexible fabric liner coated with a
thermosetting resin is inserted in the existing pipeline and cured to form into a new liner. The liner is
typically inserted in the existing pipe through an existing manhole. The fabric tube holds the resin in
place until the tube is inserted in the pipe and ready to be cured. Commonly manufactured resins
include unsaturated polyester, vinyl ester, and epoxy, each having distinct chemical resistance to
domestic sewage. The CIPP method can be applied to rehabilitate pipelines with defects such as
cracks, offset joints and structurally deficient segments.
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Source: EPA, 1996

Figure 2.35 Cured-in-place pipe installation procedure
The thermosetting resin material bonds with the existing pipe materials to form a tighter seal than
most other trenchless techniques. The two primary methods of installing CIPP are winch-in-place and
invert-in-place. These methods are used during installation to feed the tube through the pipe. The
winch-in-place method uses a winch to pull the tube through the existing pipeline. After being pulled
through the pipeline, the tube is inflated to push the liner against the existing pipe walls.
The more typically applied inversion-in-place method uses gravity and either water or air pressure
to force the tube through the pipe and invert it, or turn the tube inside out. This process of inversion
presses the resin-coated tube against the walls of the existing pipe. During both the winch-in-place
and invert-in-place methods, heat is then circulated through the tube to cure the resin to form a strong
bond between the tube and the existing pipe.
2.4.2.4 Modified Cross-section Lining
The modified cross-section lining methods include deformed and reformed methods, sewage
lining and roll down. These methods either modify the pipes cross-sectional profile or reduce its
cross-sectional area so that the liner can be extruded through the existing pipe. The liner is
subsequently expanded to conform to the existing pipe’s size. During deformed and reformed pipeline
renewal, a new flexible pipe is deformed in shape and inserted into the host pipe. While the method
of deforming the flexible pipe varies, with many processes referred to as fold and form methods,
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a typical approach is to fold the new liner into a “U” shape, reducing the pipe’s diameter by about
30 %. After the liner is pulled through the existing line, the liner is heated and pressurized to
conform to the original pipe shape. Another method of obtaining a close fit between the new lining and
existing pipe is to temporally compress the new liner before it is drawn through the existing pipeline.
The sewage lining and roll down processes use chemical and mechanical means, respectively, to
reduce the cross-sectional area of the new liner. During sewage lining and a typical draw down
process, the new liners are heated and subsequently passed through a reducing die. A chemical
reaction between the die and liner material temporarily reduces the liner’s diameter by 7 to 15 % and
allows the liner to be pulled through the existing pipe. As the new liner cools, it expands to its original
diameter. The roll down process uses a series of rollers to reduce the pipe-liner’s diameter. As in
deform-and-reform methods, heat and pressure are applied to expand the liner to its original pipe
diameter after it has been pulled through the existing pipe. Unlike CIPP, the modified cross-section
methods do not make use of resins to secure the liner in-place. Lacking resin-coated lining, these
methods do not have the curing time requirement of CIPP. A tight fit is obtained when the folded
pipe expands to the host pipe’s inside diameter under applied heat and pressure. As with the CIPP
method, dimples are formed at lateral, junctions and similar methods of reconnecting the laterals
can be employed. Materials typically used for modified cross-section linings include Unplasticised
Polyvinyl Chloride (UPVC) and High Density Polyethylene (HDPE).
2.4.3 Maintenance of Machinery and Apparatus for Rehabilitation
Emergency cleaning and a repair are required in case of an emergency response.
Therefore, a maintenance engineer should repair machinery and equipment to the original.
In addition, he should have enough maintenance and repair materials required (for example pipes,
lid, the mounting tube). In addition, the maintenance engineer should stock construction materials
such as sand, rock crushing and asphalt for the cave-in repair of roads.
The maintenance engineer should ensure that the materials, equipment and facilities, necessary
safety equipments are in standby state at all times.
2.5 PROTECTION OF SEWER SYSTEMS
A sewer may get damaged if other facilities such as water pipe or electric cable work are done
beside or at the cross-section of a sewer. Especially, fluctuations due to ground excavation (pile,
underground water drops and pile method) may have a serious impact.
To avoid damages of sewer, the maintenance engineer should do the following:
1. Collect all related information about the construction activities which are planned around the
sewer location,
2. Advise appropriate construction methods to minimize impact for sewer, and
3. If necessary, request the concerned agencies to adopt the protective measures for sewer prior to
the work commencement.
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Typical protective measures are as follows:
1. Protection for existing sewer (an example is shown in Figure 2.36)

2. Temporary laying of supported sewer pipe
3. Changing sewer material in advance
Figure 2.36 Protection method for existing sewer
2.6 PROTECTION AGAINST INFILTRATION & EXFILTRATION
Infiltration and inflow, while overlooked in many collection systems for decades, have now gained
recognition as major defects that can cause failure of a collection system. In most cases, this
failure results in hydraulic overloads (too much water) of the collection system or the sewage
treatment plant. In the case of a collection system, hydraulic overloads result in surcharged manholes,
overflowing manholes and exposure of community to diseases and pollutants carried by the waste
water in a collection system.
This type of failure is also known as a sanitary sewer overflow. In the case of an STP, infiltration and
inflow can result in plant loads exceeding the plant capacity.
Bypassing raw sewage to the environment has been the only answer in the past, but this practice is
no longer allowed.
2.6.1 Measures against Infiltration of Rainwater
Inflow detection and collection depend upon the type and source of inflow causing the problem.
Inflow is water that enters a sewer as a result of a deliberate illegal connection or by deliberate
drainage of flooded areas into the sewer system.
In many areas the main line portion of the collection system is relatively tight.
A major source of infiltration in this situation can be the house service lines. They can be tested
for leaks using smoke tests and by deployment of small cameras and robotic equipment. Collection
or elimination of inflow/ infiltration depends on the type and location of the source of problem.
Typical solutions to inflow / infiltration problems are shown overleaf.
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A. Manholes
• Raise rim elevation by use of grade rings if not located in streets (inflow).
• Install watertight covers where needed (inflow).
• Install inflow protection covers (inflow).
• Seal covers (inflow).
• Seal or repair barrels (infiltration).
B. Sewer Pipes (Infiltration)
• Seal segment of damaged pipes and joints.

• Dig up and replace damaged pipes and joints.
• Line sewer with a plastic liner and/or fibre liner material.
2.6.2 Measures against Exfiltration of Untreated Sewage
Exfiltration is the leakage of sewage out of the collection system through broken or damage pipes
and manholes as shown in Figure 2.37.
Source: EPA/600/R-01/034
Figure 2.37 Sewage leaking locations
All the sewage collection systems, except some constructed in recent years, have many leaks. These
systems may exfiltrate sewage through defective pipe joints and cracks. The sewage that does
exfiltrate may contaminate shallow wells or open ditches where children and pets play. To make an
old collection system airtight would be extremely expensive and not very cost-effective. Major points
of infiltration or exfiltration in a collection system can be identified by the use of television or smoke
testing and can then be corrected.
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The proper selection of corrective or rehabilitation methods and materials depends on a complete
understanding of the problems to be corrected, as well as the potential impacts associated with
the selection of each rehabilitation method. Pipe rehabilitation methods to reduce exfiltration (and
simultaneously infiltration) fall into one of the two following categories:
1. External Rehabilitation Methods

2. Internal Rehabilitation Methods
Certain conditions of the host pipeline influence the selection of the rehabilitation method. It is
therefore necessary to assess these factors to prepare the pipe for rehabilitation. Rehabilitation is
preceded by surface preparation by cleaning the pipes to remove scale, tuberculation, corrosion and
other foreign matter.
The concerned departments, corporations, urban local bodies, town planning authority, Jal Nigam,
etc. have to participate in the total sanitation programme. These departments should be part of a
co-ordination committee constituted at a local level and are required to meet half yearly to plan
appropriate co-ordination specific to total sanitation. These meetings however, can be more frequent
during specific items such as drought, floods, etc.
2.6.2.1 External Sewer Rehabilitation Methods
External rehabilitation methods are performed from above the ground surface by excavating adjacent
to the pipe, or the external region of the pipe is treated from within the pipe through the wall. Some
of the methods used include:
1. External Point Repairs

2. Chemical Grouting (Acryl amide Base Gel and Acrylic Base Gel)
3. Cement Grouting (Cement , Micro fine Cement and Compaction)
2.6.2.2 Internal Sewer Rehabilitation Methods
Internal sewer rehabilitation methods are the same as infiltration measures.
2.7 MANHOLES AND APPURTENANCES
Because they are part of the collection system, manholes require the same inspection and attention
as the rest of sewer network.
When located in streets, these structures are subject to vibrations and pounding by vehicle traffic.
Manholes may settle at a different rate than connected sewer, creating cracks in sewer pipe joints.
The objectives of manhole inspection are therefore, to determine the proper elevations or grades
around the lid, to confirm that the lid is not buried, and to examine structural integrity (look for cracks)
of the manhole and its functional capacity.
The condition of the pipelines coming into a manhole may be known merely by observing the content
and volume of flows from a specific direction.
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2.7.1 Inspections and Examinations
Manhole inspection and examination are made by visually inspecting the condition of the cover and
the internal parts.
Manhole inspection should be carried out together with the inspection and examination of sewer. It is
generally carried out together with the cleaning of the sewer.
Before entering any manhole, adequate safety measures should be taken in accordance with
subsection 2.11.1.2.
Safety measures during the work should be formulated giving consideration to traffic safety, oxygen
deficiency, poisoning due to toxic gas such as hydrogen sulphide and so on.
2.7.1.1 Manhole
Damage or wear in the manhole cover obstructs passage and is a risk. The facility manager should
inspect the manhole cover for damage, wear, play, non-coincidence of heights of cover and road
surface, offset of manhole block and so on as in Figure 2.38, Figure 2.39 and Figure 2.40.
Figure 2.38 Wear of cover
Figure 2.39 Offset of manhole block
Figure 2.40 Not coinciding with height of road surface
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2.7.1.2 Conditions inside Manhole
Manhole is an essential structure for O&M of sewers. It helps the O&M to be performed safely.
For smooth flow of sewage through the sewer pipe, the following are to be properly inspected:
scouring of sewer bottom, differential settlement, manhole block, crack in side wall, sediments and
condition of mouth of connected sewer pipe.
Inspection should be performed on ground, while examination should be performed by the

relevant person entering the manhole and working inside. The inspection items and their descriptions
are given in Table 2.14.
Table 2.14 Inspection and Examination items for Manhole
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An example of the form for recording inspections is shown in Table 2.15.
Table 2.15 Inspection record
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2.7.2 Judgment of Examination Results
Judgment criteria for inspection and examination show ranked levels of abnormal locations, and can
be used for judging the need for cleaning and repairs and for selecting repair methods, etc.
Judgment criteria are used to categorize by symptom the abnormal locations detected during
inspection and examination, to assess the risk level and their impact on others, to judge the need for
cleaning and repairs and to select repair methods, etc.
2.7.3 Cleaning
Manhole cleaning should be performed by the most appropriate work method that suits the actual
conditions of the work location.
In manholes at starting point, junction manholes and manholes at sharp curve of sewers, sand
and silt get deposited and environmental problems such as foul odours occur. For this reason,
periodic cleaning is necessary. Moreover, when large debris flows in, it should be removed immediately
otherwise there is a possibility of an overflow accident, float-off and dispersion of cover.
Manhole inspection should be generally carried out together with the cleaning of the sewer. The work
on the silt and sand in the bottom part should be pursuant to cleaning of the sewer pipe, while the dirt
on the sidewall should be cleaned by high-pressure jet washing vehicle.
2.7.4 Rehabilitation
Degradation of functions due to damage should be confirmed and necessary repairs and
rehabilitation of the manhole should be carried out.
Manhole repair methods may be classified into watertight construction method, lining method, partial
repair method (open-cut method), and manhole cover replacement method. (Refer to Sec. 3.37 of
the Part A manual)
Before repairs, the objectives of the repairs should be clarified, work conditions studied, and items
below should be paid attention to, and then repairs should be carried out.
1. If cover is worn out or damaged, it should be replaced immediately.
2. If steps are corroded, and if they need to be replaced, they should be replaced with corrosion
resistant fittings.
If internal parts of manhole and sewer bottom are damaged or worn out, the entire manhole should
be replaced immediately.
2.8 CROSS DRAINAGE WORKS
For sewer collection system, cross drainage work in an inverted siphon is a typical work. Therefore,
in this section, maintenance work is described hereafter.
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2.8.1 Inspection and Examination
Inspection of inverted siphon should be carried out by inspection methods similar to those of the
manhole and this is shown in Table 2.16 .
Table 2.16 Typical inspection items for inverted siphon
However, inspection of inverted siphon itself should be carried out considering the characteristics
listed below.
• The inverted siphon pipe is always in full flow, and the inverted siphon chamber in the upstream
part is constructed such that suspended substances and sand/silt are likely to accumulate
and deposit easily. There are risks of corrosion or gas generation in the facility because of the
decomposition of these substances.
• The inverted siphon chamber is provided with a flashboard, and it should be checked to confirm
that it is usable.
2.8.2 Criteria for Judging Examination Results
Judgment criteria for inspection and examination show ranked levels of abnormal locations, and
can be used for judging the need for cleaning and repairs and for selecting repair methods. The
judgment criteria for inverted siphon should be the same as the judgment criteria for sewer pipe.
2.8.3 Cleaning
The construction of the inverted siphon is such that wastewater always remains in it at all times,
hence sand, silt and sludge is likely to deposit easily. This requires periodic cleaning to prevent
overflow and foul odour problems beforehand. An effective cleaning method should be selected when
cleaning the inverted siphon, and work that gives adequate consideration to safety measures should
be implemented. Cleaning should be performed at least once a year.
A. Replacing water in the inverted siphon
The submersible pump and generator used for replacing water in the inverted siphon should be
selected appropriately considering the influent flow rate and the head, and a replacement plan with
adequate margin should be formulated.
B. Cleaning of inverted siphon manhole
The main cleaning methods of sand trap of inverted siphon manhole are vacuum truck cleaning
and manual cleaning. Table 2.17 mentions the cleaning method.
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Table 2.17 Cleaning method
C. Cleaning of inverted siphon sewer
Inverted siphon sewer should be cleaned together with the cleaning of general sewers. After
sucking up the sewage in the manhole by submersible pump, the manhole on the upstream side
should be cleaned, and then the manhole on the downstream side and the insides of the sewer
should be cleaned. The ease or difficulty of work depends on the pipe diameter, number of cables
and closing equipment, but if the head exceeds 20 m, especially powerful vacuum trucks may need
to be used. Work should be performed according to sewer cleaning by combining mechanical and
manual means. Figure 2.41 shows the cleaning work.
Figure 2.41 Inverted siphon cleaning work
2.9 PRESSURE / VACUUM SEWER
2.9.1 Pressurized Sewer System
Pressure sewers are meant for collecting sewage from multiple sources to deliver to an existing
collection sewer, and/or to the STP. These sewers are not dependent on gravity. The principle
advantages are the ability to sewer areas with undulating terrain, rocky soil conditions and high
groundwater tables as pressurized sewers can be laid close to the ground and anchored well
without infiltration. Exfiltration can be quickly detected and corrected. Moreover, this sewer
allows smaller diameter pipes and road crossings by CI or DI pipes with trenchless technology to be
laid inside a casing pipe and installation without disrupting traffic, without opening trenches across
paved roadways, or moving existing utilities, etc. A disadvantage is the need to ensure unfailing
power supply to the grinder pump.
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2.9.2 Vacuum Sewer System
The vacuum sewer collects sewage from multiple sources and conveys it to the STP. As the name
suggests, a vacuum is maintained in the collection system and when a house sewer is opened to
atmospheric pressure, sewage and air are pulled into the sewer, whereby the air forms a “plug” in
the line, and air pressure pushes the sewage towards the vacuum station. This differential pressure
comes from a central vacuum station. These sewers can take advantage of available slope in the
terrain, but have a limited capacity to pull water uphill may be to approximately 9 m. A disadvantage
is the need to ensure unfailing power supply to the grinder pump.
2.9.3 O&M of Systems
The pressurized systems or vacuum systems are not familiar in India. Therefore, O&M is not
explained here. Only systems characteristics of pressurized sewer and vacuum sewer are shown
in Table 2.18.
Table 2.18 Pressurised sewer and vacuum sewer
2.10 HOUSE SERVICE CONNECTION
House connections or service connections to the public or municipal sewer, should preferably be
approved by the Maintenance Engineer. It is necessary to ensure that the fittings and pipes in the
houses are according to the bye laws or rules or regulations in force.
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If such bye laws, rules or regulations do not exist, then reference may be made to the relevant
IS code of practice. House connections may be of minimum size of 100 mm in diameter and should
preferably be connected to the Municipal or Public sewer through a manhole. When the “Y or T”
connections are allowed, extreme care must be taken when breaking the sewer pipeline and
inserting the “Y or T” saddle. It should be noted that “Y or T” connections are not allowed for future
systems and is allowed only for existing in public sewers. Similarly, the connection to the manhole
must be properly done and closed. Care has to be taken so that the brickbats or construction
materials are not allowed to fall and gather in the manhole. This extraneous material is largely
responsible for persistent clogging of the sewer lines.
It should also be ensured that the house fittings are properly equipped with traps not only to prevent
the ingress of sewer gases into the houses but also to ensure that large objects do not find their
way into the sewers. Similarly, it should be ensured that any liquid or material which is likely to be
injurious to the material of the sewer line or to prejudicially interfere with its contents or be a hazard
to the workmen engaged in the maintenance of the sewer lines, like very hot water, acids, chemicals,
etc., are not allowed.
2.10.1 Inspection and Examination
Inspection of lateral sewer and house inlet (household) should be carried out if deemed necessary
from documents and data, and cross connections and mains should be studied. Clogging of lateral
sewer and sedimentation of house inlet are the items to be inspected.
Examination of lateral sewer by TV camera should be carried out after high pressure washing of the
lateral sewer. The insides of the pipe should be examined by TV camera, and recorded on video tape.
TV camera for lateral sewer is used as a direct view camera, and the camera head is pushed by a
rod towards the main from the public inlet. In addition, there is a method of examination by which
the camera head is pushed in by a hard cab tire cable. Figure 2.42 and Figure 2.43 (overleaf) show
working diagrams of examination of lateral sewer by TV camera.
Source: EPA, 2003

Figure 2.42 Portable TV system for small-diameter pipe
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Source: EPA, 2003
Figure 2.43 Applications of portable TV system in difficult to access locations
Features of examination of lateral sewer by TV camera
1. If power supply is ensured, the vehicle loaded with TV camera can work even in locations where
access for humans is not possible.
2. By connecting the monitor to the vehicle loaded with TV camera, character data can be displayed
on the monitor screen.
3. The standard examination distance per location during examination of lateral sewer by TV camera
is 5 m maximum.
4. Procedure for examination of lateral sewer by TV camera is shown in Figure 2.44.
Figure 2.44 Work procedure for examination of lateral sewer by TV camera
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2.10.2 Criteria for Judging Examination Results
These criteria should adhere to the inspection criteria for sewer pipes.
2.10.3 Cleaning
Cleaning should conform to the cleaning procedure for sewer pipes.
Rehabilitation should conform to the rehabilitation procedure for sewer pipes.
2.11 SAFETY PRACTICES
Sewer cleaning is an occupation that has an overall accident frequency rate that is relatively higher
than any other industry. The employer has the responsibility of providing the worker with a safe place
to work. Nevertheless, the worker has the overall responsibility and must ensure that it is a safe place
to work. This can only be done by constantly thinking of safety and working safely.
The worker has the responsibility of protecting not only himself, but also all other plant personnel
or visitors by establishing safety procedures for the plant and then ensuring they are followed. He
must train himself to analyze jobs, work areas and procedures from a safety standpoint and learn to
recognize potentiality hazardous actions or conditions. When he recognizes a hazard, he must take
immediate steps to eliminate it through corrective action. If correction is not possible, guard against
the hazard by proper use of warning signs and devices / by establishing and maintaining safety
procedures. As an individual, the supervisor can be held liable for injuries or property damage, which
results from an accident caused by his negligence.
Remember, “accidents don’t happen - they are caused!” Behind every accident, there is a chain
of events, which leads to an unsafe act, unsafe condition or a combination of both. Accidents may
be prevented by using common sense, applying a few basic safety rules and acquiring a good
knowledge of the hazards unique to the job as a plant supervisor.
2.11.1 Accidents related to Sewer Facilities
2.11.1.1 Need for Traffic Control
The primary function of streets is to provide for the movement of traffic. A common secondary
use within the right-of-way of streets is for the placement of public and private utilities such as
sanitary sewers. While the movement of traffic is very important, streets need to be constructed,
reconstructed or maintained, and utility facilities need to be repaired, modified or expanded.
Consequently, traffic movements and street or utility repair work must be regulated to provide
optimum safety and convenience for all.
Working in a roadway represents a significant hazard to a collection-system operator as well as

pedestrians and drivers. Motor vehicle drivers can be observed doing random things like reading,
talking on cell phones, etc., rather than concentrating on driving.
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At any given time of the night or day, a certain percentage of drivers may be expected to be driving
while under the influence of drugs or alcohol. Given the amount of time collection-system operator’s
work in traffic while performing inspection, cleaning, rehabilitation and repairs, the control of traffic
is necessary, if we want to reduce the risk of injury or death while working in this hazardous area.
The purpose of traffic control is to provide safe and effective work areas and to warn, control,
protect, manage vehicular and pedestrian traffic. It can be accomplished by appropriate use of
traffic control devices.
Most states, counties, and cities have adopted regulations to control traffic and reduce the risk
under different circumstances. This section illustrates examples of traffic control, which may or may
not meet the specific requirements of the laws in all geographical areas, but should serve to create
awareness of various aspects of traffic control.
At any time traffic is affected, appropriate authorities in the area must be notified before leaving for
the job site. These could be state, country or local depending on whether it is a state, country or local
street. Frequently, a permit must be issued by the authority that has jurisdiction, before traffic can
be diverted or disrupted. In some cases, traffic diversion or disruption may have an impact on the
emergency response system in the area, such as access by fire or police, and so these
agencies may be involved as well in most cases, to plan ahead to secure permits and notify
authorities. This may mean only a phone call or two or it could mean several days or weeks of
advance planning, if the need is to make extensive traffic control arrangements.
Upon arrival at the job site, look for a safe place to park vehicles. If they are to be parked in the street
to do the job, route traffic around the job site before parking vehicles in the street. If practical, park
vehicles between oncoming traffic and the job site to serve as a warning barricade and to discourage
reckless drivers from ploughing into operators.
2.11.1.2 Safety Measure to be taken before any manhole entry
All workers assigned to enter sewer manholes should be provided with proper safety equipment
as recommended here.
1. Approved gas detector (Properly calibrated)

2. Fresh air blower
3. Safety harness, rope and tripod safety system
4. Approved hard hat
Following guidelines may be adopted to ensure safety in manhole:
A. Oxygen content must be at least 19.5 % in the confined space of the manhole measured at all
levels (bottom, middle and top). Safe oxygen level is considered if it ranges between 19.5 % and
21 %. Nobody should enter the manhole if oxygen level is below 19.5 % and more than 21 %.
B. Ventilate the sewer line by opening at least two or three manholes on both upstream and
downstream where work is to be carried out. This is mandatory where adequate
blowers for ventilating sewers are not available. The manholes should be opened at least one
hour before the start of operation.
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The opened manhole must be properly fenced or barricaded to prevent any person, especially
children, from accidentally falling into the sewer. Dummy cover with BRC welded fabric or
wire-net may be used.
C. Fresh air blower ventilation system should be used as far as practicable. It is desirable to operate
blowers for at least 30 minutes before start and during the cleaning operation.
D. Measure gas inflammability in manholes using detector.
E. Presence of toxic gases may be tested before entry of a person in manhole/ sewer line and also
in between if the operations are for longer period.
F. All workers should use safety harness and lifeline before entering the sewer line. At least one
support person at the top must be provided for each person entering the manhole. The person
entering the manhole/ sewer line must be monitored using signal/camera /CCTV etc., throughout
the operation period.
G. Structural safety of manhole rungs or steps must be tested before entering the manhole. Portable
aluminium ladder must be available during the work period where necessary. The portable ladder
must be properly seated or fixed during use.
H. Ensure that no material or tools are located near the edge, which can fall into the manhole and
injure the workmen.
I. Lower all tools to the workmen in a bucket fixed with rope and pulley.
J. Lighting equipment used during sewer cleaning must be explosion-proof and fire-proof.
K. Caution signboards must be displayed around open manholes during working period.
L. Smoking, lighting open flames or gadgets producing sparks must be prohibited inside the
manhole as well as in the immediate vicinity of open manholes.
M. All workers entering the manhole must be provided with protective gear and proper equipment.
Use of portable gear and equipment must be monitored strictly.
N. Gas masks for respiratory protection must be available for use by the workers. The workers must
be trained to use the gas masks properly.
O. Sewer inspection and examination guidelines referred to in Section 2.2.5 may be followed as and
when necessary.
(The Honourable Supreme Court of India has directed the need for proper equipment, adequate
protection and safety gear to sewer workers, who enter into the manhole for cleaning blocks.
Ref: Delhi Jal Board Vs. National Campaign for Dignity & Rights of Sewerage and Allied Workers and
others.). Please refer to Appendix B.9.3 of this manual.
When entering a large sewer system, it may be required to use special equipment. The type of
equipment might include atmospheric monitoring devices with alarms.
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In the event of a sudden or unpredictable atmospheric change, an emergency escape breathing

apparatus (EEBA) with at least a 10-minute air supply should be worn for escape purposes.
2.11.2 Measures against Accidents
These are dealt with in Chapter 9.
2.11.3 Information to Prevent Accidents and Records
Information to prevent accident and records are dealt with in Chapter 9.
2.12 TROUBLESHOOTING
Refer to appendices for troubleshooting for sewerage collection system.
2.13 SUMMARY
The purpose of maintenance of sewerage collection system is to minimize stoppage of functions.

The following cycle should be adhered to:
O&M engineers find out problems related to their sewer system based on information obtained from
inspections or examinations on the facilities. To solve the problems, they need to make a decision on
rehabilitation actions considering prioritization of each facility.
When the facilities are rehabilitated, records of inspections as well as those of rehabilitation
should be kept.
The following cycle shown in Figure 2.45 is regarded as essential to achieve the goal of sewer
system O&M: “Inspection”, “Condition assessment”, “Decision making on rehabilitation actions”,
“Rehabilitation”, and “Next inspection.”
Figure 2.45 O&M cycle
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Part B: Operation and Maintenance CHAPTER 3: PUMPING STATION
CHAPTER 3: PUMPING STATION
3.1 INTRODUCTION
Pumping stations are either as in-line for lifting the sewage from a deeper sewer to a shallow sewer or
for pumping to the STP or the out fall. They are required where low lying development areas cannot
be drained by gravity to existing sewerage infrastructure, and/or where development areas are too far
away from available sewerage infrastructure to be linked by gravity. The O&M of pumping systems
presented here applies to all such types of pumping stations.
3.2 TYPES AND STRUCTURE OF PUMPING STATIONS
The type of pumping stations can be (a) Horizontal pumps in dry pit, (b) Vertical pumps in dry pit,
(c) Vertical pumps in suction well and (d) Submersible pumps in suction sump. All these types
include a sewage-receiving sump, which is called suction sump or wet well. These types of pump
arrangements are shown in Figure 3.1.
Source: CPHEEO, 1993

Figure 3.1 Typical drywell and wetwell installations
3.2.1 Dry Pit
The size of the dry pit should be adequate for the number of pumps planned and should be such
as to handle the sewage load at the desired pumping capacity. Allowance should also be made for
future requirements of additional or larger pumps. In the configuration, (a) separate dry pit and wet
well are required: one to hold the sewage, and one to house the pumps and appurtenances. This
option is required for installations where the pumps will otherwise need separate priming and
where-as otherwise long suction pipes are needed.
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It is typically used to pump large volumes of raw sewage, where uninterrupted flow is critical
and sewage solids could clog suction piping. It is also used to pump solids in pipe galleries
between digesters or other solids-handling equipment. While construction costs may be
higher and a heating, ventilation and cooling system is necessary when installed below
the floor level, this configuration is best for O&M activities because operators can see and
touch the equipment.
3.2.2 Suction Sump or Wet Well
Sewage sump is a compartment or tank in which sewage is collected. The suction pipe of a
pump may be connected to the wet well or a submersible pump may be located in the wet well.
Sewage sump design depends on the type of pumping station configuration (submersible or
dry well) and the type of pump controls (constant or variable speed). Wet wells are typically
designed to prevent rapid pump cycling but small enough to prevent a long detention time and
associated odour release.
Sewage sumps should always hold some level of sewage to minimise odour release. Bar screens
or grinders are often installed in or upstream of the wet well to minimise pump clogging problems.
Instead of manually operated screens at the bottom, which requires the staff to get down into the
screen sump, it is better to install mechanical bar screens, which can automatically remove the
screenings and lift the same safely above the ground level. There can also be two such screens one
after the other for coarse screenings and fine screenings. This will require rectangular channels to
maintain longitudinal non-turbulent linear flow.
3.2.3 Lift Stations
In general, lift stations are invariably used in gravity sewer network where depth of cut of
sewers poses a problem in high water prone areas. The procedure is to sink a wet well on the road
shoulder or an acquired plot after the shoulder and divert the deeper sewer there. The submersible
pump will lift the sewage and discharge it to the next on line shallow sewer. This is a very useful
practice in such locations.
Equipment located in the wet well should be minimized, including suction and discharge valves,
check valves, or other equipment that require routine, periodic maintenance. This equipment can be
located in separate and suitable dry pits located adjacent to the wet well to facilitate accessibility and
maintenance for the operator.
3.2.4 Operation and Maintenance
Pumping machinery is subjected to wear & tear, erosion and corrosion due to its nature of
functioning, and therefore it is vulnerable to failures. Generally, failures or interruptions are mostly
attributed to pumping machinery rather than any other component. Therefore, correct operation
and timely maintenance and upkeep of pumping stations and pumping machinery are of vital
importance. Sudden failures can be avoided by timely inspection, follow up actions on observations of
inspection and planned periodical maintenance. Downtime can be reduced by maintaining inventory
of fast moving spare parts. Obviously due attention needs to be paid to all such aspects for efficient
and reliable functioning of pumping machinery.
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3.2.4.1 Operation of the Pumps
The following points should be observed while operating the pumps.
A. Dry running of the pumps should be avoided.
B. Centrifugal pumps if installed with negative suction should be primed before starting.
C. Pumps should be operated only within the recommended range of the head-discharge
characteristics of the pump.
• If pump is operated at a point away from duty point, the pump efficiency normally reduces.
• Operation near the shut-off point should be avoided, as it causes substantial recirculation
within the pump, resulting in overheating of sewage in the casing and consequently,
overheating of the pump.
D. As far as possible positive suction is to be provided to avoid priming during design itself.
E. Voltage during operation of the pump-motor set should be within ±10 % of the rated voltage.
Similarly, current should be below the rated current shown on the name plate of the motor.
F. When parallel pumps are to be operated, the pumps should be started and stopped with a time
lag between two pumps to restrict change of flow velocity to minimum and to restrict the dip in
voltage in the incoming feeder and should be adequate to allow the pump head to stabilise.
G. When the pumps are to be operated in series, they should be started and stopped sequentially,
but with minimum time lag. Any pump next in sequence should be started immediately after the
delivery valve of the previous pump is even partly opened. Due care should be taken to keep
open the air vent of the pump next in sequence, before starting that pump.
H. The stuffing box should allow a drip of leakage to ensure that no air passes into the pump and that
the packing gets adequate wetness for cooling and lubrication. When the stuffing box is sealed
with grease, adequate refill of the grease should be maintained.
I. The running of duty pumps and standby pumps should be scheduled so that no pump
remains idle for a long period and all pumps are in ready-to-run condition. Similarly, the running
schedules should be ensured so that all pumps do not wear equally needing simultaneous
overhaul.
J. If any undue vibration or noise is noticed, the pump should be stopped immediately and the cause
for vibration or noise should be checked and rectified.
K. Generally, the number of starts per hour shall not exceed four. Frequent starting and stopping
should be avoided as each start causes overloading of motor, starter, contactor and contacts.
Although overloading lasts only for a few seconds, it reduces the life of the equipment.
L. Troubles in a sewage pumping station can be mostly traced to the design stage itself. This is
all the more true when too much grit is likely to come into the sewage pumping stations from
sewage at monsoon time, which is difficult to handle. Hence, sewers should not collect any
storm water.
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3.2.4.2 Undesirable Operations
The following undesirable operations should be avoided:
A. Operation at higher head
A pump should never be operated at a head higher than the maximum recommended head
otherwise such operation may result in excessive recirculation in the pump, and overheating of the
sewage and the pump. Another problem that arises if a pump is operated at a head higher than the
recommended maximum head is that the radial reaction on the pump shaft increases causing
excessive unbalanced forces on the shaft, which may cause failure of the pump shaft. As a useful guide,
appropriate marking should be made on the pressure gauge. Efficiency at a higher head is normally
low and such an operation is also inefficient.
B. Operation at lower head
If a pump is operated at a lower head than the recommended minimum head, the radial reaction
on the pump shaft increases causing excessive unbalanced forces on the shaft, which may cause
premature wear of bearings and possibly shaft failure if persisted. As a useful guide appropriate
marking should be made on both pressure gauge and ammeter. Efficiency at a lower head is
normally low, hence such an operation is inefficient. In such cases, it is advisable to throttle the
delivery side valve to create more head to work within safe head. This will also reduce the power. If
this is a design flaw additional head has to be created at tail end by elevating the delivery. However,
these are not energy efficient solutions; change of impeller to suit the actual head is the solution.
C. Operation on higher suction lift
If a pump is operated on suction lift higher than the permissible value, pressures at the eye of impeller
and the suction side fall below vapour pressure. This results in flashing of sewage into vapour. These
vapour bubbles collapse during passage, resulting in cavitation in the pump, causing pitting on the
suction side of impeller and casing, and excessive vibrations. In addition to mechanical damage due
to pitting, pump discharge also reduces drastically. Typical damage to impeller and sometimes to the
casing is shown in Figure 3.2.
Source: http://greathub.hubpages.com/hub/piping-and-pipes#
Figure 3.2 Typical Cavitation Damage of an Impeller
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D. Operation of the pump with low submergence
Minimum submergence above the bell-mouth or foot-valve is necessary to prevent entry of

air into the suction of the pump, which gives rise to the vortex phenomenon, causing excessive
vibration, overloading of bearings, reduction in discharge and in the efficiency. As a useful guide, the
lowest permissible sewage level should be marked on the water level indicator. Usually the pump
manufacturer indicates the minimum height of submergence. In the case of submersible pumps, the
minimum depth is needed to ensure cooling of the motor while running.
E. Operation with occurrence of vortices
If vibration continues even after taking all precautions, vortex may be the cause. Vortex should be
stopped by using anti vortex fittings as described in chapter 4 of Part A of the manual:
A well-planned maintenance programme for pumping systems can reduce or prevent unnecessary
equipment wear and downtime. (The following maintenance information applies to both sewage and
solids pumping systems.)
The following is a maintenance checklist for a basic pumping-station:
• Check the wet well level continuously (whenever necessary).
• Record each pump’s “run time” hours (as indicated on the elapsed-time meters) at least once in
a day and confirm that the pumps’ running hours are equal.
• Ensure that the control-panel switches are in their proper positions.
• Ensure that the valves are in their proper positions.
• Check for unusual pump noises.
• At least once a week, manually pump down the wet well to check for and to remove debris that
may clog the pumps.
• Inspect the float balls and cables and remove all debris to ensure that they operate properly.
Twisted cables are to be released that may affect automatic operations.
• If a pump is removed from service, adjust the lead pump selector switch to the number that
corresponds to the pumps remaining in operation. (This allows the lead pump levels to govern the
operating pump’s starts and stops.).
3.2.4.3 Piping and Appurtenance Maintenance
Properly maintaining pumping-station pipelines and other appurtenances can minimize pump loads.
Excessive head losses on either the suction or the discharge side of a pump can increase energy
use and the wear rate and consequently, the O&M costs. Excessive head losses also may lead to
process or treatment problems because solids move slower, so the proper solids balance is not
maintained. Operators can monitor head losses by routinely checking the pressure gauges on both
sides of the pumps.
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When operators notice excessive head losses (indicated by a pressure drop on the suction side
of the pump or an increase in pressure on the discharge side), they should determine whether the
losses are a result of partial clogging, a restriction somewhere in the line, or materials built up on
the pipe wall. To find clogs, operators should start by checking the pressure at various points in the
suction and discharge piping, and look for spots with abrupt head loss (such as valves or other
constrictions). If something is caught in a valve or other appurtenance, the operator should stop the
pump and physically open out the valve head and remove the blockage. In smaller pumps, it is easier
to remove the entire valve, disassemble and remove the blockage, reassemble and refit. During such
time, other pumps shall be run. Scum build-up problems typically are addressed via source control
(for instance, by installing grease traps in the collection system at locations suspected or known to
generate grease, such as restaurants, etc.).
3.3 GATES, VALVES AND ACTUATORS
3.3.1 Sluice Gate
A sluice gate (Figure 3.3) is traditionally a wooden or metal plate, which slides in grooves in the sides
of the guide channel.
Sluice gates are commonly used to control sewage levels in STPs.
Source: EPA, 2008

Figure 3.3 Sluice gate
Attention should be paid to the following points for proper operation:
A. Test for proper operation
Operate inactive sluice gates by smearing grease on stem threads.
B. Clean and paint
Clean sluice gate with wire brush and paint with proper corrosion-resistant paint.
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C. Adjust for proper clearance.
For gates seated against pressure, check and adjust top, bottom, and side wedges until each
wedge applies nearly uniform pressure against gate in the closed position. This shall be done by the
manufacturer and not the operator.
D. Check for the following:
• Ensure unobstructed operation of gate and headstock.

• Ensure that the spindle is not touching the stem guide.
• Remove foreign matter like paint, concrete, etc. in the fully open position of gate.
E. Do’s for sluice gates
• Operate the gate at least once in every three months.

• Check the nuts of all construction and foundation bolts once in a year. Tighten the bolts, if loose.
• Examine the entire painted surface for any signs of damage to the protective paint.
F. Don’ts for sluice gates
• Do not remove lock plates until the gate has been properly installed.
• Do not keep the gate out of operation for more than three months.
• Do not forget to set the stop nut in the correct position.
• Do not disturb the adjustment of wedge block bolts/studs.
• Do not over torque the crank handle/hand wheel.
3.3.2 Valve
On the delivery side of centrifugal pumps, a non-return valve is necessary to prevent back-pressure
from the delivery head on the pump, when the pump is shut off. To avoid water-hammer, which is
likely to be caused by the closure of the valve, the valve may be provided with an anti-slam device,
which may be either a lever and dead-weight type, a spring-loading type or the dash pot type.
Pumps may be run in parallel with different permutation of the standbys. Isolation valves would be
needed to isolate those pumps, which are to be idle. Generally, the isolating valves are gate valves,
which should preferably be of the rising stem type, since this type offers the advantage of visual
indication of the valve-position.
For exterior underground locations, gate valves are generally used.
3.3.2.1 Gate Valve
A gate valve is a valve that opens by lifting a round or rectangular gate/wedge out of the path of the
fluid as shown in Figure 3.4 overleaf. The distinct feature of a gate valve is that the sealing surfaces
between the gate and seats are planar. The gate faces can form a wedge shape or they can be parallel.
Typical gate valves should never be used for regulating flow, unless they are specifically designed for
that purpose. Gate valves require maintenance as indicated overleaf:
3-7
Source: EPA, 2008

Figure 3.4 Gate valve
A. Replace packing
Modern gate valves can be repacked without removing them from service. Before repacking, open
the valve wide. This prevents excessive leakage when the packing or the entire stuffing box is
removed. It draws the stem collar tightly against the bonnet bushing on a rising stem valve.
B. Operate valve
Operate inactive gate valves to prevent sticking.
C. Lubricate gearing

Lubricate gate valves as recommended by the manufacturer. Lubricate thoroughly any gearing in
large gate valves. Wash open gears with solvent and lubricate with grease.
D. Lubricate rising stem threads
Clean threads on rising stem gate valves and lubricate with grease.
E. Lubricate buried valves
If a buried valve is hard for working, lubricate it by pouring oil down through a pipe that is bent at the
top end oiling the packing follower below the valve nut.
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3.3.2.2 Non-Return Valve (Check Valve)
Normally, a check valve is installed in the discharge of each pump to provide a positive shutoff from
force main pressure when the pump is shut off and to prevent the hydraulic force from draining
back into the wet well. The most common type of check valve is the swing check valve, which is
shown in Figure 3.5.
Figure 3.5 Check valve
This valve consists of a valve body with a clapper arm attached to a hinge that opens when the pump
starts operating and closes to seal when the pump is shut off.
Check valves must close before the water column in the pipe reverses flow; otherwise, severe
water hammer can occur when the clapper arm slams against the valve body seat. If this occurs, an
adjustment of the outside weight or spring is usually required. A traditional clapper type of check
valve has a lever on the extended shaft, which allows adjustment of the weight on the arm or spring
to vary the closing time. Wear occurs within the valve primarily on the clapper hinge-and-shaft
assemblies and should be checked annually for looseness.
The preventive maintenance is to be done only by the manufacturer.
A. Inspect Clapper Facing
Open valves to observe condition of facing on swing check valves equipped with neoprene
seats on clapper.
If metal seat ring is scarred, dress it with a fine file and lap with fine emery paper wrapped
around a flat tool.
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B. Check Shaft Wear
Check shaft wear on balanced disc check valve since disc must be accurately positioned in
the seat to prevent leakage.
3.3.2.3 Non-Return Valve (Ball Type)
Non-return valve depends on a light weight and suitable coated ball moving inside the flowing pipe
to occupy an elevated angular position while the fluid is in pumping and dropping back to close the
reverse flow through the pipe. Because it is a sphere sitting over a circular opening, it is expected
to seat properly and seal the reverse flow. The material of the ball, the coating and its sturdiness
against dents caused by the slide are important aspects. The ball is replaced by opening the top
flange after switching off the pump. This can be installed in any position, vertical or horizontal.
A non-return valve is shown in Figure 3.6.
Figure 3.6 Typical ball type check valve
When flow occurs, the ball is lifted into the angular piping and is held there because its weight is
lighter than the sewage and the velocity of flow. When the flow stops, it slides back and seals.
3.3.2.4 Butterfly Valve
Butterfly valves are another type of valve that have been successfully used as suction and discharge
isolation valves in pumping stations. They are frequently used in sewage plants where waste streams
with a high solids content are encountered, such as in sludge pumping systems. A butterfly valve
consists of the valve body and a rotating disc plug that operates through 90 degrees.
This is usually a disc rotated by 90 degrees by external handle. In the open position, the disc is in
line with the flow. In the closed position, the disc is at 90 degrees to the flow and it stops the flow.
Usually, the axis is vertical although horizontal axis arrangement may also be used in smaller sizes.
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The closing and opening can be manual or mechanized. The butterfly valves occupy less space and
are generally preferred for pipe sizes larger than 150 mm.
Many agencies specify butterfly valves as opposed to gate valves because they are less susceptible
to plugging.
Butterfly valves require the following preventive maintenance to be done by the manufacturer:
A. Adjust gland
The adjustable gland holds the plug against its seat in the body and acts through
compressible packing, which functions as a thrust cushion.
Keep gland tight enough at all times to hold plug in contact with its seat. If this is not done, the
lubricant system cannot function properly, and solid particles may enter between the body
and plug and cause damage.
B. Lubrication
Apply lubricant by removing lubricant screw and inserting stick of butterfly valve lubricant for
stated temperature conditions.
Be sure to lubricate valves that are not used often to ensure that they are always in operating
condition. Leave lubricant chamber nearly full so that extra supply is available by turning
the screw down. Use lubricant regularly to increase the valve efficiency and service, promote easy
operation, reduce wear and corrosion, and seal valve against internal leakage.
3.3.3 Actuators
These are replacements for physical operation by the operators. Actuators are used for automation
of valves. An actuator rotates the valve spindle or lifts and drops the same.
A. Electric geared motor actuator
The actuator consists of a rotor stator unit driving an output shaft through a single stage-worm
reduction gear, which incorporates an automatic mechanical device for changing manual
drive to power drive. The actuator includes a travel-limit switch unit and a torque switch unit,
and is of totally enclosed construction. When power fails, electric motor driven gear actuators
retain their positions. When power supply returns, pay attention how the valves move. The electric
motor driven gear actuator is shown in Figure 3.7 overleaf.
B. Solenoids
Solenoids are the most common actuator components. It consists of a moving ferrous core
(a piston) that moves inside wire coil. Normally the piston is held outside the coil by a spring.
When a voltage is applied to the coil and current flows, the coil builds up a magnetic field that
attracts the piston and pulls it into the centre of the coil. The piston can be used to supply a
linear force. Diaphragm valve have small holes on it. The holes should be free from clogging
by debris otherwise the diaphragm may not open.
3 - 11
Figure 3.7 Electric motor driven gear actuator
C. Pneumatics
Pneumatic systems have much in common with hydraulic systems with a few key differences. The
reservoir is eliminated as there is no need to collect and store the air between uses in the pneumatic
system. Also because air is a gas, it is compressible and regulators are not needed to recirculate the
flow; however, since the gas is compressible, the systems are not as stiff or strong.
In general, the pneumatics are liable to cause accidents such as when the air hose suddenly
pulls out of the hose clamp and jets high pressure air on persons nearby. This should be avoided.
The electric geared motor type is to be preferred. The pneumatic valve is shown in Figure 3.8.
Figure 3.8 Pneumatic valve
D. Hydraulic system
Actuator (hydraulic motor and hydraulic cylinder) is operated by hydraulic fluids (hydraulic oil),
which is pressurised by hydraulic pump driven by an electric motor. Generally, a smooth movement
and variable speed can be achieved. Moreover, the installed relief valve can prevent the system
from breakdown. It should be noted that hydraulic oil leaks as pressure increases. Check for
oil leakage regularly. Hydraulic system should be kept clean because it is vulnerable to dust
or rust. Take precautions to avoid fires because the hydraulic oil is combustible.
3 - 12
In all cases, preventive maintenance by manufacturer shall be done periodically and a wall chart
exhibited on site.
3.4 SCREEN
Screenings in sewage from the incoming sewer below the ground level need to be separated and
lifted above ground level, and removed either by mechanical or manual method.
3.4.1 Types of Screens
3.4.1.1 Coarse Screens
Coarse screens are usually bar screens consisting of vertical or inclined bars spaced at equal
intervals across a channel through which sewage flows. The openings are usually 25 mm.
Hand-cleaned screens are usually inclined at 45 degrees to the horizontal.
3.4.1.2 Medium Bar Screens
Medium bar screens have clear openings of about 12 mm.
3.4.1.3 Fine Screens
Fine screens are mechanically-cleaned devices. Fine screens may be of the drum or disc type,
mechanically cleaned and continuously operated. They are also used for protecting the beaches
where untreated sewage may have to be discharged into the sea for disposal by dilution.
3.4.2 Screenings Removal Method
3.4.2.1 Manual Bar Screen
Hand cleaned screens should be cleaned as often as required to prevent backing up of sewage.
A manually-cleaned bar screen is shown in Figure 3.9.
Source: EPA, 2008

Figure 3.9 Manual bar screen
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The following are important for O&M of manual bar screen:
A. Preventive maintenance for checking and repairing the following once a week
Check whether the standing platform is at least 2 m wide with the first 1 m as slotted. An example of
a risky platform is presented in Figure 3.10.
Figure 3.10 An example of risky platform

There is no space for the operator to stand after he has lifted and dumped screenings on the
platform. Because of the lack of space, he may move backwards and fall into the sewage channel.
Also, screens should be inclined to the horizontal by an angle of 60 degrees or more, otherwise, the
operator has to bend forward. The rear side of the platform should have handrails. If handrails are not
provided, enter this point in the site book.
1. Check the condition of ladders and paint them periodically.

2. Verify that there are no broken metal parts that protrude outside.
3. Once a month check the rigidity of handrails.
4. Verify the platform for its sturdiness by gently setting the foot on it.
Verify that the lighting is not in front or behind the operator. It should be above the operator, at least
2.5m high and mounted on the sidewall or separate lamp posts. These lights should not have local
on-off switches and must be fully lit in the nights. Verify that the operator platform and slotted platform
have 3m head room and provided with roof so that the operator is not drenched and he can lift the
cleaning rake freely.
B. Regular maintenance on a daily basis and repairs
1. Verify that the screen rods have not broken loose.

2. Verify that the cleaning rake is well washed in running water after each use.
3. Verify that gum boots are kept inside a locker covered with mesh.
4. Verify that disposable gloves are available for all 3 shifts and a stock of one month is available.
5. Verify that helmet is available.
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C. Operation
1. Before daily operation, verify all the above. If these points are not met, do not enter the screen
area. Enter all missing items in the site register.
2. If all items are in order, do the cleaning once in four hours in each shift.
3. Ensure that operators do not stand one behind the other. This may cause an accident because
while pulling the rake backwards, the operator in the front may hit and push the operator in the
rear into the sewage channel.
4. Once the screens are cleaned and screenings are deposited on the slotted platform allow them
to drip dry till the next cleaning after 4 hours.
5. Push the screenings with the rake to the side of the platform to drop them into the tipper
positioned there.
6. Move the tipper to the vermin compost site, dump the contents in the pit and cover with earth as
prescribed in Sec.3.4.4 “Disposal of Screenings.”
3.4.2.2 Mechanical Screen (Intermittent and Continuous)
Mechanically cleaned racks are generally erected almost vertically. Additional provision should be
made for manual raking in case the mechanical rakes are temporarily out of order. Plants using
mechanically cleaned screens have controls for:
a. Manual start and stop

b. Automatic start and stop by clock control
c. High level switch
d. High level alarm
e. Starting switch or overload switch actuated by loss of head and
f. Overload alarm.
There are various types of mechanisms in use, the more common being traveling rakes that bring
the screenings up out of the channel and drop them into hoppers or other debris containers.
A typical mechanically cleaned bar screen is shown in Figure 3.11 overleaf. The rotary drum screen
otherwise known as arc screen by United Nations Industrial Development Organization (UNIDO)
is shown in Figure 3.12 overleaf.
In the drawing, the screening rods are in the form of arc. The cleaning takes place when the
meshing teeth at both ends of a diametrical rotating arm plough through the screen openings and
push the screenings upwards. Upon exiting the upper end of the screen, which is well above the
operating sewage level, a built in spring loaded arrangement in the diametrical rods jacks out the
meshing teeth gently, which pushes the screenings gently into a collection trough.
The screenings can be manually removed or a conveyor belt can collect the screenings and drop
them into a container on the ground through a drop chute.
3 - 15
Source: WEF,2010
Figure 3.11 Mechanically-cleaned bar screen
Refer to Sec.5.6 of Part A of the manual for details of screens.

A. Preventive Maintenance
• Verify the equipment manufacturer’s manual for preventive maintenance
instructions and carry out the same (if permitted to be done by the operator).
• Switch off electrical power before doing any work on the mechanical screen.
B. Regular maintenance on a daily basis and repairs
• Before start of the day’s work, check for any friction between metal parts. If friction exists
and the sound is disturbing, disconnect the electric supply and divert all sewage to manual
screens. Enter this action in the site register. Do not perform repairs by unauthorized
personnel because it is dangerous.
3 - 16
Source: TWAD, 2012

Figure 3.12 UNIDO type arc screen
• Check the alignment of the tipper plates. If the screenings are slipping back and are not
going up, allow the machine to work and do not stop it. Enter the abnormality in the site
register and request for visit by the manufacturer’s engineer. Do not perform repairs by
unauthorized personnel because it is dangerous.
C. Operation
• Before start of the day’s work, do not approach the mechanical screen unless you are
wearing, electrical gloves, safety helmet and safety boots.
• Before start of the day’s work, switch off the mechanical screen and restart it. Watch for
any friction or sparks. If you notice sparks, disconnect the electric supply and divert all
sewage to manual screens. Enter the abnormality in the site register. Sometimes, these sparks
can be dangerous and may cause electrocution.
• Follow the procedure for disposing screenings as described earlier.
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3.4.3 Accessories (Conveyors)
Belt conveyors are used in conveying the screenings to the trolley parked by the side of the screen
chamber. Generally, these are meant only for mechanical screens. For manually operated screens,
the water content has to first drip out fully before the screenings can be put on the conveyor. In the
case of mechanical screens, the angle is close to vertical, the height is more and dewatering is
automatic, but this is not the case with manual screens. If it is to be used, then the conveyor belt has
to be behind the operator. The operator first picks up the screenings, drops it on the slotted platform
and allows four hours for the screenings to drip fully. Thereafter, he can lift it by the same fork and
turn it around 180 degrees and place it on the conveyor belt behind him. On the other hand, in smaller
plants he can directly push the screenings to the slotted platform and into the trolley on the ground
after the sidewall. All the guidelines for preventive maintenance, regular day-to-day maintenance and
operation, and site register entries by the operator are the same as before.
3.4.4 Disposal of Screenings
Screenings generally consist of non-bio degradable stuff like plastic sachets, milk packets, shampoo
packets, etc., with very little organic content. Hence, it is best disposed of as a secure landfill, which
should be prevented from direct rainfall and flow of overland rainwater. The procedure specified by
the pollution control authority should be adhered to without fail.
3.5 GRIT REMOVAL
The different types of grit removal equipment are given in chapter 5 of Part-A of the manual. These
are velocity controlled channels, detritors, aerated grit chambers, vortex type, etc.
Almost all these equipment are patented. Each manufacturer has proprietary schedules for preventive
maintenance. These schedules should be followed. Preventive maintenance should be done only by the
manufacturer or the erection contractor who has installed the equipment, and not by the operators.
3.5.2 Regular Day to Day Maintenance
The operator should hose the mechanical parts using the high-pressure hose, and pump the final
treated sewage so that slime does not accumulate. Where flap gates or turnstiles are provided, the
operator should necessarily “exercise” these once a day.
The operator should not enter the chambers unless the sewage entry is blocked, the chamber
has been dry for at least two hours and the operator is wearing an oxygen mask. In the case of
velocity-controlled channels, the trip switch controlled traveling bridge with suspended suction
hoses for each channel connected to a vacuum pump set are standard items. If this system fails
and grit accumulates in the channel, each channel should be taken out of sewage flow. The
scour valve should be opened below the chamber and the sewage after filtering through the
in-built filter port should be allowed to drain to the site drain. Thereafter, the chamber should be
allowed to air dry for at least two hours, high pressure water jetting, draining and air drying cycle
carried out at least three times.
3 - 18
Subsequently, labourers can be deployed to scrap the grit, provided the labourers wear goggles,
gloves, safety shoes and oxygen masks.
In general the vacuum pump is the main source of failure and these types of channels are to be used
only in large STPs where other such equipments are also functioning and qualified operators are
available in all the shifts.
The vortex type grit separators described in chapter 5 of part A manual are simpler devices to lift and
clean the grit and discharge at a convenient elevation above the ground level.
3.5.3 Disposal of Grit
The grit is usually pre-rinsed in the grit removal chamber itself before it is evacuated from it.
Figure 3.13 shows a typical grit chamber.
Figure 3.13 Typical grit chamber
Clean grit is characterized by the lack of odour. Washed grit may resemble particles of sand and
gravel, interspersed with inert materials from households. Grit washing mechanism has to be
included whenever the detention time is more and flow through velocity is less. Unless washed, it may
contain considerable amount of organic matter. This becomes an attraction to rodents and insects
and is also unsightly and odorous. The grit should be contained in a secure landfill as directed by the
local pollution control authority or disposed along with the municipal solid wastes, if permitted.
3.6 PUMP EQUIPMENT
The types of pumps are dealt with in chapter 4 of Part-A of the manual. These are horizontal
centrifugal, vertical shaft centrifugal, dry submersible and wet submersible pumps.
This shall be done only by the manufacturer / his authorized service agency / properly trained staff.
The operator shall not carry out preventive maintenance.
3 - 19
3.6.2 Regular Day-to-Day Maintenance
This should include the tasks as given in Table 3.1.
Table 3.1 Tasks to be addressed in day-to-day regular maintenance
Note: D: Daily, W: Weekly, M: Monthly, Y: Yearly
Proper operation of submersible pump systems requires that minimum submergence should
always be maintained. This is for two primary reasons:
• Prevention of motor overheating

• Prevention of “vortex” and associated problems
The following should be inspected:
• Inspect seal for wear or leakage and repair, if required.

• Visually inspect the oil in the motor housing.
• Remove pipe plug from housing.
• Make sure oil is clean and clear, light amber in colour and free from suspended particles.
• Milky white oil indicates the presence of water.
If the system fails to operate properly, carefully read the instructions supplied during the time of
purchase and perform maintenance recommendations.
Before starting the pump, check the following:
• Check insulation resistance by megger at free end of cable and verify with pump manual.
3 - 20
• Check continuity between ends of motor in the same phase and in all phases.
• Check resistance across moisture sensing wires and verify with pump manual.
• Physically rotate the coupling joint and verify smooth movement.
• Check for leaky oil plug and fix it before starting.
• Check for the bulbs indicating the on–off status of the pump and replace fused bulbs.
• Look for warning lamps for alerting the pumped liquid entering the oil chamber.
• Close the discharge valve before starting the pump. This is also taken care by check valve.
• Open the discharge valve gradually and not all of a sudden.
• While the pump is running at full flow, check the power consumed to be within the duty point.
• If the power consumed is very high, stop the pump and inform the manufacturer.
• Switch off the pump only after the discharge valve is closed.
3.6.4 Accessories
3.6.4.1 Oil and Grease
• Pumps, motors and drives should be oiled and greased strictly in accordance with the
recommendations of the manufacturer. Cheap lubricants may often become the most
expensive in the end.
• Oil should not be put in the housing while the pump shaft is rotating because a considerable
amount of oil will be picked up and retained due to the rotary action of the ball bearings. When the
unit comes to rest, an overflow of oil will occur around the shaft or oil will flow out of the oil cup.
3.6.4.2 Bearing
• Pump bearings should usually last for many years if serviced properly and used correctly.
• There are several types of bearings used in pumps such as ball bearings, roller bearings and
sleeve bearings. Each bearing has a special purpose, such as thrust load, radial load and speed.
The type of bearing used in each pump depends on the manufacturer’s design and application.
• Whenever a bearing failure occurs, the bearing should be examined to determine the cause and,
if possible, to eliminate the problem.
3.6.4.3 Packing Gland
• Check packing gland, which is usually neglected and is a troublesome part as shown in
Figure 3.14 overleaf.
• If the stuffing box leaks excessively when gland is pulled up with mild pressure, remove the
packing and examine the shaft sleeve carefully.
• Replace grooved or scored shaft sleeve because packing cannot be held in stuffing box with
roughened shaft or shaft sleeve.
• Replace the packing a strip at a time, tamping each strip thoroughly and staggering the joints.
Position the lantern ring (water sealing) properly.
3 - 21
Source: EPA, 2008

Figure 3.14 Packing gland
• If grease sealing is used, completely fill the lantern ring with grease before placing remaining
rings of packing in place.
• The proper size of packing should be available in the plant’s equipment files.
3.6.4.4 Mechanical Seal
Many pumps use mechanical seals instead of packing as shown in Figure 3.15.
Source: EPA,2008
Figure 3.15 Mechanical seal
3 - 22
• Mechanical seals serve the same purpose as packing; that is, they prevent leakage between the
pump casing and shaft. The seals have two faces that close tightly and prevent the sewage from
passing through them.
• The different materials are selected for their best application. Some of the factors for selection of
material are:
• Liquid and solids being pumped

• Shaft speed
• Temperature
• Corrosion resistance
• Abrasives
• Initially, mechanical seals are more expensive than packing when installed in a pump. This cost
is recovered through maintenance savings over a period of time.
• Some of the advantages of mechanical seals are as follows:
• They last from three to four years without any maintenance, resulting in labour savings.
• Usually, there is no damage to the shaft sleeve at the time of their replacement.
• Continual adjusting, cleaning, or repacking is not required.
The construction of a mechanical seal is shown below.
• Whatever be the method used, the mechanical seal must be inspected frequently.
• Grease cups must be kept full at all times and inspected to make sure they are operating
properly. When a pump is fitted with a mechanical seal, it must never run dry or the seal faces will
be heated up and ruined.
• Mechanical seals should not leak from the gland. If a leak develops, the seal may require
resurfacing or it may have to be replaced.
• Repair or replacement of mechanical seal requires the pump to be removed and dismantled.
• Seals are quite delicate and special care must be taken when installing them. Mechanical
seals differ widely in their construction and installation, and the manufacturer’s instructions
must be followed.
3.7 FLOW MEASURING DEVICES
Flow, similar to water level (Refer to Sec.6.5.2 “Level Measuring Equipment”), is one of
the most important parameters to be measured. The various types of flow-measuring
devices have three basic criteria that determine their performance namely: area, velocity, and device
characteristics. The two basic types of flow measurements are open-channel and closed-pipe.
For good measuring device performance, both types require approach conditions free of
obstructions and abrupt changes in size and direction. Obstructions and abrupt changes produce
velocity-profile distortions that lead to inaccuracies.
3 - 23
3.7.1 Weir Flow-Meter
A weir measures the liquid flowing in open channels or partially filled pipes under atmospheric
pressure as shown in Figure 3.16.
Source: WEF,2008
Figure 3.16 Typical weir section and elevation
This device causes the flow to take on certain characteristics (such as shape and size)
depending on the device used.
Changes in flow-rate produce a measurable change in the liquid level near or at the device.
This level is related to flow-rate by an appropriate mathematical formula. The specific device
determines the location and accuracy of level measurements and is extremely important for
accurate performance.
Measurement errors occur if the actual crest height differs from the designed height due to
accumulated matter on the channel floor.
The sediments must be removed.
Floating matter or surface wave may cause incorrect level measurements and lead to errors in flow
measurements. Therefore, floating matter should be removed immediately.
Section 3.10 of Part A of the manual provides the equations to calculate flow rates of weirs.
3 - 24
3.7.2 Electromagnetic Flow-Meter
Magnetic flow meters are used extensively in applications ranging from filtered sewage to
thickened or digested solids. They function by electromagnetic induction, in which the induced voltage
generated by a conductor moving through a magnetic field is linearly proportional to the conductor’s
velocity. As the sewage (the conductor) moves through the meter (generating the magnetic field),
the voltage produced is measured and converted to a velocity and, thus, a flow-rate. Magnetic
meters require a full pipe flow for proper operation. Proper grounding is important for certain brands. In
applications where greasing of electrodes is likely, additional equipment for degreasing the
electrode may be required. Magnetic flow meters provide no obstructions and are manufactured with
abrasion-and corrosion-resistant liners, which is why they are frequently used in solids metering.
Repairs should be done only by the manufacturer’s representatives. Electromagnetic flow meters
rarely break down because they have no moving parts. Dirt on sensors should be cleaned because
that may cause error in measurements. The working principle is shown in Figure 3.17.
Source: WEF,2008
Figure 3.17 Magnetic flow meter
3.7.3 Ultrasonic Flow-Meter
Ultrasonic flow meters are based on the measurement of ultrasonic wave transit time or
frequency shift caused by the flowing fluid. An instrument that measures wave-transit time is called a
time-of-flight or counter-propagation ultrasonic flow meter.
Ultrasonic waves of known frequency and duration are beamed across the pipe at known angles.
The waves are sensed either directly by an opposing receiver or indirectly as reflected waves.
The changes in wave transit time or frequency caused by the flowing liquid are linearly
proportional to the liquid velocity. This velocity is converted from flow and output to a display by
conversion electronics. The presence or absence of air bubbles and density of solids in the fluid
being metered affect the meters. Operators should follow the manufacturer’s specifications and
carefully match the meters to the application. The working principle is shown in Figure 3.18.
3 - 25
Source: WEF,2008
Figure 3.18 Reflecting ultrasonic flow meter
3.7.4 Fluorescent Tracers
Florescent tracer method requires the use of a tracer like Rhodamine B Dye, which is injected
using a peristaltic pump from a small volume of a known concentration of dye solution. The dye is
injected into the gravity or pumping main. After traveling and getting mixed, the dye concentration is
measured at a distance away. The mass of the dye is the same in the beginning and after traveling.
The instrument used is called Fluorometer. The dye will automatically degrade and it does not
affect the water body.
3.8 PREVENTIVE MAINTENANCE
Equipment has become more complex with the application of advanced technologies and
automation systems in recent years. Thus, high technical knowledge is required and technicians,
technical tools and special instruments are necessary for implementing preventive maintenance of
the equipment. Unlike O&M contractors, manufacturers can provide such skilled staff and special tools.
The manufactures can provide safe and secure maintenance based on their long experience and
abundant information on their products. Preventive maintenance after expiry of warranty period
should be availed from the manufacturers continuously.
A good maintenance programme is essential for a pumping station to operate continuously at

peak design efficiency. A successful maintenance programme will cover everything from
mechanical equipment, such as pumps, valves, scrapers and other moving equipment, to the
care of the plant grounds, buildings and structures. For preventive maintenance, it is advisable to
follow a schedule for the maintenance of the equipment.
The schedule covers recommendations for checks and remedial actions to be observed at different
intervals such as daily, monthly, quarterly, bi-annually and annually.
3 - 26
Operators should receive training to obtain more knowledge of characteristics and structure of
machinery and to improve their maintenance skill.
A. Mechanical Maintenance
Mechanical maintenance is of prime importance, as the equipment must be kept in good

operating condition for the plant to maintain peak performance. Manufacturers provide
information on the mechanical maintenance of their equipment. Operators should thoroughly read
manuals on the plant equipment, understand the procedures, and contact the manufacturer
or the local representative if there are any questions. The instructions should be followed very
carefully when performing maintenance on equipment. Operators also must recognise tasks
that maybe beyond their capabilities or repair facilities, and should request assistance
when needed.
B. Maintenance of Civil Structures
Building maintenance is another programme that should be maintained on a regular

schedule. Buildings in a treatment plant are usually built of sturdy materials to last for many years.
Buildings must be kept in good condition by repairs. For selecting paint for a treatment plant, it
is always a good idea to have a painting expert help the operator select the types of paint
needed to protect the buildings from deterioration. The expert also will have some good ideas
as to colour schemes to help blend the plant in with the surrounding area. Consideration
should also be given to the quality of paint. A good quality, more expensive material will usually
give better service over a longer period of time than the economy-type products.
Building maintenance programmes depend on the age, type and use of a building. New
buildings require a thorough check to ensure that essential items are available and are working
properly. Older buildings require careful observation and prompt attention to detect leaks,
breakdowns and replacements beforehand. Attention must be given to the maintenance
requirements of many items in all plant buildings, such as electrical systems, plumbing,
heating, cooling, ventilating, floors, windows, roofs, and drainage around the buildings. Regularly
scheduled examinations and necessary maintenance of these items can prevent many costly
and time-consuming problems in the future.
In each plant building, periodically check all stairways, ladders, catwalks and platforms for
adequate lighting, head clearance, and sturdy and convenient guardrails. Protective devices
should be around all moving equipment.
Whenever any repairs, alterations or additions are made, avoid building accident traps such as
pipes laid on top of floors or hung from the ceiling at head height, which could create serious
safety hazards.
Keep all buildings clean and orderly. Supervisory work should be done on a regular schedule.
All tools and plant equipment should be kept clean and in their proper place. Floors, walls and
windows should be cleaned at regular intervals to maintain a neat appearance.
3 - 27
C. Valve Maintenance
Valves should be lubricated regularly (according to the manufacturer’s instructions), and valve
stems should be rotated regularly to ensure ease of operation. These activities should be part
of a regular pump-maintenance programme.
D. Electric Actuator Maintenance
• Declutch and operate the manual hand wheel.

• Check oil level and top up, if required.
• Re-grease the grease lubricated bearing and gear trains, as applicable.
• Check the insulation resistance of the motor.
• Check for undue noise and vibration and take necessary rectification measures.
• Tighten limit switch cam ends. Check for setting and re-adjust, if necessary.
• Examine all components and wiring thoroughly and rectify as necessary.
• Change oil or grease in the gearbox and thrust bearing.
• Check the condition of the gears and replace them if teeth are worn out.
E. Flow Meter Maintenance
Each individual sensing meter will have its own maintenance requirements.
The single most important item to be considered in sensor maintenance is good housekeeping.
Always keep sensors and all instrumentation very clean. Good housekeeping and the act of
providing preventive maintenance for each of the various sensors, includes ensuring that foreign
bodies do not interfere with the measuring device. Check for and remove deposits that will build up
from normal use. Repair the sensor or measuring device whenever it is damaged.
External connections between the sensing and conversion and readout devices should be checked
to ensure such connections are clean and connections are firm. Be sure no foreign obstruction will
interfere or promote wear. On mechanical connections, grease as directed; on hydraulic or
pneumatic connections, disconnect and ensure free flow in the internal passage.
F. Maintenance of Pumps
The maintenance schedule should list out items to be attended to at different periods, such as daily,
semi-annually, annually and as needed.
i. Daily Observations
• Leakage through packing

• Bearing temperature
• Undue noise or vibration
• Pressure, voltage and current readings
3 - 28
ii. Semi-annual Inspection
• Free movement of the gland of the stuffing box
• Cleaning and oiling of the gland bolts
• Inspection of packing and repacking, if necessary
• Alignment of the pump and the drive
• Cleaning of oil-lubricated bearings and replenishing fresh oil.
• If bearings are grease-lubricated, the condition of the grease should be checked and replaced
with correct quantity, if necessary.
• An anti-friction bearing should have its housing packed with grease so that the void spaces in
the bearings and the housing are 1/2 to 2/3 filled with grease. A fully packed housing will cause
the bearing to overheat and will result in reduced life of the bearing.
iii. Annual Inspection
• Cleaning and examination of all bearings for flaws developed, if any
• Examination of shaft-sleeves for wear or scour.
• Checking clearances
Clearances at the wearing rings should be within the limits recommended by the manufacturer.
Excessive clearances indicate a drop in the efficiency of the pump. If the wear is only on one side,
it means misalignment. Not only should the misalignment be corrected, but also the causes of the
misalignment should be investigated and the clearances reset to the values recommended by
the manufacturers. If the clearance on wear is seen to be 0.2 or 0.25mm more than the original
clearance, the wearing ring should be renewed or replaced to obtain the original clearance.
These are to be done by the equipment representative.
• Impeller-hubs and vane-tips should be examined for any pitting or erosion.

• End-play of the bearings should be checked.
• All instruments and flow-meters should be re-calibrated.
• Pump should be tested to ensure proper performance is being obtained.
• In the case of vertical turbine pumps, the inspection can be bi-annual. Annual inspection is not
advisable because it involves disturbing the alignment and clearances.
iv. Annual Maintenance and Repairs
• Consumables and lubricants
Adequate stock of items as packing glands, belts, lubricating oils, greases should be maintained.
3 - 29
• Replacement of spares
To avoid downtime, a stock of fast-moving spares should be maintained. A set of recommended

spares for two years of trouble-free operation should be ordered along with the pump.
• Repair workshop
The repair workshop should be equipped with tools such as bearing-pullers, clamps, pipe-wrenches,
and other general-purpose machinery such as welding set grinder, blower, drilling machine, etc.
3.9 TROUBLESHOOTING
Refer to Appendix B.3.1 to Appendix B.3.3.
3.10 RECORD KEEPING
The purpose of recording data is to track operational information that will identify and avoid
duplicating optimum operating conditions.
A record of equipment performance and repairs allow O&M personnel to properly evaluate
equipment’s effectiveness and determine if the equipment meets the objectives to justify its
purchase and installation.
As a minimum, the following basic information should be maintained for each equipment in the
pumping station:
• Plant equipment identification number

• Manufacturer
• Model number and serial number
• Type
• Dates of installation and removal from service
• Reasons for removal
• Location when installed
• Calibration data and procedures
• Hours required to perform maintenance
• Cost of replacement parts
• O&M manuals, references and their locations
• Apparatus failure history
Inspection reports should be prepared for each sewage pumping station according to the
equipment installed.
An example of an annual inspection report for pumping station is shown in Table 3.2 overleaf.
3 - 30
Table 3.2 Annual inspection report for pumping station
Source: JICA,2011
Recommended maintenance/inspection tasks for equipment in pumping stations are summarised
by frequencies and are listed in Table 3.3. Because the required maintenance / inspection and their
frequencies may differ depending on the equipment installed, maintenance plans should be prepared
according to manufacturer’s instruction manuals of related equipment.
3 - 31
Table 3.3 Recommended maintenance for pumping equipment
Source: JICA,2011
3 - 32
3.11 DUTIES OF SITE ENGINEER IN CHARGE AND HIGHER UPS
The site engineer should first check the entries of the operator in the previous three shifts and take
corrective action, or alert the supervisor by e-mail and make an entry in the site register. If the site
engineer cannot correct the problem within two weeks, he should directly send an e-mail message to
the plant incharge. If no action is taken even after two weeks, the complete responsibility will rest with
the plant incharge from then onwards, including the responsibility for any accidents/fatalities caused
by not taking the requisite action.
3.12 IF THE PUMPING STATION IS UNDER O&M BY THE CONTRACTOR
The references to operator, site engineer and plant incharge inevitably apply to the staff of the
contractor also. The engineer in charge of supervising the contractor’s work should review the site
register once a fortnight and institute such remedies as available under the contract.
3.13 SUMMARY
The most important thing for O&M of pumping stations is to minimize suspension time due to
equipment failures and to maximize the life of pumps. For accomplishing these targets, the following
causes of breakdown of pumps should be eliminated:
• Inflow of screenings into pumping stations

• Overloading of pumps
Preventive maintenance is also essential for detecting abnormalities in their early stages.
3 - 33
CHAPTER 4:
Part B: Operation and Maintenance SEWAGE TREATMENT FACILITIES
CHAPTER 4: SEWAGE TREATMENT FACILITIES
4.1 INTRODUCTION
Sewage treatment is a multi-stage process designed to treat sewage and protect natural water
bodies. Municipal sewage contains various wastes. If improperly collected and improperly treated,
this sewage and its related solids could hurt human health and the environment.
A treatment plant’s primary objectives are to clean the sewage and meet the plant’s discharge
standards The treatment plant personnel do this by reducing the concentrations of solids, organic
matter, nutrients, pathogens and other pollutants in sewage. The plant must also help protect the
receiving water body, which can only absorb a certain level of pollutants before it begins to degrade,
as well as the human health and environment of its employees and neighbours.
One of the challenges of sewage treatment is that the volume and physical, chemical, a limited
quantity of pollutants and biological characteristics of sewage continually change. Some changes are
the temporary results of seasonal, monthly, weekly or daily fluctuations in the sewage volume and
composition. Other changes are long-term, being the results of alterations in local populations, social
characteristics, economies, and industrial production or technology. The quality of the receiving water
and the public health and well-being may depend on a treatment plant operator’s ability to recognize
and respond to potential problems. These responsibilities demand a thorough knowledge of existing
treatment facilities and sewage treatment technology.
4.2 PUMP EQUIPMENT
Refer to Chapter 3 of the Part B Manual. (Sec.3.6 “Pump Equipment”)
4.3 FINE SCREEN AND GRIT CHAMBER
Refer to Chapter 3 of the Part B Manual. (Sec.3.4 “Screen” and Sec.3.5 “Grit Removal”)
4.4 OIL AND GREASE REMOVAL
4.4.1 Manual Process
The oil and grease removal unit consists of simple tanks with an underflow baffle where the
floating oil and grease is retained on the sewage surface. These are fit only for small STPs of about
1 MLD capacity or less. The floating oil & grease is removed by a rotating slotted pipe as in
Figures 4.1 & 4.2 overleaf.
In actual operation, the scum of oil and grease is removed by rotating the slotted pipe so that the scum
flows over the slit, through the pipe and goes to a holding high-density polyethylene (HDPE) tank
below the pipe on the outside. The scum is then sold to pollution board-authorized oil re-refining
firms. The grit that settles in the trough below is drained to a sump and pumped to the beginning of
the grit chamber.
The maintenance is very simple and requires periodic cleaning only.
4-1
CHAPTER 4:
Source: http://en.wikipedia.org/wiki/Industrial_wastewater_treatmen
Figure 4.1 Typical gravity type oil and grease removal unit
Source: http://en.wikipedia.org/wiki/Industrial_wastewater_treatment
Figure 4.2 Parallel plate separator
4-2
CHAPTER 4:
4.4.2 Mechanized Process
This process involves floating the oil and grease by either fine bubbles of compressed air or directly
by steam liberated near the floor. The same process as in Figures 4.1 & 4.2 can also be used by
releasing fine bubbles of compressed air or steam near the floor. The air is dispersed into very fine
bubbles in the raw sewage and the mixture is released in a shallow tank, where the fine bubbles
coalesce with the oil and rise to the surface and are skimmed-off by a scoop pipe as shown in
Figure 4.3 and is typically called a dissolved air floatation (DAF) unit as shown in Figure 4.4.
Source: http://www.tradeindia.com
Figure 4.3 DAF unit
Source: http://www.sciencedirect.com
Figure 4.4 Schematic of DAF unit
4-3
CHAPTER 4:
All these units are almost patented types and there are no fixed O&M guidelines. Each unit has to
follow the guidelines of the respective manufacturer.
4.5 EQUALIZATION
Flow equalization can be either side stream or in-line. With in-line flow equalization, all of the flow
enters the flow equalization basin, and a constant outflow rate is maintained. With side stream flow
equalization, only that portion of the flow above a given flow rate (typically the average flow) is
diverted into the flow equalization basin. The accumulated flow is then released during low-flow
periods to adjust the total flow to average rate of flow for the day.
The in-line flow equalization is the easiest to control. Typically, the flow is pumped out using
flow-controlled variable-speed pumps or is pumped in and flows out by gravity using a flow control
valve and flow meter. If the latter is used, careful selection of the flow control valve is needed to
prevent clogging, even if screened or primary treated sewage is to be equalized.
For side stream flow equalization, flow control gates or variable speed pumps can be used. If a
constant elevation side weir is used, achieving a controlled flow rate over the side weir is difficult and
is not recommended. Variable speed pumps are a better choice.
4.5.1 Operation
The fill-and-draw mode is the most efficient method of operating an equalization basin. The basin is
filled during the day when peak flows are occurring, and then it is pumped at night when the plant is
receiving low flows and, hence, is more capable of treating excessive flow. If an equalization basin
is not operated in fill-and-draw mode, it will act as a mass loading equalization basin only, assuming
the basin is completely mixed.
The successful operation of equalization basin requires proper mixing & aeration. The design of
mixing equipment provides for blending the contents of the tank and preventing deposition of solids.
Mechanical aerators, which offers a method of providing both mixing and aeration, have higher
oxygen transfer in clean water under standard conditions than in sewage. The minimum operating
depth for floating aerators are typically 1.5 m and varies with the motor kilowatts and design of the
unit. Low-level shutoff controls are needed to protect the unit. If the equalization basin floor is subject
to erosion (earthen basins), concrete pads on the basin floor are recommended. Baffling may be
necessary to ensure proper mixing, particularly with a circular tank configuration.
Some of the recommended monitoring elements required in flow equalization basins are
1. Basin liquid level

2. Basin dissolved oxygen level
3. Influent pH
4. Mixers and/or aeration blower status
5. Influent/effluent status pumps
6. Influent/effluent flow
4-4
CHAPTER 4:
4.5.2 Maintenance
Because grit removal is rarely provided before equalization, grit tends to accumulate in the basins.
Therefore, provisions for collecting these solids should be made in the design. If the primary purpose
of the equalisation basin is flow equalising, then, after the basin has been emptied, following the peak
flow event, primary sludge solids will be present in the basin floor. Water cannons or strategically
placed cleaning hoses, ideally supplied with plant effluent water, will allow for cleaning the basins.
Other equalization basin types that do not operate in a fill/draw mode will also accumulate solids
over a period of time and will have to be emptied.
The cleaning interval depends on the influent sewage characteristics and has to be established by
operational experience.
4.6 PRIMARY TREATMENT
4.6.1 Primary Sedimentation Tank Management
This is a simple gravity controlled separation for removing the settleable solids and the Biochemical
Oxygen Demand (BOD) that is caused by the settleable solids.
Preventive maintenance of the equipment should be done by the equipment supplier as

per the manual.
4.6.3 Day to Day Maintenance
The most important is the daily cleaning of the overflow weirs and the weekly scraping of the floor
and walls of the launder. Moreover, periodical checking of the walkway for corrosion is important. In
actual day-to-day working, the operator should not lean or put his weight on the handrails.
4.6.4 Troubleshooting
Troubleshooting is as given in Appendix B.4.1.
4.7 ACTIVATED SLUDGE PROCESS (ASP)
The activated sludge process is still the most widely used biological treatment process for
reducing the concentration of organic pollutants in sewage. Well-established design standards
based on empirical data have evolved over the years.
The basic ASP has many different process modifications. The process selected in a
specific STP depends on the treatment objectives, site constraints, operational constraints, etc.
The process can be categorized by loading rates, reactor configuration, feeding and aeration
patterns, and other criteria including various biological nutrient removal (BNR) processes.
A typical plan layout of a basic ASP is illustrated in Figure 4.5 overleaf.
4-5
CHAPTER 4:
Figure 4.5 Typical plan layout of activated sludge plant
4.7.1 Description of ASP
4.7.1.1 Biological Treatment Processes
In the biological treatment of sewage, the stabilisation of organic matter is accomplished

biologically using a variety of microorganisms, principally bacteria. They convert the colloidal
and dissolved carbonaceous matter into gases and non-degradable matter and incorporate it into
their cell tissue. The resulting cell tissue has a specific gravity slightly greater than that of water. The
portion of organic matter that has been converted to various gaseous and non-degradable end
products, which itself is organic, will be measured as the difference between the inlet and outlet.
The conversion of organic matter can be accomplished either by aerobic, anaerobic or

facultative processes. Oxidation of organic matter to various end-products is carried out to obtain the
energy required for the synthesis of new cell tissues. In the absence of organic matter, the cell tissue
undergoes endogenous respiration. In most treatment systems, these three reactions, oxidation,
synthesis and endogenous respiration occur simultaneously.
The microbial mass comprises a heterogeneous population of microorganisms, mostly heterotrophic

bacteria. Various groups of organisms carry out their metabolic reactions independently as well as
sequentially. The combination of organisms in the treatment process occurs naturally, depending
upon the sewage characteristics and the environmental conditions maintained.
4.7.1.2 Design and Operational Parameters
The ASP operation is commonly controlled by maintaining the design Mixed Liquor Suspended
Solids (MLSS), or sometimes, by maintaining the design Food to Microorganisms (F/M) ratio. The
latter approach takes care of fluctuations in the quality of raw sewage.
4-6
CHAPTER 4:
If actual F/M is to be assessed, then measurement of active biomass measured as Mixed Liquor
Volatile Suspended Solids (MLVSS) is needed.
The solids retention time (SRT), which is directly related to F/M, is not being used for operational
control. Some of the important design and operational parameters are as follows.
The operational parameters and their formula are explained in Appendix B.4.2 and examples of their
calculations are described in Appendix B.4.3.
4.7.1.3 Choice between SRT and F/M as Operation Control Parameter
The evaluation of the active mass of microorganism often makes the use of F/M as a control
parameter impractical. Biological solids are commonly measured as volatile suspended solids.
This parameter is not entirely satisfactory because of the variety of volatile matter not related to active
cellular material.
On the other hand, the evaluation of SRT as a plant control parameter is simple. Since SRT is the
ratio of total suspended solids in the system and the total suspended solids wasted per day, it
requires only measurement of the suspended solids in the system and the solids wasted, either
from the aeration tank or from the recycle line is the same. Use of SRT as a plant control parameter
becomes simpler if sludge wasting is done directly from aeration tank, as the ratio of “total solids in
system to solids wasting per day” reduces to the ratio of “aeration tank volume to volume of sludge
wasted per day,” provided the mass of solids escaped in treated effluent is negligible.
4.7.1.4 Effect of SRT on Settling Characteristics and Drainability of Sludge
It has been established that as a system is operated at higher solids retention time, the settling
characteristics of the biological flocs improve. For domestic sewage, SRT of the order of 3 to 4 days
are required to achieve effective settling. Further, it is established that drainability of waste sludge
also improves when a system is operated at higher SRT.
The SRT at which a process is operated approximately represents the average age of biomass
present in the process. As the biomass ages, it contains increasing proportion of dead cells and
inert matter. Presence of higher proportion of mineralised sludge in a process operated at high
SRT is responsible for better setting characteristics and better drainability of sludge.
4.7.1.5 Effect of SRT on Excess of Sludge Production
SRT is inversely related to F/M ratio. A higher operational SRT represents a low F/M ratio, a
condition of limiting substrate. The Bacteria undergoes endogenous respiration or decay under a
limiting substrate environment. More biomass undergoes endogenous respiration, resulting in lesser
net bacterial growth.
Therefore, excess sludge production is reduced if a system is operated at high SRT. Further, since
the settling characteristic of sludge improves at high SRT, concentrated underflow can be
withdrawn from the sedimentation tank. This results in reduction in excess sludge.
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4.7.1.6 Excess Sludge Wasting
Excess bio-sludge is commonly wasted from return sludge line. It can also be wasted directly from
aeration tank. If excess bio-sludge is directly wasted from aeration tank, then increased volume of
sludge is a disadvantage. However, if excess bio-sludge is mixed with influent of primary settling tank
and wasted as mixed sludge of primary settling tank, then direct wasting from aeration tank has no
influence on final volume of sludge and therefore, can easily be adopted.
The operator of a plant needs to have an idea of actual volume of excess sludge wasting required.
4.7.1.7 Return Sludge Flow
Sufficient return sludge capacity should be provided if the biological solids are not to be lost in the
effluent. However, a return flow rate higher than what is required unnecessarily increases solids
loading on settling tank and results in withdrawal of dilute sludge. The ratio of return sludge flow to
average flow can be set on the basis of sludge volume index (SVI). It is defined as the volume in ml
occupied by one gram of activated sludge mixed liquor solids, dry weight, after settling of 30 min. in
a 1,000mL graduated cylinder.
The procedure of SVI measurement is shown in Figure 4.6.
Figure 4.6 Sludge settling analysis
a. Collect a sample of mixed liquor or return sludge.
b. Gently mix sample and pour into a 1,000mL graduate cylinder. (Vigorous) shaking or mixing tends
to break up the flocs and produces slower setting or poorer separation and should be avoided.
c. Record settleable solids percentage at regular intervals.
Table 4.1 provides SVI values and probable indication of settling properties of activated sludge.
For all cases refer to remedies in Troubleshooting in Appendix B.4-1.
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Table 4.1 Relations between Sludge Volume Index and settling characteristics of sludge
Source: JICA, 2011
The quantity of return sludge flow is linked to settled sludge volume as in Figure 4.7.
Figure 4.7 Recirculated sludge flow ratio
4.7.2 Conventional Activated Sludge Process
The conventional activated sludge process typically consists of a concrete aeration tank followed by
a concrete clarifier.
Sewage and return activated sludge (RAS) enter together or separately into the reactor and leave as
mixed liquor.
This mixed liquor flows into the clarifier where it is allowed to settle and the treated effluent separates
from the activated sludge.
The settled sewage from the process flows over the clarifier weirs.
The settled activated sludge is recycled to the aeration tank and a portion wasted out of the system
as waste activated sludge (WAS).
This is shown in Figure 4.8 overleaf.
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Figure 4-8 Conventional activated sludge process
4.7.2.1 Start Up
The start-up help should be available from the design engineer, vendors, nearby operators, or other
specialists. During start-up, the equipment manufacturer should be present to be sure that any
equipment breakdowns are not caused by improper start-up procedures.
The operator may have several options in the choice of start-up procedures with regard to number of
tanks used and procedures to establish a suitable working culture in the aeration tanks. The method
described in this section is recommended because it provides the longest possible aeration time,
reduces chances of solids washout and provides the opportunity to use most of the equipment for a
good test of its acceptability and workability before the end of the warranty.
First, start the air blowers and have air passing through the diffusers before primary effluent is
admitted to the aeration tanks. This prevents diffusers clogging from material in the primary effluent
and is particularly important if fine bubble diffusers are used.
Fill both aeration tanks to the normal operating sewage depth, thus allowing the aeration equipment
to operate at maximum efficiency. Using all of the aeration tanks will provide the longest possible
aeration time. The operators are trying to build up a micro-organism population with a minimum
amount of seed organisms, and this will need all the aeration capacity available to give the organisms
a chance to reach the settling stage.
After a biological culture of aerobes is established in the aeration tanks, sufficient oxygen must be
supplied to the aeration tank to overcome the following demands:
1. Dissolved Oxygen (DO) usually is low in both influent sewage and return sludge to the aerator.
2. Influent sewage may be septic, thus creating an immediate oxygen demand.
3. Organisms in the presence of sufficient food create a high demand for oxygen.
The effluent end of the aeration tank should have a dissolved oxygen level of at least 1.0 mg/L. DO
in the aeration tank should be checked every two hours until a pattern is established.
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Thereafter, DO should be checked as frequently as needed to maintain the desired DO level and to
maintain aerobic conditions in the aerator. Daily flow variations will create different oxygen demands.
Until these patterns are established, the operator will not know whether just enough or too much air is
being delivered to the aeration tanks. Frequently, D O is high during early mornings when the inflow
waste load is low and may be too low during the afternoon and evening hours because the waste
load tends to increase during the day.
If sewage enters the tank before air is diffused, the diffusers could become plugged. If the plant is
the diffused-air type with airlift pumps for return sludge, the airline valve to the pumps will have to
be closed until the settling compartment is filled. Otherwise, all the air will attempt to go to the empty
compartment and no air will go to the diffusers. Once the settling compartment is filled from the
overflow of the aeration tank, the air lift valves may be opened. They will have to be adjusted to return
a constant stream of water and solids to the aeration tank. This adjustment is usually two to three
turns of opening on the air valve to each air lift.
There may be a build-up of foam in the aeration compartment during the first week or so of start-up.
A 25mm water hose using local surplus fresh water with a lawn sprinkler may be used to keep it under
control until sufficient mixed liquor solids are obtained.
Try to build up the solids or MLSS as quickly as possible during start-up.
This can be achieved by not wasting sludge until the desired level of MLSS is achieved.
4.7.2.2 Routine Operation and Maintenance
4.7.2.2.1 Aeration Tanks
The operational variables in an activated sludge plant include:
1. Rate of flow of sewage

2. Air supply
3. MLSS
4. Aeration period
5. DO in aeration and settling tanks
6. Rate of sludge return and sludge condition.
The operator should possess a thorough knowledge of the type of system adopted, namely,
conventional, high rate, extended aeration or contact stabilisation so that effective control of the
variables can be exercised to achieve the desired efficiency of the plant.
Inspection of mechanical aerators should be done for bearings, bushes and transmission gears.
The lubrication of the bearings, bushes and transmission gears should be carried out as per the
schedule suggested by the manufacturer.
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The whole unit should be thoroughly inspected once a year, including replacement of worn out parts
and painting with anti-corrosive paints to achieve the desired efficiency of the plant. A record of
operations should be maintained.
When inhibitory substance for activated sludge (such as industrial sewage) is contained in
influent, the treatment may be affected. To avoid such an inhibition, colour and odour of plant
influent should be checked through daily inspections such as at the grit chambers or the primary
sedimentation tanks where sewage flows in at first. If any abnormal condition is observed, report to
a person in charge of water quality or the plant manager.
4.7.2.2.2 Sewage Flow
Since the activated sludge treatment is biochemical in nature, conditions in the aeration tank should
be maintained as uniform as possible at all times. A sudden increase in the rate of flow or sludge
of flow should be avoided. If supernatants from digester containing more than 3,000mg/L of SS are
taken into the settling tank, then they should be pre-treated as otherwise heavy load will be imposed
on the activated sludge system. Measurement of sewage flow and the BOD applied to the aeration
tank should be made.
4.7.2.2.3 Air Supply
Frequent checks of DO at various points in the tank and at the outlet end should be made; it should
not be less than 1mg/L. It will help in determining the adequacy of the air supply. The uniformity of
air distribution can be easily checked by observing bubbling of the air at the surface, which should
be even over the entire surface area of the tank. If the bubbling looks uneven, clogging of diffusers
is indicated. Clogging is also confirmed by the increase of 0.01 to 0.015 MPa in the pressure gauge
reading. Adding chlorine gas to the air may help in removing clogging of diffusers on air side if it is
due to organic matter. Other methods of cleaning will have to be resorted to if this procedure does not
clear up the clogging. Air flow meters should be checked periodically for accuracy; air supply and air
pressures should be recorded hourly and daily, respectively, to avoid over-aeration or under-aeration.
Mechanical or surface aerators should be free from fungus or algae by cleaning them periodically.
4.7.2.2.4 Mixed Liquor Suspended Solids
Control of the concentration of solids in the mixed liquor of the aeration tanks is an important
operating factor. It is most desirable to hold the MLSS constant at the suggested concentration. The
test of MLSS should be done at least once a day on large plants, preferably during peak flow. As the
MLSS will be minimum when the peak flow starts coming in and will be maximum in the night hours
when the flow drops, operating MLSS value would be the average hourly value in a day; the same should
be verified at least once a month. In case of large plants, daily check at a fixed time is desirable.
4.7.2.2.5 Return Sludge
The return sludge pumps provided in multiple units should be operated according to the increase
or decrease in return sludge rate of flow required to maintain the necessary MLSS in aeration unit,
based on the SVI. The SVI should be determined daily to know the condition of sludge.
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A value of over 200 definitely indicates sludge bulking. A good operation calls for prompt
removal of excess sludge from the secondary tanks to ensure that the sludge is fully aerobic. This
should be recorded daily. The excess sludge is sent directly or through the primary settling tank.
4.7.2.2.6 Foaming
Foaming or frothing is sometimes encountered in activated sludge plants when the sewage
contains materials, which reduce the surface tension, the synthetic detergents being the major
offender. Froth, besides being unsightly, is easily blown away by wind and contaminates all the
surfaces it comes into contact with. It is a hazard to workers because it creates a slippery surface even
after the foam collapses. Foam problems can be overcome by the application of a spray of screened
effluent or clear water, increasing MLSS concentration, decreasing air supply or addition of other special
anti-foam agents. The presence of synthetic anionic detergents in sewage also interferes with the
oxygen transfer and reduces aeration efficiency.
4.7.2.2.7 Microscopic Examination
Routine microscopic examination of solids in aeration tank and return sludge to identify the biological
flora and fauna will enable good biological control in the aeration tanks.
4.7.2.2.8 Records
Activated sludge operation should include recording of flow rates of sewage and return sludge, DO,
MLSS, MLVSS, biota, SRT (sludge age), air, BOD, COD (Chemical Oxygen Demand) and nitrates in
both influent and effluent.
4.7.2.2.9 Biological Uptake Rate Procedure
After de-aerating the sample of at least 250 mL of mixed liquor with sodium meta-bi-sulphite start
the diffuser and record the dissolved oxygen with time by a dissolved oxygen probe and plot the
saturation deficit with time in semi log paper. The slope of the graph is the uptake rate. Generally this
is not for a plant control test. It is used for alpha value by comparing it with the value for tap water.
4.7.2.2.10 Nutrient Control
Nutrient control should be as in subsection 5.8.1.7.6, 5.8.1.7.7 and 5.8.1.7.8 in the Part A manual.
4.7.2.2.11 DO Saturation
DO saturation table should be referred as in Table 5-9 and 5-10 in the Part A manual.
4.7.2.3 Aeration Equipment
4.7.2.3.1 Air Blowers
The blower system is designed to provide sufficient airflow to meet the system process requirements.
Blower systems are available with either positive displacement (PD) or centrifugal units.
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Typically, PD units are used for plants with smaller air volume requirements. Output airflow from a PD
blower remains relatively constant with varying discharge pressure. Centrifugal blower systems are
generally equipped with additional controls to regulate the flow as the discharge pressure varies.
A. Positive Displacement Blowers

The positive displacement blower provides a constant volume (cubic meters) output of air per
revolution for a specific set of rotors or lobes. Blower output is varied by changing the rotor or lobe
speed or revolutions per minute (RPM). The higher the RPM, the greater is the air output.

Small positive displacement blowers are usually installed to be operated at a fixed volume output
These smaller units are directly driven by electric motors through a direct coupling or through belts
and pulleys.

If a change in air volume output is required, it is accomplished by changing the motor to one with
a higher or lower RPM or by changing the pulleys to increase or decrease blower rotor or lobe
RPM, thus increasing or decreasing air output.
Note: These small units are commonly used with package plants, pond aeration systems, small
aerobic digesters, gas mixing in digesters and gas storage compressors.
Large positive displacement blowers may also be driven by internal combustion engines or variable
speed electric motors in order to change blower outputs as required in activated sludge plants.
By increasing or decreasing engine or motor RPM, the positive displacement blower output can be
increased or decreased.
The air pipeline is connected to the blower through a flexible coupling in order to keep vibration
to a minimum and to allow for heat expansion. When air is compressed, heat is generated; thus
increasing the discharge temperature as much as 56 °C or more.
A check valve follows next, which prevents the blower from operating in reverse should other blowers
in the same system be operating while this blower is off.
The discharge line from the blower is equipped with an air relief valve, which protects the blower from
excessive back pressure and overload. Air relief valves are adjusted by weights or springs to open
when air pressure exceeds a point above normal operating range, around 0.04 to 0.07 MPa in most
STPs. An air-discharge silencer is also installed to provide decibel noise reduction.
Ear protective devices should be worn when working near noisy blowers.
The impellers are machined on all exterior surfaces for operating at close tolerances; they are
statically and dynamically balanced. Impeller shafts are made of machined steel and are securely
fastened to the impellers. Timing gears accurately position the impellers.
Lubrication to the gears and bearings is maintained by a lube oil pump driven from one of the impeller
shafts. An oil pressure gauge monitors the system oil pressure.
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An oil filter is located in the oil sump to ensure that the oil is free from foreign materials. An oil level
is maintained in the gear housing so that gears and bearings will receive lubrication in case of lube oil
pump failure. Air vents are located between the seals and the impeller chamber to relieve excessive
pressure on the seals.
B. Centrifugal Blowers
The centrifugal blower is a motor connected to a speed-increasing gear-driven blower that provides
a variable air output.
Minimum to maximum air output is controlled by guide vanes. These guide vanes are
located on the intake side of the blower. These vanes are positioned manually or by plant
instrumentation based on either DO in the aeration tanks or plant influent flows.
The blower consists of an impeller, volute casing, shaft and bearings, speed-increasing gearbox and
an electric motor or internal combustion engine to drive unit. Air enters the volute casing through an
inlet nozzle and is picked up by the whirling vanes of the impeller where it is hurled by centrifugal
force into the volute casing.
Air enters the volute in its smallest section and moves in a circular motion to the largest section of the
volute where it is discharged through the discharge nozzle.
The air pipeline is connected to the blower through flexible couplings in order to keep variation to a
minimum and to allow for heat expansion. The air suction line is usually equipped with manually
operated butterfly valves that are usually electrically or pneumatically operated.
The impeller is machined on all surfaces for operating at close tolerances and is statically and
dynamically balanced. The impeller shaft is supported in a shaft-bearing stand, which contains a
thrust bearing and journal bearings.
Lubrication to the bearings and gears is maintained by a positive displacement main oil pump, which
is driven by the speed-increasing gear-unit.
An auxiliary centrifugal oil pump is also used to provide oil pressure in the event of failure of the main
oil pump and to lubricate the blower shaft bearings before start-up and after shutdown.
The oil reservoir is located in the blower base plate. Cartridge or disc-and-space oil filter is based on
the degree of filtration required.
Due to the very high speeds of operation and the resultant high oil temperature, an oil cooler unit is
installed. This unit, in most cases, is a shell-and-tube, oil-to-water heat exchanger.
A typical schematic of centrifugal blower is shown in Figure 4.9 overleaf.
C. Air Filters
Filters remove dust and dirt from air before it is compressed and sent to the various plant processes.
Clean air is essential for the protection of blowers and downstream equipment.
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Figure 4.9 Schematic of centrifugal blower
1. Large objects entering the impellers or lobes may cause severe damage on blowers.
2. Deposits on the impellers or lobes reduce clearances and cause excessive wear and vibration
problems on blowers.
3. Clean air prevents fouling of air conduits, pipes, tubing or dispersing devices on diffusers.
The filters may be constructed of a fibre mesh or metal mesh material that is sandwiched between the
screen material and encased in a frame. The filter frames are then installed in a filter chamber. Other
types of filters include bags, oil-coated traveling screens and electrostatic precipitators.
The preventive maintenance schedule for the blowers is as follows:
1. Weekly
a. Maintain proper lubricant level
2. Quarterly
a. Check for abnormal noises and vibration
b. Check if air filters are in place and not clogged
c. Check motor bearing for rise in temperature
d. Check that all covers are in place and secure
e. Lubricate motor ball-bearings
f. Check that electrical connections are tight
g. Check wiring integrity
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3. Biannually
a. Lubricate motor sleeve bearing
b. Inspect and clean rotor ends, windings and blades
c. Check that electrical connections are tight and corrosion is absent
4. Annually
a. Check bearing oil
4.7.2.3.2 Air Distribution
The air distribution system is to deliver air from the blowers to air headers in the aeration tanks and
other plant processes and consists of:
1. Pipes,
2. Valves, and
3. Metering devices
An air-metering device should be located in a straight section of the air main on the discharge side
of the blower. Air headers are located in or along the aeration tank and are connected to the air
distribution system from which they supply air to the diffusers. The two most common types of air
headers are the swing header and the fixed header. The swing header is a pipe with a distribution
system connector fitting, a valve, a double pivot upper swing joint, upper and lower riser pipes, pivot
elbow, levelling tee and horizontal air headers. An air blow-off leg, as an extension of the lower tee
connection, is fabricated with multiple alignment flanges, gaskets and jackscrews for levelling of the
header. The fixed header is a pipe with a distribution system connector fitting, a valve, union, a riser
pipe, horizontal air headers and header support “feet.” These headers are generally not provided
with adjustable levelling devices; they rely on the fixed levelling afforded by the “feet” attached to the
bottom of the horizontal air headers. Raising and lowering the air header is commonly found in
package plants, channel aeration and grit chamber aeration. Header valves are used to adjust the
airflow to the header assembly and to block the air flow to the assembly when servicing the header
or diffusers. A typical air distribution system is shown in Figure 4.10.
Figure 4.10 Typical air distribution system in aeration tank
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4.7.2.3.3 Diffusers
An air diffuser or membrane diffuser is an aeration device used to transfer air and oxygen with
oxygen into sewage. Oxygen is required by microorganisms/ bacteria resident in the water to break
down the pollutants. Diffusers use the following to produce fine or coarse bubbles.
1. Rubber membrane, or
2. Ceramic elements
The shapes of the diffusers can be:
1. Disc
2. Tube
3. Plate
A. Bubble size
The subject of bubble size is important because the aeration system in a STP consumes an average
of 50 – 70 % of the energy of the entire plant. Increasing the oxygen transfer efficiency decreases the
power the plant requires to provide the same quality of effluent water.
• Fine bubble
• Fine bubble diffusers produce very small air bubbles, which rise slowly from the floor of tank and
provide substantial and efficient mass transfer of oxygen to the water.
• Fine bubble diffusers evenly spread out (often referred to as a “grid arrangement”) on the floor of
a tank and provide the operator of the plant a great deal of operational flexibility.
• This can be used to create zones with high oxygen concentrations (toxic or aerobic), zones with
minimal oxygen concentration (anaerobic) and zones with no oxygen (anoxic). This allows for
more precise targeting and removal of specific contaminants.
• Coarse bubble
• There are different types of coarse bubble diffusers from various manufactures, such as the stain-
less steel wide band type coarse bubble diffuser.
• Fine bubble diffusers have largely replaced coarse bubble diffusers and mechanical aerators in
most of the developed world and in much of the developing world
B. Maintenance
The preventive maintenance schedule of bubble diffusers is as follows:
• Daily maintenance
• Check biological reactor surface pattern
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• Check air mains for leaks
• Check and record operating pressure and airflow
• Weekly maintenance
• Purge water and moisture from distribution piping
• Check bumps in the diffuser system
• Annual maintenance
• Drain biological reactor
• Remove excess solids that may accumulate in the reactor
• Clean diffusers
• Check that retaining rings are in place and are tight
• Check that fixed and expansion joint retaining rings are tight
4.7.2.3.4 Surface Aerators
A surface aerator is a mechanical aeration device for various types of aerobic sewage treatment
systems. Surface aerators may be either stationary or floating. The major components of the
mechanical surface aerators are motor, gear box and impeller/ aerator/ propeller. More commonly,
these components come combined, for the purpose of maintenance, they can be easily separated.
Floating aerators generally employ reinforced fibreglass foam-filled pontoons connected to the
aerator platform by a triangular tubular structural frame. The platforms are sized to provide adequate
work area around the drive. Pontoons are placed to minimise any interference with the flow pattern
and maximise stability. Each of the pontoons has a ballast compartment, which can be filled with
water or other liquid or other suitable material to adjust submergence and level the unit.
4.7.3 Extended Aeration Process
This is a modification of the activated-sludge process using long aeration periods to promote
aerobic digestion of the biological mass by endogenous respiration as in Figure 4.11.
The process includes stabilization of organic matter under aerobic conditions and disposal of the
gaseous end products into the air. The plant effluent has finely divided suspended and soluble matter.
Figure 4.11 Typical extended aeration plant
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Extended aeration is similar to a conventional activated sludge process except that the organisms
are retained in the aeration tank longer and do not get as much food. The organisms get less food
because there are more of them to feed. Mixed liquor suspended solids (MLSS) concentrations
are from 3,000–5,000 mg/L and F/M ratio is 0.1 – 0.18. In addition to the organisms consuming the
incoming food, they also consume any stored food in the dead organisms.
The new products are carbon dioxide, water, and a biologically inert residue. Extended aeration
does not produce as much waste sludge as other processes; however, wasting is still necessary to
maintain proper control of the process.
4.7.3.1 Operation of Aeration Equipment
Aeration equipment should be operated continuously 24 x 7, non-stop. In a diffused-air system, the

operator controls air flow to the diffuser with the header control valve. This valve forces excess air to
the air lifts in the settling compartment. The operator can judge how well the aeration equipment is
working by the appearance of the water in the settling compartment and the effluent that goes over
the weir. If the water is murky or cloudy and the aeration compartment has a rotten egg (H2S) odour,
it means not enough air is being supplied. The air supplied or aeration rate should be increased
slightly each day until the water is clear in the settling compartment. If the water is clear in the settling
compartment, the aeration rate is probably sufficient. Try to maintain a DO level of around 2 mg/L
throughout the aeration tank, if the operator has a DO probe or lab equipment to measure the DO. Try
to measure the DO at different locations in the aeration tank as well as from top to bottom.
4.7.3.2 Operation and Maintenance
Two methods are commonly used to supply oxygen from the air to the bacteria. They are
mechanical aeration and diffused aeration. Mechanical aeration devices agitate the water surface
in the aerator to cause spray and waves by paddle wheels mixers, rotating brushes or some
other method of entraining the air into the sewage so that oxygen can be dissolved into the
mixed liquor . Mechanical aerators in the tank tend to be lower in installation and maintenance
costs. Usually, they are more versatile in terms of mixing, production of surface area of
bubbles, and oxygen transfer per unit of applied power. Diffused air systems break up the air stream
from the blower into fine bubbles in the mixed liquor. The smaller the bubble, the greater is the
oxygen transfer due to the greater surface area of rising air bubbles surrounded by water.
Unfortunately, fine bubbles will tend to regroup into larger bubbles while rising unless they are broken
up by suitable mixing energy and turbulence.
Record the pumping time and weekly waste solids for this period if results are satisfactory. If the
extended activated sludge plant does not have an aerobic digester, applying waste activated sludge
to drying beds may cause odour problems. If odours from waste activated sludge drying beds are a
problem, consider the following solutions:
• Waste the excess activated sludge into an aerated holding tank. This tank can be pumped out
and the sludge disposed of as in chapter 6 of the Part A manual. If aerated long enough, the
sludge could be applied to drying beds.
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• Arrange for disposal of the excess activated sludge at a nearby treatment plant. Annually, check
the bottom of the hoppers for rocks, sticks, and grit deposits. Also, check the tail pieces of the air
lifts to be sure that they are clear of rags and rubber goods and in proper working condition
Frequency and amount of wasting may be revised after several months of operation by examining:
• The amount of carryover of solids in the effluent
• The depth to which the MLSS settle in a one litre measuring jar
• The appearance of flocs and foam in the aeration compartment as to colour, settleability, foam
makeup, and excess solids on the surface of the tank
• Results of laboratory testing: a white, fluffy foam indicates low solids content in the aerator while
a brown, leathery foam suggests high solids concentrations. If the operator notices high effluent
solids levels at the same time each day, the solids loading may be too great for the final clarifier.
Excessive solids indicate the MLSS is too high for the flows and more solids should be wasted.
4.7.3.3 Normal Operation
Extended aeration activated sludge plants should be visually checked every day.
Each visit should include the following:
• Check the appearance of the aeration and final clarification compartments.
• Check the aeration unit for proper operation and lubrication.
• Check the return sludge line for proper operation. If air in the airlift is not flowing properly, briefly
close the outlet valve, which forces the air to go down and out of the tail piece. This will blow it out
and clear any obstructions.
• Reopen the discharge valve and adjust to desired return sludge flow.
• Check the comminuting device for lubrication and operation.
• Hose down the aeration tank and final compartment.
• Brush the weirs when necessary.
• Skim off grease and other floating material such as plastic and rubber goods.
• Check the plant discharge for proper appearances, grease, or material of sewage origin that is
not desirable.
4.7.3.4 Abnormal Operation
Remember that changing conditions or abnormal conditions can upset the microorganisms in the
aeration tank. As the temperature changes from season to season, the activity of the organisms
speeds up or slows down. Also, the flows and waste (food as measured by BOD and suspended
solids) in the plant influent change seasonally.
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All of these factors require the operator to gradually adjust aeration rates, return sludge rates and
wasting rates. Abnormal conditions may consist of high flows or solids concentrations as a result of
storms or weekend loads.
4.7.3.5 Counter Measures
Extended aeration plant problems may cause solids in the effluent, odours, and foaming. These
problems could be caused by under-or-over aeration, too little or too much solids in the aeration tank,
improper return sludge rate, improper sludge wasting or disposal of waste activated sludge, and
abnormal influent conditions such as excessive flows or solids or toxic wastes.
When problems develop in the activated sludge process, try to identify the problem, the cause of
the problem, and select the best possible solution. Remember that the activated sludge process is
a biological process and may require from three days to a week or longer to show any response to
corrective action. Allow seven or more days for the process to stabilize after making a change in the
treatment process.
A. Solids in the Effluent
i If effluent appears turbid (muddy or cloudy), the return activated sludge pumping rate is out of
balance. Try increasing the return sludge rate. Also, consider the possible presence of something
toxic to the microorganisms or a hydraulic overload washing out some of the solids.
ii If the activated sludge is not settling in the clarifier (sludge bulking), several possible factors
could be causing this problem. Look for too low a solids level in the system, low dissolved oxygen
concentrations in the aeration tank, strong, stale, septic influent, high grease levels in influent, or
alkaline wastes from a laundry.
iii If the solids level is too high in the sludge compartment of the secondary clarifier, solids will
appear in the effluent. Try increasing the return sludge pumping rate. If odours are present
and the aeration tank mixed liquor appears black as compared with the usual brown colour, try
increasing aeration rates and look for septic dead spots.
iv If light-coloured floating sludge solids are observed on the clarifier surface, try reducing the
aeration rates. Try to maintain the DO at around 2 mg/L throughout the entire aeration tank.
B. Odours
i If the effluent is turbid and the aeration tank mixed liquor appears black as compared with the
usual brown colour, try increasing aeration rates and look for septic dead spots.
ii If clumps of black solids appear on the clarifier surface, try increasing the return sludge rate. Also,
be sure the sludge return line is not plugged and that there are no septic dead spots around the
edges or elsewhere in the clarifier.
iii Examine the method of wasting and disposing of waste activated sludge to ensure this is not the
source of the odours.
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iv Poor housekeeping could result in odours. Do not allow solids to accumulate or debris removed
from sewage to be stored in the plant in open containers.
C. Foaming/Frothing
Foaming is usually caused by too low a solids level while frothing is caused by too long a solids
retention time.
i If too much activated sludge was wasted, reduce wasting rate.
ii If over aeration caused excessive foaming, reduce aeration rates.
iii If plant is recovering from overload or septic conditions, allow time for recovery.
iv Foaming can be controlled by water sprays or commercially available de-foaming agents,

until the cause is corrected by reducing or stopping, wasting and building up solids levels in the
aeration tank.
i. Learn more about the operation of an activated sludge process under both normal and abnormal
conditions. The operator can also use the troubleshooting guide for activated sludge plants.
4.7.3.6 Maintenance
Maintenance of equipment in extended aeration plants should follow the manufacturer’s instructions.
Items requiring attention include:
A. Plant Cleanliness
Wash down tank walls, weirs, and channels to reduce the collection of odour-causing materials.
B. Aeration Equipment:
i. Air blowers and air diffusion units
ii. Mechanical aerators
C. Air Lift Pumps

D. Scum Skimmer
E. Sludge Scrapers
F. Froth Spray System
G. Weirs, Gates and Valves
H. Raw Sewage Pumps
4.7.4 Sequencing Batch Reactor (SBR)
In SBR operations, the cycle processes Fill-react, React, Settle and Decant are controlled by time
intervals to achieve the objectives of the operation. Each process is associated with particular
reactor conditions (turbulent/quiescent, aerobic/anaerobic) that promote selected changes in the
chemical and physical nature of the sewage. These changes lead ultimately to a fully treated effluent.
Figure 4.12 shows a typical SBR operation.
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Source: Nishihara Environment Co., Ltd.

Figure 4.12 Operating cycles of intermittent SBR process
• Fill or Fill-react
The purpose of Fill-React operation is to add substrate (raw sewage) to the reactor. The addition
of substrate can be controlled either by limit switches to a set volume or by a timer to a set time
period. If the volume is set, the Fill-React process typically allows the liquid levels in the reactor to
rise from 50–80 %– 100 %. If controlled by time, the Fill-React process normally lasts approximately
25 %– 50 % of the full cycle time. Period of aeration and/or mixing during the fill are critical to the
development of organisms with good settling characteristics and to biological nutrient removal
(Nitrogen (N), Phosphorus (P)). An advantage of the SBR system of time control is its ability to modify
the reactor conditions during the phases to achieve the treatment goals. This phase ends when the
liquid level in the tank reaches a predetermined level.
• Settle
The purpose of Settle is to allow solids separation to occur and providing a clarified supernatant to
be discharged as effluent. In the SBR, this process is normally more efficient than in a continuous
flow system, because in the Settle mode the reactor contents are completely quiescent. The Settle
process is controlled by time and is usually fixed between 30 minutes to an hour so that the sludge
blanket remains below the withdrawal mechanism during the next phase.
• Decant/Discharge
The purpose of Decantation is to remove the clarified, treated water from the reactor.
Sludge wasting is another important step in SBR operation that greatly affects process performance.
It is not included as one of the three basin processes because there is no set time-period within the
cycle dedicated to wasting. The amount and frequency of sludge wasting is determined by process
requirements, as with conventional continuous flow systems. In an SBR operation, sludge wasting
usually occurs during the Settle or Decant phases. A unique feature of the SBR system is that the
RAS system is in the SBR basing itself. Since the aeration and settling occurs in the same tank, no
sludge is lost in the reaction phase and none has to return from clarifier to maintain the MLSS in the
aeration tank. This eliminates the hardware of the conventional ASP.
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The sludge volume and, thus, sludge age in the reactor of the SBR system is controlled by sludge
wasting only.
The manual given by the equipment supplier should be followed. Usually these units are controlled
automatically by programmable logic controllers (PLCs). The precaution needed is to make sure that
power supply is available continuously. If power supply fails, immediately bring the genset on-line.
If there is no genset or if there is no diesel, do not operate the SBR and close it. Inform the plant in
charge and also report to the official responsible for overall O&M in the head office directly.
4.7.4.1 Process Control
The SBR has in built process control. Depending on the BOD load, it adjusts the Dissolved Oxygen
(DO) supply by sensing the residual DO and varying the speed of air compressor and hence the rate
of air supply. The most important thing for day-to-day testing is to understand the SBR as designed.
It may have fully aerobic or anoxic and aerobic or anaerobic, anoxic and aerobic cycles.
If anaerobic cycle is there, check whether the floor level mixer is working and if it is out of order, start
the installed standby mixer. If both are not in order, enter in the site register and inform the plant
in charge. Make sure that hydrogen sulphide gas is not sensed in the ambient air near the SBR. If
it is sensed by smell, then going near the tank is not advisable. Make sure it is entered in the site
register and it is reported directly to the plant-in-charge. The operator should not try and remedy the
position. The supervisor should institute and take steps to get the designer, contractor and O&M team
together and rectify the situation. There is a theory that COD to sulphate ratio is deciding the process.
This needs to be checked and corrected. A method of correcting the imbalance will be to recycle the
treated effluent from a treated sewage sump to dilute the COD of incoming sewage. The daily tests
shall be pH, COD and dissolved phosphate measured by colorimetric method or Nessler Tubes of 50
ml with fresh standards prepared every week. BOD can be a weekly test.
In the anoxic cycle, check whether the floor level mixer is working and if it is out of order, start the
installed standby mixer. If both are not in order, enter it in the site register and inform the plant in
charge. Daily tests will be nitrate estimated by Nesslerization procedure in 50 ml Nessler tubes.
The test is to be done in the beginning, in the mid cycle and at the completion of the cycle of anoxic
phase. If there is no reduction in the nitrate, then something is not in order. Proceed to check the
MLVSS. It should be at least 75 %. If this is not so, enter the value in the site register and inform the
plant-in-charge. The supervisor should institute and take steps to get the designer, contractor and
O&M team together and rectify the situation.
In the aeration cycle, check the residual DO. This is to be indicated by the built in sensor. If the
sensor is not working use the Winkler method by collecting the mixed liquor and filtering it through
Whatman filter paper number 4 in a BOD bottle and with the tip of the funnel connected by a rubber
tubing so that the filtrate enters the BOD bottle in the submerged condition always and avoids additional
aeration. A procedure for easy use in the field for instantly testing the BOD is to use a “Palintest tube.”
This has been introduced in the Chennai Metropolitan Water Supply and Sewerage Board (CMWSSB)
by M/S Severn Trent of UK as part of a twinning arrangement. Details of the tube can be obtained from
CMWSSB. A photograph of the CMWSSB chemist using the tube is shown in Figure 4.13.
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Source: CMWSSB
Figure 4.13 Use of a BOD tube for instantaneous assessment of the BOD at site
The principle of the test is related to the BOD caused by colloidal and suspended organics as
relatable to the BOD. The BOD related to suspended solids is inbuilt in the calibration. This tube
is developed only for sewage and not for industrial effluents. The test is performed by holding the
tube as in the photo after filling the treated sewage to incremental heights and finding out at which
point, the black coloured + mark at the bottom vanishes. There is a reading etched on the side of the
tube and this is read at the sewage level when the + mark vanishes from sight. The principle is the
colloidal solids and SS have their portion of BOD. The more the volume needed to “hide” the bottom
+ mark, the less is the colloidal solids and SS and hence, the lesser is the BOD due to this portion.
It is a combination of nephelometry and theory. Usually the results are within 90% accuracy .
The Palintest tube
The Palintest Tube is a specially calibrated plastic tube and is the simplest possible method of
performing the instantaneous probable BOD and SS tests on secondary treated sewage in
the field to help the operator to get a feel of these parameters quickly. The test kit is a tube
graduated at 30 to 500 turbidity units. A double length tube with additional graduations from 5 to
25 turbidity units is optionally available. These were calibrated by the Department of Public Health
Engineering, University of Newcastle upon Tyne. It has an etched black cross mark at bottom.
• Procedure
• Hold the tube vertically over a white surface and view downwards.
• Gradually pour secondary sewage and watch the cross mark.
• Stop pouring when the cross mark is no longer visible.
• Read the graduation at the top of the sample in the tube.
• This represents the turbidity in Jackson Turbidity units (JTU).
• For secondary sewage, the graduation may also be taken as SS.
• Half the value of JTU plus 5 is also the probable BOD.
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If the DO is lesser than 20 % of the design value, enter it in the site register and inform the plant in
charge. Check the MLVSS if the above situation occurs. This can be a weekly test. Check the COD.
In the settling cycle, check the SS of the decanted effluent and its COD. There is no need to
check the BOD at the end of every cycle. Prepare a curve of BOD to COD for the treated
sewage and verify the BOD by testing for the COD. This will show the trend every two hours itself
instead of 3 days for BOD actual test. This can however be a weekly test. If the SS and BOD varies
by more than 10 % in the treated sewage, enter the values in the site register and inform the
plant-in-charge. The decanter cannot be subjected to preventive maintenance in a functioning SBR.
The raw sewage has to be bypassed with prior permission of the supervisor before this is carried out.
The electrical drive of the decanter will require its greasing in some equipment. Make sure there is
a grease guard and grease does not fall into the SBR basin. Where the rope and pulley method is
used, change the rope every month.
4.7.4.2 Records
The limited parameters as above and the flow rate and cycle times are the records.
4.7.4.3 Housekeeping
In all SBR systems, verify the build-up of slime on the sidewalls in the freeboard. If noticed, scrub it
down into the SBR basin itself during the filling phase. This can be done by standing on the peripheral
walkway and using a long handle wire brush. If there is no such walkway, leave the slime as it is.
4.7.5 Oxidation Ditch
An oxidation ditch (OD) is a modified activated sludge biological treatment process that
utilizes long Solids Retention Times (SRTs) to remove biodegradable organics. OD are typically
complete mix systems, but they can be modified to approach plug flow conditions. (Note: As conditions
approach plug flow, diffused air must be used to provide enough mixing. The system will
also no longer operate as an oxidation ditch). Typical OD treatment systems consist of a
single or multichannel configuration within a ring, oval, or horseshoe-shaped basin. As a result,
OD are called “racetrack type” reactors. Horizontally mounted rotors or vertically mounted
aerators provide circulation and aeration in the ditch.
Preliminary treatment, such as bar screens and grit removal, normally precedes the OD. Primary
settling prior to an OD is sometimes practiced, but is not typical in this design.
Flow to the OD is aerated and mixed with return sludge from a secondary clarifier. A typical process
flow diagram for an activated sludge plant using an OD is shown in Figure 4.14 overleaf.
There is usually no primary settling tank or grit removal system used in this process. Inorganic
solids such as sand, silt and cinders are captured in the OD and removed during sludge wasting or
cleaning operations. The raw sewage passes directly through a bar screen to the OD.
The bar screen is necessary for the protection of the mechanical equipment such as rotor and
pumps. Comminutors or barminutors may be installed after the bar screen or instead of a bar screen.
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Figure 4.14 Oxidation ditch
The OD forms the aeration basin and here the raw sewage is mixed with previously formed
active organisms. The rotor is the aeration device that entrains (dissolves) the necessary oxygen
into the liquid for microbial life and keeps the contents of the ditch mixed and moving.
The velocity of the liquid in the OD must be maintained to prevent settling of solids, normally 0.3 to
0.45 m/sec. The ends of the OD are well rounded to prevent eddying and dead areas, and the outside
edges of the curves are given erosion protection measures.
The mixed liquor flows from the OD to a clarifier for separation. The clarified water passes over the
effluent weir and is chlorinated. Plant effluent is discharged either to a receiving stream, percolation
ditch, a subsurface disposal or leaching system.
The settled sludge is removed from the bottom of the clarifier by a pump and is returned to the OD or
wasted. Scum that floats to the surface of the clarifier is removed and either returned to the OD for
further treatment or disposed of by burial.
Since the OD is operated as a closed system, the amount of volatile suspended solids will gradually
increase. It will periodically become necessary to remove some sludge from the process. Wasting
of sludge lowers the MLSS concentration in the OD and keeps the microorganisms more active.
4.7.5.1 Operation
Process controls and operation of an OD are similar to the activated sludge process. To obtain
maximum performance efficiency, the following control methods must be maintained.
A. Proper Food Supply for the Microorganisms

Influent flows and waste characteristics are subject to limited control by the
operator. Municipal ordinances may prohibit discharge of materials that are damaging to
treatment structures or to human safety. Control over wastes dumped into the collection system
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requires a pre-treatment facility inspection programme to ensure compliance. Alternate means of

disposal, pre-treatment, or controlled discharge of significantly damaging wastes may be required
in order to permit dilution to an acceptable level by the time the sewage arrives at the STP.

B. Proper DO Levels

Proper operation of the process depends on the rotor assembly supplying the right amount of
oxygen to the waste flow in the OD. For the best operation, a DO concentration of 0.5 to 2.0
mg/L should be maintained just upstream of the rotors. Over oxygenation wastes power and
excessive DO levels can cause a pinpoint flocs to form that does not settle and is lost over the
weir in the settling tank. Control of rotor oxygenation is achieved by adjusting the OD outlet level
control weir. The level or elevation of the rotors is fixed but the deeper the rotors submerge in the
water, the greater the transfer of oxygen from the air to the water (greater DO). The ditch outlet
level control weir regulates the level of sewage in the OD.
C. Proper Environment
The OD process with its long-term aeration basin is designed to carry MLSS concentrations
of 3,000 to 5,000mg/L. This provides a large organism mass in the system.
Performance of the OD and its environment can be evaluated by conducting a few simple
tests and general observations. The colour and characteristics of the flocs in the OD as well
as the clarity of the effluent should be observed and recorded daily. Typical tests are settleable
solids, DO upstream of the rotor, pH, and residual chlorine in the plant effluent.
Laboratory tests such as BOD, COD, suspended solids (SS), volatile solids (VS), total solids(TS),
and microscopic examinations should be performed periodically by the plant operator or an
outside laboratory. The results will aid operator in determining the actual operating efficiency and
performance of the process.
OD solids are controlled by regulating the return sludge rate and waste sludge rate.
Remember that solids continue to deteriorate as long as they remain in the clarifier. Adjust the
return sludge rate to return the microorganisms in a healthy condition from the clarifiers to the
OD. If dark solids appear in the clarifier, either the return sludge rate should be
increased (solids remaining too long in clarifier) or the DO levels are too low in the OD.
Adjusting the waste sludge rate regulates the solids concentration (number of
microorganisms) in the OD. The appearance of the surface of the OD can be a helpful
indication of whether the sludge wasting rate should be increased or decreased. If the foam on
the surface is white and crisp, reduce the wasting rate. If the foam on the surface is thick and
dark, increase the wasting rate. WAS may be removed from the ditch by pumping to a sludge
holding tank, to sludge drying beds, to sludge lagoons, or to a tank truck. Ultimate disposal may
be to larger treatment plants or as in chapter 5.
Remember that this is a biological treatment process and several days may be required
before the process responds to operation changes. Make operator changes slowly, be patient, and
observe and record the results.
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D. Proper Treatment Time and Flow Velocities
Treatment time is directly related to the flow of sewage and is controlled by an adjustable weir.
Velocities in the ditch should be at 0.3 to 0.45 m/sec to prevent the deposition of flocs.
E. Proper Water/Solids Separation
MLSS that have entered and settled in the secondary clarifier are continuously removed from
the clarifier as return sludge, by pump, for return to the OD. Usually, all sludge formed by the
process and settled in the clarifier is returned to the ditch, except when wasting sludge. Scum
that is captured on the surface of the clarifier also is removed and either returned to the OD for
further treatment or disposal by burial.
F. Observations
Some aspects of the operation of an OD can be controlled and adjusted with the help of
some general observations. General, daily observations of the plant are important to help
operator determine whether the oxidation ditch is operating as intended. These observations
include colour of the mixed liquor in the ditch, odour at the plant site, and clarity of the ditch
and clarifier surfaces.
i. Colour
Operator should note the colour of the mixed liquor in the ditch daily. Mixed liquor from a
properly operating OD should have a medium to rich, dark brown colour. If the MLSS,
following proper start-up, changes colour from a dark brown to a light brown and the MLSS
appears to be thinner than before, the sludge waste rate may be too high, which may cause
the plant to lose efficiency in removing waste materials. By decreasing sludge wasting rates
before the colour lightens too much, the operator can ensure that the plant effluent quality will not
deteriorate due to low MLSS concentrations.
If the MLSS becomes black, the OD is not receiving enough oxygen and has gone anaerobic.
The oxygen output of the rotors must be increased to eliminate the black colour and return the
process to normal aerobic operation.
This is done by increasing the submergence level of the rotor.
ii. Odour
When the OD is operating properly, there will be little or no odour. Odour, if detected,
should have an earthy smell. If any odour other than this is present, the operator should
check and determine the cause. Odour similar to rotten eggs indicates that the ditch
may be anaerobic, requiring more oxygen or a higher ditch velocity to prevent deposition
of solids. Odour may also be a sign of poor housekeeping. Grease and solids build-up
on the edge of the ditch or clarifier will cause odours and become anaerobic.
In an OD, odours are much more often caused by poor housekeeping than by poor operation.
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iii. Clarity
In a properly operating OD, a layer of clear water or supernatant is usually visible about a meter
upstream from the rotor. The depth of this relatively clear water may vary from almost nothing to
as much as five or more cm above the mixed liquor. The clarity will depend on the ditch velocity
and the settling characteristics of the activated sludge solids. Two other good indications of a
properly operating OD are the clarity of the clarifier water surface and the OD surface free of foam
build-up. Foam build-up in the ditch is usually caused by insufficient MLSS concentration. Most
frequently foam build-up is only seen during plant start-up and will gradually disappear. Clarity of
the effluent from the secondary clarifier discharged over the weirs is the best indication of plant
performance. A very clear effluent shows that the plant is achieving excellent pollutant removals.
A cloudy effluent often indicates a problem with the plant operation.
4.7.5.2 Equipment Maintenance
Scheduled equipment maintenance must be performed regularly according to manufacturers’

instruction manuals. The operator should check each piece of equipment daily to see that it is
functioning properly. There may have very few mechanical devices in the oxidation ditch plant, but
they are all important.
The rotors and pumps should be inspected to ensure that they are operating properly. If pumps
are clogged, the obstructions should be removed. Listen for unusual noises. Check for loose bolts.
Uncovering a mechanical problem in its early stages could prevent a costly repair or
replacement at a later date.
Lubrication should also be performed with a fixed operating schedule and properly recorded. Follow
the lubrication and maintenance instructions furnished with each piece of equipment. Make sure that
the proper lubricants are used. Over lubrication is wasteful and reduces the effectiveness of lubricant
seals and may cause overheating of bearings or gears.
4.7.6 Chemical Clarification
Chemicals are used for a variety of municipal treatment applications, such as to enhance
flocculation / sedimentation, condition solids, add nutrients, neutralize acid base, precipitate
phosphorus, and disinfect or to control odours, algae, or activated-sludge bulking. Chemical
precipitation is a widely used, proven technology for the removal of metals and other inorganics,
suspended solids, fats, oils, greases, and some other organic substances (including
organophosphates) from sewage.
Precipitation is assisted through the use of a coagulant, an agent which causes smaller
particles suspended in solution to gather into larger aggregates. Frequently, polymers are used as
coagulants. The long-chain polymer molecules can be either positively or negatively charged
(cationic or anionic) or neutral (non-ionic). Since sewage chemistry typically involves the interaction
of ions and other charged particles in suspension, these electrical qualities allow the polymers to act
as bridges between particles suspended in solution, or to neutralize particles. The specific approach
used for precipitation will depend on the contaminants to be removed, as described below.
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4.7.6.1 Metals Removal
Hardness is caused primarily by the dissolution of calcium and magnesium carbonate and
bicarbonate compounds in water, and to a lesser extent, by the sulphates, chlorides, and silicates
of these metals. The removal of these dissolved compounds, called water softening often proceeds
by chemical precipitation. Lime (calcium oxide), when added to hard water, reacts to form calcium
carbonate, which itself can act as a coagulant, sweeping ions out of solution in formation and
settling. To achieve this with lime alone, a great deal of lime is typically needed to work effectively; for this
reason, the lime is often added in conjunction with ferrous sulphate, producing insoluble ferric
hydroxide. The combination of lime and ferrous sulphate is only effective in the presence of dissolved
oxygen, however. Alum, when added to water containing calcium and magnesium bicarbonate
alkalinity, reacts with the alkaline substances to form an insoluble aluminium hydroxide precipitate.
Soluble heavy metal ions can be converted into insoluble metal hydroxides through the
addition of hydroxide compounds. Additionally, insoluble metal sulphides can be formed with the
addition of ferrous sulphate and lime.
Once the optimal pH for precipitation is established, the settling process is often accelerated by
addition of a polymer coagulant, which gathers the insoluble metal compound particles into a coarse
flocs that can settle rapidly by gravity. However, these reactions cannot occur in raw or primary
treated sewage due to interference from organic matter.
4.7.6.2 Phosphorus Removal
Metal salts (most commonly ferric chloride or aluminium sulphate, also called alum) or lime,
have been used for the removal of phosphate compounds from water. When lime is used, a
sufficient amount of lime must be added to increase the pH of the solution to at least 10, creating an
environment in which excess calcium ions can react with the phosphate to produce an insoluble
precipitate (hydroxyl apatite). Lime is an effective phosphate removal agent, but results in a
large sludge volume.
When ferric chloride or alum is used, the iron or aluminium ions in solution will react with
phosphate to produce insoluble metal phosphates. The degree of insolubility for these
compounds is pH dependent.
4.7.6.3 Suspended Solids
Finely divided particles suspended in solution can escape filtration and other similar removal
processes. Their small size allows them to remain suspended over extended periods of time.
More often than not, the particles in sewage are negatively charged. For this reason, cationic
polymers are commonly added to the solution, both to reduce the surface charge of the particles, and
also to form bridges between the particles, thus causing particle coagulation and settling.
Alternatively, lime can be used as a clarifying agent for removal of particulate matter. The calcium
hydroxide reacts in the sewage solution to form calcium carbonate, which also acts as a coagulant,
sweeping particles out of solution.
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4.7.6.4 Additional Considerations
The amount of chemicals required for treatment depends on the pH and alkalinity of the sewage, the
phosphate level, and the point of injection and mixing modes, among other factors.
Competing reactions often make it difficult to calculate the quantities of additives necessary for
chemical precipitation. Accurate doses should be determined by jar tests and confirmed by field
evaluations. Chemicals are usually added by a chemical feed system that can be completely
enclosed and may also include storage space for unused chemicals.
Choosing the most effective coagulant depends on jar test results, ease of storage, ease of
transportation, and consideration of the O & M costs for associated equipment.
Chemical precipitation is normally carried out through a chemical feed system, most often a totally
automated system providing for automatic chemical feeding, monitoring, and control. Full automation
reduces manpower requirements, allows for less sophisticated operator oversight, and increases
efficiency through continuous operation.
An automatic feed system may consist of storage tanks, feed tanks, metering pumps (although
pumpless systems do exist), overflow containment basins, mixers, aging tanks, injection quills,
shot feeders, piping, fittings and valves.
Chemical feed system storage tanks should have sufficient capacity to run for some time
without running out and causing downtime. At least one month supply of chemical storage capacity
is recommended, though lesser quantities may be justified when a reliable supplier is located nearby,
thus eliminating the need for maintaining substantial storage space. Additive chemicals come in
liquid and dry form.
4.7.6.5 Jar Testing
Secondary treated sewage from STPs may sometimes carry over the microbes from the
clarifier. When chlorination of the treated sewage is to be carried out, these suspended microbes will
consume the added chlorine before the organic matter in the treated sewage can be oxidized and
pathogenic faecal organisms can be killed. Hence, it may be necessary to carry out coagulation,
flocculation and sedimentation before chlorine is applied. For details of the theory of coagulation,
flocculation and sedimentation, the CPHEEO Manual on Water Supply and Treatment may be
consulted. The purpose of a jar test is to find out which chemical and at what dosage is
needed to improve the clarity of secondary treated sewage. In general, such coagulation,
flocculation and sedimentation are not recommended for raw sewage because the disposal of the
resulting sludge becomes difficult due to a mix of biological and chemical sludge.
At the same time, the phosphorous present in sewage at even as low as 1 mg/L is known to
form a coating around the flocs and prevent them from settling and this in fact increases the
turbidity of raw sewage.
This is the reverse of addition of phosphate to cooling waters to prevent the precipitated scales from
settling out in the heat exchanger surfaces.
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Jar testing entails adjusting the amount of treatment chemicals and the sequence in which they
are added to samples of raw sewage held in jars or beakers. The sample is then stirred so that the
formation, development, and settlement of floc can be watched just as it would be in the full-scale
treatment plant. A typical laboratory bench-scale jar test apparatus is shown in Figure 4.15.
Source: http://www.neutecgroup.com
Figure 4.15 Typical Jar Testing apparatus
The apparatus allows for six samples each of 1-2 litre in size, to be tested simultaneously. The
procedure of jar testing is as follows;
The following jar test procedure uses alum (aluminium sulphate) a chemical for coagulation/
flocculation in sewage treatment, and a typical six jar tester.
A. First, using a 1,000 millilitre (ml) graduated cylinder, add 1,000 ml of raw water to each
of the jar test beakers. Record the temperature, pH, turbidity, and alkalinity of the raw water
before beginning of the test.
B. Prepare a stock solution by dissolving 10.0 grams of alum into 1,000 ml distilled water. Each 1.0
ml of this stock solution will equal 10 mg/L (ppm) when added to 1,000 ml of water to be tested.
C. Using the prepared stock solution of alum, dose each beaker with increased amounts of the
solution. The increments and dosage are shown in Table 4.2 overleaf.
D. After dosing each beaker, turn on the stirrers. This part of the procedure should reflect the actual
conditions of the plant to the extent possible. This indicates that if the plant has a static mixer
following chemical addition, followed by 30 minutes in a flocculator, then 1.5 hours of settling time
before the filters, then the test also should have these steps. The jar test would be performed as
follows: Operate the stirrers at a high RPM for 1 minute to simulate the rapid mixer.
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Table 4.2 Dosing in Jar Test
E. Reduce the speed of the stirrers to match the conditions in the flocculator and allow them to
operate for 30 minutes. Observe the floc formation periodically during the 30 minutes.
F. At the end of 30 minutes turn off the stirrers and allow settling. Most of the settling will be
complete after one hour.
G. Use a pipette to draw a portion from the top of each beaker, and measure its turbidity.
H. Plot supernatant turbidity versus alum dose as in Figure 4.16 for the sewage sample and
comment on the shape of the graph .
Figure 4.16 Supernatant turbidity vs. Alum dose
I. Find out the optimum alum dose. i.e., 25 mg/L from Figure 4.16.
If none of the beakers appear to have good results, then the procedure needs to be run again using
different dosages until the correct dosage is found
4.8 AERATED LAGOON
The aerated lagoon process consists of aeration of the facultative pond of the stabilization pond by
means of an aerator. (Refer to Section 4.13 “Waste stabilization pond”)
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Aerated lagoons are generally provided in the form of simple earthen basins with inlet at one end
and outlet at the other to enable the sewage to flow through while aeration is usually provided by
mechanical means to stabilize the organic matter. The major difference between activated sludge
systems and aerated lagoons is that the clarifiers and sludge recirculation are absent in the later.
4.8.1 Process Control
Daily tests will be for SS and COD. The BOD will be obtained from the standard curve made out for
this sewage from a curve of BOD to COD. The BOD tube is also useful. There is nothing much to
do by way of process control in aerated lagoon except making sure that all surface aerators are in
working condition. Some aerated lagoons have a final section of the lagoon itself as the
settling compartment. Some other lagoons have a dedicated clarifier outside the lagoon. In such a
case, the return sludge is also provided in some STPs. This return sludge arrangement must run
continuously. The excess sludge disposal is not provided for in aerated lagoons normally. In case
of clarifiers it may be used. Mechanical dewatering facilities are generally not advised because the
MLSS concentrations will be much lesser than in conventional ASPs. Sludge drying beds with
green cover to prevent direct rainfall on the beds is the answer to such situations.
The DO concentration in an aerated lagoon is the best means to determine if the lagoon is
operating properly. Depthwise measurement of DO is to be carried out. Typical practice is to
maintain 1 to 2 mg/l DO in the lagoon. A minimum DO level of 1 mg/l should be maintained in the lagoon
during the heaviest loading periods. Often the heaviest oxygen demand is during the night
when the algae are respiring. The pH range in the lagoon should range from 7 to 8. The pH can
exceed 9 during algal blooms, especially in low-alkalinity sewage. Surface mechanical aerators
when used should produce good turbulence and a light amount of froth.
4.8.2 Records
The limited parameters as above and the flow rate and cycle times shall be maintained as
per records.
4.8.3 Housekeeping
Keep the bunds free of any grass or weeds. Do not allow branches of trees to hang over the lagoon.
Follow all guidelines for motors. If high speed floating aerators are used, pull them out of the lagoon
before attending to it. Check if the power cable is having sufficient slack. Verify that the power cable
is tied at about 3m centers to vertical secure posts. Do not enter the lagoon unless you are wearing
a life vest and are on a boat with an aide if the aerators are not connected by a platform.
In all aerated lagoons, weeds and over hanging tree branches shall be avoided. A photo of such a
situation is shown in Figure 4.17 overleaf.
• The tree roots will enter the lining and break the concrete slab joints easily.
• Once this occurs, the slabs will lose their strength and start falling down into the lagoon itself.
• Once this sets in, the earth in the bund will be easily eroded in rains and the bund will cave in.
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Figure 4.17 Over hanging Tree branches and the small area of the Lined bund may be seen
• This leads to the lagoon sewage running out on land and polluting the land and water in
wells and streams.
• The hanging tree branches will be dropping leaves, which will support growth of mosquitoes.
• Manual scraping shall be done from the top of bund and not by persons entering the lagoon.
• In such cases, the branches shall be cut and the cut portions sealed with cow dung.
The biggest danger is if the bund gets broken and sewage escapes; it is very difficult to control
• Reconstructing the bund is also a problem when raw sewage keeps coming daily.
• Stopping the sewage escaping from the broken bund can be done by the following:
• Pack cement bags with mix of 90 % clay and 10% sewage and stack them one over the other.
• These have to be dumped to form a cofferdam inside the sewage spread.
• Thereafter, the reconstruction of the bund can be taken up easily.
4.9 ATTACHED GROWTH SYSTEMS
One of major attached growth systems adopted in sewage treatment lately is a “fixed film
synthetic media filter”, which consists of synthetic media such as inclined corrugated media
placed in cube sized packs and the inclinations changed to opposite directions in successive
layers as shown in Figure 4.18 overleaf.
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Figure 4.18 Fixed Film Synthetic Media Filters
Primary sedimentation is a pre-requirement in these applications. In Figure 4.18, the applied

sewage is distributed from the top of the media pack by stationary or hydraulically driven
reverse jet arms on opposite radii or rotated by a mechanical drive. The requirements to
apply the sewage on the entire plan are to uniformly and simultaneously allow the gas exchange
by releasing at the top and fresh air automatically forcing itself from the bottom.
The microbial films develop on the fixed media and bring about the metabolism as the sewage
passes over them as a film. In due course of time, the thickness of the film increases and results
in sloughing and getting carried away to secondary settling tanks. Recirculation of the treated
effluent is sometimes practiced to the attached system so that the enzymes released by the
microbes are returned to the reactor for solubilising the sewage organic matter. In all attached
growth systems wastewater should be applied 24 x 7.
4.9.1 Operation
Many operating problems may be avoided by changing one or more of the following process control
variables: distribution rates, and clarifier operation.
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A. Distribution Rates

As a principal process control measure, operators can control the rates at which sewage and filter
effluent are distributed to the filter media. Recirculation can serve several purposes, as follows:
• Reduce the strength of the sewage being applied to the filter.

• Increase the hydraulic load to reduce flies, snails, or other nuisances.
• Maintain distributor movement during low flows.
• Produce hydraulic shear to encourage solids sloughing and prevent ponding.
• Reseed the filter’s microbial population.
• Provide uniform flow distribution.
• Prevent filters from drying out.
B. Clarifier Operation.
The manner in which secondary clarifiers are operated can significantly affect the filter
performance. Although clarifier operation with fixed film reactors is not as critical as that with
suspended-growth systems, operators must still pay close attention to final settling.
Sludge must be removed quickly from the final settling tank before gasification occurs or
denitrification causes solids to rise. Use of the secondary clarifier as a principal means of
thickening (rather than simply for solids settling) may not produce the best effluent quality,
especially during summer months, when denitrification is likely to occur. The sludge blanket depth
in the secondary clarifier should be limited to 0.3 to 0.6 m. Continuous pumping or intermittent
pumping with automatic timer controls are used to accomplish solids wasting.
4.9.2 Maintenance
Planned maintenance will vary from plant to plant, depending on unique design features and
equipment installed. Although this chapter cannot address all of these items, a summary of the most
common and important maintenance tasks follows. The information provided in Table 4.3 overleaf is
not equipment or plant-specific. Therefore, both the manufacturer’s literature and engineer’s
operating instructions should be consulted and followed. The frequency of maintenance procedures
depends on site specific conditions. However, until operating experience is gained, frequent plant
inspections and maintenance should continue.
Maintenance schedules should consider the increased performance of fixed film synthetic media
filters in warm weather months, which may reduce the effect of removing process units from service.
4.10 MOVING BED BIO REACTOR (MBBR)
4.10.1 Configuration
The moving bed biofilm reactor (MBBR) is based on the biofilm carrier elements. Several types of
synthetic biofilm carrier elements have been developed for use in activated sludge process.
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Table 4.3 Planned maintenance for fixed film synthetic media filters
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Source: WEF, 2008
These biofilm carrier elements may be suspended in the activated sludge mixed liquor in the
aeration tank by air from the diffusers in aerobic reactors and by means of propeller mixers in
anaerobic and anoxic reactors. The carrier elements are retained by suitably sized sieves or plates.
These processes are intended to enhance the activated sludge process by providing a greater
biomass concentration in the aeration tank and thus offer the potential to reduce the basin size
requirements. They have also been used to improve the volumetric nitrification rates and to
accomplish the denitrification in aeration tanks by having anoxic zones within the biofilm depth.
Because of the complexity of the process and issues related to understanding the biofilm area and
activity, the process design is empirical and based on prior pilot-plant or limited full-scale results.
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The typical diagram of MBBR is shown in Figure 4.19.
Figure 4.19: Moving bed bioreactor
There are now more than 10 different variations of the process in which a biofilm carrier material of
various types is suspended in the aeration tank of the activated sludge process.
Differently varied processes have their own characteristics and require specific O&M. Therefore,
operators should have thorough knowledge on their systems and implement daily O&M according to
the manufacturers’ instruction manuals. Refer to Part-A 5.18.13 MBBR for system description on the
varieties of MBBR.
4.11 MEMBRANE BIO REACTOR (MBR)
The membrane bioreactor (MBR) process is a combination of activated sludge process and
membrane separation process. Low-pressure membranes (ultra-filtration or microfiltration) are
commonly used. Membranes can be submerged in the biological reactor or located in a separate
stage or compartment and are used for liquid-solid separation instead of settling process as in
Figure 4.20 overleaf. Basically, primary sedimentation tank, final sedimentation tank and disinfection
facility are not installed in this process. The reaction tanks comprise an anoxic tank and an aerobic
tank, and the membrane modules are immersed in the aerobic tank. Pre-treated, screened influent
enters the membrane bioreactor, where biodegradation takes place. The mixed liquor is withdrawn by
water head difference or suction pump through membrane modules in a reaction tank, being filtered
and separated into solid and liquid. Surfaces of the membrane are continuously washed down during
operation by the mixed flow of air and liquid generated by air diffuser set at the bottom of the reaction
tank. Permeate from the membranes constitutes the treated effluent.
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Source: JSWA
Figure 4.20 Configuration of membrane bioreactor system
4.11.1 Operation
All MBR systems require some degree of suction or pumping to force the water flowing through the
membrane. One type of membrane systems uses a pressurized system to push the water through the
membranes. The major systems used in MBRs draw a vacuum through the membranes so that
the water outside is at ambient pressure. The advantage of the vacuum is that it is gentler to the
membranes; the advantage of the pressure is that throughput can be controlled. Both systems also
include techniques for continually cleaning the system to maintain membrane life and keep the
system operational for as long as possible.
All the principal membrane systems used in MBRs use an air scour technique to reduce build-up of
material on the membranes. This is done by blowing air around the membranes out of the manifolds.
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The permeate from an MBR has low levels of suspended solids, as also levels of bacteria, BOD,
nitrogen, and phosphorus. Disinfection is easy and may not even be required, depending on
discharge standards.
The solids retained by the membrane are recycled to the biological reactor and build up in the
system. As in conventional biological systems, periodic sludge wasting eliminates sludge build-up
and controls the SRT within the MBR system. The waste sludge from MBR goes through standard
solids-handling technologies for thickening, dewatering, and ultimate disposal. Chemical addition
increases the ability of solids to settle. As more MBR facilities are built and operated, a more
definitive understanding of the characteristics of the resulting sludge will be achieved. However,
experience to date indicates that conventional sludge processing unit operations are also applicable
to the waste sludge from MBR.
4.11.2 Maintenance
The key to the cost-effectiveness of an MBR system is membrane life. If membrane life gets curtailed
such that frequent replacement is required, costs will increase significantly. Membrane life can be
increased in the following ways:
Good screening of solids before the membranes to protect the membranes from physical damage.
Throughput rates that are not excessive, i.e., that do not push the system to the limits of the design.
Low rates reduce the amount of material that is forced into the membrane, and thereby reduce the
amount that has to be removed by cleaners or that will cause eventual membrane deterioration.
Mild cleaners/cleaning solutions most often used with MBRs include regular bleach (sodium) and
citric acid, which are regularly used. The cleaning should be in accordance with manufacturer’s
recommended maintenance protocols.
4.12 UP FLOW ANAEROBIC SLUDGE BLANKET REACTOR (UASB)
The Up flow Anaerobic Sludge Blanket reactor (UASB) maintains a high concentration of biomass
through formation of highly settleable microbial aggregates. The sewage flows upwards through a
layer of sludge. Separation between gas-solid-liquid takes place at the top of the reactor phase.
Any biomass leaving the reaction zone is directly recirculated from the settling zone. The process is
suitable for both soluble wastes and those containing particulate matter. The process has been used
for treatment of municipal sewage at few locations and hence performance data and experience
available presently are limited. The Up flow Anaerobic Sludge Blanket reactor (UASB) is shown in
4.12.1 Plant Commissioning and Operation
Two to three months are needed to build up a satisfactory sludge blanket without the addition of
“seed” sludge from a working UASB. A shorter time is sufficient, if seeding is done.
During the start-up period, COD removal in the UASB gradually improves as sludge accumulation
occurs. This may be called the sludge accumulation phase.
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Figure 4.21 Schematic diagram of an Up flow Anaerobic Sludge Blanket Reactor
The end of the sludge accumulation phase is indicated by sludge washout. At this time, the reactor
is shut down to improve the quality of the sludge. This may be called the sludge improvement phase.
After sludge improvement, blanket formation starts. Once the blanket is formed, again some surplus
sludge washout could occur and to stabilise the stable operation, the excess sludge needs to be
removed periodically. The excess sludge so removed can be sent directly for sludge treatment.
The sludge in the UASB is tested for pH, volatile fatty acids (VFA), alkalinity, COD and SS. If the
pH reduces while VFA increases, the sewage should not be allowed into the UASB until the pH
and VFA stabilise. Daily operation of the UASB requires minimum attention. No special
instrumentation is necessary for control, especially where gas conversion to electric power
is not practiced. As stated, surplus sludge is easy to dry over an open sand bed. The reactor
may need to be emptied completely once in five years, while any floating material (scum)
accumulated inside the gas collector channels may have to be removed every two years to ensure
free flow of gas.
4.12.2 Daily Operation and Maintenance of UASB
A. Cleaning of Effluent Gutters

All V-notches must be cleaned in order to maintain the uniform withdrawal of UASB effluent
coming out of each V-notch. The irregular flow from each V-notch results in the escape of more
solids washout. Similarly, blocking of the V-notches of the effluent gutters will lead to uneven
distribution of sewage in the reactor. Therefore, the effluent gutters have to be inspected on a
regular basis to remove any material blocking and even the outflow over the V-notches in the
gutters. The regular maintenance involves cleaning of V-notches with a broom three times a day
and removing sludge with a brush or with a water jet once a day as in Figure 4.22 overleaf.
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Figure 4.22 Cleaning of effluent gutters
B. Unclogging Feeder Pipes
The feeder pipes should be checked regularly for clogging. Flexible iron rods can be used for this
purpose. A submersible pump can be used to unclog the feeder pipes as in Figure 4.23.
Submersible pump
Cleaning of feed pipes by submersible pumps Clean feed pipes (equal flow distribution)
Source: PWSSB
Figure 4.23 Cleaning of Feed Inlet Pipes
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The appropriate valve can be closed and the treated sewage can be pumped through the clogged
feeder pipe and this will unclog the feeder pipe. The valve can be opened after the feeder pipe
is free of the blockage. Compressed air if available at the location can also be used to unclog
the feeder pipe. An air lift pump can also be used for this purpose. These feeder pipes are
generally clogged due to rags and floating material. It is necessary to provide a fine screen or extra
prevention at the screen to capture floating material at the pre-treatment unit itself.
C. Removal of Floating Mat
Floating mat must be removed from the top of the surface of reactor with a rake. The removed
material should be disposed at the dumping site.
D. Check of Leakage of Biogas
The gas collectors should be checked for leakage. Leakage is easily detected by applying
soap solution to the piping. This should be done on a regular basis. If the gas collectors are
leaking, the valve at the end of one bay in the gas leak should be first closed and then repaired
as soon as possible.
Regular maintenance includes opening of hatch boxes and removing floating layer inside the
gas collectors.
E. Scrubbing of Biogas
Waste at the Top of UASB Reactor

The risk of the corrosion of dual fuel engine parts, as biogas contains H2S, can be minimised if
biogas can be scrubbed before using it as fuel for dual fuel gas engines.
F. Check for Sludge Withdrawal Ports
The ports of the sludge withdrawal must be free from any clogging which reduces the
chances of checking of sludge height in reactor. The feeder pipes should be checked regularly
for clogging. Flexible synthetic rods can serve the purpose. A submersible pump can be used
to unclog the feeder pipes.
G. Methanogenic Activity
Successful operation of a UASB reactor depends upon maintaining a satisfactory balance

between methane and acidogenic bacteria. The methane formers are susceptible to changes
in environmental conditions such as pH, temperature etc. The methanogenic activity must be
analysed monthly. The testing can be outsourced.
H. Proper Sludge Wasting
Sludge must be removed or transferred from the UASB reactor occasionally based on the sludge
yield or concentration of TSS or VSS. Higher sludge withdrawal points to a poor performance of
the reactor in terms of treatment.
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I. Biogas Analysis
The biogas analysis is used largely at STP where information on fuel value of gas is
important. In addition, knowledge of gas composition can be of considerable help in the control of
digestion units. Sudden changes in gas composition can signal a change either in the operation
of the treatment unit or in the amount or composition of incoming sewage. Such changes
can thus be used as a warning sign to suggest the need for closer observation and control of
treatment unit. The testing can be outsourced.
J. Hydrogen Sulfide Determination
The determination of hydrogen sulphide will continue to be an important consideration wherever

gas is used for fuel in gas engines, particularly in areas where the sulphate content of sewage
is very high.
K. Sludge Pumping Station Maintenance
After every sludge withdrawal operation, clean the pipeline by opening the top flushing valve until
all the sludge in the pipeline is washed out. The sump has to be cleaned with water.
Never keep the sludge in the sump, it may damage the pumps. Before getting into the sumps
for any maintenance, keep the top cover open for an hour before anybody gets in so that any
accumulated biogas will vent to the atmosphere. Keep the valve chamber dry and valves clean.
Check the electrical components regularly.
L. Biogas Holder Operation and Maintenance
The biogas produced in the reactors is taken in the common Fibre Glass Reinforced Plastic (FRP)
pipes to the biogas holder. The biogas before being sent to the gas holder has to pass through a
moisture trap. The gas coming to the gas holder is measured through gas flow meters connected
to FRP pipe after the moisture trap
The biogas before going to the holder is branched off. One branch is taken to the flaring system,
the other to the biogas engine. Before going to the engine, the gas is measured from the flow
meter provided on pipeline going to the engine. Sluice valves are provided on the lines to isolate
the flow, which is manually operated.
In case of sudden reduction in dome levels, the reactor FRP dome connector and its
connection to the gas pipe header should be checked with soap water for any leakage of gas.
This is one of the reasons for having a gas holder level trap.
The typical UASB preventive maintenance check list is mentioned below.
• Date and time

• Check and clean weir levels of division boxes
• Clean-up- feed inlet points
• Cleaning of V-notches
• Removal of sludge from effluent gutter by water jet or brush
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• Removal of floating layer on the top of reactor

• Cleaning and scrubbing of effluent channels
• Check gas pipes for leakage
• Leakage greasing of spindle of sludge valves
• Cleaning of sludge sump
4.12.3 Routine Maintenance
4.12.3.1 Quarterly Maintenance
• The spindles of the valves have to be greased every three months.

• The glands and packing of the valves have to be checked every three months and
replaced, if necessary.
4.12.3.2 Annual Maintenance
The reactor should be emptied after the first year of full operation to check the complete feeder and
sludge withdrawal systems, especially the valves and the internal pipes for any accumulation of
debris, sludge etc.
• A first check of the complete system including valves and holes should be made after one year,
or earlier when required. Routine check can be established on the basis of the first inspection
observation.
• The effluent gutters should be checked for levelling and alignment once a year. Each gutter
should be horizontally levelled and all gutters in one reactor should be at the same level.
• Electrical wiring should be checked every year.
• Corrosion of electrical connections should be corrected every year.
• The cement structures should be checked yearly and repaired when necessary.
• The sludge filtrate water pumps should be maintained.
4.12.3.3 Five-Yearly Maintenance
Every five years, the following maintenance should be carried out.
• Each reactor should be alternately put out of operation.
• Clean the inside concrete surface.
• Apply new coating of epoxy to the concrete surface.
• Check quality of feed inlet pipes and replace when necessary.
• Check fixing of the feed inlet pipes, both at the distribution boxes and at the bottom.
• Change corroded fixing material when necessary.
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• Check position of PVC sheets.

• Check the fixing-material of the PVC sheets and replace when necessary.
• Check the quality of gas collectors and carry out repairs where necessary.
4.12.4 Decision Schemes for Sludge Removal
The removal of sludge is subject to a number of choices such as
• How much sludge should be removed and

• From where should it be removed, etc.
4.12.5 Shut-Down and Standstill
At shutdown of the plant, the sludge will settle at the bottom of the reactor. The biological activity
of the sludge decreases slowly during standstill. Care should be taken to ensure that the sludge is
not exposed to aerobic conditions. This might occur, for instance, when the reactor is flushed with
clean water for prolonged periods.
At shutdown of the plant, the gas production will decrease. At a prolonged period of plant standstill,
the pressure in the gas collection system can drop and air may enter into the system. In this situation,
internal parts of the gas flare, the gas metre and the pressure/vacuum release valves that normally
are not in contact with the atmospheric air may start to corrode. These parts have to be protected,
for instance by greasing.
If the water level in the tank is lowered during shutdown, the limited capacity of the vacuum release
valves should be kept in mind. It is possible that imploding of the gas collectors may occur due to fast
withdrawal of the reactor contents. At lowering of the water level in the reactor, it is advised to open
the manholes on the top of the gas collectors. Only after re-establishing the maximum water level,
the manholes can be closed and sealed.
In general, any type of work on the gas collectors requires the opening of the manholes as the
explosive moisture of air and methane can develop in or around the gas collectors. When it is
necessary to enter the reactor while sludge is present, it should be realised that methane is being
formed continuously. A proper ventilation of the reactor is necessary. Very strict rules concerning open
fire, spark emission, etc., should be followed. When entering the reactor plant, personnel should wear
respiration equipment. Measurement of explosion risk and hydrogen sulphide concentration should
be taken frequently when repair work is carried out.
4.12.6 Operational Cautions
• Do not get upon the UASB unless you have a gas mask, safety shoes, goggles and helmets.
• Do not carry any ignitable matters on your person.
• Once you reach the walking platform at top, check the H2S by hand held meter.
• Unless it registers safety, immediately climb down the UASB.
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• Once all the above mentioned issues are ensured, proceed to check any overflows of
sewage and if so, stop the UASB.
• Check for corrosion at least once in 6 months and get it rectified.
4.12.7 Final Polishing Unit (FPU)
Not much maintenance is required for this unit. The algal growth needs to be maintained, and the
dead algae floating on the top of water surface has to be periodically removed. The baffles provided
at the outlet unit have to be cleaned regularly. Keep the floating material away from the unit. See that
dead algae do not pass out into the pond. Sewage flow should be maintained to avoid development
of anaerobic/septic conditions. These ponds should be de-sludged/de-silted regularly depending on
the depth of sludge accumulation. A record of maintenance should be maintained.
4.12.8 Duckweed Pond
The bund sides shall not be grown over by weeds. Figure 4.17 illustrates the same.
4.13 WASTE STABILIZATION POND (WSP)
Waste stabilization ponds are open, flow-through earthen basins specifically designed and
constructed to treat sewage. They provide comparatively long detention periods extending from a
few days to several days.
There are three principal types of WSP:
• Anaerobic,
• Facultative, and
• Maturation ponds.
Anaerobic ponds and facultative ponds are designed for BOD removal, and maturation ponds
are designed for faecal bacteria removal. These three types of WSP can also be arranged in a
series – first an anaerobic pond, then a facultative pond, and finally (if needed to achieve the required
faecal coliform removal) followed by one or more maturation ponds.
Apart from the above three types, there is another type of WSP called aerobic pond, which are
seldom used. When used, follow the same procedures as in facultative ponds.
4.13.1 Start-up Procedures
Pond systems should preferably be commissioned at the beginning of the hot season so as to
establish as quickly as possible the necessary microbial populations to effect waste
stabilization. Prior to commissioning, all ponds must be free from vegetation. Facultative ponds
should be commissioned before anaerobic ponds: this avoids odour release when anaerobic pond
discharges into an empty facultative pond. It is best to fill facultative and maturation ponds with
freshwater from a river, lake or well; water from public water supply is prohibited.
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The developments of the algal and heterotrophic bacterial populations are gradual. Alternatively,
facultative ponds should be filled with raw sewage and left for three to four weeks to allow the
microbial population to develop; a small amount of odour release is inevitable during the period.
4.13.2 Routine Maintenance
The maintenance requirements of ponds are very simple, but they must be carried out regularly.
Otherwise, there will be serious odour, fly and mosquito nuisance.
Maintenance requirements and responsibilities must therefore be clearly defined at the design stage
so as to avoid problems later. Routine maintenance tasks are as follows:
• Removal of screenings and grit from the inlet works.
• Cutting the grass on the embankments and removing it so that it does not fall into the pond (this is
necessary to prevent the formation of mosquito-breeding habitats; the use of slow-growing grass
minimizes this task).
• Removal of floating scum and floating macrophytes, such as Lemna, from the surface of
facultative and maturation ponds (this is required to maximize photosynthesis and surface
re-aeration and prevent fly and mosquito breeding).
• Spraying the scum on anaerobic ponds (which should not be removed as it aids the treatment
process), as necessary, with clean water or pond effluent, or a suitable biodegradable larvicide,
to prevent fly breeding.
• Anaerobic ponds, during times of low pH produce odour. In such cases addition of NaOH or lime
to raise the pH to above 7 is recommended to eliminate the odour caused due to H2S. However,
addition of NaOH will produce less sludge as compared to lime which produces more sludge.
• Repair of any damage to the embankments caused by rodents, rabbits or other animals.
• Repair of any damage to external fences and gates.
Additional precautions and practices are described below:
• The scum has a tendency to form at the corners of the ponds and supports mosquito growth.
• In anaerobic ponds, during times of low pH, odour is produced. In such occasions, addition of
sodium hydroxide is required to raise the pH to 7. The advantage of sodium hydroxide is that it
produces less sludge. In case, production of sludge is not a concern then lime can be added to
raise the pH to 7. Once the pH is raised to 7, odour can be eliminated.
• In anaerobic ponds, low pH produces odours. In such cases addition of NaOH produces less
sludge, or lime can be added to raise the pH to 7 to eliminate odour caused by H2S
• The scum need not be taken out of the ponds.
• What is needed is breaking the surface of the scum by a light long pole while standing at
the bank.
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• This releases the gases that are supporting the scum layer and automatically the
mat sinks back.
• These are dealt with like any other organic matter, which are stabilized by the organisms
of the pond.
• Fish shall not be allowed to breed in these.
• The precautions involved in manually operating the scum removal must be adopted.
• Sometimes sludge removal would become necessary.
• The thumb rule will be to verify the depth of sludge and de-sludge once it is about
30 % of depth.
4.13.3 De-Sludging
The biggest challenge to an operator in the management of pond systems is to identify when
a pond requires de-sludging, and to carry it out safely without giving rise to environmental
problems. These issues are addressed in this section so as to help the operator develop adequate
confidence in this task.
4.13.3.1 When to De-Sludge
When raw sewage without grit removal is admitted to the pond, a general rule of thumb to calculate
the grit accumulation is 0.5 meters depth for a ten year period. Similarly, the accumulation of sludge
can be taken as 0.7 meters for a ten year period. Generally, the pond has to be de-sludged when
the combined depth of this grit and sludge exceeds 30 % of the designed liquid depth of the pond.
However, the “as constructed drawing” may not be available sometimes. Hence, it becomes
necessary to physically measure the total depth of the pond from the top of the bund to the floor,
the free board and the depth of accumulated sludge. The procedure will be needed, in general after
10 years or when the BOD removal is getting reduced drastically or when black sludge is constantly
overflowing in the treated sewage from the pond.
4.13.3.1.1 Preparatory for the Measurement
In order to do the actual measurements in the pond, manual and mechanical methods as also
remote instrumentation can be used. In the manual method, the minimum requirements are a clear
sunny day with no rains, broad daylight, working between 9 AM and 3 PM only, fire service personnel
available at site, minimum of three able bodied persons on a good water tight row boat with a
set of extra spare oars, number of people on the boat not to exceed 50 % of the safe carrying
capacity of the boat, life vests for all those on board, the boat doubly checked for water tightness, an
experienced boatman and oxygen masks for all on board. In the mechanical method, a long arm
boom crane which can reach at least one third of the sides from the bund, an apparatus to hold tightly
a dip pipe (described later) and an experienced operator. In the instrumentation method, the same
crane as above, but equipped with an ultra sound sensor mounted on the end of the boom arm with
transmission of the readings by a modem to a personal computer nearby.
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4.13.3.1.2 The Dip Tube
This is a light weight tube of strong aluminium and about 30 mm inner diameter and with striations
lightly carved as lines all over its outer length. The length of the tube must be at least the depth of
the pond plus a minimum of two meters. A white fluffy “terry” towel is wrapped around the tube three
times for a length equal to the depth of the pond plus 0.5 m and securely tied using good nylon thread
as a spiral at interval of 30 cm between the windings and finally tied securely in a knot at the top side.
At the bottom end, separate thread must be tied and knotted to hold the towel in place. Once this is
done, check the towel for tightness before using it.
4.13.3.2 The white towel test
The test uses the dip tube and is used to understand the depth of the sludge, Malan (1964). The dip
tube wrapped with the white towel is lowered vertically into the pond until it reaches the pond bottom
and held there for about 10 to 15 minutes and it is then slowly withdrawn. The depth of the sludge
layer is clearly visible since some of the blackish sludge particles will have been entrapped in the
towel material and this can be measured. The length of wetness of the towel will indicate the liquid
depth. A demonstration is shown in Figure 4.24.
Source: Duncan Mara, 2004
Figure 4.24 The White Towel test
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The sludge depth should be measured at various points throughout the pond, away from the
embankments, and its mean depth calculated. Duncan Mara (2004).
In order to do this test, the boat as described earlier can be used by staying close to the sides of the
bund at about 3 to 5 m only.
It is not necessary to measure at the pond center because normally, the sludge settles uniformly over
the entire plan area of the pond.
Alternatively, if the crane with boom is available, the dip tube can be securely tied to the free end of
the boom which can be positioned at chosen locations and the dip tube gently lowered till it comes to
rest and the same can be taken out of the bund and measured.
This is a type of remote measurement. Do not send any person on the boom arm.
4.13.3.3 De-Sludge Procedure
• Repeat the above depth measurements slowly without hurry. Always do this in clear non-rainy
weather. Make sure you have at least four readings, which are fairly close.
• Once the sludge depth is thus measured, consult the chemist for any tendency of efficiency drop
in the pond for BOD removal. If the chemist feels that there is a steady decline and efficiency is
going down, consult the plant superintendent.
• As a rule of thumb, if the liquid height is less than 1.2 meters in a facultative or anaerobic pond,
it is time for de-sludging. Take the decision jointly and never by yourself.
• The best method of de-sludging is to take one pond out of operation during the beginning of
summer and pump out the water portion to the other ponds. Thereafter, it normally takes two
months for a sludge depth of about 2 meters to dry out.
• Deploy manpower equipped with oxygen mask to gently turn the dried sludge upside down
uniformly over the whole area so that drying is hastened. Never use a machine during this
operation as methane may get released.
• Once this is completed and the sludge is dried, deploy a suitable earthmoving equipment and
evacuate the sludge over the bund and on to the ground on the earth side of the bund.
• The sludge can be heaped into a pile by manual labourers who should wash their hands
thoroughly with soap after finishing their work.
4.13.3.4 Special cautions for anaerobic pond / maturation pond
All the points listed earlier in aerated lagoon and facultative ponds apply here also except that the
depth of sludge before de-sludging will be according to the original design.
The boat ride to measure the sludge depth shall not be used in these ponds. Instead, the white towel
test shall be conducted and a long boom crane shall be used without making any person stand at the
end of the boom.
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4.13.4 Process Control
There is nothing much to control in the process of purification of sewage in WSP except
making sure that the sludge accumulation does not exceed 30% of the total liquid depth or the
design depth of sludge.
4.13.5 Record Keeping
4.13.5.1 Records necessary for Anaerobic Pond
• Daily tests and records will be the flow and SS.
• Monthly tests shall be the BOD after filtering through Whatman 42 filter paper and pH.
4.13.5.2 Records necessary for Facultative Pond
• Weekly tests will be identification of organisms as per “Standard Methods” drawings.
4.13.5.3 Records necessary for Maturation Pond
• Yearly test of faecal and total coliforms at peak summer and peak monsoon shall be conducted.
4.14 FARM FORESTRY
Please hand over the O&M work to the local forestry department who are competent in this.
4.15 FISH POND
Fish ponds otherwise referred to as pisiculture cannot be looked upon as a method of stand-alone
sewage treatment.
However, treated / diluted sewage if used for pisiculture on the lines of the on-going East Kolkata
wetlands, this needs to be strictly monitored by
• Department of Health (DOH)

• Department of Environment (DOE)
• State Pollution Control Board (SPCB)
More important is public hearing and acceptance.
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4.16 SECONDARY SEDIMENTATION TANK
The terms settling tank, sedimentation tank and clarifiers are synonymous and mean the same.
A typical plant may have clarifiers located at two different points.
The one that immediately follows the bar screen, comminutor, or grit channel is called the primary
sedimentation tank or primary clarifier, merely because it is the first sedimentation tank in the plant.
The other, which follows other types of treatment units, is called the secondary sedimentation tank
or the final sedimentation tank or secondary clarifier. The two types of sedimentation tanks operate
almost exactly the same way. The function of a primary clarifier is to remove settleable and
floatable solids. The reason for having a secondary sedimentation tank is that other types of
treatment following the primary sedimentation tank convert more solids to the settleable form, and
they have to be removed from the treated sewage. Because of the need to remove these additional
solids, the secondary clarifier is considered part of these other types of processes.
The main difference between primary and secondary sedimentation tanks is in the density of the
sludge handled. Primary sludge is usually denser than secondary sludge. Effluent from a secondary
clarifier is normally clearer than primary effluent.
Solids that settle to the bottom of a sedimentation tank are usually scraped to one end (in rectangular
clarifiers) or to the middle (in circular clarifiers), into a sump. From the sump, the solids are pumped to
the sludge handling or sludge disposal system. Systems vary from plant to plant and include sludge
digestion, vacuum filtration, filter presses, incineration, land disposal, lagoons and burial.
Disposal of skimmed solids varies from plant to plant.
Skimmed solids may be buried with material cleaned off the bar screen, or pumped to the digester.
Even though pumping of skimmed solids to a digester is not considered good practice because
skimming can cause operational problems in digesters, it is a common practice.
4.16.1 Operation
Of all the different types of clarifiers that an operator must regulate, secondary clarifiers in the
ASP are the most critical and require the following attention from the operator.
• Levels of sludge blanket in the clarifier

• Concentration of suspended solids in the clarifier effluent
• Control and pacing of return sludge flows
• Concentration of dissolved oxygen (DO) in the clarifier effluent
• Level of pH
• Concentration of RAS
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4.16.2 Maintenance
Annually, during periods of low flow, each clarifier should be shut down for inspection, routine
maintenance, and any necessary repairs. Even though the clarifier and all equipment are working
properly, an annual inspection helps to prevent serious problems and failures in the future when the
STP may break down.
During normal operations, the operator should schedule the following daily activities:
A. Inspection
Make several daily inspections with a “stop, look, listen, and think” routine.
B. Cleanup
Using water under pressure, wash off accumulations of solid particles, grease, slime, and other
material from walkways, handrails, and all other exposed parts of the structure and equipment.
C. Lubrication
Grease all moving equipment according to manufacturer’s specifications and check oil levels in
motors where appropriate.
4.17 ADVANCED TREATMENT
Advanced sewage treatment processes typically are used to further reduce the concentrations of
suspended solids, nutrients (nitrogen or phosphorus) and soluble organic chemicals in secondary
treatment effluent. These processes may be physical, chemical, biological, or a combination
of these processes.
4.17.1 Sand Filtration
Sand filters have influent and effluent distribution systems consisting of pipes and fittings. Head
loss is a measure of solids trapped in the filter. As the filter becomes full with trapped solids, the
efficiency of the filtration process falls off, and the filter must be backwashed. Filters are back
washed by reversing the flow so that the solids in the media are dislodged and can exit the
filter and sometimes air is dispersed into the sand bed to scour the media.
Sand filters can be automatically backwashed when the differential pressure exceeds a pre-set
limit or when a timer starts the backwash cycle.
4.17.2 Multimedia Filtration
A multimedia filter operates with the finer, denser media at the bottom and the coarser, less dense
media at the top. A common arrangement is as follows.
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• Top: Anthracite
• Middle: Sand
• Bottom: Garnet
These media can be used alone, such as in sand filtration, or in a multimedia combination. Some
mixing of these layers occurs and is anticipated. During filtration, the removal of the suspended solids
is accomplished by a complex process involving one or more mechanisms, such as:
• Straining,
• Sedimentation,
• Interception,
• Impaction, and
• Adsorption.
The size of the medium is the principal characteristic that affects the filtration operation. If the medium
is too small, much of the driving force will be wasted in overcoming the frictional resistance of the
filter bed. If the medium is too large, small particles will travel through the bed, preventing optimum
filtration. As same as “sand filtration”, back wash is required to keep adequate filtration efficiency.
4.17.3 Membrane Filtration (MF, UF, NF, RO)
The membrane filtration is used for polishing water for specific uses like industry process water,
or for aquifer infiltration. In India, membrane filtration as in Figure 4.25 is used in the water and
sewage sectors.
Figure 4.25 Filtration spectrum
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MF – Microfiltration membranes are porous membranes with pore sizes between 0.1 and 1 micron
(1 micron=one thousandth of a millimeter). They allow almost all dissolved solids to get through and
retain only solids particles over the pore size.
UF – Ultra filtration membranes are asymmetric or composite membranes with pore sizes
between 0.005 and 0.05 micron. They allow almost mineral salts and organic molecules to get
through and retain only macromolecules
NF – Nano filtration membranes are with pore sizes 0.001 micron. They retain multivalent ions and
organic solutes that are larger than 0.001 micron.
RO – Reverse osmosis membranes are dense skin, asymmetric or composite membranes that let
water get through and rejects almost all the salts.
A. Operational Unit Processes

All membrane filtration systems have associated operational unit processes that are essential for
maintaining and optimizing system performance and therefore critical to the implementation of
the technology.
The unit processes include backwashing, chemical cleaning, and integrity testing.
For the purposes of this discussion, pre-treatment and post-treatment are also considered
operational unit processes associated with membrane filtration.
Each of these processes and its role in the operation of a membrane filtration system are
described in the following sections. Although not every membrane filtration system utilizes
all of these processes, they utilize each process to a certain degree.
B. Pre-treatment
Pre-treatment is typically applied to the feed water prior to entering the membrane system in
order to minimize membrane fouling, but in some cases may be used to address other water
quality concerns or treatment objectives. Pre-treatment is most often utilized to remove foulants,
optimize recovery and system productivity, and extend membrane life. It may be used to prevent
physical damage to the membranes.
Different types of pre-treatment can be used in conjunction with any membrane filtration system,
as determined by site-specific conditions and treatment objectives.
Pilot testing can be used to compare different pre-treatment options, optimize them and / or
demonstrate pre-treatment performance.
Various methods of pre-treatment for membrane filtration systems are discussed in the following
sub-sections.
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C. Pre-filtration
Pre-filtration, including screening or coarse filtration is common membrane filtration systems that
are designed to remove large particles and debris. Pre-filtration can either be applied to the
membrane filtration system as a whole or to each membrane unit separately. The particular pore
size associated with the pre-filtration process (where applicable) varies depending on the type
of membrane filtration system and the feed water quality. For example, although hollow fibre
microfiltration (MF) and ultrafiltration (UF) systems are designed specifically to remove
suspended solids, large particulate matter can damage or plug the membrane’s fibres.
Because spirally wound nanofiltration (NF) and reverse osmosis (RO) utilize non-porous semi
permeable membranes and are almost exclusively designed in a spiral-wound configuration for
municipal water treatment applications, these systems must utilize much finer pre-filtration in
order to minimize exposure of the membranes to particulate matter of any size.
A summary of the typical pre-filtration requirements associated with the various types of
membrane filtration is presented in Table 4.4.
Table 4.4 Typical membrane system pre-filtration requirements
* Pre-filtration is not necessarily required for MCF systems

Source: WEF, 2008
D. Backwashing
The backwash process for membrane filtration systems is similar in principle to that for
conventional media filters and is designed to remove contaminants accumulated on the
membrane surface. Each membrane unit is backwashed separately and in a staggered pattern
so as to minimize the number of units in simultaneous backwash at any given time. During a
backwash cycle, the direction of flow is reversed for a period ranging from about thirty seconds
to three minutes.
The force and direction of the flow dislodge the contaminants at the membrane surface
and washout accumulated solids through the discharge line.
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Membrane filtration systems are generally backwashed more frequently than conventional media
filters, with intervals of approximately 15 to 60 minutes between backwash events. Typically, the
membrane backwash process reduces system productivity in the range of 5 to 10 % due to the
volume of filtrate used during the backwash operation.
Backwashing is conducted periodically according to manufacturer’s specifications and

site-specific considerations. Although more frequent backwashing allows for higher fluxes
during filtration, this benefit is counterbalanced by the decrease in system productivity. In general,
a backwash cycle is triggered when a performance-based benchmark is exceeded, such as a
threshold for operating time, volumetric throughput, increase in trans-membrane pressure (TMP),
and/or flux decline. Ideally, the backwash process restores the TMP to its baseline (i.e., clean)
level; however, most membranes exhibit a gradual increase in the TMP that is observed after
each backwash, indicating the accumulation of foulants that cannot be removed by the backwash
process alone. These foulants are addressed through chemical cleaning.
Because the design of spiral-wound membranes generally does not permit reverse flow, NF
and RO membrane systems are not backwashed. For these systems, membrane fouling is
controlled primarily with chemical cleaning, as well as through flux control and cross flow velocity.
The inability of spiral-wound membranes to be backwashed is one reason that NF and RO
membranes are seldom applied to directly treat water with high turbidity and/or suspended solids.
E. Chemical Cleaning
Chemical cleaning is another means of controlling membrane fouling, particularly for those
foulants such as inorganic scaling and some forms of organic and bio-fouling that are not
removed via the backwash process. As with backwashing, chemical cleaning is conducted
for each membrane unit separately and is typically staggered to minimize the number of units
undergoing cleaning at any time. While chemical cleaning is conducted on both MF/UF and
NF/RO systems, because non-porous, semi-permeable membranes cannot be backwashed,
chemical cleaning represents the primary means of removing foulants in NF/RO systems.
Although cleaning intervals may vary widely on a system-by-system basis, the gradual
accumulation of foulants makes eventual chemical cleaning virtually inevitable. Membrane
cartridge filters are an exception, however, in that cartridge filters are usually designed to be
disposable and thus are typically not subject to chemical cleaning.
As with backwashing, the goal of chemical cleaning is to restore the TMP of the system to its
baseline (i.e., clean) level. Any foulant that is removed by either the backwash or chemical
cleaning process is known as reversible fouling. Over time, membrane processes will also
typically experience some degree of irreversible fouling which cannot be removed through
either chemical cleaning or backwashing.
Irreversible fouling occurs virtually in all membrane systems, albeit over a wide range of rates,
and eventually necessitates membrane replacement. A summary of chemical cleaning is given in
Table 4.5 overleaf.
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Table 4.5 Chemical cleaning agents
Source: WEF, 2008
4.17.5 Integrated Nutrient Removal
4.17.5.1 Nutrient Removal
Sewage may contain high levels of the nutrients nitrogen and phosphorus. Excessive release of
these nutrients to the environment can lead to a build-up of nutrients, called eutrophication, which
can in turn encourage the overgrowth of weeds, algae and cyanobacteria (blue-green algae). This
may cause an algal bloom, and a rapid growth in the population of algae. The algae numbers are
unsustainable and eventually most of them die. The decomposition of the algae by bacteria uses
up so much of oxygen in the water that most or all of the species die, which creates more organic
matter for the bacteria to decompose. In addition to causing de-oxygenation, some algal species
produce toxins that contaminate drinking water supplies.
Different treatment processes are required to remove nitrogen and phosphorus.
4.17.5.2 Nitrogen Removal
Nitrogen is removed through the biological oxidation of nitrogen from ammonia to nitrate
(nitrification), followed by de-nitrification, i.e., the reduction of nitrate to nitrogen gas. Nitrogen gas is
released into the atmosphere and is thus removed from the sewage.
Nitrification itself is a two-step aerobic process, each step facilitated by a different type of bacteria.
The oxidation of ammonia (NH3) to nitrite (NO2) is most often facilitated by Nitrosomonas spp.
(nitroso referring to the formation of a nitroso functional group). Nitrite oxidation to nitrate (NO3),
though traditionally believed to be facilitated by Nitrobacter spp. (nitro referring the formation of
a nitro functional group), is now known to be facilitated in the environment almost exclusively by
Nitrospira spp.
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De-nitrification requires anoxic conditions to encourage the appropriate biological communities to

form. It is facilitated by a wide diversity of bacteria. Sand filters, lagoons and reed beds can all be
used to reduce nitrogen, but the activated sludge process (if designed well) can do the job the most
easily. Since de-nitrification is the reduction of nitrate to nitrogen gas, an electron donor is needed.
This can be, depending on the sewage, organic matter (from faeces), sulphide, or an added donor
like methanol. Sometimes the conversion of toxic ammonia to nitrate alone is referred to as tertiary
treatment. Many sewage treatment plants use axial flow pumps to transfer the nitrified mixed liquor
from the aeration zone to the anoxic zone for de-nitrification. These pumps are often referred to as
Internal Mixed Liquor Recycle (IMLR) pumps. A schematic is shown in Figure 4.26.
Figure 4.26 Configuration of Recycled Nitrification/De-nitrification Process
4.17.5.2.1 Process Control
Operators of biological nitrogen removal (BNR) facilities need more process-control knowledge
than those of conventional treatment facilities to keep them operating smoothly. The key operating
parameters for a BNR facility typically include:
A. SRT
SRT is the key to understanding whether the BNR process has enough time to function
effectively. When evaluating SRT, operators should answer such questions as:
• Is the SRT long enough to establish nitrification?

• How much sludge should be wasted to maintain a desired SRT?
• Can the SRT be increased by maintaining a higher MLSS?
B. F/M Ratio
F/M ratio is a good indicator of how well selector reactors will promote the growth of
floc-forming bacteria. When the F/M ratio is high, floc-forming bacteria have a competitive
advantage over filamentous bacteria. Selector loading also helps ensure that nuisance
bacteria will not cause operating problems. The selector cells should be arranged so
BOD is taken up rapidly.
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C. HRT (Hydraulic Retention Time)
Although not used in daily BNR operations, HRT indicates whether the plant is operating
within a normal contact time. Nitrifying facilities, such as conventional activated sludge and A2O
(Anaerobic, Anoxic, and Oxic process), typically have an HRT between 5 and 15 hours.

D. Oxygen Levels
When a conventional activated sludge system is converted into a BNR facility, its dissolved oxygen
requirements typically increase, requiring changes in the aeration equipment or diffuser layout.
E. Alkalinity and pH Control
For every 1 mg of ammonia-nitrogen oxidized to nitrate, 7.14 mg of alkalinity is consumed.

Likewise, for every 1 mg of nitrate reduced to nitrogen gas, 3.57 mg of alkalinity is recovered.
F. ORP (Oxidation–Reduction Potential).
Automated control systems for the internal anoxic mixing process measure the ORP so they can
detect nitrate depletion in the mixed liquor. This variable indirectly measures nitrate availability in
an aqueous media, although there is no direct correlation between any specific ORP value and
nitrate concentration.
ORP measures the net electron activity of all oxidation–reduction reactions occurring in
sewage. It is affected by temperature, pH, biological activity, and the system’s chemical
constituents, but its response pattern to changes in a solution’s oxidative state is reproducible in a
specific system.
In continuous-flow suspended-growth systems, the control system’s ORP breakpoints must be

constantly reviewed and revised. In batch systems (e.g., SBR or cyclic
aeration systems), however, a characteristic “knee” (change in ORP values) indicates when the
system is changing from an oxidized state to a reduced one.
G. Recycle Flows
For sewage facilities with either ammonia and/or nitrate limitations, it will be necessary to adjust
recycle flows (typically RAS flow) to achieve operational goals.
H. Secondary Clarification
It is essential that the secondary clarifier be able to do both, separate biological solids from
the treated effluent and, concentrate the solids without a build-up of sludge within the clarifier.
Parameters of concern with clarification are the hydraulic loading rate (HLR) and the
solids loading rate (SLR).
4.17.5.3 Phosphorus Removal
Phosphorus removal is important as it is a limiting nutrient for algae growth in many fresh water
systems. It is also particularly essential for water reuse systems where high phosphorus
concentrations may lead to fouling of downstream equipment such as reverse osmosis.
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Phosphorus removal in excess of metabolic requirements can be achieved by using enhanced

biological phosphorus removal (EBPR) or chemical addition.
In the EBPR process, specific bacteria, called Polyphosphate Accumulating Organisms (PAOs),
are selectively enriched and accumulate large quantities of phosphorus within their cells (up to 20
% of their mass). When the biomass enriched in these bacteria is separated from the treated water,
these biosolids (sludge) have a high fertilizer value.
The EBPR process consists of anaerobic and aerobic zones. By definition, the anaerobic zone
contains no usable dissolved oxygen or nitrate. In this zone, PAOs do not grow, but consume
and convert readily available organic material (i.e., VFAs) to energy-rich carbon polymers called
poly-hydroxyalkanoates (PHA). The energy required for this reaction is generated through
breakdown of the stored polyphosphate (poly-P) molecules, which results in phosphorus
release and an increase in the bulk liquid soluble phosphorus concentration in the anaerobic stage.
Magnesium and potassium ions are concurrently released to the anaerobic medium with phosphate.
In addition, a substantial amount of reducing power is required PAOs to produce PHA. The
breakdown of glycogen, another form of internal carbon storage, generates the reducing power.
Phosphorus removal can also be achieved by chemical precipitation, usually with salts of iron (e.g.
ferric chloride), aluminium (e.g. alum), or lime. This may lead to chemical sludge production as
hydroxides precipitate and the added chemicals can be expensive. Chemical phosphorus removal
requires significantly smaller equipment footprint than biological removal, is easier to operate and is
often more reliable than biological phosphorus removal. Another method for phosphorus removal is
the use of granular laterite. Once removed, phosphorus, in the form of a phosphate-rich sludge, may
be stored in a land fill or resold for use in fertilizers.
4.18 DISINFECTION FACILITY
Disinfection of sewage from STP is required to decrease the disease risks associated with the
discharge of treated sewage containing human pathogens (disease causing organisms) into
receiving waters. These microorganisms are present in large numbers in the treated sewage.
The chlorine gas is controlled, metered, introduced into a stream of injector water and then
conducted as a solution to the point of application.
The primary advantage of vacuum operation is safety. If a failure or breakage occurs in the
vacuum system, the chlorinator either stops the flow of chlorine into the equipment or allows air to
enter the vacuum system rather than allowing chlorine to escape into the surrounding atmosphere.
In case the chlorine inlet shutoff fails, a vent-valve discharges the incoming gas to the outside of
the chlorinator building.
The operating vacuum is provided by a hydraulic injector. The injector operating water absorbs
the chlorine gas and the resultant chlorine solution is conveyed to a chlorine diffuser through
corrosion resistant conduit. A vacuum chlorinator also includes a vacuum regulating valve to
dampen fluctuations and allow smooth operation. Vacuum relief prevents excessive vacuum
within the equipment. Chlorine gas flows from the chlorine container to the gas inlet.
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After entering the chlorinator, the gas passes through spring-loaded pressure regulating valve, which
maintains the proper operating pressure. A rotameter is used to indicate the rate of gas flow. The rate
is controlled by V-notch variable orifice. The gas then moves to the injector where it dissolves in water
and leaves the chlorinator as a chlorine solution (HOCl) ready for application.
4.18.1 Operational Variables
The process-control variables associated with chlorination systems are:
A. Detention (Contact) Time

The chlorine solution is best injected into the effluent via a diffuser or, preferably, a flash
mixer. Otherwise, some of the chlorine gas could come out of solution un-dissolved (stratification).
This would reduce the efficiency of disinfection and increase its costs.

Typically, depending on the STPs discharge standards of the state or regional regulatory
requirements, chlorine detention time should range from 30 to 60 minutes at the average
daily flow (ADF) and should equal or exceed 15 minutes at peak flows. Such detention times
allow a safety factor for possible hydraulic inefficiency of the contact chamber, thus maximizing
pathogen inactivation.
B. Chlorine Residual
Depending on the effluent-disposal method (receiving-water discharge or reclaimed-water

reuse) the permit may require a chlorine residual in the contact chamber effluent. The three
types of chlorine residuals are; combined, free and total. Free and total residuals are
typically monitored.
The combined residual consists of chloramines and chloro-organic compounds that are formed
by the reaction of chlorine with ammonia and organic compounds in the secondary or tertiary
effluent. Each milligram per litre of ammonia consumes 10 mg/L of chlorine. The chlorine dose
that satisfies the ammonia’s chlorine demand is called the breakpoint. Note that the combined
residual decreases slightly as the chloramines and chloro-organic compounds are oxidized at a
narrow range of chlorine doses of less than the breakpoint. The breakpoint chlorination curve is
shown in Figure 4.27 overleaf.
C. Indicator Bacteria Results
Regardless of the chlorine residual method employed enough chlorine solution must be
injected into the effluent to sufficiently destroy or inactivate the indicator bacteria that signal
the likely presence of pathogens. The primary objective of chlorination is to destroy pathogenic
organisms; however, the coliform bacteria often used as indicators are not pathogenic. The
indicator bacteria inactivation concept works because coliform and other indicator bacteria
are much easier to detect than pathogens and more difficult to destroy than most pathogens,
except possibly viruses. Testing directly for pathogens is complex and costly. If the coliform
count has been sufficiently reduced through disinfection, it indicates a reduction in pathogen.
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Figure 4 - 27 Breakpoint Chlorination Curve
4.18.2 Operational Hazards
A. Chlorine Hazards
Chlorine is a gas, 2.5 times heavier than air, toxic, and corrosive in moist atmospheres. Dry
chlorine gas can be safely handled in steel containers and piping, but with moisture it must be
handled in corrosion-resisting materials such as silver, glass, teflon, and certain other plastics.
Chlorine gas at container pressure should never be piped in silver, glass, teflon, or any other
plastic material.
Even in dry atmospheres, the gas is very irritating to the mucous membranes of the nose, to the
throat, and to the lungs; a very small percentage in the air causes severe coughing. Heavy
exposure can be fatal.
B. Warning
When entering a room that may contain chlorine gas, open the door slightly and check for the
smell of chlorine. Never go into a room containing chlorine gas with harmful concentrations in the
air without a self-contained air supply, protective clothing and helpers.
Help may be obtained from the chlorine supplier and your local fire department.
4.18.3 Maintenance
Routine operations and troubleshooting. Table 4.6 (overleaf) lists routine operational checks of
chlorination equipment and remedies if these checks indicate potential problems.
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Table 4.6 Routine operational checklist and troubleshooting guide for chlorination system
( ) This will prevent sediment in the container from entering the chlorination network
and possibly damaging the process equipment.
Source: WEF, 2008
4.19 OPERATION & MAINTENANCE OF DEWATS AND JOHKASOU
The package treatment plants like DEWATS and Johkasou also have to be maintained as per the
vendors of these systems.
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Preventive Maintenance addresses the civil, mechanical, electrical, instrumentation and

automation aspects. In respect of civil works, follow the local rules, regulations and guidelines of the
local Public Works Department (PWD). These procedures are mostly annual. It will be better to hand
over such maintenance to the PWD and remit the costs to that department. In respect of mechanical
equipment, it is better to enter into a contract with the contractor who has built the STP to do this as per
the directions of the equipment suppliers and retain the equipment supplier to check and certify the
work. In respect of the electrical installations, it is better to entrust this work to the local Electricity
Department, similar to civil works. In respect of instrumentation and automation, similarly, entrust the
work to the contractor who supplied and erected these and retain a third party agency to certify the
proper completion of the work. The following checklist as in Table 4.7 is an example of a preventive
maintenance programme for activated-sludge facilities. When developing a site-specific schedule,
consult the service manuals that were provided with each piece of equipment.
Table 4.7 An example of a Preventive Maintenance Programme for

Activated-Sludge facilities Checklist
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Source: WEF, 2008
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Refer to Appendix B.4.1.
4.22 RECORD KEEPING
The importance of maintaining adequate O&M records cannot be overemphasized. The purpose of
recording data is to track operational information that will identify and duplicate optimum operating
conditions. Records of the volume and concentration of waste sludge fed to the digester and
volume and concentration of digested solids removed from the digester should be kept. Additional
information that needs to be maintained, include DO concentration and pH. Keep a monthly report
form. In plants where the aeration system capacity is marginally adequate in providing desirable DO
concentration in the digester, record DO concentration data on a trend chart.
If chemicals are added to the digester for pH or odour control, record the type and amount of
chemicals added. If mechanical aerators are used, record the power usage. In the case of
diffused-air systems, air flow records may be of interest. If airflow meters are not available, records of
power consumption may be useful. Experimenting with the aeration system often leads to significant
savings in power costs.
A record of instrument performance and repairs allow O&M personnel to properly evaluate an
instrument’s effectiveness and determine if the instrument meets the objectives used to justify its
purchase and installation.
As a minimum, the following basic information should be maintained for each instrument in
the STP:
• Plant equipment identification number

• Model number and serial number
• Type
• Dates placed into and removed from service
• Reasons for removal
• Location when installed
• Calibration data and procedures
• Hours required to perform maintenance
• Cost of replacement parts
• O&M manual references and their locations
• Apparatus failure history
4.23 SUMMARY
Appendices to this manual provide troubleshooting lists for possible problems in STPs. Operators
should check their operational problems in the troubleshooting lists so that they can take prompt
measures to solve the problem.
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Part B: Operation and Maintenance SLUDGE TREATMENT FACILITIES
CHAPTER 5: SLUDGE TREATMENT FACILITIES
5.1 INTRODUCTION
Sludge treatment processes are often the most difficult and costliest part of sewage treatment.
Untreated sludge is odorous and contains pathogens. Sludge stabilisation process reduce odours,
pathogens, and biodegradable toxins, as well as bind heavy metals to inert solids, such as
lime that will not leach into the groundwater. The resulting biosolids can be used or disposed safely.
The limiting concentrations of heavy metals and faecal coliforms in sludge are mentioned in
Table 6.14 in chapter 6 of Part-A Manual. If these concentrations exceed those values then
land application shall not be permitted and the sludge shall have to be disposed or contained
as per the Hazardous Waste (Handling and Management) rules of MoEF.
Sewage residuals include primary, secondary, mixed, and chemical sludge, as well as
screenings, grit, scum, and ash. The concentration and characteristics of chemical sludge depend on
the treatment chemicals (alum, ferric salts, or lime) used. It is typically, found at treatment plants
that have tertiary treatment, such as phosphorus removal. The use or disposal method for residuals
depends on how much treatment they have received. Biosolids are residuals that have been
stabilized can be beneficially used as a soil filler. Combustible residuals, such as screenings, may be
incinerated or landfilled. Non-combustible residuals, such as grit, may be landfilled.
5.2 SLUDGE THICKENING
The role of sludge thickening is to thicken the sludge of low concentration generated in STPs, and
to make subsequent processes such as sludge digestion and sludge de-watering more effective.
Thickened sludge may be of two kinds: primary sludge generated in the primary settling
tank and excess sludge generated in the secondary settling tank. Sludge thickening may be
broadly classified into four types, gravity thickening, centrifugal thickening, floatation thickening and
belt-type thickening.
When sludge thickening is inadequate, the efficiency of subsequent sludge treatment will reduce,
but also centrate containing large amount of suspended solids will return to the STP and degrade
the quality of the treated sewage. For this reason, excess sludge for which gravity thickening is
difficult is increasingly being mechanically thickened using centrifugal thickening machines or
floatation thickeners. When the water content of sludge is more especially, separation and thickening
should be considered.
5.2.1 Gravity Thickening
Gravity thickening is the most common practice for concentration of sludge and concentrates sludge
through simple gravity sedimentation of the suspended solids.
This is adopted for primary sludge or combined primary and waste activated sludge, but is not
successful in dealing with activated sludge alone. Independently, gravity thickening of combined
sludge is not effective when activated sludge exceeds 40% of the total sludge weight, and other
methods of thickening of activated sludge have to be considered.
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A gravity thickener is shown in Figure 5.1
Figure 5.1 Example of a gravity thickener
Continuous flow tanks are deep circular tanks with central feed and overflow at the periphery. Better
efficiencies can be obtained by providing slow revolving stirrers, particularly with gassy sludge.
It is necessary to ensure provisions for:
• Regulating the quantity of dilution water needed

• Adequate sludge pumping capacity to maintain any desired solids concentration, continuous feed
and underflow pumping
• Protection against torque overload
• Sludge blanket detection
• Variable-speed drives may be used to increase rake speed to agitate the sludge blanket and
release trapped gas bubbles. Prolonged operation at high speeds will reduce the ultimate solids
concentration and reduce the life of the thickener drive mechanism.
• Scum removal equipment may include a skimmer and scum box. The ancillary equipment
should include positive-displacement pumps (plunger, rotary lobe, diaphragm or progressing
cavity pumps). Process control equipment includes sludge blanket indicators (light path, sonic, or
variable-height taps), online process monitors on the feed or underflow, torque readouts on the
rake drive, and timers to vary the pump on/off (or speed) sequences. In cold weather areas or
areas where odours are a problem, thickeners are typically covered.
Gravity thickeners are either continuous flow or fill and draw type, with or without addition of
chemicals. Use of slowly revolving stirrers improves the efficiency. Continuous flow tanks are deep
circular tanks with central feed and overflow at the periphery.
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5.2.1.1 Process Control
Greater attention to the thickener is required when thickening waste activated sludge because it has a
large surface area per unit mass, resulting in low settling rates and resistance to being compacted.
Sludge tends to stratify in the gravity thickener while continuing biological activity, which includes the
production of gases that can cause accumulated sludge to float.
Gravity thickener operation responds to changes in process temperatures; therefore, loading

rates should be reduced to values at the lower end of the range when temperatures exceed 15
to 20°C, depending on the ratio of primary to secondary sludge. Higher temperatures will require
additional dilution.
The following should be checked before and during operation:

• Avoid starting a thickener that contains accumulated sludge. To avoid overload, the sludge should
be disposed of before starting the mechanism.

• Check and adjust the skimming mechanism to increase the amount of scum drawn into the scum
box and to reduce the amount of supernatant carried with the skimming.
There are some types of thickener equipments where the entire rotating steam raker assembly can
be raised initially to induce mixing only in the upper layers of sludge initially to avoid overloading the
drive assembly once the mixing is induced for some time.
Thereafter the raker assembly is gradually lowered to the designed position.
5.2.1.2 Maintenance
• Visually examine the skimmer to ensure that it properly comes into contact with the scum baffle
and scum box.
• Inspect skimmer wipers for wear.
• Install kick plates on the gravity thickener bridge to prevent objects from falling into the tank.
• An object lodged in the underflow discharge pipe or under the mechanism will quickly halt
operation of the thickener. If an object falls into the tank, immediately halt thickener operation to
prevent torque overload.
• During plant rounds, regularly observe and record the drive torque indicator, which is the best
indicator of mechanical overload.
• Regularly check the underflow pump capacity because pumps wear rapidly in a thickened
sludge operation.
• Follow the manufacturer’s recommended lubrication schedule and use recommended

lubricant types. Oil should typically be changed after the first 250 hours of operation and every
6 months thereafter.
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5.2.2 Centrifugal Thickening
Thickening by centrifugation is chosen only when space is limited or sludge characteristics will not
permit the adoption of other methods. This method involves high maintenance and power costs.
5.2.2.1 Configuration
Decanter centrifuges have a screw conveyor inside that transports the settled sludge along
the bowl and out of the centrifuge. They thicken and de-water the sludge simultaneously.
In the centrifuge, the process is the same, varying only in degree. They use the principle of
centrifugal force through the bowel assembly. Please see chapter 6 of part A manual for more
details. They separate the liquids from solids based on the rotary speed.
All process devices benefit from a constant feed quality, and centrifuges are no exception.
Common problems are varying ratios of primary to secondary sludge or feed material that has
become septic. Septic sludge is more difficult to thicken than fresh sludge. Holding feed material in
storage tanks under uncontrolled conditions is poor practice.
When in doubt, measure the pH drop through the storage.
The manufacturer generally sets the bowl speed. Assuming the present speed was the correct
speed several years ago is not proof that it is the best speed now. The plant engineer should adjust
the speed periodically, to confirm that it is correct and to remind operators that it is a variable.
It is a good policy to consult the manufacturer before changing the bowl speed.
A. Start-up
Most modern centrifuges have a one-button start. Manual systems take a few minutes, but
are not difficult. The start-up sequence is as follows:
• Turn on the feed and polymer to about one-third of the normal rate.
• Reduce the differential revolutions per minute and/or pond to minimum.
• When the cake thickness reaches the normal value, begin increasing the differential and
the polymer feed rate. Some plants can go directly to the normal operating condition
as soon as the cake is sealed, while others have to ramp up more slowly.
B. Shutdown

Again, modern centrifuges have a one-button stop. The shutdown sequence is as follows:
• Shut off the feed and polymer and turn the flushing water on.
• When clear water exits both ends of the centrifuge, push the centrifuge stop button.
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• At some point, as the centrifuge slows down, flush water will come around the feed tube or
around the casing seals. Note how long it took between pressing the stop button and the
water gushing out. Next time, shut the water off a minute or two sooner.
• With the flush water off, the centrifuge can usually come to a stop without operator
intervention.
C. Sampling and Testing
Sampling and testing should include Total Suspended Solids (TSS), ammonia, and/or
phosphorus (under some conditions) for centrate.
5.2.3 Air Floatation Thickening
Air floatation units employ floatation of sludge by air under pressure or vacuum and are normally used
for thickening the waste activated sludge. These units involve additional equipment, higher operating
costs, higher power requirements, and more skilled maintenance and operation. However, removal
of grease and oil, solids, grit and other material and also odour control are distinct advantages.
In the pressure type floatation units, a portion of the subnatant is pressurised from 0.3 to 0.5 MPa and
then saturated with air in the pressure tank. The effluent from the pressure tank is mixed with influent
sludge immediately before it is released into the flotation tank. Excess dissolved air then rises up in
the form of bubbles at atmospheric pressure attaching themselves to particles, which form the sludge
blanket. Thickened blanket is skimmed off while the non-recycled subnatant is returned to the plant.
Floatation thickeners are equipped with both surface skimmers and floor rakes. The surface
skimmers remove floating material from the thickening tank to maintain a constant average float
blanket depth. Floor rakes are essential for removing the non-floatable heavier solids that settle to
the bottom of the floatation thickener. Most units are baffled and equipped with an overflow weir.
Clarified effluent passes under an end baffle (rectangular units) or peripheral baffle (circular units)
and then flows over the weir to an effluent launder. The weir controls the liquid level within the
floatation tank with respect to the float collection box and helps regulate the capacity and
performance of the flotation unit.
The saturation system typically includes a recycle pressurization pump, an air compressor, an air
saturation tank, and a pressure release valve. Although the flow through the pressurization pump
typically is recycle-flow, it can also be makeup water. The pressure release valve controls pressure
loss and distributes the gas-saturated pressurized flow into the feed sludge as dissolved air emerges
from the solution. The rapid reduction in pressure causes dissolved air (under pressure) to emerge
from solution or “effervesce” into minute bubbles.
Other important equipment that forms part of an air floatation thickening system is the float handling
and pumping system. After removal of the float from the air floatation thickening unit, float solids are
deposited in a hopper and then pumped for further processing. This aspect of the operation requires
special considerations because of the following characteristics of float solids:
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The parameter that is manipulated by the operator to control the performance of a thickener is the
effective drainage time. This parameter is controlled by:
• Adjustment of skimmer on-time,

• Adjustment of skimmer off-time, and
• Adjustment of skimmer speed.
5.2.3.2 Operation
A float total solid content of 4 % represents a typical minimum for floatation thickeners handling
solids without primary sludge. Under optimum conditions, however, 5 to 6 % solids content
can be expected.
Proper operation requires reducing variations of the feed rate and concentration. A feed sludge
holding and mixing tank helps with intermittent operation.
Most units are operated continuously. Some are operated with a short period shut-down during
weekends, while others are operated only during certain hours of the day.
The speed and the on-off times of the float skimmers should be set to maximize the float solids
concentration, but should not be set too slow to cause excessive float-depth accumulation.
Dilution reduces the effect of particle interference on the rate of separation.
Concentration of the sludge increases and the concentration of effluent suspended solids decreases
as the sludge blanket detention time increases.
A. Start-up

• Fill the tank with final treated sewage or plant non-potable water until overflowing.
• Continue the flow to the air floatation unit and engage the recycle system, including the
compressor, if applicable. Adjust to proper pressures and flow and proceed after proper
functioning.

• Ensure that the float and underflow pumps are functional by pumping some water.

• Prepare the polymer, if applicable, and engage the polymer addition at proper flow or as jar
tests have indicated if starting after prolonged shutdown, start-up, or process changes.

B. Shutdown
• Stop polymer flow, if applicable, and at the same time stop waste activated sludge feed.
• If only down for a short time (30 minutes or so), there is no need to shut down the recycle
system, including the compressor. If down for longer than this period shut down
the recycle system.
• The float rake timer can be left on until most of the float is removed into the hopper and
pumped for further processing.
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• If the unit is going to be down for more than 24 hours, displace the tank contents with
non-potable water or drain and clean the tank, all troughs, and pipelines.

• In a typical operation, only the recirculation pump and retention tank discharge valves are
closed when stopping a unit’s operation. All other valves remain open, with the exception of
valves on drain lines.
5.2.3.3 Maintenance
• Checking all oil levels and ensuring that the oil fill cap vent is open.
• Checking all condensation drains and removing any accumulated moisture.
• Examining drive control limit switches.
• Visually examining the skimmer to ensure that it is in proper contact with the scum baffle
and scum box.
• Inspecting skimmer wipers for wear.
• Adjusting drive chains or belts.
• Semi-annual inspections of major elements for wear, corrosion, and proper adjustment include:
• Saturation systems - eductors (if used) or nozzles to be inspected for wear or cleaned whenever
the efficiency begins to decline, or on a semi-annual basis;
• Mechanical systems, including shaft bearings and bores, bearing brackets, baffle boards, flights
and skimming units, suction lines and sumps, and sludge pumps.
5.2.4 Belt Type Thickening
Gravity belt thickeners work by filtering free water from conditioned sludge by gravity drainage
through a porous belt. The gravity drainage area is usually horizontal but may be inclined under
certain circumstances.
Chemical conditioning is generally required to flocculate the sludge and separate the solids from
the free water. This may be accomplished by injecting the chemical through an injection ring and
mixing it with the sludge. After chemical injection, the sludge velocity is reduced in a retention tank
and the sludge is allowed to fully flocculate before overflowing by gravity onto the moving belt.
As the moving belt carries the sludge, plows clear portions of the belt for the filtrate to drain through
and gently turn over the solids, thereby exposing more free water. Prior to the discharge, most gravity
belt thickeners have some type of dam or an adjustable ramp.
The hydraulic capacity of the equipment is determined by multiple factors including sludge type,
sludge concentration, polymer type and polymer dosage, belt speed, belt type, as well as the obvious
machine width and length.
The gravity belt thickener is shown in Figure 5.2 overleaf.
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Figure 5.2 Gravity belt thickener process
A. Polymer Addition
Polymer addition usually occurs by injection through a multiport injection ring; it is mixed with the
sludge as it flows through an inline mixing device. In some cases, the polymer may be mixed
mechanically in the retention tank. However, this generally results in higher polymer
consumption.
B. Flocculation Tank

The flocculation tank allows the incoming sludge velocity to be reduced so that flocculation can
fully occur before the sludge overflows onto the moving belt. Design of the tank is critical to
prevent short-circuiting within the tank.

C. Belt and Supports

Belts are typically woven from polyester fibre. High pH and other unusual conditions may require
special materials. The belt is supported on grid strips that also serve as wipers on the bottom of
the belt. This wiping action increases the drainage capacity of the belt.

D. Belt Tensioning

Unlike a belt press, the performance of the belt thickener is not dependent on belt tension.
Once the de-watering belt on a thickener is tight enough to prevent slippage on the drive roller,
additional tension is unnecessary. Additionally, the belt tension on a thickener is not dependent
on the type or amount of sludge loading. As such, the requirements for belt tension are much
lower on a gravity belt thickener compared to a belt filter press.
Belt tension is a result of moving one roller closer to or further away from the other roller (s).
This displacement may be through hydraulic, pneumatic, or mechanical actions. Once the belt is
tensioned, it is not necessary to relax the tension until the belt is replaced.
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E. Belt Drive

All belt thickeners have a variable-speed belt drive with a typical speed range of 8 to 40 m/min.
The belt speed may be either mechanically or electrically varied with speed controls at the local
control panel. Typically, the belt drive is attached to a rubber-coated drive roller.

F. Belt Tracking

During operation of a belt thickener, the belt should more or less remain in the center and not
move laterally on the machine. Although the belt should not move, some type of belt tracking
device is included on most machines. Comparatively, the belt on a belt thickener is similar to a
conveyor belt; all tracking devices have some roots in the conveyor or paper making industry.
A. Start-up
• Start the hydraulic unit (or air compressor) and allow tension to develop in the belt.
• Start the belt drive and use an initial setting of approximately 20 m/min belt speed.
• Start the wash water pump and allow the belt to pre-wet.
• Start the polymer pump and allow the fresh polymer to reach the polymer injection point.
• After thickened sludge is available, start the thickened sludge pump (or the thickened
sludge conveyor).
After the system is running, begin fine-tuning the process by adjusting the sludge flow, polymer dose,
mixing energy, belt speed, and so on until the results are within the desired process parameters.
It is important to only adjust one item at a time and to allow time for the adjustment to take effect
before making another change.
B. Shutdown
• Shut down sludge feed pump.
• Shut down polymer feed pump.
• As the thickened sludge hopper empties, shut down the thickened sludge pump (or thickened
sludge conveyor).
• Drain the flocculation tank.
• Wash the machine down from top to bottom.
• Allow the belts to be completely washed (this could take 15 to 45 minutes) without
sludge or polymer.
• Shut down the wash water pump.
• Shut down the belt drive.
• Shut down the hydraulic unit/air compressor.
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C. Sampling and Testing
At a minimum, gravity belt thickeners should be sampled and analysed as follows:
• Sample influent feed for total solids, TSS, total volatile solids, pH, and flow.
• Sample wash water for TSS and flow.
• Sample thickened sludge for total solids and flow.
• Sample filtrate for TSS and flow.
• Measure flow and quantity of polymer used.
• Measure any dilution water used to make up polymer.
D. Process Control
Numerous variables affect the overall thickening process. Listed below are some of these variables:
• Sludge feed, polymer, dosage of polymer, mixing energy, retention time

• Belt speed, belt tension, belt type, ramp angle
• Upstream variables, slurry pump selection, solids concentration
• Biological sludge content, sludge storage time, wash water characteristics
5.3 ANAEROBIC DIGESTION
In anaerobic digestion, anaerobic bacteria thrive in an environment without dissolved oxygen.
Two major types of bacteria are present in the digester. The first group starts degrading the organic
portion of the sludge to form organic acids and carbon dioxide gas. These bacteria are called
acid formers. The second group breaks down the organic acids to simpler compounds and forms
methane and carbon dioxide gas. These bacteria are called gas formers. The methane gas is usually
used to heat the digester or to run engines in the plant. The production of gas indicates that organic
material is being degraded by the bacteria. Sludge is usually considered properly digested when
50 % of the organic matter has been destroyed and converted to gas. The time taken is shown in
chapter 6 of Part A manual.
Most digestion tanks are mixed continuously to bring the food to the organisms, to provide a uniform
temperature, and to avoid the formation of thick, scum blankets. When a digester is not being mixed,
the solids usually settle to the bottom, leaving a liquid known as supernatant above the sludge. In
many plants, however, there is no separation of solids and liquids after two days of sitting without
mixing due to the type of sludge. The supernatant is displaced from the tank each time a fresh charge
of raw sludge is pumped. The displaced supernatant usually is returned from the digester back to
the plant head-works and mixed with incoming raw sewage. Supernatant return should be slow to
prevent over-loading or shock loading of the plant.
In most new plants, sludge digestion takes place in two tanks. The first or primary digester is
mixed and sometimes the feed sludge is pre-heated and rapid digestion takes place along with
most of the gas production.
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In the secondary digester, the digested sludge and supernatant are allowed to separate,
thus producing a clearer supernatant and better-digested sludge.
Digester sludge from the bottom of the tank is periodically removed for de-watering.
5.3.1 Digestion Types
Two different types in anaerobic sludge digestion process namely, Low rate and High rate, are used
in practice. The basic features of these processes are shown in Figure 5.3.
Figure 5.3 Sludge digestion system
5.3.1.1 Low Rate Digestion
Low rate digestion is the simplest and the oldest process; essentially a low rate digester is a large
storage tank, occasionally, with some heating facility.
Raw sludge is fed into the digester intermittently. Bubbles of sewage gas are generated and their
rise to the surface provides some mixing. In the case of few old digesters, screw pumps have been
installed to provide additional intermittent mixing of the contents, say once in 8 hours for about
an hour. As a result, the digester contents are allowed to stratify, thereby forming four distinct
layers: a floating layer of scum, layer of supernatant, layer of actively digesting sludge and a bottom
layer of digested sludge; essentially the decomposition is restricted to the middle and bottom layers.
The stabilized sludge, which accumulates and thickens at the bottom of the tank is periodically drawn
off from the center of the floor.
The supernatant is removed from the digester and returned back to the STP.
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5.3.1.2 High Rate Digestion
The essential elements of high rate digestion are complete mixing and more or less uniform feeding
of raw sludge. Pre-thickening of raw sludge and heating of the digester contents are optional features
of a high-rate digestion system. All these four features provide the best environmental conditions for
the biological process and the net results are reduced digester volume requirement and increased
process stability.
Complete mixing of sludge in high rate digesters creates a homogeneous environment

throughout the digester. It also quickly brings the raw sludge into contact with microorganisms and
evenly distributes toxic substances, if any, present in the raw sludge. Furthermore, when stratification
is prevented because of mixing, the entire digester is available for active decomposition, thereby
increasing the effective solids retention time.
5.3.2 Configuration
5.3.2.1 Anaerobic Digestion Tank
Anaerobic digestion tanks may be cylindrical or egg shape in shape. Most tanks constructed today
are cylindrical. The floor of the tank is sloped so that sand, grit, and heavy sludge will tend to be
removed from the tank. Most digesters have either fixed or floating covers.
A fixed cover digester may develop an explosive mixture in the tank when sludge is withdrawn if
proper precautions are not taken to prevent air from being drawn into the tank. Each time a new
charge of raw sludge is added, an equal amount of supernatant is displaced because the tank is
maintained at a fixed level.
A floating cover moves up and down with the tank level and gas pressure. Normally, the vertical travel
of the cover is about 2.5m, with stops (corbels) or landing edges maximum water level is controlled
by an overflow pipe that must be kept clear to prevent damage to the floating cover by overfilling. Gas
pressure depends on the weight of the cover. The advantages of a floating cover include less danger
of explosive mixtures forming in the digester, better control of supernatant withdrawal, and better
control of scum blankets. Disadvantages include higher construction and maintenance costs.
5.3.2.2 Agitator
Propeller mixers are found mainly on fixed cover digesters. Normally, two or three of these units are
supported from the roof of the tank with the propeller blades submerged 3 to 3.5 m in the sludge. An
electric motor drives the propeller stirring the sludge. The various types of mixers are described in
chapter 6 of Part A manual. Digested sludge may contain some debris depending on the efficiency
of screen and grit removal in the STP. This unit usually has reversible motors so the propeller may
rotate in either direction. In one direction the contents are pulled from the top of the
digester and forced down the draft tube to be discharged at the bottom. By operating the motor in the
opposite direction, the digested sludge is pulled from the bottom of the tank and discharged over
the top of the draft tube to the surface. Reversible motors also assist in minimizing accumulations of
rags on the propeller.
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If two units are installed in the same tank, an effective way to break up a scum blanket is operating
one unit in one direction and the other unit in the opposite direction, thereby creating a push-pull
effect. The direction of flow in the tubes should be reversed every day.
A limitation of draft tube-type mixers is the potential formation of a scum blanket. If the water level is
maintained at a constant elevation, a scum blanket forms on the surface. The scum blanket may be a
thick layer and the draft will only pull liquid sludge from under the blanket, not disturbing it, Lowering
the level of the digester to just 7 –10 cm over the top of the drain tube forces the scum to move over
and down the draft tube. This applies mainly to single-direction mixers.
Pumps are sometimes used to mix digesters. This method is common in smaller tanks. The tank may
or may not be equipped with a draft tube positioned in such a way that the pump suction may be from
the top or through valve from the bottom of the digester. Control of scum blankets with this method of
mixing depends on how the operator maintains the sludge level and where the pump is pulling from
and discharging to the digester. Pressure gauges should be installed on the pump suction and
discharge pipes. A change in pressure could indicate that the pump is not functioning properly and the
desired mixing may not be taking place in the digester.
5.3.2.3 Digester Gas Equipment
A. Gas Tank

Several types of gas storage are available. The most common means of low-pressure gas
storage is the floating gas-holder cover. Membrane storage can be installed either on the
digester, to serve both as cover and storage space, or on the ground as a standalone structure.

B. Flow Meter

Gas production is a measure of digester performance. Reliable monitoring equipment
alerts plant operators to process malfunctions and gas leaks. The flow meters used for gas
monitoring can be broadly classified as positive-displacement, thermal-dispersion and differential
pressure flow meters.

Separate flow meters are recommended for each digester because digester gas-production
rates vary. Separate flow meters are also recommended to monitor gas use by the utilization
equipment. The gas may contain moisture and impurities, which may cause maintenance
problems for the metering devices. The gas system safety and control devices are
listed in Table 5.1 overleaf. The gas flow indication and metering are listed in Table 5.2 overleaf.
5.3.2.4 Gas Scrubbers
A. Foam and Sediment Removal
Many systems are equipped with sediment traps and foam separators for cleaning
the digester gas. These devices provide a “wide spot” in the gas piping system for slowing
velocities, collecting foam and particulates entrained in the gas, and removing collected
condensate. The foam separator is a large vessel with an internal plate fitted with water nozzles
that provide a continuous spray.
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Part B: Operation and Maintenance CHAPTER 5: SLUDGE TREATMENT FACILITIES
Table 5.1 Gas system safety and control devices
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Part B: Operation and Maintenance CHAPTER 5: SLUDGE TREATMENT FACILITIES
Source: WEF, 2008
5 - 15
CHAPTER 5:
Table 5.2 Gas-flow indication and metering
Source: WEF, 2008
The foam and sediment laden gas enters the vessel near the top and travels down through the
spray wash under the baffle wall and up through a second spray wash, exiting the vessel through
an elevated discharge nozzle. The spray wash and the internal plate reduce foam in the gas to
prevent carryover to gas utilization equipment.
B. Hydrogen Sulphide Removal
The generation of hydrogen sulphide can also be inhibited by using ferric chloride injection
into the digester. But this is usually very difficult as handling ferric chloride is not easy because
it is very acidic and reactions with skin can be troublesome. Injection of ferric chloride can
however be used as a temporary measure when sulphates in raw sewage become very high in
drought situations when the population may use a lot of hard water for many purposes other than
drinking, and which may increase the sulphate in raw sewage. Iron salts can be added at the
following locations in the treatment process:
• The primary clarifier (helps settling and improves overall facility odour control)
• The suction side of the digester sludge-recirculation pump
• The forward side of a mechanical mixer
Iron salts should not be added directly upstream from the heat exchangers because this can
result in deposits of vivianite on heat exchanger surfaces.
Refer to section 6.4.15.3 of the Part-A manual for the methods in use in India for removing
hydrogen sulphide from digester gas.
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C. Moisture Reduction
Moisture is condensed from digester gas as it cools. Gas piping should have a slope of at least
1% toward the condensate collection point. To effectively remove the moisture, the gas flow
should not exceed 3.7 m/s countercurrent to condensate flow.
The condensate is collected in traps that should be located at low points in long pipe runs and
wherever gas is cooled. Drip taps, which can be controlled manually or automatically, provide a
convenient and safe means for removal of accumulated condensate. Manually operated drip taps
are recommended for indoor applications. Float-controlled, automatic drip taps are also available,
but these require frequent maintenance to keep the valves operating. Should the float stick, gas
can escape to the surrounding atmosphere, which limits their use to outdoor installations (where
permitted by local codes and safety considerations).
D. Carbon Dioxide Removal
Carbon dioxide can be removed from the digester gas by water or chemical scrubbing, carbon
sieves, or membrane permeation; however, all of these technologies are expensive and their use
may be cost-effective only if the gas is to be used for power generation.
E. Siloxane Removal
Siloxanes are components of toiletries and personal care cosmetics such as sprays, deodorants,
lipsticks, gels, lotions, shaving creams, cleaning fluids, and so on. Their use is growing every
year. Not much data is available on their removal in STPs. It has been reported that siloxanes
find their way in digester gas. The concern is in cold climates, if digesters are to be heated to
maintain temperature of about 35°C, silicon dioxide deposits on the heat exchanger tubes, which
reduces heat transmission. Hence, it becomes necessary to protect equipment from siloxanes.
This problem can occur also when digester gas is burned in gas engines. However, this has
not been reported as a serious problem in digester gas usage in India. A typical photograph is
shown in Figure 5.4
Source : Internet
Figure 5.4 Silicon dioxide deposits on boiler tubes
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F. Activated Carbon Scrubbers
Activated carbon scrubbers can be used to remove siloxanes from digester gas
according to the same principles as the carbon scrubbers used for odour control in STPs.
The digester gas is passed through a vessel filled with activated carbon, which captures the
organics, including siloxanes, hydrogen sulphide, and several other compounds in digester gas.
With proper maintenance and replacement of the carbon, the siloxanes in the digester gas
can be removed to less than detection limits. However, activated carbon is not selective with
regard to siloxanes and will remove other compounds as well. Consequently, if the digester gas
contains other organics, the carbon will require frequent replacement. In India, the cocoanut shell
activated carbon is locally available and is economical. Removal of hydrogen sulphide before
it passes through the carbon scrubbers will provide better siloxane removal and extend the life
of the carbon bed.
5.3.2.5 Gas Power Generator
Refer to Sec.6.2.4 of the Part B Manual “Gas Engines”.
5.3.3.1 Feeding Schedule
Uniformity and consistency are keys to digester operation. Sudden changes in feed solids volume
or concentration, temperature, composition, or withdrawal rates will inhibit digester performance and
may lead to foaming. The ideal feeding procedure is a continuous,24-hour-per-day addition of a
blend of different types of feed solids (primary and WAS). Where continuous feeding is impossible,
a 5 – 10min/h feed cycle is used. Smaller STPs that operate a single 8-hour shift use a schedule
of at least three feedings: at the beginning, middle, and end of the shift. Typical causes of organic
overloads include the following:
• Starting the digester too rapidly
• Excessive volatile solids loading as a result of erratic feeding or a change in feed solids
composition
• Volatile solids loadings exceeding the daily limits by more than 10%,
• Loss of active digester volume because of grit accumulation, and
• Inadequate mixing
5.3.3.2 Withdrawal Schedule
Solids should be withdrawn from the primary digester immediately prior to feeding raw sludge to
prevent short-circuiting. In digesters with surface overflow, the timing and rate of solids withdrawal
and feed are coordinated to occur concurrently. Solids should be withdrawn at least daily to avoid
a sudden drop in the active microorganism population. The primary digester may be regulated to
simply overflow to the secondary digester or to the digested sludge storage tank as raw sludge is
added. Solids may be withdrawn from the following locations:
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• The bottom of the digester

• The overflow structure
• Any point within a well-mixed digester
A benefit of removing solids from the bottom of the digester is that it may also remove the grit
that accumulates on the bottom of the digester. If possible, solids removal should be performed
periodically.
It is important to recognize that because digestion destroys volatile solids, the concentration
of the biosolids removed from the digester will be lower than the feed concentration unless the
digester is decanted.
5.3.3.3 Scum Control
Scum accumulation in digesters is common. Scum is a combination of undigested grease & oil and
often contains buoyant materials, such as plastics that are not removed at the plant’s headworks.
Scum floats on the digester liquid surface and can accumulate, forming a dense mat. Properly
designed and operated digester mixing systems can typically blend the scum into the tank contents.
If the digester operates without mixing for longer than 8 hours, scum may rise and float on the liquid
surface. After mixing is restarted, the scum is re-suspended within the liquid. The primary method of
scum control is to keep the digester mixing system well-maintained during operation.
5.3.3.4 Precipitate Formation and Control
The digestion process can produce crystalline precipitates that affect both the digestion system and
downstream solids-handling processes. The precipitates can accumulate on pipes and de-watering
equipment, causing damage and blockages and requiring costly and time-consuming maintenance.
Common precipitates include struvite, vivianite and calcium carbonate. The constituents that form
these precipitates are present in undigested sludge and are released during the digestion process
and converted to soluble forms that can react and crystallize. Their formation varies from site to
site, depending on the chemistry of the digested sludge and the treatment processes. Because
precipitates preferentially form on rough or irregular surfaces, glass-lined sludge piping and
long-radius elbows help minimize their accumulation.
5.3.3.5 Digester Upsets and Control Strategies
The four basic causes of digester upsets are hydraulic overload, organic overload, temperature stress
and toxic overload. Hydraulic and organic overloads occur when the design hydraulic or organic
loading rates are exceeded by more than 10% per day. The overload conditions can be controlled by
managing digester feeding, as well as ensuring that the effective digester volume is not diminished
by grit accumulation or poor mixing.
Digester feeding is controlled by proper operation of upstream headworks, clarifiers, and thickeners
to ensure the feed sludge concentrations. In the event of a digester upset, an effective control
strategy includes the following steps:
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• Stop or reduce sludge feed

• Determine the cause of the imbalance
• Correct the cause of the imbalance
• Provide pH control until the treatment returns to normal
If only one digester tank is affected, the loading on the remaining units can be carefully increased to
allow the upset unit to recover. If overloading is affecting several units, reducing the feed will require a
method of dealing with the excess sludge by hauling it to another facility, providing temporary storage
on site, or chemically stabilizing and disposing of the sludge.
5.3.3.6 Temperature
Temperature-related stress is caused by a change in digester temperature of more than 1 or

2°C in less than 10 days, which would reduce the biological activity of the methane-forming
microorganisms. If the methane formers are not quickly revived, the acid formers, which are
unaffected by the temperature change, continue to produce volatile acids, which will eventually
consume the available alkalinity and cause the pH to decline.
The most typical causes of temperature stress are overloading sludge and exceeding the
instantaneous capacity of the heating system. Most heating systems can eventually heat the digester
contents to the operating temperature, but not a harmful temperature variation.
5.3.3.7 Toxicity Control
The anaerobic process is sensitive to certain compounds, such as sulphides, volatile acids,
heavy metals, calcium, sodium, potassium, dissolved oxygen, ammonia and chlorinated organic
compounds. The inhibitory concentration of a substance depends on many variables, including pH,
organic loading, temperature, hydraulic loading, the presence of other materials, and the ratio of the
toxic substance concentration to the biomass concentration.
5.3.3.8 pH Control
The key to controlling the digester pH is to add bicarbonate alkalinity to react with acids and buffer
the system pH to about 7.0. Bicarbonate can be added directly or indirectly as a base that reacts
with dissolved carbon dioxide to produce bicarbonate. Chemicals used for pH adjustment include
lime, sodium bicarbonate, sodium carbonate, sodium hydroxide, ammonium hydroxide and gaseous
ammonia. Lime addition can be messy and will produce CaCO3. Although ammonia compounds can
be used for pH adjustment, they may cause ammonia toxicity and increase the ammonia load on the
liquid treatment processes through return streams.
Consequently, their use is not recommended.
Sodium salts will not cause precipitates.
During a digester upset, volatile acid concentrations may begin to rise before bicarbonate alkalinity
is consumed. Because pH depression does not occur until alkalinity is depleted, it may be observed
only after the digester is well on its way to failure.
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5.3.3.9 Digester Foaming
Digester foam consists of fine gas bubbles trapped in a semi-liquid matrix with a specific gravity of
0.7 to 0.95. The gas bubbles are generated below the sludge layer and are trapped as they form.
While some foaming always occurs, it is considered excessive if it plugs piping or escapes from the
digester. Excessive foaming can cause the loss of active digester volume, structural damage,
spillage and damage to the gas-handling system, as well as being malodorous and unsightly. The
most common cause of digester foaming is organic overload, which results in the production of
more VFAs (volatile fatty acids) than can be converted to methane. The acid formers (which release
carbon dioxide) work much more quickly than the methane-forming microorganisms. The resulting
increase in carbon dioxide typically increases foam formation. Factors that can contribute to organic
overload include:
• Intermittent digester feeding

• Separate feeding or inadequate blending of primary sludge and waste activated sludge
• Insufficient or intermittent digester mixing
• Excessive amounts of grease or scum in digester feed (especially problematic if the digester is fed
in batches)
Organic overload can be minimized by feeding the digesters continuously (or as often as
possible), blending different feed sludge well before feeding, ensuring that the digester-mixing
system is operable, and limiting the quantities of grease or scum in the digester feed.
5.4 SLUDGE DE-WATERING
Most of the digested primary or mixed sludge can be compacted to a water content of about 90% in
the digester itself by gravity but mechanical de-watering with or without coagulant aids or prolonged
drying on open sludge drying beds (SDBs) may be required to reduce the water content further. The
de-watering of digested sludge is usually accomplished on sludge drying beds, which can reduce
the moisture content to below 70%. But excess oil or grease in the sludge will interfere with the
process. Where the required space for sludge drying beds is not available, sludge conditioning,
followed by mechanical de-watering on centrifugation, belt press, filter press, screw press, rotary
press and vacuum filters is the better choice.
5.4.1 Chemical Dosing Equipment
5.4.1.1 Coagulant
Chemical conditioning is the process of adding certain chemicals to enable coalescence of sludge
particles facilitating easy extraction of moisture. The chemicals used are ferric and aluminium salts
and lime, the more common being ferric chloride with or without lime.
Digested sludge, because of its high alkalinity exerts a huge chemical demand and therefore the
alkalinity has to be reduced to effect a saving on the chemicals. This can be accomplished by
elutriation. Polyelectrolytes show promise for sludge with finely dispersed sludge. The choice of
chemical depends on pH, ash content of sludge, temperature and other factors.
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Optimum pH values and chemical dosage for different kinds of sludge have to be based on standard
laboratory tests. The dosage of ferric chloride and alum for elutriated digested sludge is of the order
of 1.0 kg/m3 of sludge. Alum, when vigorously mixed with sludge, reacts with the carbonate salts
and releases CO2, which causes the sludge to separate and water drains out more easily. Hence
for effective results, alum must be mixed quickly and thoroughly. Alum can be easier if used as Poly
Aluminium Chloride (PAC) or Poly Aluminium Sulphate (PAS) as these can be used as true solutions
with dosing pumps. The alum floc, however, is very fragile and its usefulness has to be evaluated as
compared with ferric chloride before resorting to its application.
Feeding devices are necessary for applying chemicals; the mixing of chemicals with sludge should
be gentle but thorough, taking not more than 20 – 30 seconds. Mixing tanks are generally of the
vertical type for small plants and of the horizontal type for large plants. They are provided with
mechanical agitators rotated at 20 – 80 rpm.
A. Inorganic Chemicals
Inorganic chemical conditioning is associated principally with vacuum and pressure filtration
de-watering. The chemicals typically are lime and ferric chloride. Ferrous sulphate, ferrous
chloride, and aluminium sulphate are also used, although less commonly.
i. Ferric Chloride
Ferric chloride solutions typically are used at the concentration received from the supplier
(30 to 40%); however, some STPs dilute the ferric chloride to approximately 10% to improve
mixing and reduce the acidity and corrosivity of the material. This can be done in day tanks or
inline. Dilution may lead to hydrolysis reactions and the precipitation of ferric chloride crystals.
An important consideration in the use of ferric chloride is its corrosive nature. It reacts with water
to form hydrochloric acid, which attacks steel and stainless steel. When diluted with sludge, the
acidity is neutralized by the alkalinity of the sludge and thoroughly diluted so that the end product
is quite benign. Interlocks must be used to ensure that ferric chloride is always added to sludge
in the proper ratio and is never pumped into sludge lines or process equipment by itself.
Special precautions must be taken when handling this chemical. The best materials are
epoxy, rubber, ceramic, polyvinylchloride and vinyl. Contact with the skin and eyes must be
avoided. Rubber gloves, face shields, goggles and rubber aprons must be used at all times. Ferric
chloride can be stored indefinitely without deterioration. Customarily, it is stored in above ground
tanks constructed of resistant plastic and surrounded by a containment wall. Ferric chloride can
crystallize at low temperatures, which means that the tanks must be kept indoors
or appropriately warmed.
ii. Lime
Vacuum filters and filter press commonly use lime and ferric chloride to make the sludge easier
to filter and improve the release of the sludge from the filter media. Lime is available in two dry
forms–quicklime (calcium oxide) and hydrated lime [Ca(OH)2].
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When using quicklime, it is first slurried with water and converted to calcium hydroxide, which is
then used for conditioning. Because this process (known as slaking) generates heat, special
equipment is required.
Quick lime must be stored in a dry area, because it reacts with moisture in the air and can
become pasty and unusable.
Hydrated lime is much easier to use than quicklime, because it does not require slaking,
mixes easily with water with minimal heat generation and does not require any special storage
conditions.
Lime typically is used in conjunction with ferric salts. Although lime has some slight dehydration
effects on colloids, odour reduction and disinfection, it is used because it improves filtration and
release of the cake from the filter media. The lime reacts with bicarbonate to form a precipitate
of calcium carbonate, which provides a granular structure that increases porosity and reduces
compressibility of the sludge.
B. Organic Flocculants
Organic flocculants are widely used in many industries and processes involving the separation of
sludge from liquids. These liquid-sludge separation applications may involve processes related
to the recovery of finished products, clarification or purification of liquids, and volume reduction of
waste materials.
While polyelectrolytes are commonly used in applications involving liquid-sludge separation, the
processes of sewage sludge thickening and de-watering are completely dependent on their use.
i. Polymer Characteristics
• The product characteristics of these complex and proprietary polyacrylamide flocculants may
vary according to the following:
• Electronic charge (anionic, nonionic, or cationic)
• Charge density
• Molecular weight (standard viscosity)
• Molecular structure
ii. Polymer Specifications and Quality Control
Along with the product identification and type and form of product, the following standard product
specifications should be obtained to determine storage conditions, pumping requirements, and
potential hazards:
• Total solids
• Specific gravity
• Bulk viscosity
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• Flash point
• Freezing point
5.4.1.2 Equipment
A. Liquid Feeders
A typical solution-feed system consists of a bulk storage tank, transfer pump, day tank
(sometimes used for dilution) and liquid feeder. Some liquid chemicals can be fed directly without
dilution, and these may make the day tank unnecessary, unless required by a regulatory agency.
Nonetheless, dilution water can be added to prevent plugging, reduce delivery time and help
mix the chemical with the sewage. However, sometimes, the dilution water can have adverse
chemical effects. For instance, dilution water that has not been softened can potentially cause
calcium carbonate scale to build up on the piping. Special consideration should be given to the
final water chemistry of the solution before adding dilution water.
Liquid feeders are typically metering pumps and are generally of the positive-displacement
type using either plungers or diaphragms.
Positive-displacement pumps can be set to feed over a wide range (10:1) by adjusting the
pump stroke length.
The chemical addition rate can be set manually by adjusting a valve or the stroke / speed
on a metering pump.
B. Dry Chemical Feeders
Lime and alum are typical of the kinds of chemicals used with a dry chemical-feed system. It
consists of a feeder, a dissolver tank, and a storage bin or hopper. These systems are complex
because of their many storage and handling requirements. The simplest method of feeding dry
or solid chemicals is by hand. Solid chemicals may be pre-weighed and added or poured by
the bagful into a dissolving tank. This method generally applies only to small plants where dry
chemical-feed equipment is used.
Most dry feeders are of the belt, grooved-disk, screw, or oscillating-plate type. The feeding device
(belt, screw, disk, etc.) is typically driven by an electric motor. Many belt feeders, particularly the
gravimetric type, also contain a material flow-control device such as a movable gate or rotary inlet
for metering or controlling flow of the chemical to the feed belt.
5.4.1.3 Operation
Many metering pump systems handle chemicals that coat or build a layer of residue or slurries that
can settle out solids during operation. Strainers are helpful in removing large particulates, and the
operator must keep these cleaned. Periodic flushing to remove residues and deposits is often
required. Piping and valve arrangements should allow the system to be isolated so that a clear
liquid, such as water, can be used to pressurize the system for flushing the residue or solid
build up. These can be operated manually or automatically by solenoid valves with a timer control.
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The systems where the metering pumps and piping are required to be periodically shut down will
require flushing connections to remove solids.
Most feeders, regardless of type, discharge their material to a small dissolving tank equipped with
a nozzle system or mechanical agitator, depending on the solubility of the chemical being fed.
The surface of each particle needs to be completely wet before it enters the feed tank to ensure
thorough dispersal and avoid clumping, settling, or floating. When feeding some chemicals, such
as polymers, into dissolvers, care must be taken to keep moisture inside the dissolver backing
up into the feeder.
5.4.1.4 Maintenance
Systems where the metering pumps and piping are periodically shut down will require flushing
connections to remove solids. In addition, an allowance for T-and-Y cleanouts should be included for
the piping system where longer horizontal piping runs cannot be adequately flushed.
A metering pump will lose capacity and become erratic when the suction or discharge valves become
worn or when poor hydraulic conditions exist. These conditions will be indicated by the cylinder test.
Also, debris in the chemicals being fed may obstruct or block the check valves, thus impeding their
operation and decreasing the pump’s performance.
• Check dust filters periodically.
• Periodically clean and calibrate level measurement and indication instrumentation in liquid and
dry storage tanks.
• Check the level and condition of the oil in the gear reducer.
• Check the condition of all painted surfaces.
• Clean dirt, dust or oil from equipment surfaces.
• Check all electrical connections.
• Stop and start equipment, checking for voltage and amp draw and any movement restrictions
because of failed bearings, improper lubrication, or other causes.
• Check the drive motor for any unusual heat, noise, or vibration.
• Check the packing for leakage and wear.
5.4.2 Sludge Feed Pump
5.4.2.1 Operation
The following operations directly affect sludge pump performance.
Positive-displacement pumps need a drive system that can operate the pump at the speed
needed to perform adequately under all operating conditions. Sometimes, this involves manually and
automatically timed starts and stops, as well as variable pump discharge rates. This variable-speed
arrangement can be provided via mechanical variable-drives; variable pitch pulleys; direct-current,
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variable-speed drives; alternating-current, variable-frequency drives; eddy-current magnetic

clutches; or hydraulic speed-adjustment systems. Each has various advantages and disadvantages
with respect to cost, amount and ease of maintenance required, efficiency, turndown ratio and
accuracy. Because positive-displacement pumps are constant torque machines, operators should
ensure that the output torque of variable-speed drive exceeds the pump’s torque requirement at
all operating points. Although variable-speed drives are often either a necessity or an enhancement
to proper plant operation, the challenge is providing the continued maintenance and
servicing required.
Operators should check the following items:
• Inlet and outlet flow rate
• Noise or vibration
• Bearing housing temperature
• Running amperage
• Pump speed
• Pressure
5.4.2.2 Maintenance
Following is the maintenance checklist for sludge pumps:
• Check the level and condition of the oil in the gear reducer
• Check the shaft alignment
• Check the condition of all painted surfaces
• Visually inspect mounting fasteners for tightness
• Clean dirt, dust or oil from equipment surfaces
• Check all electrical connections
• Stop and start equipment, checking for voltage and amp draw and any movement restrictions
because of failed bearings, improper lubrication or other causes
• Check the drive motor for any unusual heat, noise or vibration
• Check mechanical seals and packing for leakage or wear
5.4.3 Mechanical De-watering
5.4.3.1 Centrifugal De-watering
Centrifugation is the process of separating solids from liquids by the process of solid liquid
separation, enhanced by centrifugal force.
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5.4.3.1.1 Operation
A centrifuge can thicken or dewater the sludge with only a minor change in the weir setting (also
called pond setting). Likewise, it can de-water sludge to a moderate consistency at low polymer dose
or produce very dry solids using higher polymer dosages.
A. Sludge Type and Quality
The operation of the wet end of the plant determines the quality of the sludge, which, in turn,
greatly affects the dry end.
B. Polymer Activity and Mixing with the Sludge
If the polymer does not react well with the sludge, performance suffers. In addition, adding the
polymer closer to or further from the centrifuge will affect performance.
C. Polymer Type and Dosage
Some polymers are designed to obtain drier cakes than others do.
Likewise, the dosage will increase and decrease with cake dryness. Some polymers become less
effective at higher dosages. This will be apparent from a quick jar test or observing that adding
more polymer results in either poorer operation or the same operation.
• Hydraulic Loading
• Centrifuges are less limited by the volume of water that passes through the centrifuge than
filtration devices. As a result, thinner feed sludge will have less effect on performance than in
filtration devices.
• Solids Loading
• The solids residence time is important. If there is more sludge to de-water, there will be less
solids residence time and therefore wetter solids, all else being equal.
• Capture
• The solids capture is generally fixed by the plant management, and is not an operating
variable.
D. Torque Control
In recent years, nearly all centrifuges have a controller that allows the operator to choose a scroll
drive load or torque set point, and the controller then adjusts the differential speed to maintain
that set point. In this manner, the torque and therefore the cake dryness is fixed.
One way of looking at the centrifuge is that it is a very expensive viscometer. The conveyor is
turning at a controlled speed immersed in the sludge. The effort or torque, needed to turn the
conveyor, is measured by the scroll drive device.
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As the cake becomes drier, its viscosity increases, which, in turn, increases the torque or load
on the scroll drive. When operating in load control, the controller automatically adjusts the
differential revolutions per minute to maintain a constant torque level, and the operator’s only task
is to observe the centrate quality from time to time and adjust the polymer rate to maintain the
desired centrate quality.
This is a simple control; one of its virtues is that the major operating cost–cake-dryness is fixed,
and any operator error shows up in the centrate, which is easy to see and is not so costly if it is
off slightly.
Consult the manufacturer of the centrifuge for a recommendation on operating speed changes.
E. Process Control
The following shutdown procedures are suggested:
• Stop sludge and polymer feed to the centrifuge
• Flush with treated sewage until the centrate is clear and the torque level begins to drop
• Turn the centrifuge off
• Continue flushing at 25% of normal feed flow until the centrifuge reaches 7 –800 r/min.
• Turn off the lubrication system and cooling water when the unit has completely stopped
5.4.3.1.2 Maintenance
During operation, the operator should check for the following:
• The oil level and the flow of oil to the bearings in circulating oil systems
• Flow of cooling water and oil temperature, to ensure it is operating in the proper range
• Machine vibration
• Ammeter reading on the bowl motor
• Bearing temperatures, by touching them
• System for leaks
• Centrate quality
• Scroll drive torque
• Because the centrifuge will shut itself down in the event of a fault, the operator typically only looks
at the mechanical parameters once per shift.
5.4.3.2 Belt Filter Press De-watering Equipment
The operation of a Belt Filter Press (BFP) is based on the principles of filtration and is comprised of
the following zones.
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• Gravity drainage zone, where the feed is thickened

• Pressure zone
• Shear zone
A belt filter press is shown in Figure 5.5.
Figure 5.5 Belt filter press
5.4.3.2.1 Operation

A. Process Variables
There are several process variables that affect the performance of all de-watering systems.
In general, de-watering devices must run at 95% capture or better, so capture is not really an
operating variable. Of the remaining parameters–cake dryness, loading and polymer
dosage–within limits, the operator can take from one to give to another. For drier cake, one can
reduce the loading and/or increase the polymer dosage.
• Cake Dryness
Increased cake dryness comes at the price of lower capacity and/or higher polymer dosage. The
ability to obtain higher cake dryness is, to a great extent, a function of the design of the press.
Press with extended gravity zones to better pre-concentrate the feed and additional pressure
rollers give longer sludge residence times and drier cake.
• Polymer Type and Dosage
Some polymers are designed to obtain drier cakes than others do. Likewise, the dosage will
increase and decrease with the cake dryness. Some polymers become less effective at higher
dosages. This will be apparent from a quick jar test or observing that adding more polymer results
in either poorer operation or same operation.
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• Hydraulic Loading
Belt filter Press (BFP) is limited by the volume of water that can go through the belts. As a result,
thinner feed sludge will result in less quantity of dry solids produced, all else being equal.
• Solids Loading
Likewise, more solids will result in less solids residence time inside the press and therefore wetter
sludge, all else being equal.
• Capture
The solids capture is typically fixed by the plant management and is not an operating
variable like.
• Belt composition and condition, speed and tension

• Size and number of rollers
• Wash water flow, pressure and suspended solids concentration
B. Sequence of Operation
The sequence of operation for a BFP is typically set up in the following order:
• Open wash water valve

• Start wash water pump
• Start pneumatic/hydraulic belt tension system
• Start belt drive and de-watered cake conveyor
• Start polymer solution feed pump
• Start sludge feed pump
Modern BFP typically has a one-button start system, so the operator only has to manually start
the feed and polymer pumps. In any event, one benefit of filling out the operating log is that the
operating conditions the last operator used are known, as are the conditions of the previous week
and month.
Rollers and bearings require frequent lubrication. Follow the manufacturer’s O&M manual for
lubrication schedule. This extends the life of the roller bearings and belt drive motor.
Replacement of filter belts is a common maintenance requirement.
The following procedures will extend the life of the BFP and reduce its operating cost:
• Wash down the BFP every day after finishing the dewatering shift. This prevents cake from drying
and accumulating in different sections of the BFP.
• Confirm that all rollers are turning freely.
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• Check the press weekly for damaged bearings.
• Check the grinder that prevents large particles from entering the press twice per year.
• Clean the wash water nozzles as frequently as necessary (this depends on the quality of the
wash water). This ensures proper cleaning of the belts.
• Inspect and change sludge containment and washbox seals, as necessary.
• Inspect and clean doctor blades from any accumulated debris, hair, or any other
foreign materials.
• Clean the chicanes (plows) in the gravity section after shutting down the press.
• For maintenance of complex mechanical parts of the BFP, contact the manufacturer for advice.
5.4.3.3 Filter Press
Filter Press for de-watering are generally either recessed plate filters or diaphragm filter Press. With
the advent of better organic polymers, belt filters and centrifuges have largely displaced filter Press
in the market. Filter Press can be attractive in unusual circumstances.
The fixed-volume recessed plate filter press consists of a series of plates, each with a recessed
section that forms the volume into which the feed enters for de-watering. Filter media or cloth, placed
against each plate wall, retains the cake-solids while permitting passage of the filtrate.
The plate surface under the filter media is specifically designed with grooves between raised
bumps to facilitate passage of the filtrate while holding the filter cloth. Before pumping into the press,
the feed must be chemically conditioned to flocculate the solids and release the water held within
the solid mass. Most typical conditioning systems use inorganic chemicals and polymers.
High-pressure pumps force the feed into the space between the two plates. The filtrate passes through
the cake and the filter media and out of the press through special ports drilled in the plate.
Pumping continues up to a given pressure and is stopped when solids and water fill the void volume
between the filter cloths and filtrate flow slows to a minimal rate. The press then opens mechanically
and the cake is removed, one chamber at a time.
5.4.3.3.1 Operation
A. Process Variables -Chemical Conditioning
Polymers have a narrow range of effective dosage. A dose that is too low or too high will result
in a wet cake. Lime and ferric chloride have a broader range of effective dosage. While it is
desirable for an operator to reduce the chemical usage to reduce costs, if erratic equipment
operation or erratic feed qualities occur, a higher lime dose typically will protect against a wet
cake. Polymer conditioning requires much less chemical per unit mass of solids de-watered,
which results in more room in the press for organic sludge, and increased capacities.
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• A torn cloth immediately results in a filtrate flow that is very dirty and heavy with solids
• Feed sludge concentration. A very thin feed may blow out through the plate surfaces during the
initial high-volume fill of the press because there would be too much filtrate flow for the drain
capacity. A thin feed will at least require a longer filtration time and produce a wetter cake. A thick
feed typically will produce a drier cake with a much shorter filtration time.
For a conventional filter press, the operator can control the following machine variables:
• Feed application rate by varying the flow to the filter press.
• Overall filtration time, including such variables as the time at each pressure level in multiple
pressure level operations.
• Use and amounts of pre-coat or body feed. Typically, pre-coat is unnecessary when inorganic
chemicals, such as lime and ferric chloride, are applied. Pre-coat may be needed if particle sizes
are extremely small, filterability varies considerably or a substantial loss of fine solids to and
through the filter media is anticipated.
• Conditioning chemicals, type, dosage, location, and mixing efficiency. Polymer addition versus
lime and ferric chloride conditioning typically are not interchangeable, as each chemical requires
special mixing and flocculation energies and reaction times. Polymers only need a quick mix
before injection to the press. Modifications to the piping and mixing systems are typically needed
if a change in the type of chemical for conditioning is desired.
• Flocculation efficiency and energy vary with the type of chemical being used. Polymer floc shears
easily and remains stable for only a few minutes. Lime floc is more durable and remains stable
for a few hours.
• Filter media. Filter cloth media vary widely, with different filament composition, weave pattern,
and weave tightness.
B. Operational Considerations
• The press is very noisy when in operation. Hearing protection may be needed.
• Never insert objects between the press plates as they are being discharged, without first shutting
the unit down by tripping the light curtain or flipping the emergency shutdown switch.
• Lime treatment results in considerable ammonia fumes being released during cake discharge.
Make sure that adequate ventilation pulls these fumes away from the operator, preferably with
a high-capacity, down-draft blower system. If an adequate ventilation system is not operational,
short-term exposure may be allowed. If an approved ammonia respirator is worn by all operators
assisting with the cake discharge.
• Hydrochloric acid washing of the press releases volatile acid fumes, which should not be
inhaled or exposed to moist body tissues, such as eyes and lungs. A high-capacity ventilation
system, as previously noted, is essential. If approved, short-term exposure may be allowed, with an
approved respirator and complete coverage of all exposed skin.
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CHAPTER 5:
• Lime powder is very caustic when it comes into contact with moist body tissues. Therefore, an
approved respirator and complete coverage of all exposed skin is necessary when
working around lime.
5.4.3.4 Screw Press
Screw press dewater sludge first by gravity drainage at the inlet section of the screw and then by
squeezing free water out of the sludge as they are conveyed to the discharge end of the screw
under gradually increasing pressure and friction. The increased pressure to compress the sludge is
generated by progressively reducing the available cross-sectional area for the sludge. The released
water is allowed to escape through perforated screens surrounding the screw while the sludge
is retained inside the press. The liquid forced out through the screens is collected and conveyed
from the press, and the de-watered sludge drops through the screw’s discharge outlet at the end
of the press.
Screw speed and configuration, as well as screen size and orientation, can be tailored for
each de-watering application.
Solids are combined with polymer and pumped into the flocculation vessel. After flocculation, sludge
is transferred to the screw press. In the horizontal screw press configuration, sludge is fed by
gravity from the flocculation tank into the screw press head box. If a rotary screen thickener is used,
sludge flows from the flocculation tank to the rotary screen thickener and then to the screw press
head box. Sludge then flows from the head box into the inlet of the screw press. A typical screw press
is shown in Figure 5.6.
Figure 5.6 Screw press
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CHAPTER 5:
5.4.3.4.1 Operation
Screw press operates continuously at low speeds and do not require close operator
supervision; therefore, they are easy to maintain and have low power consumption. The manual
cleaning schedule ranges from once per week to once every 30 days.
A. Chemical Conditioning
Polymer addition promotes particle flocculation and increases the de-watering and solids-capture
rates. Jar testing and pilot testing can be used to estimate the type and quantity of polymer
necessary for each application, because it may vary significantly depending on sludge
characteristics. Polymer consumption is affected by multiple parameters (e.g., grit content of the
sludge, the presence or absence of primary clarifiers, the type of biological treatment and the type
and duration of sludge digestion).
B. Cleaning System
Screw press systems have automatic cleaning systems, which involve plant water and spray
nozzles. During automated wash cycles, wash water from solenoid valves sprays onto the screw
press screen to remove built-up sludge.
The brushes are made of nylon with stainless steel mounting hardware. This mainly cleans the
screen to allow water to drain by gravity (especially in the lower part of the screen) and minimize
resistance to water filtration. Clean screens require less de-watering pressure, which improves
the solid capture rate.
The second cleaning process is an automatic spray wash system, which cleans the screen
from the outside. It is comprised of a rotating spray-bar washing system and spray nozzles
fed by solenoid valves.

C. Rotation Speed
Typical rotation speeds range from 0.1 to 2.0 rpm for horizontal screw press and from 0.5 to
2.0 rpm for inclined screw press. In general, an increase in screw rotation speed increases
production capacity but decreases cake solids concentration. In a full-scale application,
increasing rotational speed from 1 to 1.25 rpm reduced the cake concentration from 23 to 20%.
Maintenance checkpoints are as follows:
• Check the drive of the screw for abnormal sound and vibration during operation
• Check the screen for any damage or clogging
• Check the cleaning nozzle for clogging
• Check the amount and the leakage of lubricating oil
• Check the reading of the ammeter and indicator lamps
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CHAPTER 5:
5.4.3.5 Rotary Press
Rotary Press is a relatively new technology that can achieve cake solids and solid capture
performance similar to belt Press and centrifuges. Rotary press and rotary fan press de-watering
technology relies on gravity, friction and pressure differential to de-water sludge.
The major elements of a rotary press are the polymer feed and mixing system, parallel filtering
screens, a circular channel between the screens, the rotation shaft and a pressure-controlled outlet
as shown in Figure 5.7.
Figure 5.7 Schematic of a rotary press system
The press screens of rotary fan consist of fabricated wedge wire with small openings and linear gaps.
The rotary press drive configuration allows up to six rotary press channels to be operated on a single
drive. Each channel has bearings, and the combined unit has an outboard bearing cantilevered on
one end. The rotary fan-press drive configuration uses a maximum of two rotary press channels on
a single drive with isolated bearings in a sealed gearbox.
A key feature of both rotary press and rotary fan press de-watering technology is their slow
rotational speed. Typical installations use speeds of 1 to 3 rpm. This provides low vibration, low shear
and low noise.
5.4.3.5.1 Operation
A. Operational Control
Operators can control the performance of the rotary press or rotary fan press by changing
polymer type and dosage, feed rate, feed pressure, wheel speed and outlet pressure.
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CHAPTER 5:
Both types of press require minimal supervision and can be unattended between start up
and shutdown.
• Hydraulic Loading Rate
The hydraulic loading rate is a function of the equipment’s size and number of channels.
The technology is modular, and the hydraulic loading rate of single-drive units ranges from
0.5 to 15 L/s, although a maximum hydraulic loading rate of 3 L/s per channel is typical. Rotary
press provides better performance on residuals with higher fibre content (e.g., primary sludge).
• Chemical Conditioning Requirements
Chemical conditioning is mandatory to attain design performance in rotary press or rotary fan
press dewatering. Polymer feed systems can be supplied by the manufacturer or can be procured
independently. In both cases, the feed systems typically include a polymer storage tank and
metering pump, which feeds the polymer into the mixing or flocculation tank, where it is blended
with the sludge. Dry or emulsion polymers can be used.
• Solids Loading Rate
Because solids capture is a function of the adjustable back pressure, the solids loading rate
varies with the hydraulic loading rate. At higher solids concentrations, residuals will accumulate
in the outlet zone, form as a cake and extrude more quickly.
B. Cleaning System
Rotary Press and rotary fan Press include a self-cleaning system that must run for 5 minutes per
day at the end of use to flush all lines and equipment. The system does not require high-pressure
water for flushing. Typically, the normal in-plant water source has sufficient pressure, but in some
cases, high-pressure booster pumps may be required.
Maintenance checkpoints are as follows:
• Check the drive of the rotary for abnormal sound and vibration during operation
• Check the rotary for any damage or clogging
• Check the amount and the leakage of lubricating oil
• Check the reading of the ammeter and indicator lamps
5.4.3.6 Vacuum Filter
The vacuum filter consists of a cylindrical drum over which a filtering medium of wool, cloth or felt,
synthetic fibre or plastic or stainless steel mesh or coil springs is laid.
The drum is suspended horizontally so that one quarter of its diameter is submerged in a tank
containing sludge.
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CHAPTER 5:
5.4.3.6.1 Operation
A. Process Variables
The principal variables that affect vacuum filter operation are as follows:
• Chemical conditioning
• Filter media type and condition
• Drum submergence
• Drum speed
• Vacuum level
Chemical conditioning most significantly influences de-waterability, because it changes the

physical and chemical nature of the feed. Conditioning agents produce a feed that releases water
more freely, thereby producing a drier cake. Conditioning agents also add to the sludge to be
discarded.
B. Sludge Conditioning
Sludge conditioning is accomplished by the addition of various coagulants or flocculating agents

such as ferric chloride, alum, lime and polymers. The amount of chemical solution added to the
conditioning tank is normally established by laboratory testing of sludge grab samples.
The installation of a blanket may require several days’ work.
A blanket will usually last from 200 – 20,000 hours, but this depends greatly on the blanket material,
conditioning chemical, backwash frequency and acid bath frequency. An improper adjustment of the
scraper blade, or accidental tear in the blanket, will usually require its replacement.
Both cloth blankets and coil springs filters require a high pressure wash after 12 to 24 hours of
operation and, in some instances, an acid bath after 1,000 to 5,000 operating hours.
5.5 SLUDGE DRYING BED
These are age-old practices in India and are still preferred in arid parts where land is available and
affords employment opportunities to unskilled labour. Other areas, where rainfall is frequent are not
suited for drying beds.
5.5.1 Applicability
This method can be used at all locations where adequate land is available and dried sludge can be
used for soil conditioning. When digested sludge is deposited on a well-drained bed of sand and
gravel, the dissolved gases tend to buoy up and float the solids leaving a clear liquid at the bottom,
which drains through the sand rapidly. The major portion of the liquid drains off in a few hours after
which drying commences by evaporation.
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CHAPTER 5:
The sludge cake shrinks producing cracks, which accelerates evaporation from the sludge surface.
In areas having greater sunshine, lower rainfall and lesser relative humidity, the drying time may
be about two weeks while in other areas, it could be four weeks or more. Covered beds are not
generally necessary unless in heavy monsoon and sludge holding tanks can be used.
5.5.2 Unit Sizing
The sludge drying process is affected by weather, sludge characteristics, system design (including
depth of bed) and length of time between scraping and lifting of sludge material. High temperature
and high wind velocity improve drying while high relative humidity and high rainfall retard drying.
5.5.3 Area of Beds
The area needed for de-watering and drying the sludge is dependent on the volume of the sludge,
cycle time required to retain sludge for de-watering, drying and removal of sludge and making the
sand bed ready for next cycle of application and depth of application of sludge on drying bed. The
cycle time between two dryings of sludge on drying beds primarily depends on the characteristics of
sludge including factors affecting its ability to allow drainage and evaporation of water, the climatic
parameters that influence evaporation of water from sludge and the moisture content allowed in dried
sludge. The cycle time may vary widely, lesser time required for aerobically stabilized sludge than
for an aerobically digested sludge and for hot and dry weather conditions than for cold and/or wet
weather conditions.
5.5.4 Percolation Type Bed Components
A sludge drying bed usually consists of a bottom layer of gravel of uniform size over which is laid
a bed of clean sand. Open-jointed tile under drains are laid in the gravel layer to provide positive
drainage as the liquid passes through the sand and gravel.
Sludge that is drawn to the beds contains 4 to10 % solids depending upon the type of sludge. Wet
sludge should be applied to the beds to a depth of 20 to 30 cm. After each layer of dried sludge has
been removed, the bed should be raked and levelled. Sludge should never be discharged on a bed
containing dried or partially dried sludge. It is preferable to apply the sludge at least a day or two after
the sludge cakes are removed.
Removal of dried sludge from bed surfaces should be done with shovel, taking care that as little as
possible of the sand is removed. When the sand layer is reduced to as low as 10 to 15 cm, it should
be examined for clogging by organic matter and if found, the entire sand should be removed and the
bed re-sanded to the original depth of 20 to 30 cm.
The dried sludge cakes may be sold as fertiliser. Some part of the sludge should be used in the plant
itself for gardening, lawns, etc. to demonstrate its fertilizer value and to develop a market value for the
digested and dried sludge. Suitable storage facilities may be provided for the dried sludge.
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CHAPTER 5:
Records of operation of sludge drying beds should show the time and quantity of sludge drawn to
each bed, the depth of loading, depth of sludge after drying time and the quantity of dried sludge
removed. The solids content of wet digested sludge, its volatile portion and pH should be determined
and recorded. Likewise, the moisture content and fertilizer value in terms of NPK of dried sludge
should also be analysed and recorded. An operation sheet of sludge drying bed is in Table 5.3.
Table 5.3 Typical operation sheet of sludge drying beds
Source: JICA, 2011
All preventive maintenance of equipment is to be done as per the equipment manufacturer only.
Preventive maintenance of process control resides only in digestion process and has
been discussed above.
5.7 TROUBLESHOOTING
5.8 RECORD KEEPING
There is no standard format for record keeping. Each STP has to have its own format. The crucial
parameters to be recorded are the pH and temperature of the digesters on a daily basis. The gas
analysis can be recorded once a week.
5.9 SUMMARY
Treatment of sludge, which is converted from organic matter removed from sewage, as well as
quality and quantity of sewage inflow, and quality of treated sewage, are quite important in STPs.
Problems likely to be encountered in the course of operation are shown in Appendix B.5.1 as
troubleshooting and the operators can make use of these to take appropriate remedial measures.
5 - 39
CHAPTER 6: ELECTRICAL AND
Part B: Operation and Maintenance INSTRUMENTATION FACILITIES
CHAPTER 6: ELECTRICAL AND INSTRUMENTATION FACILITIES
6.1 INTRODUCTION
Electrical systems that are to supply electrical power for an entire STP consist of power receiving
and transforming equipment, power distributing equipment, cables, drives and standby generators.
Instrumentation facilities are also installed for the purpose of measuring and collecting process data
such as flow rate, pressure, water qualities, and so on, at all times. These are utilized to monitor and
control treatment processes at optimal conditions for a stable treatment. The instrumentation facilities
consist of sensors for processes, signal converters, operating devices (actuators), controllers (PLC:
Programmable Logic Controller), monitoring devices (PC: personal computer), etc.
This chapter describes the following electrical and instrumentation facilities:
A. Power receiving and transforming equipment (Substation & transformers)

B. Standby power supply system (Generators, Engines, UPS: Uninterruptible Power Supply)
C. Prime movers and motor controllers (Motors, Starters, Cabling)
D. Instrumentation system
E. Supervisory control and data acquisition system (SCADA)
A typical single line diagram (SLD) depicts the entire electrical power flow system of an STP. The
single line diagram not only presents the type and number of equipment but also the electrical
specifications. This is an important document for an O&M person who would like to refer to it in case
of any operational or maintenance need. Every STP should have:
• A SLD kept for record and displayed properly in the STP facility particularly near the
electrical sub-station
• SLD periodically reviewed and updated suitably in case of any change
• All those personnel involved in the electrical and instrumentation work should understand
the SLD
A typical electrical SLD is shown in Figure 6.1 overleaf.
6.2 POWER SUPPLY SYSTEM
Power supply systems have the following three major functions:
• Transfer power from the transmission system to the distribution system
• Reduce the voltage to the specified level (Typical voltage level is 415 volt for STPs) suitable
for connection to local loads
• Protect the entire network by identifying and isolating electrical faults selectively
6-1
CHAPTER 6:
Part B: Operation and Maintenance ELECTRICAL AND INSTRUMENTATION FACILITIES
Figure 6.1 Typical Electrical Single Line Diagram of 11 KV Yard and Master Switch Board
6-2
6.2.1 Power Receiving and Transforming Equipment
If the STP facility receives the electrical supply at high voltage i.e., 66kV, 11kV, 6.6 kV, or 3.3 kV, it
has to be reduced to the operating voltage level, which is usually 415V. A substation, which is used
to step-down high voltage to low voltage, consists of the following equipment or devices:
6.2.1.1 High Tension (HT) Substation
The HT substation is composed of the following equipment and devices.
6.2.1.1.1 Disconnecting Switch
Disconnecting switches are devices to open/close a high voltage circuit when high-voltage
equipment are inspected, tested or cleaned. The devices are capable of safely breaking no-load
current but not load current. For safe O&M work, be sure to open/close the disconnecting switch
only after opening a circuit breaker, which is located on the secondary side, just downstream of
the disconnecting switch.
6.2.1.1.2 Circuit Breaker
Circuit breakers are switches that open/close electric-circuits in normal and abnormal conditions
(especially in short circuit). Therefore, the circuit breakers must be capable of tripping the circuits
in conjunction with protective relays and by cutting off the short-circuit current definitely and safely,
avoiding accidents due to high current.
Circuit breakers for high voltage are categorised into the following types according to their techniques
of eliminating arcs:
A. Air Circuit Breakers (ACB)

B. Vacuum Circuit Breaker (VCB)
C. Inert Gas Method (SF6)
6.2.1.1.3 Power Fuses
The function of a power fuse is to sense and prevent flow of excess current in electrical devices and
electrical wire by melting the fuse element and thereby breaking the electric circuit when subjected
to a short-circuit. Power fuses are typically used for smaller electrical systems because they have the
capability and speed for breaking the circuit as compared with circuit breakers.
A proper O&M, practice is that even if only one fuse melts due to an accident such as a short-circuit
in a three phase switch, all power fuses including the melted one should be replaced.
6.2.1.1.4 Voltage Transformer (VT) or Potential Transformer (PT)
Voltage transformers are used mainly in high-voltage distribution equipment to step-down voltage in
measurement circuit for safe measurement; single-phase and three-phase types are manufactured.
6-3
The typical secondary voltage of the voltage transformer is 110 volt (Phase-to-Phase). They are also
applied to protective relays.
O&M issues to be observed in case of a PT are as follows:
• If once short circuit occurs on the secondary side of a VT, excess current flows into the primary
side and that may cause the fuse on the primary side to blow. The primary fuse has also to be
checked when there is a fault trip or metering mismatch.
6.2.1.1.5 Current Transformer (CT)
Current transformers are used for stepping down current to be measured safely. It is also applied to
protective relays.
The typical secondary current of the current transformer is 5 Amp or 1 Amp.
O&M issues to be checked are as follows:
• If the secondary side of CT is open-circuited, all the current flowing to primary side is excited by
magnetic saturation and causes damages to the CT by over-heating. Therefore, the secondary
side should never be left open-circuited. Even when the downstream instrument is removed for
any repair, the secondary should be shorted.
6.2.1.1.6 Protective Relay
Protective relays should detect electrical faults promptly, isolate the faults from system and activate
alarms when there is a faulty condition sensed in the electrical supply to the circuits or electrical
equipment (short circuit, earth fault, single-phase, reverse power flow etc.)
The protective relays should have the following three characteristics:
A. Certainty: The relay should always be sensing the parameters for action when there is a
fault or specified abnormality.
B. Selectivity: The relay should obey a selection of the limits beyond which a fault will be judged.
C. Promptness: The relay should sense and operate within the shortest possible time.
Categories according to protective functions are as follows:
A. Over current relay (OCR): Monitor and protect against over load and short-circuit.
B. Under voltage relay (UVR) and over voltage relay (OVR): Detect and protect under voltage
(power failure) or over voltage.
C. Earth fault relay: Protect by detecting current leakage to earth.
Protective relay is shown in Figure 6.2 overleaf.
6-4
Figure 6.2 Electromagnetic Protective relay
Categories according to design as follows.
An electrochemical protective relay converts the voltages and currents to magnetic and electric
forces and torques that press against spring tensions in the relay. The tension of the spring and
taps on the electromagnetic coils in the relay are the main processes by which a user sets a relay.
In a Solid State relay, the incoming voltage and current waveforms are monitored by analog
circuits, not recorded or digitized. The analog values are compared to settings made by the user
by a potentiometer in the relay.
A Digital Relay converts all measured analog quantities into digital signals. Compared to
static relays, digital relays introduce Analogue to Digital Converter (A/D conversion) of all
measured analogue quantities and use a microprocessor to implement the protection algorithm.
The microprocessor may use some kind of counting technique, or use the Discrete Fourier Transform
(DFT) to implement the algorithm. Since late 1990s most of the protective relays are of digital type.
Advantages of Digital Relays
• High level of functionality integration
• Additional monitoring functions
• Functional flexibility
• Capable of working under a wide range of temperatures. Internal power requirement is very low.
• They can implement more complex functions and are generally more accurate
• Self-checking features and self-adaptability
• Able to communicate with other digital equipment of contemporary design
• Less sensitive to temperature-related aging
• Economical because can be produced in required numbers and can be set at site
• More accurate
• Signal storage is possible
6-5
Limitations of Digital Relay
The devices have short lifetime due to the continuous development of new technologies.
• Needs to be protected against power system transients
• As digital systems become increasingly more complex they require specially trained staff
for operation
• Proper maintenance of the settings and monitoring data
These limitations are overcome by progressive improvements in design, ruggedness, cost,

low power and heat generation factors, standardized modular design, scalability and simpler
training to operating staff.
6.2.1.2 Transformer
A transformer is the most important component in substations. Transformers receive electrical power
at high voltage and transform it to lower service voltage. They also provide isolation between high
voltage and low voltage supply.
Cooling system for oil-immersed transformer: Oil serves as direct cooling medium to disperse the
heat that is generated from windings and core. The oil is in turn cooled by indirect cooling medium
such as air at the oil radiator.
Cooling system for dry transformer: Utilize surrounding air or SF6 as cooling medium.
Transformer Efficiency: The efficiency of a transformer varies between 96% and 99%. It not only
depends on design, but also on operating load. The transformer losses are mainly attributed to:
• Constant Loss: This is also called iron loss or core loss, which mainly depends upon the
material of the core and magnetic circuit of the flux path. Hysteresis and eddy current loss are
two components of constant loss.
• Variable Loss: This is also called load loss or copper loss, which varies with the square of the
load current.
The best efficiency of a transformer occurs at a load when constant loss and variable
loss are equal.
For distribution transformers, installed in an STP, the best efficiency would occur around 50% load.
O&M checks to be made are as follows:
• Check connections of cables for looseness and overheating

• Check the transformer for abnormal vibration and noise
• Check oil and winding temperature regularly with respect to manufacturer’s manual
• Check for moisture ingress by observing the colour of the silica gel
• Check for level of oil in the conservator
6-6
A typical transformer is shown in Figure 6.3.
Figure 6.3 Transformer
6.2.1.3 Low Tension (LT) Panel
LT panels or LT switchboards are designed to distribute stepped-down voltage to power

equipment and control panels.
They typically consist of moulded case circuit breakers (MCCBs), power contactors (PCs), protective
relays (PRs), meters, indication lamps, control switches, etc.
A. MCCB
An MCCB is designed to “open/close” low voltage feeder circuit or branch circuit at normal
condition. It also breaks the circuit automatically in case of abnormal condition such as overload,
short circuit, etc.
B. Power Contactor
A power contactor is typically used for “on / off” control of motors. A relay can be installed on the
circuit for overload protection. Electromagnetic force works to “open /close” the contacts.
The O&M checks to be made are as follows:
• Check for abnormal noise or overheating of exciting coils, abnormal noise and discolouration of
contacts (carbonized or worn contact surfaces by arcing)
• Check for the proper working of all display indicators like voltmeters, ammeters,
energy meters and indicator lamps
• Check whether the name of the panel is written on it and it is correct as per the SLD
• Check for the proper earthing of the panels
6-7
6.2.1.4 Bus-bar
Bus-bars are conductors to carry power among the various components in the power circuit in
an outdoor station or distribution board. They are to be rated to carry the maximum rated current
continuously and short-circuit current for a short time without damage.
The O&M issues to be cared for:
• Check connections for looseness and overheating, and check the bus bar for discolouration
• Check bus bars are properly colour coded (Red, Yellow or Blue) to represent the phases
• Check bus bars are properly enclosed within panels
6.2.2 Power Control
Correcting power factor is a typical power control technique. Power factor correction is described in
this section.
6.2.2.1 Power Factor Correction
Active power, measured in kilowatt (kW), is the real power (shaft power, true power) used by a load
to perform a certain task. However, there are certain loads like motors, which require another form
of power called reactive power (kvar) to establish the magnetic field. Although reactive power is
virtual, it actually determines the load (demand) on an electrical system. Electrical capacity required
for some electrical equipment is referred to as “apparent power (kVA)”, that is, the vector sum of
“active power” and “reactive power (lagging / leading)”.
Most of the power machineries in STPs are driven by three-phase induction motors, which are
inductive loads. When an inductive load is driven, the sine wave of the load current flows at the
same frequency as the sine wave of the voltage, but lags the voltage wave cycle slightly. When both
current and voltage source waves cross zero and maximum value at the same time, the power factor
is said to be unity, and the entire power can be utilised as real power. The ‘Apparent Power-kVA’ is
equal to ‘the real Power-kW”. When the current wave is slightly lagging the voltage wave, the power
factor is said to be lagging and is less than unity. The real power is less than the apparent power due
to this lag.
A lagging power factor is not beneficial to a power consumer as the billing is includes
charges towards the kVA used, while the actual utilisation is less.
It is also not beneficial for the power supplier whose system power factor is also affected.
Equipment used in most industries such as drives, controllers, etc., are inductive loads, which
lower the power factor. The power factor is the ratio between active power (kW) and total
power (kVA), or the cosine of the angle between active and total power. A high reactive power will
increase this angle and as a result the power factor will be lower. A vector diagram of power factor is
shown in Figure 6.4 overleaf.
6-8
Figure 6.4 Vector diagram of Power Factor
In a typical STP since a large number of induction motors are used, the power factor will be low and
needs to be improved or corrected. The power factor can be improved by installing power factor
correction capacitors to the plant’s power distribution system.
They act as advancing reactive power generators and therefore reduce the amount of lagging
reactive power, and thus the total power, generated by the utilities.
To improve or correct the power factor, apparent electrical capacity required for the electrical
equipment should be decreased by canceling the lagging reactive power by the use of leading
reactive power unit that can also reduce energy loss in cables, transformers, etc., before reaching to
load equipment.
Rating of capacitor to be required for power factor correction can be calculated by the following
vector equation.
(6.2)
Where, Qc: Capacitor rating in kvar
A vector diagram of power factor control is shown in Figure 6.5 overleaf.
6.2.2.2 Capacitor Panel
Capacitor panels consist of some equipment such as condensers for power factor correction, series
reactors meters, relays, etc.
6-9
Where, S1 : Apparent power (kVA) = P – jQ1 (Before correction)

S2 : Apparent power (kVA) = P – jQ2 (After correction)
P : Active power (kW)
Q1 : Lagging reactive power (kvar) (Before correction)
Q2 : Lagging reactive power (kvar) (After correction)
Qc : Capacity of condenser (Advancing reactive power) (kVA)
cosφ1 : Power factor before correction
cosφ2 : Power factor after correction
Figure 6.5 Vector diagram of power factor control
6.2.2.2.1 Condenser (Capacitor)
Induction motors, which are inductive loads, generate lagged-phase reactive power.
Phase-advanced condensers (capacitor) have the function of compensating the lagged-phase
reactive power to improve power factor.
The effects gained from the condensers vary according to the points to be installed. For
example, it is effective to install a condenser on the secondary side of a transformer if reduction in
load and loss of the transformer is targeted.
With regard to O&M, the capacitor’s reactive power acts during light load (when power equipment
has stopped), and when the current leads the voltage in the circuit so that leading power factor
occurs, and the terminal voltage of the load increases causing adverse effects on the equipment.
To prevent this phenomenon, the capacitor may need to be isolated, or an automatic power factor
regulator may need to be installed.
Normally, a capacitor unit comprises of individual capacitor elements arranged in parallel/ series
connected groups within a steel enclosure. An internal discharge device is a resistor that reduces the
unit residual voltage to 50V or less in 5 minutes. Capacitor units are available in a variety of voltage
ratings from 240 V – 66,000 V and sizes (2.5 kvar – about 1,000 kvar).
6 - 10
The capacitors can be with external fuses or internal fuses, or both. An internal fuse is a small fuse
wire connected to each capacitor element, encapsulated in a wrapper. When a fault occurs in a
particular element, the particular fuse melts, disconnecting the affected element only, and
permitting the other elements to function without interruption. An external fuse unit typically protects
each capacitor unit in a bank. In an oil-impregnated capacitor, the internal pressure may increase
resulting in expansion due to excessive current because of the failure of internal elements. This leads
to leakage of oil from the capacitor unit and failure of the capacitor. Care should be taken to select
capacitors with sufficient cooling volume.
When a capacitor circuit is switched on, there is an inrush current, which is likely to damage the
capacitor. A choke or series reactor is used to control the inrush current.
6.2.2.2.2 Series Reactor
The major functions of a series reactor are to protect the capacitor by means of the following:
• Limiting inrush current during switching

• Limiting resonance and protection of capacitor banks
• Harmonic filtration
• Lower loss and noise level
6.2.2.3 Power Factor Correction at Motor Panel
Power factor can be increased by installing low voltage capacitor in parallel with the motor. This
enables the current to be reduced. Moreover, distortion waveform can also be stabilized by
connecting a series reactor.
6.2.3 Operation of Electrical Equipment During Power Supply Interruption
Power interruption is classified into two types: a scheduled power interruption and an unscheduled
power interruption.
The former requires specific operational procedure before interrupting the power supply, which is
to “open” the switches from the load side (power distribution panel) to the power source (power
receiving panel) sequentially. To restart the power supply, “close” the switches from the power source
(power receiving panel) to the load side (power distribution panel) one by one.
Make sure that the personnel in charge of the interruption/ restart operation thoroughly knows the
configuration of the machinery, the operational characteristics, the operational procedures, the place
or position of switches installed, the electrical scheme diagram and the load circuit diagram to avoid
incorrect procedures.
During the work of starting, operating and stopping the load equipment, pay attention to meter
readings, vibration, heat, and sound of equipment. If some abnormal state is found, report to the
related person in charge immediately, investigate the causes and take appropriate measures.
6 - 11
In the latter case, investigate the cause of the power failure first. Power failures can be caused by
the following: some failure attributed to the power company (outside power suppliers) and some
local fault in the STP. To identify the causes, read indicated values or signs on the incoming supply
voltmeter, under-voltage relay, earth fault relay, over current relay, etc.
Judgement by incoming supply voltmeter or under-voltage relay
• If the receiving voltmeter indicates “0” and the under voltage relay is “tripped,” it implies that
power is interrupted on the power source side (attributed to power company). After confirming
that the receiving circuit breaker is “opened,” the contact person or authority prescribed by the
power company should be asked about the causes and the estimated recovery time. However,
the related substation should try to restore power at the earliest.

• If the reading of the receiving voltmeter is within a specified range, the under voltage relay is
“untripped” and the earth fault relay or the over current relay is “tripped,” that implies some
failure (overload, short, earth fault, etc., in equipment or lines) has occurred in the STP and the
circuit breaker for receiving power is “opened.” By studying the protective relay, circuit breakers,
etc., which were tripped or opened, identify the line with fault and isolate the broken down point
immediately before recovering from the failure.
6.2.4 Gas Engines
Generally, digester gas is used as fuel in boilers for heating sludge digestion tanks; surplus gas is
incinerated in biogas combustion units or flared and discharged to the atmosphere. An example of
flow of power generated from digester gas is shown in Figure 6.6.
Figure 6.6 Example of flow of power generated from digester gas
A sewage gas generator uses the sewage gas as fuel to a gas engine and generates electricity, which
is supplied to equipment within a STP. The digester gas engine consumes gas as fuel and employs
spark-ignition method, which is the same as the one used in petrol car engines.
The O&M issues to be noted are mentioned overleaf;
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• Typical concentration of NOx in exhausted gas from digestion gas engines is about 2,000 ppm.
NOx should be reduced to prevent air pollution

• Replace the ignition plugs in the spark-ignition system periodically
• Periodic opening up, cleaning and inspection of a digestion gas engine is extremely important
because siloxane compound gets deposited in the combustion chamber of such an engine, which
causes faults in engine parts
6.2.5 Dual Fuel Engine
Dual-fuel (gas-diesel) engines are compression-ignition, not spark-ignition engines. To ignite, they
simultaneously burn gas and a small amount of diesel fuel as pilot fuel. Their controls also allow
automatic switchover to 100 % diesel fuel operation without changing load if the digestion gas supply
is inadequate or is interrupted. This capability is a beneficial feature for standby units because they
can start and operate even during power failures.
Dual-fuel engines typically use 1 to 5 % diesel fuel oil, but many can, if necessary, operate on
1 to 100 % diesel fuel. Such fuel flexibility is an excellent advantage, especially if the digester gas
supply is disrupted. This option includes storage and handling equipment for diesel fuel, along with
gas compressors to supply digester gas to these engines. The same O&M checks should be made
for the diesel engine and the gas engine. Please refer to 6.3.2 and 6.2.4.
6.3 STANDBY POWER SUPPLY SYSTEM (GENERATOR)
Standby or emergency power can be supplied through AC(alternating current) generator and diesel
engine. Most generators of STPs are installed for the purpose of standby power supply.
Therefore, they should be highly reliable because the STPs have to keep functioning without
hindrance even in the event of unexpected power cut from the power company.
6.3.1 AC Generator
A generator is a machinery that converts mechanical energy to electrical energy by electromagnetic

action to generate electrical power.
Synchronous generator, the principle of which is reverse as that of an electric motor, is an

AC generator, which generates electric power synchronizing to rotating rate of magnetic field
passing through armature windings.
Frequency of the synchronous generator is determined according to the rate of rotation, and
accordingly, the frequency decreases as the rate of rotation becomes lower than the
synchronous rate.
Therefore, the rate of the engine for the synchronous generator should be regulated to maintain
the level of synchronous rate.The O&M issues to be taken care of are mentioned overleaf:
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• Winding
• Oil or dust on windings or air vent sleeves obstructs air ventilation and leads to overheating of
the generator and deterioration of insulators, which may cause short circuit and ground fault.
The dust should be blown-off by a compressed air and the oil and grease should be removed
with cloth, cleansing oil, etc.
• In the case of severe accumulation of oil and dust, it is recommended to have the winding
cleaned and varnished with insulation paint after drying thoroughly, by a professional
cleaning company.
• Insulation coating over terminals should be checked for overheat or discolouration

due to cracks or slacks.
• Bearing
• Pay full attention to any abnormal noise from bearings during running to detect any defect at early
stage. It is the simplest way to check bearing conditions.
• Grease should be supplied through the openings periodically while the generator is running.
If a drain valve is provided to the grease chamber, always open the valve during filling grease to
purge out old grease.
• Brush (Static excitation system)
• Worn brush reduces brush pressure and causes sparks that may make the surface of a slip
ring rough. To prevent it, always check for abrasion, unsymmetrical wear or damage to brush,
and pressure of the brush holder. The brush-lifting device should be inspected to ensure
that it works properly.
• Brushes should be replaced with new ones when the wear level reaches the designated value.
The newly installed brushes should preferably be of the same material and shape as the
currently used ones.
• Exciter (brushless)
• Exciters hate moisture and dust. Dust should be blown-off by low-pressure compressor and
wiped with dry cloth.
• Check bolts and nuts on terminal area and terminal block for looseness, wires for discolouration
and conditions of earthing and installation.
6.3.2 Diesel Engine
Diesel engines are generally used as drives for back-up power generators.
The diesel engine works by the action of high-speed diesel combustion, which pushes out pistons
by the expansion based on self-ignition. The compressed air is hot enough to self-ignite when diesel
fuel is injected. Piston action caused by the energy is converted in the crank-shaft to rotating energy,
which drives the generator. High-speed diesel is typically used as fuel.
6 - 14
The O&M issues to be handled are as follows:
• For details of maintenance and inspections, follow the manufacturer’s manual
• Regularly check the fault alarm to ensure it works properly
• During inspection and maintenance, take care not to allow dust contamination especially into fuel
or lubrication system
• Check wiring for loose connection and check piping for leakage
• Do not place anything around an inlet port that obstructs suction
• Pay attention to abnormal noise and overheat
• Where it is necessary to store diesel for such engines, mandatory precautions regarding
storage-area fire protection, clearances, etc., should be followed. Appropriate clearance from the
jurisdictional authorities on pollution control and inflammable fuel storage should be obtained.
6.3.3 UPS
UPS stands for Uninterruptible Power Supply and is a power supply device, which works when the
usual power source is interrupted. UPS is used to keep critical systems like monitoring, SCADA,
communication and alarm systems running even when power is not available form main
source. A typical UPS circuit is shown in Figure 6.7.
Figure 6.7 UPS circuit
In the normal condition, commercial AC (alternating current) power is sourced and converted to
DC (direct current), which is then supplied to an inverter, and charges a battery.
6 - 15
When the commercial power source is interrupted, power charged in the battery is converted to AC
and supplied to the load.
The UPS has a rectifier to convert AC supply to DC for charging the battery, a DC to AC inverter to
convert the battery output to AC voltage, and a battery to act as a source of power during normal
power interruption. Other components like protection, fuses, indication, surge controlling circuit etc.,
are also built into the unit.
The following points should be checked as maintenance tasks:
• Check for abnormal noise, smell and heat in UPS

• Check for looseness in each connection
• Check appropriate time for battery replacement
• Check for clogged ventilation opening
• Ensure spare fuses are kept in stock and are easily accessible nearby.
6.4 PRIME MOVERS
6.4.1 Induction Motor
Three-phase induction motor is widely used as a general-purpose motor due to high reliability and
low price among driving forces for general industrial machinery. Most prime movers used for pumps
or blowers in STPs are three-phase induction motors.
A three-phase induction motor rotates the rotor by a rotating electromagnetic field, which is generated
in the stator core by AC current flowing in the stator winding.
(6.3)
Where, f : Frequency (Hz)

p : Number of magnetic poles
s : Slip
Rotating speed of the revolving magnetic field is referred to as “synchronous speed” and expressed
as Ns (rpm). The speed of the rotor itself is slightly lower which is expressed as N (rpm). The ratio of
Ns to the differential speed (Ns/N) is referred to as “slip”.
6.4.2 Starters
An extremely large current of about five to eight times the rated current flows when a motor is started.
The power factor is at an extremely low value of about 0.2 at the start. The duration of the starting
current is short, but the motor winding coil is subjected to thermal stress load as Joule heat. Voltage
fluctuation occurs in the power system and its effect becomes more pronounced.
6 - 16
The starting method of three-phase induction motor includes a method of restricting current at start
as mentioned above, and other methods described below.
A. Direct-on-line Starter
Power supply voltage is applied as-is, and a starting current which is several times the rated
current flows. This starter is used in motors requiring comparatively small starting currents.
B. Star Delta Starter
1/√3 of power supply voltage is applied on the Y (star) connection winding at start, while Δ (delta)
connection is used during operation. Compared to the full voltage starter, the starting current is
one third and the starting torque is also one third.
C. Reactor Starter
The voltage to be applied to the motor at start is reduced by the reactor and full voltage is applied
after the motor picks up speed, and is operated. The starting current can be restricted to a smaller
value compared to the Y-Δ starting method.
The circuit diagram of some of the starting methods are shown in Figure 6.8.
Figure 6.8 Starters

Another starting method is to use a starting compensator.
6 - 17
6.4.3 Characteristics of Induction Motor
Theoretical analysis should be carried out to study torque characteristics and overheating of
three-phase induction motor due to fluctuation in frequency and variation in voltage of the motor.
A. When power supply voltage is greater than the rated voltage
According to the equation for induced electromotive force, the frequency is constant, therefore
the maximum magnetic flux Φm increases and the over-excitation phenomenon occurs. Heat is
generated because of this excitation current. In a submersible pump, when a thermal protector is
built-in in the internal coil for protection, it may activate.
B. When power supply voltage is smaller than the rated voltage
According to the torque equation, when the frequency is constant, the power supply voltage V
reduces, so the torque reduces.
C. When the power supply voltage is unbalanced
When the power supply voltage is unbalanced, reverse phase current flows and the temperature
increases because of load loss in the coil resistance.
D. When the frequency f is higher than the rated frequency
According to the torque equation, when power supply voltage is constant, the torque reduces.
E. When the frequency f is lower than the rated frequency
When the power supply voltage is constant, the maximum magnetic flux φm increases, and heat
is generated because of the excitation current. According to the torque equation, when the power
supply voltage is constant, the torque increases.
6 - 18
6.4.4 Performance Assessment of Motors
6.4.4.1 Efficiency of Motors
The efficiency of a motor is determined by intrinsic losses that can be reduced only by changes in
motor design and operating condition. Losses can vary from approximately 2 to 20 %.
Table 6.1 shows the types of losses and their typical shares for an induction motor.
Table 6.1 Type of losses and shares for induction motors
The efficiency of a motor can be defined as “the ratio of a motor’s useful power output to its total
power output”. Factors that influence motor efficiency include:
• Age - New motors are more efficient
• Capacity - As with most equipment, motor efficiency increases with the rated capacity
• Speed - Higher speed motors are usually more efficient
• Type - For example, squirrel cage motors are normally more efficient than slip-ring motors
• Temperature - Totally-enclosed fan-cooled (TEFC) motors are more efficient than screen
protected drip-proof (SPDP) motors
• Rewinding of motors can result in reduced efficiency
• Load, as described below
There is a clear link between the motor’s efficiency and the load. Manufacturers design motors to
operate at a 50–100% load and to be most efficient at a 75% load. But, once the load drops below
50% the efficiency decreases rapidly as shown in Figure 6.9 overleaf. Operating motors below 50%
of rated loads has a similar, but less significant, impact on the power factor. High motor efficiencies
and power factor close to 1 are desirable for efficient operation and for reducing costs down of the
entire plant and not just the motor.
6.4.4.2 Motor Load
Because the efficiency of a motor is difficult to assess under normal operating conditions, the motor
load can be measured as an indicator of the motor’s efficiency. As loading increases, the power factor
and the motor efficiency increase to an optimum value at around full load. It is necessary to see the
percentage loading of the motor. If the motor runs at more than 70% load, then the power factor and
efficiency will be good.
6 - 19
Figure 6.9 Motor part load efficiency
6.4.4.3 Energy Efficiency Opportunities
Apart from operational point of view, the motors should be seen from energy efficiency opportunities
also. The following points may be considered:
A. Replace standard motors with energy efficient motors

B. Reduce under-loading
C. Avoid over-sized motors
D. Improve power quality
E. Do not go for multiple time rewinding
F. Improve maintenance practices
6.4.5 Condition Monitoring Techniques
6.4.5.1 Vibration Monitoring
The vibration in rotating machinery is caused by many reasons like unbalance, misalignment, loose
foundation, mechanical looseness, bearing damage etc.
Vibration monitoring is the most common, versatile and powerful condition monitoring technique
adopted in rotating machinery to identify problem areas. The severity of the vibration is
specified by IS 2372, which is measured with reference to class of machine.
The criteria for class of machine are given in Table 6.2 overleaf. For the above class of machine,
the vibration severity can be judged by the guidelines shown in Table 6.3 overleaf.
6 - 20
Table 6.2 Criteria for class of machine
Table 6.3 Vibration severity chart for machine vibration limits
The guidelines for vibration frequencies and likely causes are mentioned in Table 6.4 overleaf.
6 - 21
Table 6.4 Vibration frequencies and likely causes
6.4.5.2 Vibration Analysis
If the measured vibration level is more than the acceptable level, then it calls for vibration analysis,
which is a captured time waveform plotted as amplitude versus time, or data can be transformed
using a Fast Fourier Transform (FFT) and expressed as amplitude versus frequency. Any random
vibration signal can be represented by a series (a Fourier series) of individual sine and cosine
functions that can be summed to yield an overall vibration level. The amplitude of this vibration
signal defines the severity of the problem. Plotting the amplitude versus the frequency (the Fourier
spectrum) allows for identification of discrete frequencies contributing most to the overall
vibration signal, commonly referred to as a “signature analysis” or a “frequency spectrum”, Machine
looseness, misalignment, imbalance, and soft foot conditions are all fairly easily identified in the
frequency spectrum generated by an analyser. The vibration monitoring and analysis should be done
periodically, typically once in 6 months for all rotating equipment.
6 - 22
6.4.5.3 Thermographic Analysis
Commonly identified with electrical equipment monitoring, thermography is also a useful tool for
monitoring plant machinery.
Thermography measures infrared radiation energy emissions (surface temperatures) to detect

anomalies. Infrared cameras have resolution to within 0.1 °C and digitally store captured images.
Both the absolute and relative temperatures can be obtained on virtually all types of electrical
equipment, including switchgear, connections, distribution lines, transformers motors, generators
and bus work.
This technique is very popular because of the following reasons:
• It is a non-contact type technique
• Fast, reliable and accurate output
• A large surface area can be scanned quickly
• It can be easily scanned from a distance up to 50 m.
• Presented in visual and digital form
• Software back-up for image processing and analysis
• Requires very little skill for monitoring
This technique can be used very well for seeing the loose contact, corrosive contact of all types of
electrical joints, body temperature of motor and transformers, panels, etc.
The criteria shown in Table 6.5 may be used to know the severity of the problem.
Table 6.5 Criteria for differential temperature of electrical equipment
The typical thermographic measurements are illustrated in Figure 6.10 overleaf.
6 - 23
Hot-spot in a Transformer Hot-spots in a 11kV cable Hot-spot in LT cable joints

Bushing terminal
Overheating of a Bearing Loose Contact of a MCC Choked fins of a

Panel Transformer Radiator
Figure 6.10 Thermographic measurement
6.4.6 Speed Control Equipment
The following five types of ASDs (Adjustable Speed Device) are available.
• VFD: Electronic devices to control the speed of the motor by controlling the frequency of the
voltage at the motor.
• Direct current ASDs: Electronic devices to control direct-current motors by changing the voltage
applied to the motor.
• Eddy-current drives: Electrical devices that use an electro-magnetic coil on one side of coupling
to induce a magnetic field across a gap, creating an adjustable coupling.
• Hydraulic Drives: Devices that operate much like an automotive hydraulic transmission.
• Mechanical speed-control products including gearing, mechanical transmissions, and belt drivers
with variable-pitch pulleys can be used.
6.4.6.1 Variable Frequency Drive (VFD)
VFD varies the revolving speed of an induction motor freely by changing the power supply
frequency and the power supply voltage. A power transistor is used for the main circuit and IC, and a
microcomputer is used for the control circuit of VFD.
6 - 24
Further advanced controlling technology has been applied due to improved semiconductor devices
in recent years.
Moreover, generally, VFD is also called inverter control equipment or variable voltage variable
frequency (VVVF) equipment. The fundamental configuration is shown in Figure 6.11.
Figure 6.11 Variable Frequency Drive
After changing an alternating power source into direct current in a converter part and
making it smooth, transform the direct current inversely to variable frequency alternating current
at an inverter part
6.4.6.2 Advantages and Disadvantages of VFD
Advantages:
• Variable speed continuous operation over a wide range is possible

• Energy-saving possibility exists
• Brush, slip rings and so on, used in induction motor are not required
• Soft start and soft stop are enabled, extending the motor life
• Settings for acceleration timing and deceleration timing can be adjusted
• Starting current can be reduced
Disadvantages:
• Harmonic protection measures are necessary since high frequency current is generated
• Generation of leakage current and noise due to high frequencies need to be restricted
• Noise prevention for other equipment (especially measuring instruments) is necessary
Affinity Laws for Pumps and Hydraulic Machinery
One of the pump characteristics is that its load torque is proportional to the square of its revolving
speed, and this torque is called square reduction torque load.
6 - 25
• Relationship between speed of revolution N (rpm) and flow rate Q (m3/sec.)

Flow rate is proportional to the speed of revolution. QαN
• Relationship between speed of revolution N (rpm) and head H (m)

Head is proportional to the square of speed of revolution. HαN2
• Relationship between speed of revolution N (rpm) and power P (kW)

Power is proportional to the cube of speed of revolution. PαN3
• Relationship between speed of revolution N (rpm) and torque T (N-m)

Torque is proportional to the square of speed of revolution. TαN2
6.4.7 Motor Protection Equipment
Protection equipment for three-phase induction motors includes the following:
• Circuit breaker
It has overload and short circuit protection functions.
The former is a thermal function and has on-delay characteristics, while the latter is an
electromagnetic function and has instantaneous characteristics.
• Thermal relay
Changes bimetal with Joule heat of overload current, opens or closes the contact, and performs
on-delay operation.
• Comprehensive motor protection relay
This unit measures the current from all the three phases and checks for single-phase,
unbalance and overload. The measurement and comparison of these three factors
provide protections against short circuit, single-phase, earth fault, phase sequence and thermal
protection to the motors.
Temperature sensing thermistors are also embedded in the stator winding of HT motors
during manufacture and connected to relays to monitor winding temperature and raise alarm
when needed
• Dry-run protection
In addition, dry-run protection is also provided by water level sensors in the sump, which
sense any low level of water and prevent dry running, thereby protecting the pump and motor.
6.5 INSTRUMENTATION FACILITIES
6.5.1 Flow Measuring Equipment
Please refer to Chapter 3 for “flow measuring equipment.”
6 - 26
6.5.2 Level Measuring Equipment
6.5.2.1 Float
A float device measures a liquid level from above. Floats, one of the oldest and simplest methods
of level measurement, are used extensively in wet-wells or sludge sumps that require a discrete
high or low level indication. They are also used for local indication of level in tanks and open
channels as in Figure 6.12 and Figure 6.13.
Source: WEF,2008
Figure 6.12 Counter weighted float-level indicator
Source: WEF,2008
Figure 6.13 Float switches
A float level meter shown in Figure 6.12 senses water level through a slide rheostat as
resistance and converts the changed resistance into current. It transmits analog output signal (DC
4 mA to 20 mA) proportional to the water level and sends the signal representing the water level
continuously to the monitoring room.
The O&M issues to be cared for are as follows:
• Clean inside the stilling well regularly and keep it free from floating matter or scum to
prevent malfunctions
6 - 27
• Check moving parts such as a counter weight, pulley and wires for corrosion or damage
The level switch shown in Figure 6.13 is used to control the pump and to issue alarms according
to water level. The signals from the level switch are “on/off” digital signals, which compromise a
sequence circuit. Float switches should be located away from the tank walls to prevent the floats
from banging against the concrete wall and internal contacts from failures.
6.5.2.2 Ultrasonic
The ultrasonic level measuring device is installed above the liquid surface and measures the level
by generating a pulse of ultrasonic waves that bounce off the liquid surface below. The instrument
detects the echo, calculates the echo’s travel time and converts it to a level measurement as shown
in Figure 6.14.
Source: WEF,2008
Figure 6.14 Acoustic level-sensor installation
Specifically, the relation between distance from sonic transmitter/ receiver to the liquid surface and
the reaching time is expressed in the following formula:
Where, H : Distance from transmitter/ receiver to liquid surface (m)

c : Sonic velocity in air= 331.5 + 0.61 × temperature in Celsius (m/s)
t : Time from transmission to receiving (sec)
O&M issues to be taken care of are as follows:
• Ultrasonic level meters require little daily maintenance because they have no moving parts
and work without contacting the measuring objects. However, the junction boxes have to be
regularly checked for any water ingress
• Keep clear the area around transmitter / receiver
• Keep liquid surface without scum, foam, wave, etc.
6 - 28
6.5.2.3 Head-Pressure
The head pressure level measuring devices, bubbler tubes and diaphragm bulbs measure the
head pressure at the liquid level and are often used in open-channels or non-pressurized tank
applications.
6.5.2.3.1 Bubbler Tube System
The bubbler tube system uses a small, regulated airflow that constantly bubbles into the liquid.
Because the airflow is small, the system produces a backpressure equal to the static head of the
liquid. A conventional pressure gauge or transmitter measures this back pressure as the height
of an equivalent water column. A schematic of bubbler tube system is shown in Figure 6.15.
Source: WEF,2008
Figure 6.15 Schematic of bubbler-level system
Corrections are required when the liquid’s specific gravity differs significantly from water. Because
air is constantly bubbling out of the bubbler tube, the system is typically self-purging. Valves may be
arranged to isolate the pressure-measuring device while providing high purge flow through the tube
for preventive maintenance blow-down if fouling occurs.
Stilling wells are often used to protect the bubbler tube from turbulence and damage. To protect
pneumatic instruments and regulators, operators should clean the air supply of excessive
moisture and oils.
When bubbles are discharged into the liquid from the front end of pipe, the pressure within the
pipe becomes equal to the static pressure of liquid at the front end of the pipe. This pressure is
proportional to the liquid height h.
6 - 29
The calculation is expressed as given below:
Where, h : Water level from tube end (m)

P : Internal pressure of tube (Pa)
γ : Specific gravity of liquid (kg/m3)
Precautions for O&M are as given below.
The bubble type liquid level gauge does not have moving parts or mechanisms, so it has
comparatively high accuracy. Moreover, it is suited to level gauges for corrosive liquids. However,
daily maintenance of air sources such as compressor, purging set and air piping is very important.
6.5.2.3.2 Diaphragm Bulb System
The diaphragm bulb system operates on the principle that air sealed between the dry side of the
diaphragm (in the capillary tube) and the receiver compresses or expands with the movement
of the diaphragm.
A change in the static head of the liquid being measured moves the diaphragm, so the pressure
of the trapped air is the same as the head pressure. Temperature changes because of
sunlight or heat build-up, particularly along the capillary tube, can cause measurement
errors as a result of expansion of the trapped air. To reduce the effect of temperature, the
capillary can be filled with a fluid unaffected by operating temperature; however, this often affects
the measurement response time.
The differential pressure from the diaphragm is detected by a piezoelectric semiconductor element.
The output signal (4 mA – 20 mA DC) generated by the converter is changed to analog data in the
central monitor and transmitted.
Where, H : Distance from transmitter/ receiver to liquid surface (m)

ΔP : Differential pressure (Pa)
ρ : Density (kg/m3)
The following precautions should be taken related to the use of differential pressure type
level gauge:
• The installed position of differential pressure transmitter should be lower than the minimum
liquid level
• When the density of the liquid changes, correction is necessary (Span adjustment on the
converter side is required)
• If the liquid has pulsing motion, the output of the differential pressure transmitter may become
unstable
6 - 30
6.5.3 pH and ORP Measuring Equipment
6.5.3.1 pH
pH is a measure of the acidity of a process liquid. Continuous measurements of pH of incoming

sewage are frequently made, particularly in plants where drastic changes in pH (as a result of
industrial discharges) cause treatment problems.
A glass electrode, which is sensitive to hydrogen ion activity, measures the pH of an aqueous
solution. The electrode produces a voltage related to hydrogen ion activity and to pH. The pH is
determined by measuring the voltage against a reference electrode. While it is generally
assumed that no other ions seriously affect the pH electrode in an aqueous system, sodium ions
can have an effect. Temperature corrections are also necessary, but are typically done automatically
by the meter. A typical pH sensor is shown in Figure 6.16.
Source: WEF,2008
Figure 6.16 Typical pH sensor
Precautions for O&M are as given below.
• Dirt on the electrode surface should be periodically removed and the surface cleaned
• Since the electrodes of the pH meter are made of glass, care is necessary to ensure that
they do not break
• Due to long period use of glass electrodes, dirt sticks on them gradually, the zero point changes,
and the electromotive force by pH reduces and it stops responding to changes in pH, making
replacement necessary
• Standard liquid should be used in the pH meter and it should be calibrated. Calibration
should include zero adjustment (standard liquid with pH7) and span adjustment (standard
liquid of pH4 or pH9)
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6.5.3.2 ORP(Oxidation-Reduction Potential)
Oxidation-reduction potential is a measure of easily oxidisable or reducible substances in

sewage. An operator can control the process better by knowing if there is a large quantity of reducing
substances (e.g., sulphide and sulphite) that may have an immediate, high oxygen demand and may
result in an inadequate supply of oxygen for the microorganisms in the secondary process. Although
not specific, the ORP measurement is instantaneous (an electrode is used) and can be used to help
maintain dissolved oxygen in the aeration tank. Another application is to evaluate the progress of
digestion and process stability in anaerobic digesters.
O&M issues to be cared for are as follows:
• Regular cleansing of electrode surface
• Precautions against breaking an ORP electrode, which is made of glass and is fragile
• Replacement of the electrode if it is insensitive to changes of potential difference, because of

stains accumulated over a long time usage
6.5.3.3 DO (Dissolved Oxygen)
A dissolved oxygen meter is an electronic device that converts signals from a probe placed in the
water into units of DO in mg/L. Most meters and probes also measure temperature. The probe is
filled with a salt solution and has a selectively permeable membrane that allows DO to pass from the
stream water into the salt solution. The DO that has diffused into the salt solution changes its electric
potential. This change is sent by electric cable to the meter, which converts the signal to mg/L on a
scale that anyone can read.
If DO is a critical analytical parameter, it is recommended to calibrate at 100 % saturated air, or use

a known dissolved oxygen concentration (determined by the iodometric method) for the upper limit,
and use a zero DO solution (even if it is not explicitly stated in a particular manufacturer’s manual) for
the lower limit. If DO meter does not allow for a second calibration point, the zero DO solution can be
used as a check standard when DO meter is set to the measurement mode. The DO meter should
be able to read less than 0.5 mg/L. If DO meter does not read less than 0.5 mg/L, then there may be
a problem with the DO membrane.
If it is determined that the DO membrane needs to be replaced, consult the manufacturer’s manual
on conditioning the new membrane before use. It is also possible that other maintenance will need to
be performed on the DO meter or the zero DO solution may need to be replaced. Other factors that
affect the accuracy of DO measurements include–improper calibration, not verifying calibration after
use and not correcting for ambient barometric pressure/altitude and instrument drift. A typical hand
held DO meter with probe for field use is shown in Figure 6.17 overleaf.
O&M issues to be cared for are as follows:
• Regular cleaning of diaphragms

• Zero calibration and span calibration
6 - 32
Source: M/S YSI.

Figure 6.17 Hand held DO meter with probe for field use
• Regular replacement of internal electrode solution

• Regular cleaning of an electrode; and replacement if broken.
6.5.3.4 Temperature
Even though most of the major sewage treatment processes are not temperature-controlled, many
temperature measurements are required. Obvious applications for temperature measurement are
anaerobic digesters, chlorine evaporators, incinerators, and equipment protection. Less obvious
are temperature controls for analyzers and flow meters. Temperature measurement devices include
liquid thermometers, bimetal thermometers, pressure on liquid or gas expansion bulbs, thermistors,
resistance temperature detectors (RTDs), infrared detectors, and crystal window tapes. The RTD is
typically used on lower, ambient-range temperatures, while thermocouples provide better reliability in
higher ranges. In addition, gas- and liquid-filled temperature sensors and thermistors are frequently
used for equipment-protection and cooling systems.
For continued accurate service, operators should periodically calibrate the instruments using a
standard temperature measurement device with high accuracy.
6.5.3.4.1 Thermocouple
The thermocouple operates on the principle that current flows in a circuit made of two different
metals when the two electrical junctions between the metals are at different temperatures. The various
combinations of metals used are tabulated in most engineering handbooks, and the selection of
metals is based on the maximum temperature to be measured. Thermocouples measure as high as
980°C, with an accuracy of 1% of the full scale.
6.5.3.4.2 Resistance Temperature
A resistance temperature detector has a temperature-sensitive element in which electrical resistance

increases repeatedly and predictably with increasing temperature. The sensing element is typically
made of small-diameter platinum, nickel or copper wire wound on a special bobbin or otherwise
supported in a virtually strain-free configuration. The detector is typically selected for high
accuracy and stability. A common application is the measurement of bearing and winding
temperatures in electrical machinery.
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6.5.3.5 MLSS (Mixed Liquor Suspended Solid)
All solids concentration meters use indirect methods (such as optical, ultrasonic and nuclear).
Indirect methods correlate the solids concentration with a measurable factor. The limitation of not
relating perfectly to the quantity of suspended matter does not seriously affect the analysers ability to
produce a repeatable signal of great value in process control.
When a light beam is directed on to liquid containing suspended particulates, the suspended
particulates scatter some of the light. The nephelometer helps observe and measure the amount of
light that the particulate matter scatters as shown in Figure 6.18.
Source: WEF,2008
Figure 6.18 Nephlometer
The amount of scattered light relates approximately to the amount of particulate matter, particle
size and surface optical properties. This is a photoelectric device that uses an incandescent light
source (lamp), which produces light in wavelengths from blue to red. The light is directed to a
liquid and if the liquid contains particles, some of the light strikes the particles and scatters. By
placing a photocell or light detector at an angle to the light beam rather than directly in front of it, the
detector receives only light scattered by the suspended particulate matter. Most nephelometers have
the photo detector placed at a 90-degree angle to the incandescent light source.
6.6 SCADA SYSTEM
SCADA is an acronym for Supervisory Control and Data Acquisition. This presents the data as
a viewable and controllable system on the screen of a computer. The data thus collected can be
stored and analysed for optimization of the process and for better real time process control. It assists
plant-operating personnel by monitoring and announcing abnormal conditions and failure of
equipment. It allows the operators to perform calculations based on the sensor inputs. Daily, weekly,
monthly reports can be prepared using the stored data. It also allows the operator to know the state
of a process by an alarm associated with it. A typical SCADA is shown in Figure 6.19 overleaf.
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Source: Kruger
Figure 6.19 Typical SCADA communication overview
6.6.1 Monitoring and Control Equipment
For maximum use and effectiveness, signals generated by various sensors and instruments are
transmitted from the sensor to a receiver installed at another location. Often, the sensor output is
transmitted to a control panel or computer system, which allows operators to inspect many process
variables simultaneously.
The three components of a signal-transmission system are the transmitter, receiver and
transmission medium (the connection between the transmitter and receiver). The transmitter
converts a mechanical or electrical signal from the sensor into a form that the transmission medium
can use. The transmission medium contains the signal and transfers it to the receiver. The receiver
subsequently converts it into a form that the receiving system can use.
6.6.1.1 Signal
6.6.1.1.1 Analog Input Signal
“Analog input signal” means continuous signal such as process data, which is transmitted from a
local transmitter to a central control unit (CCU).
For instance, process variables expressed in physical amount such as opening degree of a
sluice gate (0–100%), sewage flow rate (0– ***m3/hr), and water level in tanks (0–***m) are
converted into electrical signals and are transmitted to CCU. Standard electronic transmission
systems use 4 – 20 mA DC.
6 - 35
There are several transmission systems. One is to connect directly with the CCU I/O (Input/Output)
device via shielded cables. Another is the so-called link system with PLC, in which analog signal is
converted to digital signal and is transmitted via coaxial cables or optical fibres.
6.6.1.1.2 Analog Output Signal
“Analog output signal” means signals continuously transmitted from CCU to local control panels or
equipment to direct operational amount.
Electric operated valves and regulating valves for controlling pressure of pipe, and VFD for
controlling frequency of aerators or pumps, etc., are typical examples, which are controlled by
analog output signals. More specifically, there are electromagnetic valves and regulating valves used
to control pressure in the piping.
There are also aeration blowers or VFD (inverter) equipment used to control pump rpm.
One of the transmission systems for analog output signal connects directly to the I/O device of CCU
via shielded cables.
6.6.1.1.3 Digital Input Signal
“Digital input signal” refers to a contact output signal generated and transmitted from local
equipment. For example, answer-back signal to express equipment conditions, alarm signal for
abnormal conditions and “remote / local” switch signal of local control panels are examples of
digital input signal. Contact signals are electronically converted to an appropriate series of zeros
and ones. Link systems with PLC are widely used for transmitting the signal, with which analog
signal is converted to digital signal and is transmitted via coaxial cables or optical fibres.
6.6.1.1.4 Digital Output Signal
Digital output signal means contact output signal expressed “1 / 0” transmitted from CCU to an
auxiliary relay on the control center panel. For example, “on/off” signal for equipment is regarded as
digital output signal. Link systems with PLC are widely applied for transmitting the signal, with which
analog signal is converted to digital signal and is transmitted via coaxial cables or optical fibres.
6.6.1.2 HMI (Human Machine Interface)
The PLC is a blind device. It does not have any provision of displaying the plant status to the
operator, or to enter certain data like set points, or manual mode operation. An additional device is
needed for these provisions, to communicate with PLC, which will have a display to show the status
and also the means to enter set points. Such a unit is called Human Machine Interface (HMI).
There are two basic types of HMI:
• Industrial panel mounted type HMI as in Figure 6.20 overleaf.
• PC based system in which the computer acts as HMI as in Figure 6.21 overleaf.
6 - 36
Source: JICA, 2011

Figure 6.20 Industrial panel-mounted type HMI
Figure 6.21 PC based system in which the computer acts as HMI
6.6.1.3 PLC (Programmable Logic Controller)
A PLC is electronic equipment that senses inputs and takes the decision to change outputs
according to the set rules stored in the memory. It is primarily an electronic controller, housed in
industrial housing, which has logic programming function and can be an interface to
industrial devices.
6.6.2 Automatic Control
Automatic control systems can be categorized according to their control techniques as in

Figure 6.22
Figure 6.22 Automatic control system
6 - 37
Instrumentation facilities are established mainly based on feedback control in combination with feed
forward control in most STPs for controlling process variables such as temperature, water level,
pressure, flow rate, etc.
6.7 CABLES
The flow of power from transformer to switchgear and from there to starter and to motor and other
related equipment like capacitors are through power cables.
Table 6.6 gives information on cables for different voltages.
Table 6.6 Types of cables for different voltages
The size of the cable should be so selected that the total drop in voltage, when calculated as the
product of current and the resistance of the cable should not exceed 3%.
Values of the resistance of the cable are available from cable-manufacturers.
The following points should be considered when selecting the size of the cable:
• The current carrying capacity should be appropriate for the lowest voltage, the lowest power
factor and the worst condition of installation that is, duct-condition.
• The cable should also be suitable for carrying the short circuit current for the duration of the fault.
The duration of the fault should preferably be restricted to 0.1 sec. by proper relay setting.
• Appropriate rating factors should be applied when cables are laid in- group (parallel) and/or laid
below ground.
• Suitable trenches or racks should be provided for laying cables
The following O&M tasks should be implemented:
• Measure insulation resistance between cables and the earth
• Visually observe deterioration, corrosion and discolouration
6 - 38
6.8 ENERGY AUDIT
Among all the power consuming components, pumping installations consume a large amount
of energy in STPs. Need for conservation of energy, therefore cannot be over emphasized. All
possible steps need to be identified and adopted to conserve energy and reduce energy cost so that
sewerage charges can be kept as low as possible and gap between high cost of sewage treatment
and affordable charge to users can be reduced.
Some adverse scenarios in energy aspects are quite common in pumping installations as herein:
• Energy consumption is higher than optimum value due to reduction in efficiency of pumps.
• Operating point of the pump is away from best efficiency point (b.e.p.).
• Energy is wasted due to increase in head loss in pumping system, for instance, clogging of
strainer, encrustation in column pipes and encrustation in pumping main.
• Selection of uneconomical diameter of sluice valve, butterfly valve, reflux valve, column pipe, and
drop pipe, etc., in pumping installations.
• Energy wastage due to operation of electrical equipment at low voltage and/or low power factor.
Such inefficient operation and wastage of energy should be avoided to cut down energy cost. It
is therefore, necessary to identify all such shortcomings and causes, which can be achieved by
conducting methodical energy audit.
Strategies as given below should be adopted for the management of energy.
• Conduct thorough and in-depth energy audit covering analysis and evaluation of all equipment,
operations and system components, which have bearing on energy consumption, and identify the
scope for reduction in energy cost.
• Implement measures for conservation of energy. Energy audit as implied is auditing of billed
energy consumption and how the energy is consumed by various units, and sub-units in the
installation and whether there is any wastage due to poor efficiency, higher hydraulic or power
losses etc. and identification of actions for remedy and correction.
6.8.1 Frequency of Energy Audit
Frequency of energy audit recommended is as follows.
• Large installations: Every year

• Medium installations: Every two years
• Small installations: Every three years
6.8.2 Scope of Energy Audit
Scope of energy audit and suggested methodology includes the following, steps and processes:
6 - 39
A. Conducting in-depth energy audit by systematic process of accounting and reconciliation

between the following:
• Actual energy consumption, and
• Calculated energy consumption taking into account rated efficiency and power losses in all
energy utilising equipment and power transmission system, such as conductor, cable,
panels, etc.
B. Conducting performance tests of pumps and electrical equipment if the difference between
actual energy consumption and calculated energy consumption is significant and taking follow up
action on conclusions drawn from the tests.
C. Taking up discharge test at rated head if test in B. above is not being taken.
D. Identifying the equipment, operational aspects and characteristics of power supply causing
inefficient operation, wastage of energy, increase in hydraulic or power losses etc. and evaluating
the increase in energy cost or wastage of energy.
E. Identifying solutions and actions necessary to correct shortcomings and lacunae in D. above and
evaluating cost of the solutions.
F. Carrying out economic analysis of costs involved in D. and E. above and drawing conclusions on
whether rectification is economical or otherwise.
G. Checking whether operating point is near the best efficiency point and whether any improvement
is possible.
H. Verification of penalties if any, levied by power supply authorities, such as penalty for poor power
factor, penalty for exceeding contract demand, and so on.
I. Broad review of the following points for future guidance or long-term measure:
• C-value or f-value of transmission main
• Diameter of transmission main provided
• Specified duty point for pump and operating range
• Suitability of pump for the duty conditions and situation in general and specifically from
efficiency aspects
• Suitability of ratings and sizes of motor, cable, transformer and other electrical appliances
for the load
6.9 MANAGEMENT OF RECORDS
Records are the key to an effective maintenance programme. Records can remind the operator when
routine O&M is necessary. They help ensure that schedules are maintained and needed O&M are not
overlooked or forgotten.
6 - 40
6.9.1 Record of Operation and Maintenance
Records must be permanent, complete and accurate. Write entries clearly and neatly on data
sheets in ink. A pencil should never be used because notations can smudge or they can be
altered or erased.
Minimum record keeping that may be required for operations is listed below and shown in
Appendix C.6.1:
A. Operational record: Power receiving and transforming equipment

B. Monthly report: Electric power receiving
C. Ledger: Electrical equipment
6.9.2 Record of Operation and Maintenance and its Utilization
Records are utilized like the following:
Review of operating records can indicate the efficiency of the plant, performance of its treatment
units, past problems, and potential problems.
Records can be used to determine the financial health of the utility, provide the basic data on the
system’s property and prepare monthly and annual reports.
Generally, preventive maintenance can be described as maintenance of equipment or system before

faults occurs. Preventive maintenance should be only according to manufacturer’s manual.
It can be divided into two subgroups:
• Planned / Scheduled Maintenance (PM)
Scheduled activities to ensure that an item of equipment is operating correctly and thereby avoid
any unscheduled breakdown and downtime.
• Condition Based Maintenance (CBM)
Activities performed after one or more indicators show that the equipment is going to fail or that
equipment performance is deteriorating.
The vast majority of electrical maintenance should be predictive or preventive. This section
focuses exclusively on these activities. There are four cardinal rules to follow in any maintenance
programme:
• Keep it clean
Dirt build-up on moving parts will cause slow operation, arcing and subsequent burning.
Moreover, coils can short-circuit. Dirt will always impede airflow and result in elevated
operating temperatures.
6 - 41
• Keep it dry
Electrical equipment always operates best in a dry atmosphere, where corrosion is

eliminated. Moisture-related grounds and short circuits are also eliminated
• Keep it tight
Most electrical equipments operate at a high speed or is subjected to vibration.
• Keep it frictionless
Any piece of equipment or machinery is designed to operate with minimum friction. Dirt,
corrosion or excessive torque will often cause excessive friction.
Of the four cardinal rules, none is essentially electrical in nature. The failure of a bearing in a motor
can lead to an ultimate motor winding failure that is electrical, but the root cause of the failure could
have been mechanical.
The goal of any electrical preventive maintenance programme is to minimize electrical outages and
ensure continuity of operation.
6.10.1 Types of Planned Maintenance
Maintenance works can be classified as follows according to their inspection intervals. The results of
maintenance can be utilized for preventing possible faults or breakdowns of equipment in future.
• Routine maintenance
Routine maintenance consists of observation for signs of overheating, dirt, loose parts, noise and
any other signs of abnormalities. It will help grasping the state of electrical equipment.
• Periodic maintenance
Periodical maintenance includes inspections of electrical conditions such as electric current,

voltage, insulation resistance, ground resistance, etc.
• Detailed examination
Examinations should be pre-programmed according to manufacturer’s recommendation or

legislation. Recommended maintenance tasks for typical electrical equipment are
listed in Table 6.7 overleaf.
6.10.2 Inspection Tools
A wide, variety of instruments are used to maintain electrical systems. These instruments
measure current, voltage and resistance. They are used not only for troubleshooting, but also for
preventive maintenance as well.
These instruments may have either an analog readout, which uses a pointer and scale, or a digital
readout, which gives a numerical reading of the measured value.
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Table 6.7 Recommended maintenance on electrical equipment
* Details of the maintenance tasks of the marked equipment above are given in Appendix B.6.2.
(Legend)
6.10.2.1 Multimeter
A multimeter is used to measure voltage and low levels of current in a live system and continuity in a
switched-off system. There are several types available in the market. A digital multimeter and an analog
multimeter are shown in Figure 6.23. They are designed to be used on energized circuits and care
must be exercised when testing.
Source: HIOKI E.E. CORPORATION

Figure 6.23 Digital multimeter (left) and Analog multimeter (right)
6 - 43
By holding one lead on ground and the other on a power lead, a user can determine if power is
available, and also can tell if it is AC or DC, the intensity or voltage (1, 10, 220, 480, and so on) by
testing the different leads. A clamp-on multimeter can measure larger currents typical in a motor.
• Only qualified and authorized persons should work on electric circuits.
• Use a multimeter or other circuit tester to determine if the circuit is energized, or if voltage is off.
This should be done after the main switch is turned off to ensure that it is safe to work inside the
electrical panel. Always be aware of the possibility that even if the unit is off, the control circuit
may still be energized if the circuit originates at a different distribution panel.
• Check with a multimeter before and during the time the main switch is turned-off as a double
check. This procedure ensures that the multimeter is working and that the users have good
continuity to the tester.
• Use a circuit tester to measure voltage or current characteristics to a given piece of equipment for
checking whether the circuit is “alive” or not. Switches can fail and the only way to find out that a
circuit is dead is to test the circuit.
• In addition to checking for power, a multimeter can be used to test for open circuits, blown fuses,
single phasing of motors, grounds and many other uses.
6.10.2.2 Clamp-on Meter
The clamp-on meter measures the current or amps in the circuit as shown in Figure 6.24.
It is used by clamping the meter over only one of the power leads to the motor or other apparatus and
taking a direct reading.
Therefore, the measurement by the clamp-on meter is a safe method in a high-current circuit.
Each lead in a three-phase motor must be checked.

Figure 6.24 Clamp-on meter
6.10.2.3 Megger / Megohmmeter
A megger or megohmmeter is used for checking the insulation resistance of motors, generators,
feeders, bus bar systems, grounds, and branch circuit wiring. This device actually applies a DC test
voltage, which can be as high as 5,000 volts, depending on the megohmmeter selected.
6 - 44
Figure 6.25 shows a hand-held that applies 500 volts DC and is particularly useful for
testing low-tension motor insulation.
Battery-operated and instrument style meggers are also available in both analog and digital
models. If a low reading is obtained, disconnect motor leads from power or line leads.
A low reading in the megger for motor generally indicates that the motor winding insulation has
broken down. If this reading is low, the wiring to the motor is defective.
Figure 6.25 Hand-cranked megohmmeter
Motors and wiring should be subjected to megger test at least once a year or preferably, twice a year.
The readings taken should be recorded and plotted to determine the deterioration of insulation and
predict its breakdown.
6.10.2.4 Ground Resistance Testers (Earth Meggers)
When the electrical equipment is installed in housings, they may be charged against the ground.
Therefore, they should be connected with earth (referred to as “earth”) to reduce the potential
difference between the terminal and the earth to as low a value as possible (ideally 0 volt).
The purposes of the earth are as follows:
A. Prevent electric shock: Discharge any electricity charged in equipment housing due to electrical
insulation failure or a transformer breakdown to prevent shock; and
B. Prevent breakdown of loaded equipment: Connect a neutral line on the load side of transformer
with earth and prevent high voltage on the power source side from intruding into the load side in
case of transformer fails so as to protect the loaded equipment
Value of ground resistance is depends considerably on the soil to be earthed, and the smaller the
resistance, the better. Ground resistance testers are devices to measure the stated resistance when
the circuit is earthed. Testers with measurable range from 0 to 1,000 ohms are widely used.
A typical ground resistance tester is shown in Figure 6.26 (overleaf)
6 - 45

Figure 6.26 Ground resistance tester
6.10.3 General Precautions for Electrical Maintenance
The following should be ensured for safe electrical maintenance:
• Always refer to manufacturers manual for O&M and drawings for frequency of testing, lubrication,
replacement of any component and follow all these.
• Do not touch any energized parts directly
• Fully understand configurations and operational characteristics of related electrical facilities

and equipment
• When operating electrical equipment, follow the operational procedures, confirm the purposes of
the operation, and predict the result of the operation
• When overheat, abnormal noise, or vibration, etc, is detected during inspection, report the
condition to the person in charge of electrical work
• When overheat, abnormal noise, or vibration, etc, is detected during inspection, stop the
equipment and investigate the causes if necessary.
• Always keep the surrounding of electrical equipment tidy and clean. Never allow outsiders to
enter the electrical equipment site.
If the equipment in the electrical facility is old, frequent outages and high maintenance and repair
costs are likely to occur. If some of the equipment is beyond repair, breakdowns lead to long and
extensive power outages in the STP.
To prevent such occurrences, functional degradation of electric equipment and causes for
breakdown and stoppages should be tracked at an early stage and repaired. Causes of fault also
follow a certain trend. Training should be imparted on predicting faults beforehand, so that measures
and repairs can be implemented.
Spare parts and tools should be kept ready on site so that repairs can be carried out. Inventory of
spare parts and tools should be confirmed and the required number should be stored.
6 - 46
6.10.5 Planned Reconstruction
For reconstruction of electric facilities, plans should be formulated; therefore, scheduled O&M should
have been implemented.
Items to be studied for planned reconstruction are whether abnormalities exist from routine
inspection records, data, periodic inspections and repair records and a judgement of the condition
of equipment.
Analyse collected and accumulated data, and understand the long-term deterioration trend of
equipment.
6.12 SUMMARY
The primary function of electrical system in sewerage is to receive power from outside, transform
it and distribute it stably to each facility. The instrumentation system also plays an important role in
indicating operating conditions.
For realizing these functions properly, the electrical system requires periodic inspection and
maintenance for early detection of abnormal conditions. The instrumentation system should be
inspected and adjusted regularly so that it can provide correct readings at all times.
6 - 47
Part B: Operation and Maintenance CHAPTER 7: MONITORING OF WATER QUALITY
CHAPTER 7: MONITORING OF WATER QUALITY
7.1 INTRODUCTION
Sampling and analysis of sewage is done in the treatment units in STPs to find out whether the
organic matters are removed as designed. It is also done in locations of sewage discharge to make
sure that the discharge standards are satisfied.
7.2 NEED FOR SAMPLING AND ANALYSIS IN STP
Effective operation and control of a STP requires that the operator possess thorough knowledge of
the characteristics of the influent, effluent and internal process streams. To acquire such knowledge,
representative samples of various unit operations in a STP should be collected following standard
procedures and analysed for both the sewage and sludge.
7.3 SAMPLING
In general, the two categories of samples are to be collected for (a) physical and chemical tests and
(b) microbiological tests. In both cases, care should be taken to avoid entry of extraneous materials
such as silt, scum and floating matters into sampling bottles.
7.3.1 Overview
Understanding the principles and practices of sampling to obtain a representative sample is

important to get at a truly representative sample instead of random collection leading to misleading
results. Laboratory analyses will have little value if representative sampling is not done. Sampling
points must be located where homogeneity of the sewage with good mixing is available.
7.3.2 Grab Sample
Grab samples are collected when frequent changes in character and concentrations are likely to
occur and influence the treatment, undesirable constituents are suspected, the quality is not
expected to vary or when samples require on the spot analysis for parameters such as DO, pH and
residual chlorine. For example, the testing of the suspended solids (SS) in the clarifier overflow is an
independent sample and it needs to be correlated to the time of sampling because the SS can vary
between low flows, average flows and peak flows. Invariably the SS at peak flows of a few hours in
the early forenoon may be higher. If the timing is not given, this will give the wrong impression that the
entire performance over the 24 hours has got higher SS. Representative samples should be taken
with good judgement and should be analysed within 2 – 3 hours of sampling. A well-washed clean
PVC or plastic bucket connected to a sturdy long handle may be suitable for grab sampling.
7.3.3 Composite Sample
Since the sewage quality changes with time in a day, the best results would be obtained by
using some sort of continuous sampler-analyser.
7-1
The continuous analysis if practiced, will leave little time to the operators to pay attention for actual
operation of the STP. Hence, for tests, which cannot wait due to rapid chemical and biological change
of the sample, such as tests for dissolved oxygen and sulphide, a fair compromise may be reached
by taking samples throughout the day at hourly or two-hourly intervals.
When the samples are taken, the containers shall be preserved immediately in a suitable ice box
till they are taken to a laboratory and preserved in the refrigerator there till they are taken up for
analysis. This is required to avoid anaerobic decomposition which will alter the composition and
characteristics of especially the organic portions like BOD, etc. When all the samples have been
collected for a 24-hour period, the sample from a specific location should be combined or composite
together according to flow to form a single 24-hour composite sample. as under
• The rate of sewage flow must be known, and
• Each grab sample to be taken and in direct proportion to the volume of flow at that time.
Table 7.1 illustrates the hourly flow and sample volumes to be measured for a 12-hour sampling.
Table 7.1 Hourly flow pattern during composite sampling
Source: JICA, 2011
Large sewage solids should be excluded from a sample, particularly those greater than 6 mm
diameter. A composite sample according to the Table 7.1 would total 1,140 ml.
The factor (*) mentioned in Table 7.1 is a multiplying factor for flow. The factor is so adjusted or
decided so as to arrive at a convenient sample volume. This factor generally remains constant
for a particular STP. It also remains constant during composite sampling period so as to maintain
proportionality between flow and sample volumes.
During composite sampling and at the exact moment of testing, the collected samples must be
remixed so that they are of the same composition. Lack of mixing can cause changes in results
samples of solids that settle out rapidly, such as those in activated sludge or raw sewage. Samples
must therefore be mixed thoroughly and poured quickly before settling occurs. If this is not done, errors
of 25 to 50 % may easily occur.
7-2
For example, on the same mixed liquor sample, one person may find 3,000 mg/L SS while another
may determine that there are only 2,000 mg/L due to poor mixing. When such a composite sample is
tested, a reasonably accurate measurement of the quality of flow can be made.
7.3.4 Sampling Method and Precautions in Sampling
In all cases of sampling, procedures described in ‘Standard Methods for the Examination of Water
and Wastewater (APHA)’ or ‘Manual of Methods for the Examination of Water, Sewage and Industrial
Wastes (ICMR)’ or other standard manuals should be followed.
The sampling procedure is very important and is based on the purpose of sampling and tests to be
performed. In general, sewage samples shall not be aerated during collection. Some of the manually
operated sampling apparatuses are shown in Figure 7.1. Each has its preference, but the syphonic
bellow at A is the easiest to use anywhere.
Figure 7.1 Typical sampling apparatuses used in sampling of sewage in STPs
A-Syphonic tube with bellows; B- Electrically operated peristaltic pump, C- Hand operated rotary with
positive displacement, D- Hand operated rotary with circular movement
The use of the syphonic bellows tube involves the dipping of the free end of the tube into the liquid
surface and keeping the pump end below the liquid level outside the structure and pumping the
bellow, which starts a siphon action. Initially some portion of the sewage is to be discharged freely.
If the sample is meant for determining the dissolved oxygen, the free end after bellows shall be
extended by rubber tubing with a standard laboratory pinchcock and the free end of the tubing dipped
into the BOD bottle to effect a submerged discharge very slowly. A timing of 10 seconds to fill the
BOD bottle is considered as optimum. The sample shall be allowed to overflow for 5 seconds before
the tube is withdrawn and the bottle is corked with the ground glass cork. This is possible only in the
case of tanks with the liquid surface above ground level. If the liquid level is below ground level, a
long handle connected scoop can be easily used. In this case, the scoop shall have a minimum of
1,000 ml volume and the above procedure can be done. The electrically operated peristaltic pumps
(B) and other hand operated devices (C), (D) are fitted only for the final treated sewage samples.
In all cases, the discharge end shall be submerged in the sampling bottle and overflow of samples
shall be allowed for about 5 seconds.
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7.3.5 Sample Volumes, Quantity and Storage of Samples
One to two litres of grab sample would be enough to perform all the tests and repeat some
tests if required. For composite samples, a total quantity of 1 to 2 litres collected over a 24 hour
period is adequate. Fractional sample at intervals of 1 to 2 to 3 hours should be collected in suitable
containers, each sample being well mixed and a measured portion proportional to the flow transferred
by means of a pipette, measuring cylinder or flask and integrated to form a 1 to 2 litre sample. Hourly
records of flow normally available with the Plant Superintendent would facilitate taking representative
samples. All samples should be immediately transported to the laboratory for analysis. In case there
is any delay in transportation, the preservation time is to be as short as possible and in any case not
exceeding 24 hours and the ice shall not be found melted on receipt of the sample.
7.3.6 Selection of Sampling Location
Theoretically, there is no end to the number of sampling stations that can be used in a STP. But then,
it should be remembered that the best monitoring can be possible only when the barest minimum
and objectively oriented sampling locations and tests are carried out instead of accumulating all
and sundry data that will only confuse the situation. This is because the sewage passes through the
STP on a time-deferred scale and if samples are taken all at the same time from inlet to outfall, the
chances are that it is not representative of the true performance. A suggested set of sampling points
is shown below.
A. Raw sewage samples should be collected after screens or grit chambers.
B. Samples of sewage from primary clarifier or secondary clarifier should be taken from the trough
or pipe or before discharge weirs.
C. Inlet to top feed media units should be collected below the distribution arm and the sewage from
the outlet chamber or at the inlet to secondary sedimentation tank.
D. A point where there is good mixing should be selected for sampling of mixed liquor in aeration
tanks in the activated sludge process.
E. Inlet samples of septic tanks, Imhoff tanks, and other sole treatment units such as waste
stabilization ponds, oxidation ditches and aerated lagoons should be collected ahead of these
tanks in their inlet chambers or channels leading to these units. Outlet samples should be
collected outside the units in receiving weirs or channels or chambers.
F. Sampling within these tanks should be specified in terms of depth or distance or both.
G. Samples of raw sludge should be taken from sludge sumps or from the delivery side of the sludge
pumps through sampling cocks.
H. Return sludge sample in activated sludge plant is collected at the point of discharge
into aeration tank.
I. Samples from mixed primary and secondary sludge should be collected at the point of
delivery to the digester.
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J. Digested sludge samples may be drawn from the sampling points in the digester or from the
discharge end of the delivery pipe leading to drying beds or mechanical dewatering units.
K. Digester supernatant may be drawn from sampling cocks provided for this purpose or through
sampling ports on digester dome.
L. In case of SVI determination, samples may be collected from a suitable sampling location in
between the aeration tank and secondary clarifier.
The flow chart indicating the various treatment units and the sampling points may be exhibited
prominently in the laboratory. A list of tests to be carried out daily on the samples may
also be displayed as a wall chart.
7.4 RELEVANCE OF PARAMETERS
In general, the parameters can be classified as broadly into statutory need and plant control
need. The plant control needs are mainly to understand whether the STP is functioning as per the
design and to inform whether corrective measures are needed. Two separate records shall be
kept; one for public consumption in respect of statutory discharge standards and the other for
in-house plant control. These parameters are not for public consumption as they will be continually
changing and the public may not be able to understand its nuances. For a typical STP irrespective
of the treatment processes, such as ASP, SBR and MBBR the recommended tests are mentioned
in Table 7.2, Table 7.3 and Table 7.4 and any additional tests/parameters can be included as
indicated by the technology provider.
7.5 ANALYSIS PARAMETERS AND FREQUENCY (LIQUID AND SLUDGE)
7.5.1 Items and Frequency for ASP
For day to day plant control, various sundry data need not be accumulated. Recommended tests
to be carried out in typical STPs on a daily, weekly, and monthly to biannual basis are shown in
Table 7.2 overleaf, Table 7.3 overleaf, and Table 7.4 overleaf, shall be followed.
In respect of BOD test, a graph of BOD versus COD for the raw, primary treated, secondary treated
and outfall sewage should be prepared every week and the daily COD readings used to interpret
the BOD values. If treated sewage is to be used for agriculture then the safe limits for (a) Sodium
Adsorption Ratio (SAR) should not exceed 18 and (b) RSC should not exceed 1.25 meq/L.
The procedure for calculating SAR and RSC are shown in equation 7.1 and 7.2 respectively.
( 7.1 )
( 7.2 )
where all ionic concentrations are expressed as meq/litre
7-5
Table 7.2 Recommended Plant Control Tests on a Daily basis in a typical STP
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Table 7.3 Recommended Plant Control Tests on a Weekly basis in a typical STP
*Identify the following by microscopy.

Rotifers, Crustaceans, Protozoa, Ciliates, Nocardia, Ceronthirix, Nematodes
7-7
Table 7.4 Recommended Plant Control Tests on a Monthly to Biannual basis in a typical STP
Note: Ratioactive materials testing is to be done only by laboratories authorized for this purpose.
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7.5.2 Items and Frequency for WSP
In general parameters of testing for diurnal examinations arise only when the treatment process is
dependent on solar energy like in the case of ponds. In such cases, the tests will be as follows.
Care, safety and wisdom are paramount in taking samples from ponds especially diurnal samples as
chances of vermin and reptiles straying around in wet climates and high summer cannot be ruled out.
Proper clothing, safety wear, etc., and the presence of a qualified ambulance person with tool kit is
mandatory in the diurnal sampling.
A better way of managing this will be to leave a floating or other pump set erected in the daytime and
operate it by remote switch in the night and collect the sample from the outlet hose of the pump set
sufficiently far away at a well-lighted and safe and secure location. Table 7.5 mentioned the
recommended plant control tests on a monthly basis in a typical WSP.
Table 7.5 Recommended plant control tests on a monthly basis in a typical WSP
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7.6 SAMPLING AND MICROBIOLOGICAL TESTING OF RAW AND TREATED SEWAGE
7.6.1 Need for Microbiological Testing
Many water borne pathogenic organisms which can cause diseases as in Table 7.6 and even cause
epidemic, are transmitted through the water route when infected with sewage which is not fully
treated. This is because these organisms enter the water from the faeces of individuals suffering from
these diseases and remain as carriers of these organisms even after they are supposed to be fully
cured like the famous “Typhoid Mary” a nurse who was cured but her night soil continued to exhibit
the typhoid organisms.
Table 7.6 Diseases Attributable to Sewage Pollution of Drinking Water
It is both difficult and time consuming to check the treated sewage for each of these
organisms. A sterile laboratory is required, which is admittedly not easy in many parts of India
especially outside the metro cities. Extensive research has shown that if the coliform group of bacteria
is present, there is a probability that one or more pathogens may also be present. Therefore,
coliforms have been chosen to be the bacterial group routinely tested when there is a need for
assessing the bacteriological safety. Presence of any of the coliform group of bacteria (total coliforms)
indicates general contamination, while the presence of faecal coliforms indicates contamination
of human or animal origin. These can be differentiated from other coliforms by incubating on
selective media at 44.5°C.
7.6.2 Testing Method
7.6.2.1 Multiple Tube Fermentation Method
7.6.2.1.1 Total Coliform Test
The oldest test is the multiple tube fermentation test. In this test, three sequential steps are performed
as presumptive, confirmed and completed tests. A moderately selective Lactose broth medium
(Lactose Lauryl Tryptose Broth), containing a Durham tube is first used in the presumptive test
to encourage the recovery and growth of potentially stressed coliforms in the sample.
7 - 10
If harsher selective conditions are used, a deceptively low count may result. A tube containing both
growth and gas is recorded as a positive result. It is possible for non-coliforms (Clostridium or
Bacillus) to cause false positives in this medium, and therefore, all positive tubes are then
inoculated into a more selective medium (Brilliant Green Lactose Broth or EC Broth) to begin the
confirmed test. The confirmed test medium effectively eliminates all organisms except true coliforms or
faecal coliforms, depending on the medium and incubation conditions. If a positive result is recorded
in these tubes, the completed test is begun by first streaking a loopful of the highest dilution tube,
which gave a positive result onto highly selective Eosin Methylene Blue (EMB) agar. After incubation,
subsequent colonies are evaluated for typical coliform reactions. A schematic illustration is
presented in Figure 7.2.
Source: EPA, 2008

Figure 7.2 The Progress of the Multiple tube testing for Coliforms
7 - 11
The sample of the tubes tested either yielding gas or otherwise are shown in Figure 7.3.
Figure 7.3 The Fermentation as seen from the gas in the Inverted vials inside the tubes
7.6.2.1.2 Faecal Coliform Test
This test indicates the potential presence of pathogenic organisms. After presumptive test, which is
the same as for the total coliform test, test the sample with water bath set at 44.5°C ± 0.2°C in EC
broth media. A schematic illustration is presented in Figure 7.2. Based on the dilutions used, the
number of tubes adopted and the identified number of tubes with gasification, a statistical formulation
is made out called the Most Probable Number (MPN) in 100 mL of sample. It should be noted that a
confirmed test may require anywhere up to 72 hours.
7.6.2.2 Membrane Filter Test
In this procedure, a given size sample, generally 100 ml, is filtered through a membrane,
small-pore filter, which is then incubated in contact with a selective culture agar at 37°C. A coliform
bacteria colony will develop at each point on the membrane where a viable coliform will be left on the
membrane during filtration. After an incubation period of 24 hours, the number of colonies per plate is
counted. They represent the actual number of coliforms that were present in the volume of samples
filtered. The procedure is illustrated in Figure 7.4 overleaf. The incubated plates may appear as in
Figure 7.5 overleaf. The number of colonies in a dish can be counted using a colony counter, which
can be manual or automatic counter or hand held digital type as shown in Figure 7.6.
7.6.2.3 Colilert Test
The Colilert test is a relatively new method and has been accepted by the U.S. EPA for coliform
testing. This is a presence/absence test and it does not indicate the extent of contamination. It is
reported as having been proven to be just as accurate as the membrane filtration method. In this
method, the Colilert reagent contains a formulation of salts, nitrogen, and carbon sources that are
specific to total coliform. It contains specific indicator nutrients that create a yellow colour when
total coliforms are present and fluorescence when Escheria Coli (E. coli) is present. The reagent is
added to a 100-millilitre water sample in a sterile, non-fluorescent borosilicate glass container. The
vessel is capped and shaken vigorously by repeated inversion, to aid in mixing of the reagent. It is
incubated at 35°C for 24 hours. After 24 hours, the technician compares the reaction vessels to the
colour in a comparator supplied with the test kit. If the inoculated reagent has a yellow colour equal
to or greater than the comparator, the presence of total coliform bacteria is confirmed.
7 - 12
Source: EPA, 2008

Figure 7.4 The Progress of the Filter Technique for Coliforms
Figure 7.5 Illustrative Appearance of Cultured Plates showing the growth of Colonies
7 - 13
Figure 7-6 Colony Counters: Automatic integrating pen type and Grid plate for manual use
The sequence of Colilert testing is shown in Figure 7.7.
Figure 7.7 The Progress of the Colilert technique for Coliforms
A rapid 7-hour faecal coliform (FC) test for the detection of FC in water has been developed.
This membrane filter test utilizes a lightly buffered lactose-based medium (m-7-hour FC medium)
combined with a sensitive pH indicator system. The 7-hour FC test was found to be suitable for the
examination of surface waters and non-chlorinated sewage and could serve as an emergency test
for detection of sewage or faecal contamination of potable water.
7 - 14
It is particularly useful for rapid detection of recreational water quality changes related to storm water
runoff, sanitary waste spills or bypasses, and for sewage monitoring for treatment malfunction.
7.6.2.4 Recommended Testing for Treated Sewage
Whatever are the advancements occurring elsewhere in the world, while recommending a specific
testing procedure for Indian situation, the following must be considered:
A. The fact that maintaining a sterile microbiological laboratory in a STP is still a far cry for many
ULB once it migrates outside the metropolitan cities.
B. The testing skills are speciality oriented and employing microbiologists full time by these
ULB will be impractical especially as these microbiologists will not have promotional
opportunities as compared to their employment in other R&D institutions.

C. These tests are not mandatory testing on a daily basis and can be carried out once a fortnight
by the staff of the metropolitan laboratories by collecting and preserving the samples in suitable
iceboxes for transporting overnight to their laboratories.
Considering all the above points, the multiple tube method of MPN/100 ml should be
continued for some more time for total coliforms and faecal coliforms. The tests can be cross verified
by plate count if felt necessary. The sampling procedures and analytical procedures shall be
according to the Standard Methods (or) as in force by the concerned Pollution Control Board (PCB),
as the case may be.
7.7 QUICK AND APPROXIMATE MEASUREMENT METHODS
7.7.1 Test Paper Method
Tests which can be done with this method are pH and sulphide. These are mainly qualitative and are
of only incidental value.
7.7.2 Detector Tube Method (Transparency Tube, BOD Tube (UK))
Refer to Section 4.7.4.1 “Process Control”, Figure 4.13.
7.7.3 Cylinder Test
(Including simplified colorimetric determination and simplified absorption spectrophotometry)
The colorimetric tests depend on the two hypotheses namely, the Beer’s law and Lambert’s law,
which in simple terms correlate the concentration of a solute in a solvent to the absorbance of
monochromatic light when passed through the solution and the path length through which
such a passage has taken place. This is the principle behind estimations using a calorimeter or
spectrophotometer. There is also a possibility that these can be estimated by using Nessler tubes
in the laboratory without depending on these electrically operated meters. Standard solutions are
prepared with known concentrations of solutes and stored in tightly corked Nessler tubes of 50 ml.
7 - 15
When a new sample is to be tested, it is put through the sample preparation and thereafter
is compared by looking down through a Nessler tube filled with the prepared sample and comparing
with already prepared reference tubes. Thus, an idea of the concentration is obtained. This test is
very useful on a day to day basis.
The presence of DO in aeration tank requires the elaborate procedure of using a meter operated
electronically and keeping the probes well cleaned at all times. This is not always possible. Moreover,
typical plant control requires an answer to the question of whether residual DO is present or absent
in the secondary clarifier overflow. This can be easily carried out in the field as follows:
1. Take a 10 ml well washed test tube.

2. Hold it gently against the weir overflow sideways.
3. Allow the sewage to fill the tube and overflow for a few minutes.
4. Gently take the tube and pour out about 2 ml.
5. Add few drops of manganous sulphate solution.
6. Add a few drops of potassium iodide solution.
7. Close the top with the thumb and invert a few times.
8. Allow to stand for a few minutes.
9. If there is a yellow precipitate, DO is present.
10. If there is a white precipitate, there is no DO.
7.8 DATA ANALYSIS ( ACCURACY AND PRECISION )
All analyses carried out should be properly recorded. Routine daily analysis, periodic analysis
and special analysis should be recorded separately. Copies of these reports should be sent to the
Plant Superintendent immediately after the analysis is done with explanatory notes to indicate any
unsatisfactory conditions or abnormalities.
The Plant Superintendent should study the reports and direct the operating staff for proper
corrective measures in the operation schedule. Such measures taken should be reported to the
laboratory scientists who should check the efficiency of corrective measures by re-sampling and
analysis. Corrective measures followed by sampling and analysis should be repeated till such time
as satisfactory results are obtained.
Data collected over a period of time on various parameters of plant control should be analysed
and represented on charts and graphs and displayed in the laboratory for ready reference by the
supervisory staff and visitors. These should be included in the weekly, monthly and
annual reports of the laboratory.
7.8.1 Processing Water Quality Test Data
The analysis of results must be done judiciously. One should not jump to conclusions. Logic of the
results should be first verified instead of blindly taking it for granted. Some of the fundamentals to be
followed are listed overleaf:
7 - 16
1. The outlet BOD of any unit cannot be higher than the outlet BOD of the upstream unit
2. The ammonia of final treated sewage cannot be the same or higher than that in raw sewage
3. The ortho P of final treated sewage cannot be the same or higher than that in raw sewage
4. The SS of final treated sewage cannot be higher than that of raw sewage
5. Rotifers, Crustaceans, Protozoans cannot be absent if BOD reduction is at least 75 %
6. Follow the final BOD and SS on a graph, which will show any sudden lapses.
7. At regular intervals refer the sample confidentially to a recognised laboratory to keep a
check on the results of 2 to 5 % samples.
8. Whenever visiting a STP, verify DO qualitatively by the Winkler method
9. Whenever in the STP, take time to see through the oil immersion microscope for
live micro-organisms
10. It is most important that analysts alone are not held responsible for plant failures
7.8.2 Accuracy of Measured Values
1. If ammonia is reported as nitrified, bicarbonate alkalinity must be reduced 7 times.

2. If this is not the case, carry out a repeat test before deriving conclusions.
3. Make an “audit” for BOD removed versus kWh spent on aeration system.
4. Hypothetical ionic equilibrium may not tally in all the lab results.
5. This may be a genuine case as precise chloride estimation is very difficult.
6. In such case, it is better to adjust the chloride value to bring the ionic equilibrium.
7. The COD reduction in treated sewage Vs. raw sewage cannot be less than BOD reduction.
8. If this is the case, the results are suspect.
With the availability of personal computers and software at reasonable cost, the advantages of
electronic data processing for storage, retrieval and processing of laboratory test results are obvious.
To start with, the analysis results may be entered from the daily records into the computer. A simple
programme can be written for retrieval and presentation of data relating to any particular parameter.
This can be in the form of display of data for a fixed period or weekly or monthly averages or the
results of analysis carried out on samples collected at a particular time of the day for the period to be
studied etc. A slightly more detailed programming can be prepared for the computer to go through
the results of specified parameters entered daily and display or print out any figures, which exceed
a present value. This can be immediately passed onto the treatment plant staff for investigation and
rectification. The computer can also be programmed to display and print out graphs showing the
variation in any specified parameters over a period of time.
Analytical instruments are also available for carrying out tests automatically on a large
number of samples simultaneously and electronically feed the data directly into the computer
using a data logger module.
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7.9 FREQUENCY MANAGEMENT
Laboratory results must stop at the plant-in-charge level and should not go all the way to the official
in charge of the total O&M of the sewerage infrastructure in the head office on a daily basis. This
will only set in motion a parallel organization in detecting & reporting matters and replying to higher
authority and the staff will lose interest. On the other hand, a fortnightly concise physical reporting,
illustrating any specific changes in raw sewage or treated sewage and suggesting ways and means
and asking for specific funds / assistance alone should be sent to the official in charge of the total
O&M of the sewerage infrastructure in the head office.
7.10 PLANNING OF LABORATORY FACILITIES
This is explained in detail in Part A manual section 5.5.5 and in Appendix A.5.3, A.5.4, A.5.5, B.7.1
and B.7.2.
7.11 UPKEEP OF PLANT LABORATORY
A well designed and adequately equipped laboratory under a competent analyst is essential in all
STP. Very small STP and WSP need not have their own laboratories if the facilities of a nearby
laboratory are available. The results of the laboratory analysis will aid in the characterization of
any sewage, pinpoint difficulties in the operation and indicate improvement measures, evaluate the
composition of sewage and thus estimate the efficiency of operation and measure the probable
pollution effects of the discharge of such sewage on the receiving water bodies.
The analytical data accumulated over a period to time is an important document for safeguarding
the STP from allegations of faulty operation. The laboratory should also engage in research
and special studies for evolving improvements and innovations in plant operation. The laboratory
therefore must form an integral part of the STP.
7.12 DISPOSAL OF LABORATORY WASTES
Any office or other place where a number of people work requires a proper waste disposal system.
In the case of a laboratory in a STP, special care has to be taken since the laboratory handles harmful
chemicals and the samples themselves are capable for transmitting pathogens.
7.12.1 Solid Waste
Solid waste may include filter residues, used cotton plugs, etc. These should be collected and
disposed scientifically in an eco-friendly method approved by the local PCB.
7.12.2 Liquid Wastes
Since the laboratory is attached to a STP, it will be possible in most cases to drain the laboratory
wastes to the inlet chamber of the STP, if necessary, by pumping. However, since the laboratory
wastes may also contain concentrated acids and alkalis, it may be necessary to provide a small
holding tank where the concentrated chemicals will be diluted and neutralized to avoid the
possibility of affecting the biological activity of the STP.
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7.12.3 Radioactive Wastes
If radioactive materials are suspected to be present in the waste samples, special precautions will
have to be taken to protect the laboratory staff. Advice on this aspect may be obtained from the
Atomic Energy Department ( AED ).
7.13 PERSONNEL
Laboratories of large STP should be under the charge of a qualified and experienced analyst
supported by junior technical staff having background in the field of chemistry, biology and
bacteriology. The analyst should assimilate the details for functioning of the plants by
experience and acquire the necessary preparedness for receiving further specialized training
including performance interpretation and application of advanced techniques, which enable the
analyst to participate in the efficient operation of the STP. However, this does not mean that the
qualified and experienced analyst who has accumulated a lot of experience over the years
will replace the Engineer-in-charge of the plant but will instead progress in his own hierarchy
and become a Chief Chemist. Cross migration between these two disciplines should not be
entertained in the hierarchy.
7.14 SUMMARY
Water quality analysis in STPs provides useful parameters for judging appropriateness of
process control and quality of the treated sewage. Water quality analysts should have thorough
understanding of analysis items and frequencies prescribed for the STPs and provide the results of
analysis to the plant-in-charge.
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Part B: Operation and Maintenance CHAPTER 8: ENVIRONMENTAL CONSERVATION
CHAPTER 8: ENVIRONMENTAL CONSERVATION
8.1 INTRODUCTION
A sewerage system including both on-site and off-site treatment is an infrastructure, which
contributes to the improvement and conservation of the environment by reducing pollutants
discharged to the water environment. A sewerage system is considered to have overall positive
effects on environmental conservation. However, on the other hand, since the system handles
insanitary objects, physical, mental and aesthetically negative impacts on the surrounding
environment through both construction and operation stages are unavoidable.
Therefore, operational measures are required to minimize odour, epidemiological pollution, soil
contamination and water pollution. Plant beautification and landscaping would be also required to
maximize the aesthetics.
In addition, since the sewerage system is an essential urban infrastructure, which supports
urban domestic, industrial and business activities, the operation of the sewerage system is
also required to withstand disasters. This chapter mentions the concept of global warming
and gas regulations.
8.2 ODOUR
8.2.1 Odour from the Sewerage System
Odours are a complex combination of a wide variety of compounds; however, there are certain
compounds and groups of compounds that contribute specifically to sewage odours, and
significantly determine the selection of the control technology. These include the following:
• Hydrogen sulphide, and

• Ammonia.
8.2.2 Odour Control Methods and Technologies
8.2.2.1 Odour Control Procedure
Odour control is a complex and time-consuming challenge, often requiring a combination of methods
for treating odorous gases and for removing or reducing the potential causes of the odours. If an
odour problem is severe enough to affect the community, an emergency response and solution to
the problem must be carried out quickly.
The approach for selecting an odour control method or technology includes the following steps:
A. Identify the odour source and characteristics through sampling and analysis.
B. List and assign priorities to controlling a specific odour problem, recognizing considerations
such as cost, plant location, future upgrading of various sewage processes, severity of the
odour problem, and the nature of the affected area.
8-1
C. Select one or more odour control method or technology for implementation to meet the objectives
of steps “a” and “b”, taking into consideration the advantages and disadvantages of each.
D. Monitor odour emissions from the treated air for process adjustments and for feedback to
evaluate the solution’s effectiveness.
8.2.2.2 Sampling Methods
Solving any odour problem begins with sampling and analysing gases to identify and characterize
the odours. The principal tools for diagnosing an odour problem are the techniques used for odour
quantification and characterization. Chemical analysis of odour constituents could be performed.
This is an indirect method, because the results of a chemical analysis still need to be related to odour
concentration and intensity in some way.
8.2.2.3 Quantitative Testing-Analytical Methods
Gas chromatography can be used on many odorous organic compounds, but the analysis is complex
and expensive. Figure 8.1 shows the portable gas-monitoring devices.
Figure 8.1 Detector tubes (left) and Gas sampling pump (right)
The concentrations of individual compounds can be measured via standard analytical methods.
For example, a simple apparatus consisting of a gas detector tube can be used in the field.
These tubes are available for a number of compounds. For more accurate and complete results,
samples should be collected in bags, stainless steel vacuum canisters, or tubes filled with adsorbent
and analysed by gas chromatography in a laboratory.
Gas detector tubes are sealed glass tubes filled with an appropriate indicator chemical, which reacts
with a particular gas and gives a colour reaction. To make a determination, the seals are broken at
each end of the tube and a definite volume of the atmosphere for sampling is drawn through by a
hand-operated or mechanical pump.
The tubes are marked off in scale divisions and the concentration is determined according to the
length of discolouration of the indicator for a given volume of atmosphere.
8-2
Detector tubes are simple, easy to use devices that can provide reasonably reliable,
on-the-spot measurement of gas concentrations. Their accuracy may be in the range of 70 to 90 %
of the mean value if sampling is done carefully according to manufacturers’ directions. For taking
gas samples from difficult locations, extension tubes are available from manufacturers so that the
detector tubes can be placed at the desired site. In making use of detector tubes precautions
should be noted as per the manufacturers.
8.2.3 Hydrogen Sulphide (H2S)
Hydrogen sulphide (H2S) is the most common odorous gas found in sewage collection and
treatment systems and results from the reduction of sulphate by bacteria under anaerobic conditions.
Its characteristic rotten-egg odour is well known. The gas is corrosive, toxic and soluble in sewage.
8.2.3.1 Effects on Health
Hydrogen sulphide is considered a broad-spectrum poison, meaning it can poison several different
systems in the body. Breathing very high levels of hydrogen sulphide can cause death within just
a few breaths. Loss of consciousness can result after fewer than three breaths. Exposure to lower
concentrations can result in eye irritation, a sore throat and cough, shortness of breath, and fluid in
the lungs. These symptoms usually go away within a few weeks. Long-term, low-level exposure may
result in fatigue, loss of appetite, headaches, irritability, poor memory and dizziness.
Refer to Section 9.2.2.1.2 “Risk of Hydrogen Sulphide Poisoning in Confined Space” of Chapter 9
of this manual.
8.2.3.2 Locations of Sources
A. On-site
Septic tank, anaerobic filters and mini-package treatment plant
B. Conveyance
Sewers, manholes and closed drains (simplified sewers)
C. SPS
Collection well
D. STP
Collection well, primary settling tank, sludge thickener, sludge digester, digested sludge sump,
dewatering centrate/filtrate, sludge drying beds, UASB reactor, anaerobic lagoons, sludge
lagoons and septage treatment facility
8.2.3.3 Measurement
• Proper measurements should be performed in accordance with IS 5182 Part 7.
• Short-term detector tubes, portable gas detector, etc., can be used for simplified
measurements.
8-3
• When measuring concentration at a location where odour is generated (particularly when the
concentration level is not known), take care to perform the work after wearing a gas protection
mask. If the concentration is high, toxicity may be high; this is dangerous. Refer to Sec.9.3.1.1.1,a
“Measurement method” of chapter 9 of this manual.
8.2.3.4 Preventive Measures
Hydrogen sulphide production can be controlled by maintaining conditions that prevent the
build-up of sulphides in the sewage. The presence of oxygen at concentrations of more than
1.0 mg/L in the sewage prevents sulphide build-up because sulphide produced by anaerobic bacteria
is aerobically oxidized.
Maintaining an aerobic environment inhibits the anaerobic degradation process, which contributes
to the generation of hydrogen sulphide. A checklist is given below:
• Prevent corrosion in the collection well of the facility by blowing air through the facility
• Avoid storing screenings and grit generated in the grit chamber for a long time. Dispose of
screenings and grit at appropriate intervals
• Retention time of sludge in the sludge treatment facilities should be appropriate (Do not retain
sludge for a long time)
• Maintain sewage at neutral pH range because most of the sulphide is present at a pH value of
less than 7.
• Impossible to prevent the odour from septic tanks because we cannot expect fine quality
water to be used for ablution. Therefore, it is important to ventilate.
8.2.3.5 Control
The operator can
• Remove sand and grit deposited in house service connection or sewer immediately.
• Properly shut doors and windows of building where substances that become sources of foul
odours are stored.
• Dispose of scum and sludge in the sedimentation basin at appropriate intervals and do not store
them for a long period.
• Thoroughly clean each facility and the areas surrounding the facility.
Measures for septic tank are as follows:
• Open ventilating shaft at the cowl to the atmosphere and provide mosquito-proof netting.
The height of the pipe should extend at least 2 m above the top of the highest building
within a radius of 20 m. Refer to IS 2470 Part 1 and section 9.3.4 “Conventional Septic Tank” of
chapter 9 of Part-A manual.
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Operational precautions for deodorisation facilities are described below:
A. Soil (Bio) Deodorisation
This method makes use of oxidation and decomposition effects by micro-organisms to remove
substances with foul odour. In actual practice in STP, the ventilated air is led to the reactor or soil
bed and the odour is removed.
In this method, substance with foul odour is delivered to the bottom part of the fertile soil bed in
highly moist condition, and the substance with foul odour is removed because of the oxidative
ability of mainly heterotrophic bacteria.
The Soil (Bio) deodorisation configuration is shown in Figure 8.2.
Figure 8.2 Soil (Bio) deodorisation configuration

Notes: Air for ventilation may concentrate in a certain part of the soil. In such cases, hole may have
formed on the surface. Dig the soil so that air is vented uniformly.
B. ASP( Activated Sludge Process) - Deodorisation
This method makes use of decomposition effects by micro-organisms to remove

substances with foul odour. In actual practice in STP, the ventilated air is led to the reactor and the
odour is removed.
Ventilated air is delivered to the inlet side of the blower. The substance with foul odour is
oxidized and decomposed by aerobic micro-organisms in the reactor. The mechanism of
ASP-deodorisation is shown in Figure 8.3 overleaf.
C. Activated Carbon Deodorisation
Foul odours are passed through the adsorption tower filled with activated carbon (charcoal or
coconut shell charcoal) and removed by physical adsorption. The effect is more pronounced
when the substance with foul odour has large molecular weight.
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Figure 8.3 Mechanism of ASP-deodorization

Caution: Pipes used underwater are likely to clog easily; so periodically clean such pipes and
remove the clogged material.
Odours are selective and the method is more effective in case of hydrogen sulphide and methyl
mercaptan. However, it does not have any effect on ammonia and amines. It is suitable for faint
odours, and is used as a finishing deodorising agent.
The normal activated carbons are acid, chlorine-based or halogen-attached activated carbons.
These are effective in removing substances like hydrogen sulphide and ammonia. A typical setup
is shown in Figure 8.4.
Figure 8.4 Activated-carbon deodorization
A differential pressure gauge is installed between the inlet and outlet of gas in this equipment.
When the value indicated by this differential pressure gauge is large, clogging has probably
occurred. This is a sign that the activated carbon is to be replaced or the pipe is to be cleaned.
Measure the concentration periodically near the outlet. When the value shows a sudden increase,
it is time for replacement. (However, breakdown in the equipment may have occurred; confirm the
equipment carefully and then perform work.)
The disposal of used activated carbon shall be as per the local PCB.
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8.2.4 Ammonia (NH3)
Ammonia odour is most typically encountered at alkaline-stabilization facilities. Adding alkaline

materials raises the pH, which causes the dissolved ammonia in de-watered cake to volatilize.
Although the odours tend to dissipate quickly, the ammonia levels in mixing and drying areas can be
high if the gas is not collected and treated.
8.2.4.1 Effects on Health
Ammonia is a colourless gas with specific irritant odour which when compressed liquefies at
room temperature. Effects on the human body include irritation of the mucous membrane and
breathing organs.
8.2.4.2 Locations of Sources
Ammonia typically appears in the de-watering processes and in the solids created from de-watering.
This is especially true in digested solids. However, the small quantity of ammonia in sewage off gas
at neutral pH contributes little to odour emissions, because the odours typically are dominated by
sulphur compounds. Therefore, it is rarely necessary to provide an ammonia removal step in treating
off gas from STP, unless lime or other alkaline material is used in the process to elevate the pH.
8.2.4.3 Measurement
• Proper measurements should be performed in accordance with IS 11255 Part 6.
• Short-term detector tubes, portable gas detector, etc., can be used for simplified measurement.
8.2.4.4 Preventive Measures
In the dewatering process, do not increase the pH.
8.2.4.5 Control
Generally, deodorisation equipment is effective in controlling ammonia, similar to H2S. However, care
is necessary since there is selectivity depending on the substance.
8.2.5 General Method of Prevention of Odour
Following is a short checklist of operational considerations for controlling odours of primary treatment
facilities: (May also apply in other facilities)
• Remove scum routinely, with increased frequency during warm weather.
• Remove sludge before it can bubble or float.
• Wash weirs and other points where floatable and slime collect. Some facilities use submerged
pipes with holes rather than effluent troughs. The submerged pipes do not splash the primary
effluent, thereby reducing the release of hydrogen sulphide.
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• Wash down all spills and grease coatings.
• When draining a tank, immediately flush it completely. If sludge does not drain quickly, spray
lime, calcium hypochlorite, or potassium permanganate on the sludge surface to reduce odours.
Because even a clean tank can produce odours, flushing the tank with a chlorine solution or
keeping the tank floor covered with a low concentration of chlorine solution will reduce odours.
• If the sewage is septic, add chemicals in the collection system or at the plant, as appropriate, to
reduce sulphides.
• If tanks are covered for odour control, keep plates and access hatches in place.
• Routinely check any odour scrubbers or deodorizers for plugging, adequate supply of chemicals,
proper pressures for demisting, and/or effectiveness of carbon.
• The splashing of primary sewage into weir troughs and effluent channels can result in the
release of hydrogen sulphide. If possible, try to minimize the splashing of primary sewage into the
channel or weirs. If it cannot be accomplished operationally, then installing submerged sewer
pipes may be necessary. This will require tank modifications to verify the plant hydraulics and
provide proper control to avoid fluctuations in the tank levels.
• Minimize the stripping of hydrogen sulphide from the sewage when using channel air diffuser
systems.
Adoption of the following regular practices will not only increase removal efficiency, but will provide
better working conditions for the operator:

• Regularly remove accumulations from the inlet baffles and outlet weirs with a hose or a broom
with stiff bristles. Only experience will determine the necessary frequency.
• Clean scum removal equipment regularly; otherwise obnoxious odours and an unsightly
appearance will result.
• Keep cover plates in place except when operations or maintenance require their removal.
• Immediately flush and remove all sewage and sludge spills. Avoid hosing down motors and
enclosed control devices.
• Establish a housekeeping schedule for the primary treatment area, including galleries,
stairwells, control rooms, and related buildings, and assign responsibility for each item to a
specific employee.
• Repaint surfaces as necessary for surface protection and appearance.
8.2.6 Chemical Addition
Chemical addition can control odours in STP by preventing anaerobic conditions or controlling the
release of odorous substances. These chemicals fall into four basic groups based on their
mechanisms for odour control, shown in Tables 8.1 to 8.4 overleaf.
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Table 8.1 Chemicals used for liquid-phase odour control
Source: WEF, 2008
8-9
Table 8.2 Liquid process operational emissions control
Source: WEF, 2008
8 - 10
Table 8.3 Solids process operational emissions control
Source: WEF, 2008
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Table 8.4 Summary of odour control technology applications at sewage treatment facilities
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Part B: Operation and Maintenance CHAPTER 8:ENVIRONMENTAL CONSERVATION
Table 8.4 Summary of odour control technology applications at sewage treatment facilities - continued
Source: WEF, 2008
8 - 13
The effectiveness of chemical addition as an odour control technology depends on such variables as
cost, dosage, presence of odour-causing compounds, effects of chemical accumulations in sludge
and process waters, equipment maintenance, space limitations, and safety or toxic substance
concerns. Typical odour-control applications include collection systems, headworks, primary
clarifiers, process side streams, aeration tanks, solids-handling applications and storage lagoons.
In general, it is more cost-effective to treat odours in the liquid phase than in the vapour phase.
Common chemical agents used to control odours include iron salts, hydrogen peroxide, sodium
hypochlorite (chlorine), potassium permanganate, nitrates and ozone.
8.2.7 Monitoring
Regular monitoring of treatment processes can prevent odour releases as well as provide
valuable information on operating procedures.
8.3 EPIDEMIOLOGICAL POLLUTION
Potentially pathogenic aerosols are generated as a result of the physical processes of aeration,
trickling, spraying sewage and sludge.
The density of microorganisms in aerosols is a function of the density of a specific organism in the
sewage, aeration basin, or sludge, the amount of material aerosolized, the effect of aerosol shock
(impact), and finally, biological decay of the organisms with distance in the downwind direction.
In a STP, there are commonly either stagnant anaerobic conditions or an aerated mass of heated
microbial material. With the use of activated sludge as a standard treatment process, the
operators walk above and around a cauldron of airborne aerosols. They are often exposed to low-level
aerosolized versions of microbes, some of which may be infectious.
8.3.1 Effects on Health
These aerosols may contain bacterial and viral infectious agents, and infections may
result from contact with these aerosol mists. It is impossible to eliminate all sources of aerosol
contamination in a STP.
The immune systems of many operators build up antibodies to a variety of bacterial and viral
infectious agents. They become what are nicknamed “universal carriers” because they are often
in contact with low levels of infectious agents that will not make them ill, but that they can buildup
immunity like vaccination. However, if operator’s get run down they come into contact with
significant infectious agents and they can easily become ill. Refer to section 9.2.1 “Diseases” of
chapter 9 of this manual.
8.3.2 Locations of Sources
The aeration tanks and attached growth system are the locations of sources as shown in
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Figure 8.5 Aeration tank (left) and Attached growth system (right)
8.3.3 Measurement
Perform sampling using filter paper. Then, the samples can be collected on a Petri dish and grown in
the laboratory. These samples can later be tested.
The following are the studies to be carried out in an STP:
The total microorganism content of air immediately over the aeration tank liquid surfaces:
• Decreases exponentially with height at least within the first 100 cm above the aeration tank
liquid surface
• Approaches background concentrations by extrapolation of current data within 2.5 to 4 m above

the aeration tank liquid surface
• Appears to be influenced by several factors, including the mixed liquor suspended solids
concentration of the aeration tanks, bacterial die-off, fall-back of larger particles, and
dispersion by wind currents.
In view of the above, one should bear in mind that aerosol increases closer to aeration tanks and also
increases as one goes downwind.
8.3.4 Preventive Measures
• Cover the aeration tanks and attached growth systems. (To prevent diffusion of aerosols)
• Plant tall trees around tanks to prevent diffusion of aerosols.
• Stop using surface aerators and use diffused aerators.
8.3.5 Control
Controlling epidemic microbes in sewage is difficult. The above-mentioned preventive

measures are desirable.
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8.4 SOIL CONTAMINATION
Soil contamination has become an issue in recent years. A STP that plays an important role in
conserving the environment cannot become a source of contamination itself. Sewage leaks
sometimes become issues. To prevent leaks in an STP, the following are necessary:
A. Check for leaks in every facility. (High probability of leaks in pipe parts and connections
between facilities.)
B. Even if there are no leaks in the facility, there may be fissures or cracks. If so, immediately repair
the same on site. If this is not possible, discuss with the plant engineer and make arrangements
to get the defects repaired.
C. Sometimes, sewage overflows. In such a case, check whether the flow rate to the facility is
greater than the design flow rate.
D. If the flow rate is below the design flow rate, there is a possibility of clogging in the stage after the
problem location. The cause of the clogging should be eliminated.
E. Since sludge is thicker than sewage, it is likely to cause clogging in the sludge treatment facilities.
For this reason, care should be taken against leaks from the sludge treatment facilities. Efforts
should be made to eliminate leaks.
F. If the leak is identified clearly, and soil contamination is likely to occur, discuss with the plant
engineer to get accurate measurements to be made by an authorized laboratory of the local
PCB.
G. It is good to maintain a record of the TDS of ground water in the well waters of households
surrounding the STP so that questions of sewage seeping into ground water and polluting the
well waters can be verified.
8.5 WATER POLLUTION
Surface-water quality considerations include compliance with treated sewage standards at the
discharge point with respect to parameters like BOD, suspended and floating solids, oil & grease,
nutrients, coliforms, etc.
Special consideration may be given to the presence of public bathing ghats and intake points for
water supply downstream.
Another environmental consideration is the potential for ground water pollution presented by the
treatment units proposed to be built.
Necessary precautions should be taken to prevent water supply contamination due to

leakage from sewers. Appropriate distance between water supply pipes and sewer pipes shall be
maintained. On the other hand, early detection of sewage leakage and the repair is indispensable by
implementing sewer inspections described in 2.2 “Inspection and examination for sewer” of
Chapter 2 in this manual.
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8.6 SEWAGE TREATMENT PLANT BEAUTIFICATION AND LANDSCAPING
A STP is a facility that handles sewage. The working environment in such a plant is poor since foul
odours are generated. It is therefore essential that a clean environment be maintained within the
STP through daily cleaning of the plant. Within the boundaries of the premises, open areas should be
planted with trees and foul odours should be dispersed.
Specific measures should preferably be adopted such as providing park-like spaces within the
premises to offer residents a place for relaxation and rest. The treated sewage should be reused for
watering plants and trees within the premises.
Examples of plant beautification are shown in the Figure 8.6.
Source: BWSS Board

Figure 8.6 An example of plant beautification adopted in Bangalore
8.7 REGULATION OF GREENHOUSE GAS
8.7.1 Greenhouse Gas
Greenhouse gases such as Carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and Freon
are released in large quantities to the atmosphere with the increasingly energetic activities of human
beings, and the average temperature of the entire earth has increased. This phenomenon is known
as global warming. Global warming of the earth has a serious impact on the global environment.
Carbon dioxide (CO2) emissions and methane (CH4) generated are issues in STP operation.
A. Carbon Dioxide (CO2)
Carbon dioxide is formed from the complete combustion of any fuel that contains carbon (e.g.,
methane). Any boiler, flare or power-generation technology that combusts methane, will produce
a corresponding predictable amount of carbon dioxide.
B. Methane (CH4)
Methane is the principal component of both digester gas and natural gas. It is a light gas with a
specific gravity of less than 1.0. Methane is one of the critical greenhouse gases;
8 - 17
its global warming potential is 21 – 23 times that of carbon dioxide. From a greenhouse gas
perspective, it is vital to completely flare all methane without direct atmospheric release.
8.7.2 Control
Reduction in the use of fossil fuels (fossil fuels are used even for generating electric power; so use of
power is linked to the use of fossil fuels)
• Fuel for operating the sewerage facilities and reduced use of electricity are essential. (For
instance, change from continuous operation to intermittent operation, if possible)
• Measures against generation of CH4 from the treatment plant (since generation of this gas cannot
be inhibited, conversion of the generated gas may be considered)
Since the generation of CH4 is linked to global warming, checks on the CH4 collection facility and
leaks in piping are very important.
If there is damage or signs of damage, repairs should be carried out quickly.
8.7.3. Effective Use of Biogas
Biogas includes organic matter derived from of carbon, hydrogen, sulphur, and so on, and is
a potential energy source of high value.
Presently, the main uses are as follows.
• Used in dual fuel engines. A part of the power requirements of a STP can be met by generating
power using biogas explained in clause 5.16.1.2 and its sub clauses in Part-A manual.
8.8 CARBON CREDIT RECORD
This is a term that qualifies the holder to emit one ton of carbon dioxide into the atmosphere
and is awarded to institutions or countries that have reduced their greenhouse gases below
their emission quota, which literally means emission standards. These carbon credits can be
traded in the international market at their current market price. For details, refer to Sec. 5.17 carbon
credit of Part-A (Manual).
In STP to meet the requirements, the following are to be mainly performed:
A. An example of the Clean Development Mechanism (CDM) project in sewerage facilities is

biomass power generation. This project focuses on CH4 generated from the facilities.
B. For the project, the baseline CO2 emissions must be studied. Based on this study, the CO2
emissions in the base year and the reduction in CO2 emissions thereafter are considered for
approval of carbon credits.
C. Accurate data during operation is required for specifying the baseline.
D. Data collection and retention of accuracy of measuring instruments are the necessary
items on site.
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E. STP power and flow rate data are mainly collected through SCADA. Refer to Chapter 5
sec.5.12.12 “SCADA system” of Part-A manual.
F. Even after the project is approved, data collection and maintenance of measuring
equipment will have to continue.
8.9 SUMMARY
STPs are intended primarily for improvement of water environment. They should be operated
properly while preventing water pollution and odour problems. In addition to prevention of air
pollution and soil contamination, planting of suitable greenery and landscaping is also required
to improve the environment.
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CHAPTER 9: OCCUPATIONAL HEALTH
Part B: Operation and Maintenance HAZARDS AND SAFETY MEASURES
CHAPTER 9: OCCUPATIONAL HEALTH HAZARDS AND SAFETY MEASURES
9.1 INTRODUCTION
The sanitation workers, engaged in O&M of sewerage system or septic tanks, are exposed to
different types of occupational hazards like injuries caused by physical actions, chemicals contacts,
infections caused by pathogenic organisms, and dangers inherent with oxygen deficiency, hydrogen
sulphide, and combustible gases.
The Parliament of India is considering “Sanitation Workers (Regulation of employment and

conditions of service) Bill, 2012”. This bill will be helpful in eliminating these risks to the health and
ensure safety of sanitation workers.
As defined in the said bill, the employers are obligated to provide their employees with safety
equipment or protective gears (See 9.3.1.2 for details) as well as cleaning devices and ensure
observance of safety precautions appropriate for each hazardous condition to reduce the employees’
risks to health and safety. Moreover, to guard against human error and carelessness, proper safety
training and adequate effective supervision by safety personnel are most essential.
The GOI enacted the “Employment of Manual Scavengers and Construction of Dry Latrines
(Prohibition) Act, 1993,” which declared the employment of scavengers or the construction of dry
latrines to be an offence, considering the foregoing, another bill titled “The Prohibition of Employment
as Manual Scavengers and their Rehabilitation Bill, 2013” was introduced in the Parliament in
September 2013 and has since been passed. The Bill aims to eliminate manual scavenging and
insanitary latrines, and provides for proper rehabilitation of manual scavengers in alternative
occupations so that they are able to lead a life of dignity.
In addition to the Acts mentioned above, employees shall follow “Contract Labour Regulation and
Abolition Act, 1970” for secure operational health and safety at their sites.
O&M of sewerage facilities, which should not be discontinued at any moment, requires health and
safety consciousness equal to or greater than one that is needed for construction projects.
In India, “health and safety policy” is defined in construction project management by Bureau of Indian
Standard (BIS) (Refer to Appendix B.9.1).
Therefore, the same health and safety policy for construction projects may also be adopted for O&M
of sewerage facilities.
STPs and SPSs are subject to safety audits, which confirm the status of safety and health
organizational setup, education / training, provision / inspection of personal protection, and records
of safety, to ensure occupational safety and health at the work sites. The plant engineer should
rectify failures immediately, if any.
The audit shall be implemented as per IS: 14489 “Code of Practice on Occupational Safety and
Health Audit.” Standard safety audit procedures of the inspectorate of factories shall be at a frequency
of a month and compliance reported to that agency.
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9.2 OCCUPATIONAL HAZARDS
Occupational hazards are classified into Diseases and Accidents and are described below.
9.2.1 Diseases
Workers for sewerage and on-site systems face the risk of various health problems by virtue of their
occupation since they are exposed to a wide variety of chemicals, micro-organisms and decaying
organic matters that are present in sewage. Table 9.1 shows the types of diseases and its causes.
Table 9.1 Types of diseases and their causes
Source: Rajnarayan Tiwari, 2008
9.2.2 Accidents
Workers for sewerage systems and on-site systems are exposed to the risk of accidents during work.
This chapter deals with oxygen deficiency, hydrogen sulphide poisoning, and dangers of combustible
gas as confined space hazards.
Confined spaces are locations in sewers, SPS and STPs where fatal accidents frequently occur. A
confined space is defined as a space with:
(1) Cramped entry and exit;

(2) Absence of broad daylight and ventilation;
(3) Access is meant for very limited persons such as one or two persons. The possible hazards that
are considered to be common are
• Confined space hazards

• Oxygen deficiency / Hydrogen sulphide poisoning /Combustible gas
• Chlorine poisoning
• Fall
• Slip
• Electric shock
• Fire
9-2
The workplaces are categorized into the following five locations and Table 9.2 lists the possible
hazards for each of the following location
• On-site
• Sewer system
• SPS
• STP
• Water and sewage testing laboratory
Table 9.2 Possible Hazards by locations
Note: OD = Oxygen Deficiency, HSP = Hydrogen Sulphide Poisoning,

CG = Combustible Gas, CGP = Chlorine gas poisoning, ES = Electric Shock
9-3
The possible hazards at sewage testing laboratory include toxic substances, alkalis /acids,
glass appliances, and are described herein.
9.2.2.1 Confined Space Hazards
Possible hazards in confined space include oxygen deficiency, hydrogen sulphide poisoning, and
danger of combustible gases.
9.2.2.1.1 Risk of Oxygen Deficiency
Table 9.3 shows the change in symptoms of anoxia due to drop in oxygen concentration.
Table 9.3 Relationship between reduction in oxygen concentration and symptoms of anoxia
Source: OSHA, 2008
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9.2.2.1.2 Risk of Hydrogen Sulphide Poisoning in Confined Space
Hydrogen sulphide is extremely toxic. Sometimes it may be generated in high concentration in a STP,
also which causes immediate death.
• Hydrogen sulphide enters the body through eyes or mucous membrane of breathing organs.
• Blood seeps out from the capillaries in cavities of the lungs, causes pulmonary oedema, leading
to breathing difficulties and death by suffocation.
• In sewer facilities, it is generated in rising mains with no oxygen supply and in inverted siphons,
etc., where sludge is likely to accumulate easily.
• It is generated in grit chamber, pumping well, sedimentation basin and sludge thickening tank in
sewage treatment plants.
• Hydrogen sulphide generated in sewage and settled sludge is sealed within the static condition,
so it does not disperse into the atmosphere easily. However, when agitated, it disperses all at
once to the atmosphere.
The relationship between concentration of hydrogen sulphide gas and its toxic effect is shown
in Table 9.4.overleaf.
9.2.2.1.3 Risk of Combustible Gas in Confined Space
• Combustible gas includes methane, gasoline, volatalised thinner and so on.
• These become a mix of explosive gases in sewers.
• The minimum concentration for explosion is 5% for methane and 1.3% for gasoline.
• Combustible substances like gasoline and thinner float on the surface of water, volatilise at room
temperature and are dangerous.
• If large quantity of gasoline flows into a sewer, there is a possibility of large explosion to occur.
• At locations where sewage is likely to accumulate such as in sewers, toxic or explosive gases or
vapours may be generated.
9.2.2.2 Risk of Chlorine
• At a concentration of 2 to 5 ppm the symptoms are tear, cough, sneeze and running nose.
• At a concentration of 5 to 30 ppm, breathing becomes difficult and eyes cannot be opened. There
is a crisis of life in 30 minutes to 1 hour.
• At a concentration of 30 to 60 ppm, difficulty in breathing and loss of consciousness are caused.

If exposed with this concentration level for 30 minutes to 1 hour, it results in death.
• At a concentration of 1000 ppm, it results in death.
• Chlorine gas has specific weight that is 2.49 times heavier than air.
• It is a yellowish green gas and is a strong irritant.
• Although its disinfecting effect is high, its toxicity is also high.
9-5
Table 9.4 Relationship between concentration of hydrogen sulphide and its toxic effects
Source: JSWA, 2003
9-6
9.2.2.3 Fall
• Accidents frequently occur while climbing/descending ladders.
• Accident often occurs while working at high elevations.
9.2.2.4 Slip
Slippery surfaces are often encountered when working in an STP and sewers.
9.2.2.5 Electrical Shock
Electric shocks occur because of the following:
• Exposure of live parts and defects such as damage to insulating sheath.
• Absence of insulated protective gear,
• Getting in contact with live parts by mistake.
• Adequate care shall be taken against these and relatable issues.
9.2.2.6 Fire
Burns can be very serious and can cause painful injuries. The structural damage cause due to fires
can be very costly.
The three essential ingredients of all ordinary fires are:
• Fuel, paper, wood, oil, solvents and gas
• Heat- the degree necessary to vaporise fuel according to its nature
• Oxygen-normally at least 15 % of oxygen in the air is necessary to sustain a fire. The greater the
concentration of oxygen, the brighter the blaze and more rapid the combustion.
9.2.2.7 Risks in a Sewage Testing Laboratory
9.2.2.7.1 Toxic Substances
Persons working in the sewage testing laboratory use various chemicals including toxic
substances. Inhalation of excessive steam, gas or dust, etc., in the course of their work, is harmful
to health. Hence, adequate precautions must be observed. Typical toxic substances used in a sewage
testing laboratory and their toxicity are given in Table 9.5 overleaf.
9.2.2.7.2 Alkali / Acid
Acids and alkalis used in the sewage testing laboratory include:
• Hydrochloric acid
• Sulphuric acid
• Nitric acid
• Sodium hydroxide etc.
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Table 9.5 Toxicity of chemical used in water quality laboratory
Source: JSWA, 2003
9.2.2.7.3 Glass Appliances
Glass appliances, if not handled carefully, may break and result in injury.
9.2.3 Instances of Accidents
An instance of accident related to anoxia (due to oxygen deficiency) is described below.
• Type of work: Sewerage work
• Number of casualties: 2 dead, 1 employee in serious condition
• This casualty occurred when lifting the drain pump from the manhole during sewerage work.
• On the day of the occurrence, storm water pipes were being replaced.
• worker (A) and worker (B) opened the manhole cover to perform work in the manhole, and
entered the manhole.
• After a while, when worker (C) looked into the manhole, he found the workers (A) and (B)
have collapsed.
• He notified the other workers. worker (C) rushed into the manhole for rescue and called out but
there was no response.
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• Soon after, worker (C) also collapsed on the spot.
• Later, workers (A), (B) and (C) were rescued by the rescue team and taken to the hospital.
• Workers (A) and (B) lost their lives, while the rescued worker (C) was admitted to the hospital with
hypoxic encephalopathy (brain damage from lack of oxygen).
• Workers (A) and (B) were diagnosed with anoxia.
The probable causes of the accident were as follows:
• Was not aware that the location had the risk of oxygen deficiency.
• Did not measure the oxygen concentration and did not ventilate the manhole before entering it.
• Did not impart education and implement rescue drills related to work at dangerous locations of
oxygen deficiency.
• No safety guard was stationed.
9.3 SAFETY ASPECTS AND MEASURES
Measures to protect workers from accidents are mentioned in 9.3.1 Preventive measures are taken
to prevent accidents, and 9.3.2 Corrective measures are adopted when accidents occur. Preventive
measures and corrective measures against accidents are described below.
9.3.1.1 Hazard-specific Preventive Measures
9.3.1.1.1 Confined Space Hazards
The potential for build-up of toxic or combustible gas mixture and/or oxygen deficiency exists in all
confined spaces. Characteristics of common gases causing hazards are shown in Appendix B.9.2.
Table 9.2 lists the possible confined spaces related to sewerage works. Follow the “Confined space
entry procedure” shown in Figure 9.1 and Appendix B.9.3.
Figure 9.1 Confined space entry procedure
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The entry into confined space should not be permitted until it is ensured to be safe as in Table 9.6.
Table 9.6 Acceptable entry condition
A. Measurement Method
An example of a portable toxic gas detector that can measure oxygen, combustible gas, carbon
dioxide and hydrogen sulphide simultaneously is shown in Figure 9.2.
Source: PRISM GAS DETECTION PVT. LTD.

Figure 9.2 Portable toxic gas detector
• Before measuring the confined space atmosphere, perform zero error correction of the
instrument at a location where there is fresh air (no gas in the vicinity).
• Measure the atmosphere within the space to confirm if any hazard exists as given below.
• Oxygen : Less than 19.5 %
• Hydrogen sulphide : 10 ppm or more
• Combustible gases : 10 % LEL (lower explosive limit) or more
• Measurement should be done at three locations – top, middle and bottom of the confined space
– since the oxygen concentration differs according to the position.
• Record the measured results on “Confined space pre-entry checklist” (Appendix B.9.4)
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B. Ventilation Method
If the measured results indicate one or more of the following hazards, be sure to ventilate the location
before starting work.
• Oxygen : Less than 19.5 %
• Hydrogen sulphide : 10 ppm or more
• Combustible gases : 10 % LEL or more
To ensure the atmosphere is safe during the work, operate the ventilation equipment continuously.
Bring the blower outlet end close to the workplace and continue to blow air at the rate of 10 m3/
minute per person or greater.
C. Provisions for Evacuation
The work supervisor should make the following arrangements:
• Keep ready breathing apparatus, ladder, rope, safety belt and other equipment for use in
evacuating or rescuing workers in the event of an emergency.
• Inspect protective gear before start of work and ensure that they are ready for use at all
times. Repair or replace gear and equipment that are defective.
• Bear in mind that gas protection mask or dust protection mask is ineffective against anoxia.
• Non-spark tools should be used in confined spaces.
D. Stationing of Safety Guard
The work supervisor should station a safety guard to detect abnormality at an early stage and to take
immediate and appropriate action.
• The safety guard should be stationed outside the opening if the situation inside the confined
space can be monitored from the outside.
• The safety guard should check access to the workplace of the workers engaged in the work.
9.3.1.1.2 Chlorine Poisoning
• The chlorine containers should be stored in a cool and dry place, away from direct sunlight or
from heating units.
• Wear a face shield when changing chlorine containers.
• As chlorine is approximately two and half times heavier than air, vents should be provided
at floor level.
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9.3.1.1.3 Fall
The work supervisor and worker should take the following precautions to prevent persons from falling
into manholes, etc.:
• Ensure that nobody falls from ladders (including metal rungs) and that tools are not dropped from
ground level.
• Wear uniform suitable for the work and wear the necessary protective gear.
• Check that the ladder to the manhole is not corroded or worn out.
9.3.1.1.4 Slip
• Special anti-skid shoes with metal cladding over the “toe” should be provided by the employer for
the workers. These shoes should be used by the workers only within the STP.
• Construct anti-skid floors and keep them free from oil and grease.
9.3.1.1.5 Electric Shock
Electric shocks occur because of the following:
• Exposure of live parts and defects such as damage to insulating sheath
• Inappropriate work such as absence of using insulated protective gear, touching live parts.
Measures to prevent electric shock are as follows:
• Methods for safe handling of electric equipment should be drilled into the workers and inspection
and maintenance methods for electric equipment should be established.
• Special precautions should be taken to prevent electric shocks at locations where sewage is
likely to accumulate (grit chamber, pumping room and in pipe gallery). Rubber-soled sports shoes
may be used to prevent electric shocks.
A. Electric Room
Access to the electric room should be prohibited to all except authorized personnel. Signs should be
put up indicating danger when current is flowing into the room. The electric room should be managed
by the procedure below:
• Do not place combustible items near exposed wiring and electric equipment.
• Install fire extinguishers at easily visible locations such that they can be used immediately in the
event of a fire.
• If there is excessive lightning, do not approach equipment wiring or lightning arrester.
• Periodically inspect and store disconnecting switches, operating rods, insulating plates, etc., at
their specified positions.
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• Store electric torch at its specified position such that it can be used immediately during an
emergency such as power failure.
• Place insulating mat on the floor in front of the MCC panels.
B. Equipment Repair
Before repairs of equipment or wiring, permission should be taken from the plant engineer (Refer to
9.5.2) and the work supervisor should hold a meeting and decide the work procedure. Repair work
on electrical equipment should be prohibited to all except authorized personnel.
• Cut off circuits of equipment to be repaired before repairs.
• Put up sign indicating not to switch on power, assign a person to monitor the power switch, and
strictly enforce power ON/OFF controls.
• Before starting the repair, always detect the voltage using a voltage detector and tester.
• Electric shock due to fault in cable run may also be considered and always ground the equipment
before performing work.
• Operate switches such that you do not receive an electric shock.
• If a power capacitor exists, thoroughly discharge the remaining charge before starting work.
• If equipment breaks down at night, and if there is no emergency generator at the workplace, the
worker should perform repairs during daytime when there is daylight and not during night time.
9.3.1.1.6 Fire
Every facility should develop a fire prevention plan with input from the local fire officers, fire chief and
insurance company.
The plan may be very simple or very complex, depending on the specific facility needs. Some items,
which may be included in any plan are:
• Regulate the use, storage and disposal of all combustible materials/substances.
• Provide periodic clean-up of weeds or other vegetation in and around the plant.
• Develop written response procedures for reacting to a fire situation to include evacuation.
• Provide required service on all fire detection and response equipment (inspection, service,
hydrostatic testing).
• Routinely inspect fire doors to ensure proper operation and free access.
• Immediately repair, remove or replace any defective wiring.
• Restrict the use of any equipment, which may provide a source of ignition in areas where
combustible gases may exist.
• Maintain clear access to fire prevention equipment at all times.
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9.3.1.2 Personal Protection and Protective Devices
9.3.1.2.1 Head Protection
• All personnel working in any areas where there may be danger from falling, flying tools or
other objects must wear approved hard hats. Such hats should be according to the relevant BIS.
Specially insulated hard hats must be worn when working around high voltage to protect the
personnel from electrical shock.
.
• It is advisable to have detachable cradle and sweat bands for two reasons (1) to permit easy
replacement of cradles and sweat bands and (2) to make possible assignment of one helmet to
several workers each with its own cradle and sweat band for sanitary reasons.
• Once broken, the crown of a hard hat cannot be effectively repaired. It must be replaced.
9.3.1.2.2 Face and Eye Protection
Impact goggles must be worn mandatorily to protect against flying objects. They can be
spectacle or cup goggles.
Spectacle goggles must have rigid frame to hold lenses in proper position before the eyes. Frames
must be corrosion resistant and simple in design for cleaning and disinfection.
Cup goggles should have cups large enough to protect the eye socket and to distribute impact over
a wide area of facial bones.
• Chemical goggles and acid hoods should be used for protection against splashes of
corrosive chemicals. A hood treated with chemical-resistance material having a glass or plastic
window gives good protection. There should be a secure joint between the window (glass or plastic )
and hood material.
• Face shields can be used against light impact. Plastic shields should be non-inflammable and
free from scratches or other flaws, which introduce distortions.
• Welding masks must be used for protection from splashes and radiation produced by welding.
• Protective creams are used to protect the skin from contamination and penetration by oils,
greases, paints, dust etc.
9.3.1.2.3 Hands and Lower Arms
• Protective sleeves, gloves and finger pads are used for different types of hazards and jobs.
• Rubber and asbestos gloves should be long enough to come well above the wrist, leaving no gap
between the glove and coat or shirtsleeve.
• Gloves or mittens having metal parts should never be used around electrical equipment.
• Linemen and electricians working on energized or high voltage electrical equipment require
specially made and tested rubber gloves.
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9.3.1.2.4 Body Protection
• A good quality diver suit should be provided to the diver whose services are very necessary while
plugging the sewer line or removal of some hard blockage due to stone etc. at the mouth of the
pipe in the manholes. Depending upon the site condition, the suit should have a provision to
connect to an air-line with compressor or oxygen cylinder.
• Always use rubber aprons when working with chemicals.
9.3.1.2.5 Legs and Feet
• Leggings are provided where leg protection is necessary and are in the same category as coats,
frocks and aprons. Kneepads made of cloth, padding, rubber, cork are used on jobs where
kneeling is required.
• Ordinary work shoes are acceptable. They should have non-skid soles to prevent slips.
• Safety shoes are required where there is danger of dropping tools or materials on the feet.
Toe guards have been designed for the men to wear when operating machines like air hammers,
concrete breakers etc.
• For working on electrical equipment suitable safety shoes must be used.
9.3.1.2.6 Mask
A. Gas Mask
General purpose gas masks are used for respiratory protection from low and moderately high
concentrations of all types of toxic gases and vapours present in the atmosphere in which there is
sufficient oxygen to support life. Figure 9.3 shows a picture of a gas mask.
Source: JICA, 2011

Figure 9.3 Gas mask
The masks afford necessary respiratory protection under many circumstances but it is most
important to know the limitations of the various types available and to be familiar with their use.
Even when masks are used properly, other precautions such as never using open flames or
creating sparks in the presence of inflammable gases must be taken.
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The general purpose gas masks afford protection against organic vapours, acid gases, carbon
monoxide up to 2 % concentration, toxic dusts, fumes and smoke. The gas mask consists of a
face piece, a canister containing purifying chemicals, a timer for showing duration of service and a
harness for support. Protection against specific contaminants can be achieved by the selection
of appropriate canisters.
Persons using gas masks should practice regularly with them in order to become proficient in
putting them on quickly and breathing through them. Gas masks should not be used in
oxygen deficient atmospheres, in unventilated locations or areas where large concentrations of
poisonous gases may exist.
F. Dust Protection Mask
This mask consists of a fine particle filter due to which suspended fine particles in the air are not
allowed to enter into the respiratory system of the user. This protects the user from inhaling toxic fine
particles laden ambient air and hence, protects the health of workers using this mask.
G. Respiratory Equipment
In all dusty areas, effective filter masks should be used to guard against specific hazards. Hose
mask should be used by men entering tanks or pits where there may be dangerous concentrations of
dust, vapour, gases or insufficient oxygen. Hose mask with blower and the airline respirator are used
where the hazard is immediate, that is, hasty escape would be impossible or cannot be made without
serious injury if there is failure of the equipment.
Oxygen or air breathing apparatus, that is, self-contained oxygen breathing equipment using
cylinders or bottles of compressed oxygen or air is used where required. This is a must when the
length of the hose pipe in on-line supply of oxygen exceeds more than 45 m.
Gas masks: Canisters consist of a face piece connected by a tube to a canister. Chemicals in
the canister purify contaminated air. No single chemical has been found to remove all gaseous
contaminants. It does not supply oxygen and can be used where there is sufficient oxygen.
Various types of respirators and their suitability are as follows:
• Self-contained breathing apparatus
This apparatus is equipped with a cylinder containing compressed oxygen or air, which
can be strapped on to the body of the user or with a canister, which produces oxygen
chemically when a reaction is triggered. This type of equipment is suitable for an oxygen deficient
atmosphere. It is also suitable for spaces having high concentration of chlorine.
The self-contained breathing apparatus is shown in Figure 9.4 overleaf.
• Air-line respirator: Air-line length 90 m (maximum)
It is suitable in any atmosphere, regardless of the degree of contamination or oxygen deficiency,

provided that clean, breathable air can be reached. This device is suitable for high concentrations of
chlorine, provided conditions permit safe escape if the air supply fails.
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Source: Stylex Fire Protection Systems

Figure 9.4 Self breathing apparatus
9.3.1.2.7 Ear Protection
Where noise levels are high and exceed specified limits, effective ear-pads or earplugs to be used.
9.3.1.2.8 Safety Belt
When you work on ladders or scaffolding, use extreme caution to prevent falls. Safety belt should be
used to prevent falls.
9.3.1.2.9 Portable Lighting Equipment
The equipment normally used is portable electric hand lamps of permissible types, electric cap lamps
and explosion-proof flashlights.
9.3.1.2.10 Portable Blowers / Ventilating Fan
Replace the air in oxygen deficient and hazardous spaces with fresh air using exhaust fan and
exhaust ducts. Figure 9.5 shows the portable blower.
Source: GVT Engineering

Figure 9.5 Portable blower (ducting blower)
Ventilation also includes exhausting the air, but generally blowing in air is more effective.
9.3.1.2.11 Safety Fences
Visitors including adults and children visit the STP as part of social studies. For this reason, the
safety management officer should install fences in the facility and ensure a proper route for visitors to
prevent any accident.
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9.3.1.2.12 Safety Signs
To warn of danger to workers, visitors, and other construction workers in an STP, safety signs such
as shown in Figure 9.6 should be displayed in the STP.
Source: http://www.safetysignindia.com
Figure 9.6 Safety signs
9 - 18
9.3.1.3 Workplace-specific Preventive Measures
Good design and the use of safety equipment will not prevent physical injuries in
sewerage works unless safety practices are understood by the entire crew and are enforced.
These measures specific for the workplace are described here.
9.3.1.3.1 On-site
• Before entering the pit or tank, follow all the procedures required for work in confined spaces
defined in 9.3.1.1.1.
• When oxygen concentration is less than 19.5 % and hydrogen sulphide concentration is more
than 10 ppm, use forced ventilation to ventilate the tank before entering it.
• Wear rubber gloves to prevent wounds from infection.
9.3.1.3.2 Sewer System
A. Traffic Hazards
• Before starting any job in a street or other traffic area, study the work area and plan your work.
• Traffic may be warned by high-level signs well ahead of the job site.
• Traffic cones, signs or barricades to be arranged around the work, and signboards to
direct the traffic.
• Whenever possible place your work vehicle between the working site and the oncoming traffic.
• Use fluorescent jacket while working along roads. Figure 9.7 shows a fluorescent jacket
Source: Vibgyor Industries

Figure 9.7 Fluorescent jacket
B. Manhole
• Before entering the manhole follow safety entry procedure as shown in Figure 9.8 overleaf.
(Refer to Sec. 2.11.1.2 “Safety measures to be taken before any manhole entry”)
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Source: JICA, 2011

Figure 9.8 Photo showing typical confined space entry
• Before entering the manhole, follow all the procedures required for work in confined spaces
defined in 9.3.1.1.1.
• Manhole work usually requires job site protection by barricades and warning devices.
• Never use your fingers or hands to remove a manhole lid. Always use a tool specifically designed
for this purpose.
• Be alert for loose or corroded steps.
• Wear a properly fitted pair of rubber gloves and boots, or an approved substitute that will provide
protection from infection.
• Tools and equipment should be lowered into a manhole by means of a bucket or a basket.
9.3.1.3.3 Pumping Station
• Before entering the well, follow all of the procedures required for work in confined spaces defined
in 9.3.1.1.1.
• Do not work on electrical systems or controls unless you are qualified and authorized to do so.
• Guards over couplings and shafts should be provided and should be in place at all times.
• If stairs are installed in a pumping station, they should have handrails and non-slip treads.
• Fire extinguishers should be provided in the station, and should be properly located and
maintained. The use of liquid-type fire extinguishers should be avoided.
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• All-purpose A-B-C chemical-type fire extinguishers are recommended.
• Good housekeeping is a necessity in a pumping station to prevent slip and fall accidents.
• Properly secure and lock up an unattended pumping station when you leave, s to prevent injury
to a neighbourhood child and possible vandalism to the station.
9.3.1.3.4 Sewage Treatment Plant
A. Head Works
• Bar screens or racks
• Remove all slime, rags, grease, etc., to prevent slip and fall accidents. Never leave rake or
other tools on the floor.
• Never lean against safety chains.
• Always turn off, lock out and tag the main circuit breaker before you begin repairs.
• The time and date the unit was turned off should be noted on the tag, as well as the reason it
was turned off. No one should turn on the main breaker and start the unit until the tag and lock
have been removed by the person who placed them.
• Pump rooms
• If the room is below ground level and provided with only forced-air ventilation, be certain the
exhaust fan is working before entering the area.
• Guards should be installed around all rotating shaft couplings, belt drives, or other moving
parts normally accessible.
• Remove all oil and grease, and clean up spills immediately.
• Be sure to provide barricades or posts with safety chains around the opening to prevent falls.
• Until the area has been checked for an explosive atmosphere, no open flames (such as a
welding torch), smoking or other sources of ignition should not be allowed.
• Do not work on electrical systems or controls unless you are qualified and authorized to do so.
• Wet pits or sumps
• Before entering the pits or sumps, follow all of the procedures required for work in confined
spaces such as defined in 9.3.1.1.1.
• For access ladders to pit areas, the application of a non-slip coating on ladder rungs is helpful.
• Watch your footing on the floor of pits and sumps as the floor may be very slippery.
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• Tools and equipment should be lowered into a manhole by means of a bucket or a basket.
• Only explosion-proof lights and equipment should be used in these areas.
• Grit channels
• Keep walking surfaces free of grit grease, oil, slime or other material to prevent
accidents due to slip and fall.
• Before working on mechanical or electrical equipment, be certain that it is locked out and
properly tagged.
• Install and maintain guards on gears, sprockets, chains, or other moving parts that are normally
accessible.
• Before entering the channel, pit or tank, follow all of the procedures required for work in
confined spaces such as defined in 9.3.1.1.1.
• Rubber boots with steel safety toes and a non-skid cleat-type sole should be worn.
B. Clarifiers or Sedimentation Basins
• Always turn off, lock out and tag the circuit breaker before working on the drive unit.
• Maintain a good non-skid surface on all stairs, ladders and catwalks to prevent slipping.
• When it is necessary to actually climb down into the launder, always wear a harness with a safety
line to prevent a fall accident and have someone to accompany you.
• Watch your footing on the floor of pits and sumps as the floor may be very slippery.
• Guards should be installed over or around all gears, chains, sprockets, belts, or other moving
parts. Keep these in place whenever the unit is in operation.
C. Digesters and Digestion Equipment
• Methane gas produced by anaerobic conditions is explosive when mixed with air.
• Smoking and open flames should not be allowed in the vicinity of digesters, in digestion control
buildings, or in any other areas or structures used in the sludge digestion system.
• All these areas should be posted with signs in a conspicuous place, which forbid smoking and
open flames.
• All enclosed rooms or galleries in this system should be well ventilated with forced air ventilation.
Never enter any enclosed area or pit which is not ventilated.
• Before entering the digester for cleaning or inspection, follow all of the procedures required for
work in confined spaces such as defined in 9.3.1.1.1.
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• When oxygen concentration is less than 19.5% and hydrogen sulphide concentration is more
• Explosion-proof lights and non-sparking tools and shoes must always be used when working
around, on top of, or inside a digester.
• When working on equipment such as draft tube mixers, compressors and diffusers, ensure that
equipment is properly isolated in function by closing valves locked out and appropriately tagged,
to prevent the gas from leaking.
• If a heated digester is installed, read and obey the manufacturer’s instructions before working on
the boiler or heat exchanger because there is a risk of explosion.
• Sludge pump rooms should be well ventilated to remove any gases that might accumulate from
leakage, spillage or from a normal pump cleaning.
• Good maintenance of flame arresters will ensure that they will be able to perform their job of
preventing a back flash of the flame.
D. Aerators
• An operator should never go alone into unguarded areas.
• Approved life buoys with permanently attached hand-lines should be accessible at strategic
locations around the aeration tank.
• Operators should wear a safety harness with a lifeline when servicing aerator spray nozzles and
other items around an aerator.
• Lower yourself into the aeration tank only with a truck hoist if one is available or use a crane.
• Be extremely careful when using fixed ladders as they become very slippery.
• Watch your footing on the floor of the aerators: the floor may be very slippery.
E. Sewage Ponds
• Never go out on the pond for sampling or other purposes alone. Someone should be standing by
on the bank in case of trouble.
• Always wear an approved life jacket when working from a boat or raft on the surface of
the pond.
F. Disinfection Device
• Do not accept containers that have not been pressure tested within five years of the
delivery date.
• Do not accept containers not meeting the standards. (Refer to IS 10553 Part I “Requirement for
chlorination equipment”)
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The most common causes of accidents involving chlorine are leaking pipe connections and
excessive dosage rates.
• Bottles or cylinders should be stored in a cool, dry place away from direct sunlight and heat.
• Bottles or cylinders should never be dropped or allowed to strike each other with force. Cylinders
should be stored in an upright position and secured by a chain, wire rope, or clamp.
• One of the bottles or cylinders should be blocked so that they cannot roll.
• Always wear a face shield when changing chlorine containers.
• Connections to cylinders and tanks should be made only with approved clamp adaptors or unions.
Always inspect all surfaces and threads of the connector before threading the connection. Check
for leaks as soon as the connection is completed.
Never wait until you smell chlorine or sulphur dioxide. If you discover even the
slightest leak, correct it immediately.
• Like accidents, leaks generally are caused by faulty procedure or carelessness.
• Obtain from your supplier and post in a conspicuous place (outside the chlorination and
sulphonation room), the name and telephone number of the nearest emergency service in case
of severe leak.
• Cylinder storage and equipment rooms should be provided with some means of ventilating the
room. As chlorine is approximately two and a half times heavier than air, vents should be provided
at floor level.
• Normally ventilation from chlorine storage room is discharged to the atmosphere, but when a
chlorine leak occurs, the ventilated air containing the chlorine should be routed to a treatment
system to remove the chlorine.
• A caustic scrubbing system can be used to treat the air containing chlorine from a leak.
A caustic solution holding tank with full solution at all times should be at site so that a leaky chlorine
tonner can be rolled and dropped into it if the chlorine leak cannot be stopped. There should be a
suitable hoist for this purpose.
• Always enter enclosed chlorine cylinder storage or equipment rooms only after precaution. If you
smell chlorine or sulphur dioxide when opening the door to the area, immediately close the door;
leave ventilation on, and seek assistance.
• Never attempt to enter an atmosphere of chlorine when you are by yourself or without an
approved air supply and protective clothing.
Remember to use the “dost system” (system in which two persons work as a single unit) when
responding to a leak.
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9.3.1.3.5 Sewage Quality Test Laboratory
A. Toxic substances should be handled with the following precautions:
• Store poisonous substances in containers with tight lids. Clearly indicate the contents of the
containers; place them in a special cupboard with glass front for chemicals that can be locked and
record the quantities of the substances used.
• Some substances may decompose when exposed to light and explode and store them in cool
and dark location.
• Store gaseous substances in well-ventilated locations.
• Gaseous substances should generally be handled in well-ventilated locations. If this is not

possible, safety masks should be worn, the location ventilated thoroughly, and after use, the
persons handling the substances should gargle and wash their face.
B. Alkali / acid should be handled with the following precautions:
• Wear protective goggles, rubber gloves and protective clothing, if necessary.
• Handling hydrochloric acid
• Since this acid is highly corrosive, always wash your hands after handling it.
• Sometimes, pressure remains in sealed bottles in which this acid is stored. When opening the
bottle, take care because the acid within the bottle may gush out unexpectedly.
• Handling nitric acid
• Nitric acid vapours are strong respiratory toxins, so take care to ventilate the place thoroughly.
• Take measures not to handle vapours.
• When opening the container with nitric acid, ensure that the acid does not gush out when the
container cap is removed.
• Handling sodium hydroxide
• Take care that sodium hydroxide does not stick to the hand or other body parts because it has
the action of decomposing proteins and skin.
• Locations should be available for properly washing parts of the body, preferably where sodium
hydroxide is used.
• When dissolved in water, intense heat is generated and the solution may spray out. Take care
to dissolve in small quantities to avoid risks.
C. Glass appliances should be handled with the following precautions:
• Inspect thoroughly before use; do not use those with scratches or cracks.
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• Handle beakers, flasks, test tubes that have small thickness very carefully, since these objects
have less mechanical strength.
• Containers with reasonable thickness if heated suddenly may break; so take precautions.
• Do not use glass tubes with sharp corners.
• Use appropriate supporting stands when you handle large flasks.
• When you insert a glass tube or a thermometer into the hole of a rubber stopper or cork stopper,
do carefully as it may break and lead to an injury.
• Take care not to touch heated glass with bare hands.
• Insert solids in a beaker of flask while tilting the container and slide in the solid gently so as not
to break the bottom.
9.3.2 Corrective Measures
9.3.2.1 Emergency Contact
The plant engineer should set up an emergency contact system to prepare for emergencies, and
appropriately fix the scope of contacts and the persons responsible for contacting relevant
personnel. The contact system should include records of medical organizations, and the names and
telephone numbers of departments such as internal medicine, surgical department, ophthalmology
and general hospital nearby. Figure 9.9 shows an example of emergency contacts.
Source: JSWA, 2003

Figure 9.9 Example of emergency contacts
9.3.2.2 Emergency Measures
Workers frequently perform dangerous work or handle dangerous chemicals while working in
sewerage systems and on-site systems. For this reason, emergency measures need to be
thoroughly understood beforehand. Workers need to adopt appropriate action if such an unexpected
situation arises. Information on emergency measures is as follows.
• The supervisor of the safety personnel (organization) should always inspect and maintain rescue
appliances and clearly indicate their storage location.
9 - 26
• The supervisor of the safety personnel (organisation) should establish assistants for rescue
action at each workplace and train them beforehand.
• Medical organisations to be contacted in an emergency should be decided beforehand (names

and telephone numbers of hospitals with internal medicine, surgical department, ophthalmology
and general hospital to be kept ready so they can be summoned immediately).
• Should be able to offer first-aid immediately.
• Subsequently, the doctor, and if necessary, the rescue organisation where the patient is being
given treatment, should be notified the type and seriousness of the accident, the first aid given,
the rescue appliances in hand, etc.
• The patient should be made to lie in a relaxed manner.
• Although it is good to rest the head and the body in a horizontal condition on a bed, if the face is
flushed, the head should be raised slightly.
• If the colour of the face turns blue, the pillow should be removed from underneath and the head
to be maintained at a low level to enable better blood circulation.
• If the patient has a vomiting sensation, the face should be kept sideways to allow vomiting.
• The patient’s body temperature should be checked, and the patient should be encouraged, but
should not be moved at random.
• Attention should be paid so as not to overlook any wound, burn, bone fracture, hip dislocation, etc.
• The status of the patient, the condition of the surroundings, environment and work method should
be studied closely, a sketch should be made and photos should be taken.
• Samples of vomit, excrement and urine, bloodstain, etc., should be preserved as it is, so that they
can be tested later.
Care and treatment for injured workers are described in Appendix B.9.5 separately for each
wound or injury.
9.3.2.2.1 First Aid Tools
The plant engineer should make arrangements for quickly offering first aid measures.
The plant engineer should do the following to minimize injury during an accident or disaster:
• Provide necessary materials for offering first aid.
• Artificial respirator
• Stretcher as shown in Figure 9.10
• First aid box as shown in Figure 9.11
9 - 27
Source: Hiren Industrial Corporation

Figure 9.10 Stretcher
Source: Hiren Industrial Corporation

Figure 9.11 First aid box
• Should ensure that a responsible person always manages the first aid tools.
• Drugs and equipment set aside in a first aid box are as given below. Unnecessary and out of date
items should not be placed in the first aid box.
• Waterproof casts
• Adhesive plasters of assorted sizes
• Eye protection pads
• Disinfectant lotions
• Safety pins of assorted sizes
• Unused sealed twin blade razor
9.3.2.2.2 Extinguisher
Fires are classed as A, B, C, or D type fires, according to what is burning.
• Class A fires (general combustibles such as wood, cloth, paper or rubbish) are usually controlled
by cooling. Water is used to cool the material.
• Class B fires (flammable liquids such as gasoline, oil, grease, or paint) are usually smothered by
oxygen control - as by use of foam, carbon dioxide, or a dry chemical.
• Class C fires (electrical equipment) are usually smothered by oxygen control - use of carbon
dioxide or dry chemical extinguishers - non-conductors of electricity.
• Class D fires occur in combustible metals, such as magnesium, lithium or sodium, and require
special extinguishers and techniques.
9 - 28
Use carbon dioxide or halon compressed gas extinguishers to control fires around electrical
contacts. Do not use soda-acid type extinguishers because the electric motor will have to be rewound
and you could be electrocuted attempting to put out the fire. Also, remember that carbon dioxide can
displace oxygen.
9.3.2.2.3 Emergency Lighting
Emergency lighting is required for illuminating critical control areas and for allowing fast exit from an
area if the normal lights go out. An emergency generator that starts automatically with a power failure
is wired separately to turn on emergency lights in critical areas. Instead of an emergency generator,
battery packs are often used for evacuation. Refer to clause 5.12.4 and 5.12.6 of Part-A manual.
9.3.2.3 Searching out Hazards
The safety management officer should carry out the following safety examinations:
• Record the status of occurrence of accident (Appendix B.9.6). Study the status of occurrence and
causes of accidents, and based on the studies pick out the conditions for occurrence of accidents
(risk locations, risky work, risky actions, etc.).
• Examine which parts of the workers’ bodies were affected by accidents from the records of
accidents. Examine the necessity of protective gear.
• Check the status of work location, and study unsafe actions and inappropriate working methods
of the workers.
• Study the status of use of workers’ tools.
• The safety officer should consider the results and report them to the plant engineer.
• The safety officer should reflect the results of the examinations above in the education of
the workers.
9.4 HEALTH ASPECTS AND MEASURES
9.4.1.1 Personal Hygiene against Pathogen
The worker should take precautions because a large number of coliform groups, various kinds of
micro-organisms, and egg parasites exist in sewage.
The workers should strive to maintain good health by taking care of the following points:
• Wear clean uniform, work boots, etc.
• After work and before having a meal, always wash hands and disinfect them.
• After work, take a shower if possible.
• Do not enter the offices and lounges wearing dirty clothes.
• If necessary, take vaccinations against tetanus, leptospirosis fever and so on.
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9.4.1.2 Maintaining Cleanliness
The worker should maintain each facility in a clean and neat condition.
• The floors of workrooms, stairs and corridors should be cleaned at the appropriate frequency to
maintain them in a clean condition.
• Disinfection of relevant locations is to be carried out periodically.
9.4.1.3 Health Check
Workers should receive health check once a year to maintain their health, and prevent illnesses or
detect them at an early stage.
The results of the health check should be maintained as records.
Recommended items to be inspected during the health check are as given below.
• Examine medical history.

• Examine subjective symptoms and other objective symptoms.
• Check height, weight, vision and hearing ability.
• Chest X-ray examination.
• Blood pressure measurement.
• Check for anaemia.
• Check for liver functions.
• Check for lipids in blood.
• Check blood sugar level.
• Urine analysis.
• Electrocardiogram analysis.
9.4.2 Welfare Measures
The Draft Sanitation Workers (Regulation of Employment and Conditions of Service) Act 2012
proposes constitution of a Sanitation Workers State Welfare Board to exercise powers conferred on
it and to perform welfare functions such as the following for sanitation workers:
• Provide immediate assistance to a beneficiary in case of an accident

• Sanction of loan and advances
• Medical expenses for treatment of major ailments
• Financial assistance for education of children
• Payment of maternity benefit
• Make provision and improvement of welfare measures and facilities as may be prescribed.
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9.4.3 Corrective Measures
When a worker has symptoms of an illness listed in Table 9.1, the plant engineer should
ensure that the worker is checked-up by a specialist doctor and receives proper treatment and
care and should take the following actions considering the content of work done by the worker:
• Change the workplace if necessary

• Change the content of the work
• Shorten the working hours
• Perform relevant measurements of the working environment
• Maintain the facility or equipment
9.5 SAFETY PERSONNEL (ORGANISATION)
The plant engineer is expected to establish an appropriate safety management organisation in order
to avoid losses of workers, stoppage of operations, etc., due to accidents.
9.5.1 Institutional Arrangement
The number of workers assigned for O&M of an STP varies according to the scale of the facility, the
treatment process used, and equipment installed.
If the scale of the facility increases, the following will also increase:
• Equipment installed
• Workers
• Quantity of work
• Injuries and accidents
Accordingly, the number of safety & health supervisors varies depending on the size of the facility.
Figure 9.12 shows the safety management organisations for large STP, medium STP, and small STP,
respectively.
Figure 9.12 Safety Management Organisations for large, medium and small STP
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9.5.2 Human Resources
Safety officer is to be assigned, and safety management to suit the number of workers in the
workplace is required to be implemented.
The plant engineer should select and assign safety officer to ensure the safety and health at the
workplace. The plant engineer should give permission for any required repair works on equipment /
facilities in the STP.
The safety officer should carry out the following duties as full time service:
• Prevent risks or personal injury to workers and promote health checks and other improvements
to health of the workers.
• Select a safety supervisor to manage worker’s safety and select a health supervisor to manage
workers’ health.
• If an accident occurs, investigate its causes and take measures to prevent its recurrence.
• Perform tasks necessary to prevent accidents.
The safety supervisor is selected by the safety officer, and has the following duties:
• If there is a risk in the structure, equipment, work place or working method, adopt emergency
measures or measures to prevent such risks.
• Periodically inspect equipment and tools such as safety equipment and protective gear, etc., to
prevent risks.
The health supervisor is selected by the safety officer, and has the following duties:
• Study the working environment, working conditions and equipment in relation to how they affect
the health of the workers.
• Inspect and maintain first-aid tools.
• Provide health education and look after matters necessary for maintaining good health.
The plant engineer should nominate a safety and health promoter at a site where a safety supervisor
or a health supervisor is not selected.
The safety and health promoter is selected by the plant engineer and has the following duties:
• The safety and health promoter should inspect the facility and equipment, check their usage
stage, and based on the results of these checks, should adopt relevant measures.
• The safety and health promoter should make efforts to maintain the health of the workers through
health checks and impart safety and health education to workers.
• The safety and health promoter should examine the causes of work accidents and measures to
prevent recurrence of the same.
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• The safety and health promoter should collect information on workers’ safety and health, prepare
and maintain statistics of work accidents, diseases and absence from work.
In the absence of
(a) safety management officer,

(b) safety supervisor,
(c) health supervisor,
(d) safety & health promoter,
The plant engineer should manage all safety and health matters.
9.6 AWARENESS AND TRAINING
Safety training should aim for improving awareness and techniques of persons engaged in work
so that accidents during work are prevented. Safety training should consist of four courses to be
imparted to Manager, Technical, Skilled and Unskilled grades of personnel.
• The Manager is a person who performs labour management and manages the work environment
so as to ensure the safety of workers.
• A person in the Technical grade is an Assistant Engineer or Junior Engineer, who operates and
repairs mechanical and electrical machinery and equipment by his own judgement.
• A person belonging to the skilled grade is one who uses machines and equipment, and performs
work following the instructions of the superior using the Work Manual.
• A person belonging to the unskilled grade is one who performs manual work mainly in the plant
under the instructions of the superior.
Trainees should upgrade/acquire skills to perform their work safely through training. The overview of
training for each grade of personnel is given below.
9.6.1 Manager
Managerial training should be given to managers once-every five years on the topics below.
• Laws, regulations and latest information related to sewerage systems

• Labour and welfare matters related to workers
• Periodic performance assessment of subcontractors and vendors
9.6.2 Technical Staff
The plant engineer should ensure that training in their respective fields is imparted to the technical
staff once every three years in the mechanical and electrical sections (Technical Grade).
9.6.2.1 Mechanical
• O&M of mechanical machinery and equipment such as pumps and blowers
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• Repairs to mechanical machinery and equipment such as pumps and blowers
• Methods of examining the causes of breakdown in mechanical machinery and equipment such
as pumps and blowers
• Methods of operating machinery and equipment (welding equipment) used for repairs during
breakdown of pumps, etc.
• Emergency response procedures
9.6.2.2 Electrical
• O&M of electric equipment such as motor controls center (MCC)
• Repairs to electric equipment such as MCC
• Methods for examining causes of breakdown in electric equipment

• Emergency response procedures
9.6.3 Skilled Staff
The plant engineer should ensure that training in their respective fields is imparted to the skilled staff
once a year in the mechanical and electrical sections.
9.6.3.1 Mechanical
• Safe work
• Communication at the workplace including instructions from supervisors, communicating with

subordinates, and communication during joint work
• Maintenance of mechanical machinery and equipment such as pumps and motors
• Repairs to mechanical machinery and equipment such as pumps and motors
• Hazardous work (oxygen deficiency, hydrogen sulphide poisoning)
• Measuring instrument (oxygen concentration meter, etc.)
• Method of usage of protective gear (safety belt, breathing apparatus)
9.6.3.2 Electrical
• Safe work

subordinates and communication during joint work
• Maintenance of electric equipment such as breakers and switches
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• Repairs to electric equipment such as breakers and switches
• Electric shocks
• Method of usage of measuring instruments (oxygen concentration meter, rpm gauge, insulation
tester, etc.)
• Method of usage of protective gear (safety belt, breathing apparatus)
9.6.4 Unskilled Staff
The plant engineer should give training to unskilled staff once a year.
• Safe work (what not to do)

subordinates and communication during joint work
• Matters related to keeping things tidy and in order, cleanliness and neatness
• Names of tools and their usage (pliers, screwdrivers, etc.)
• Electric shocks
• Use of protective gear (gloves, protective goggles, etc.)
9.6.5 Training Assessment
Persons who have received safety training should be assessed on the lessons learnt.
The results of the assessment should be recorded in the assessment table shown in Table 9.7.
Table 9.7 Record of training assessment
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The plant engineer should warn the trainees on items assessed as unsatisfactory, and improve their
awareness to such items. The worker should receive safety training and should preferably not be
transferred to a different workplace within one year. Otherwise, this would result in lowering the
quality of work at the workplace and may lead to a drop in work efficiency. For this reason, work
status at the workplace, stationing of personnel and training assessment should be
considered during transfers.
9.7 EMERGENCIES
9.7.1 What is an Emergency?
An emergency is a situation developing before our eyes with full conscience and realization that soon
the situation will turn to adversity and even fatal. We may not be equipped to deal with it. We cannot
take control. This leaves us with no time to locate the source of help. We may not know where to get
help for a given situation.
9.7.2 How to Think during Emergencies?
The foremost requirement is not to jump to conclusions. Always think of what is most important and
imperative at that moment. Let us consider some situations that can arise
9.7.2.1 Situation 1
You notice a colleague during working hours trying to repair a floodlight during broad daylight at a
height of some 6 m by standing on a permanent secure ladder but he is not wearing safety gloves.
You are afraid that he may get electrocuted and nobody could reach him at that height soon enough.
This is a simple emergency situation. You have the options of (a) calling him on the cell phone to
alert him about his not wearing gloves, (b) going up the ladder personally with a spare set of gloves,
(c) quietly switching off the electrical circuit to that mast and (d) quietly slipping out of the scene
unnoticed. Each solution will merit itself under certain situations. Solution (a) is apt when the
electrical circuit is already found switched off. Solution (b) is apt when the electrical circuit is
switched off and the fuse is in your pocket. Solution (c) is apt when you find that the circuitry is
energized. Solution (d) is apt when you find the circuitry is already switched off and your colleague has
recorded in the works register that he is taking the fuse with him, so that nobody can energize the
circuit until he returns.
9.7.2.2 Situation 2
A colleague is sitting on the walkway of a clarifier and collecting a sample of the treated sewage
overflowing the weir. You notice that a snake is slowly making its way towards him. If you move in
speedily, the snake may be hustled and move away from you faster and move closer to your
colleague. This is a very serious emergency. Now, what will you do? / what should you do? The first
thing to do will be to call the colleague on cell phone and tell him not to move and sit still as reptiles are
alerted only when there is movement ahead of them. The next thing to do will be to ask your colleague
to jump into the clarifier and swim to the safety of the channel and launder only if he knows swimming.
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Suppose he does not know swimming, ask him immediately to stand upright, so that if it bites, it may
spare the body parts closer to the heart and he can be saved by tying up the limb above the bite with
a rope or a torn piece of a shirt. Simultaneously, you can follow the reptile and try to push it into the
water surface with whatever piece of extended tool that you may have.
9.7.2.3 Situation 3
During a monsoon season, let us say there is a sudden cloudburst and torrential downpour and
before the staff could realize, the entire site is flooded to about knee-height and the sludge pits are
marooned. Electrical connections are shorted somewhere and there is total darkness. The staff are
scattered at different locations in the STP area of over 25 hectares. There was no way of setting foot
forward, as they cannot locate where the pump pit is. The fear of more floods is very much there.
You can somehow make out the silhouette of the administrative building and slowly wade towards
it by announcing yourself. When all the staff members reach the building, they do not hear the
voices of two persons in that shift. Panic grips them. However, nothing could be done until next day
morning when it is discovered that of the two missing persons, one was absent and the other had gone
out on personal work without informing others. The lesson here is that in every shift, be punctual in
reporting and ensure a mini assembly of handing over and taking over at the “meeting point”.
This ensures mutual knowledge of presence or absence. Another lesson is to have solar powered
lampposts with self-contained circuits insulated against rains and located adjacent to electrical
lampposts so that when total electricity fails, these will come on at least for that interval of time.
9.7.2.4 Situation 4
When two operators were moving a portable diesel pump on a trolley over a gravel roadway, the
road caves in suddenly. They were pulled into a huge pit fortunately after the engine was pulled in.
Later, it was found that the reason was the plant bypass concrete pipeline crossing the road had
a corroded crown to such a degree that it could not take that load. There were no signs on the
site showing that the pipeline is crossing the road there. It would have been catastrophic if the
operators had fallen first and the engine after them. Hence, all pipe crossings of roads should be
through culverts with sidewalls raised above the ground. Bypass pipelines flow rarely, and gases
accumulate and corrode the pipe easily. Always provide bypass pipelines in non-corrodible pipe
material. Always erect markers over the route of big buried pipes.
9.7.2.5 Situation 5
A primary settling tank sludge-removal-arm is not rotating for sometime but the settling tank
continues to be operated. After sometime, it is noticed that the accumulated sludge is becoming
visible through the sewage liquid when seen from the top. The settling tank is stopped from service
and the sludge is allowed to dry up. Manual labourers are employed to walk into the settling tank
and scoop out the sludge and transport it as head loads. Suddenly, two of labourers are found to be
“sinking” into the sludge. Fortunately, the other labourers throw a rope and the two are able to grab
it and are pulled out. The lessons are simple. Wet grit dumps can behave like quicksand in such
locations. Suppose the two were not noticed sinking, they would have been located only after death,
while the sludge was being scooped. Removing such grit dumps should be as per regulations for
confined spaces and all personnel should be watched and accounted for, by a supervisor.
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9.8 THE NEED TO RESIST
Sometimes, tasks required to be carried out by field staff may involve risks, ignoring safety and
potential emergency. The employee must politely resist doing the same. If every staff member resists,
only then the management will know and make amends.
9.9 SUMMARY
Sanitation workers or STP operators are often forced to work under poor working conditions with high
risk of operational diseases or accidents.
Each operator or worker should ensure operational safety by wearing designated personal protection
or by using designated protection devices.
Above all, they should follow the working procedures thoroughly when working in confined spaces.
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Part B: Operation and Maintenance CHAPTER 10: ON-SITE SYSTEMS
CHAPTER 10: ON-SITE SYSTEMS
10.1 INTRODUCTION
The on-site treatment is done individually in the premises (at the point of generation itself) as an
interim measure. The on-site treatment ranges from a basic sanitary facility such as pit latrine
(twin pit with water seal) to a simple type where anaerobic treatment and infiltration treatment are
done by combining a septic tank and a soak pit and a sophisticated type where advanced sewage
treatment is done. The sludge produced in each on-site facility is collected by an exclusive vehicle
and is then treated collectively. The treatment systems of sewage in the on-site system and the
off-site system are shown in Figure 10.1.
Figure 10.1 On-site and Off-site sewage treatment system

Note: There can be cases where both black and grey water can be treated together.
10.2 ON-SITE FACILITY MAINTENANCE SYSTEMS
A system for maintaining an on-site treatment facility varies depending on its volume and treatment
method. If the volume is small, in many cases the owner controls the facility voluntarily. If the volume
is medium or large, or if the facility employs an advanced treatment method, a separate maintenance
agency controls the facility. These different volumes of facilities adopt different types of control. In
facilities of large volumes, operating and maintenance staff may be present at site in all three shifts.
In small or medium volume facilities, operating and maintenance staff are full time in day shifts and
only limited number are at site in other shifts.
Basic hygienic treatment facilities such as pit latrines and septic tanks require regular cleaning
(sludge collection) as the main maintenance work. Accordingly, the owner shall check periodically how
much sludge is accumulated in the facility and determine when it should be collected and taken out.
Meanwhile, the ULBs shall prompt the residents and the persons concerned to raise awareness of the
importance of the sludge control of their facilities.
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More specifically, both state and municipal governments should draw up an action plan for
extracting, treating, and disposing of the septage generated in these facilities in accordance
with the “Septage Management Guidelines” (MoUD, 2012) and prepare the necessary budgets
for implementation.
The precautions in septage management planning are listed below.
• The state and municipal governments should establish an on-site sanitation system (OSS) that
conforms to relevant laws.
• Efficient management requires a database of hygienic facilities including septic tanks

under control.
• Public and private agencies in charge of septage collection should establish a mechanism to
ensure that the service is done promptly.
• Selecting a septage treatment method requires a survey of land use pattern and land
requirements, traveling distance, pollution prevention, construction and O&M costs.
• It is necessary to disclose information about septage management to the residents and persons
concerned and to conduct necessary social activities for getting their cooperation.
10.3 MAINTAINING ON-SITE FACILITIES
An on-site facility is controlled by the owner, or a habitation. Its O&M may be however by a contractor
who should be familiar with the facility plan, design and specifications for the components, relevant
drawings, and maintenance records. In addition, the contractor should understand how to operate,
maintain, inspect, repair, and adjust the equipment, as well as how to take up their problems.
10.3.1 Inspecting and Maintaining the Treatment Unit
The advisory note on Septage Management prepared by the MoUD can be referred to regarding the
inspection and maintenance of these on-site facilities.
A. Inspection

The purpose of inspection is to detect an abnormal condition or failure at an early stage itself,
find out the cause and take necessary remedial measures quickly by checking the equipments for
operation and the whole treatment unit for the operating status. The number of inspections may
vary according to the treatment method and the volume and also the method of inspection being
manual and / or remote sensing techniques.
B. Maintenance and Repair
The purpose of maintenance is to ensure that the equipment performs as defined in the
specifications. If the inspection results show an abnormal condition, failure, or degradation in the
performance defined in the specifications, repairs are needed. Such repairs are made by on-site
staff or entrusted to a special agency.
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10.3.2 Cleaning
Frequent cleaning of the equipment and removing residual sludge is necessary to maintain the
performance.
The contractor should keep a record of cleaning and record it in the maintenance reports.
10.3.3 Water Quality Control
Some facilities may have to be evaluated for both the quality of influent and effluent to find out the
need for improving the treatment method itself.
10.3.4 Hygienic Measures including Infection Prevention
Excreta and sludge include many infectious pathogens and parasites. Therefore, the illegal disposal
of the sludge into the environment or its insanitary treatment causes contagious diseases and pollutes
groundwater or rivers. Table 10.1 shows the key pathogens contained in the excreta and sludge.
Table 10.1 Key pathogens contained in excreta and sludge
Source: Sudo.R, 1977
10.3.5 Measures against a Disaster or Accident
Unlike a large-scale STP, an on-site and small-scale treatment facility normally does not require
a resident engineer for operational control. Therefore, it is necessary to plan measures against
emergency situations when a resident engineer is not available. The person in-charge of
the plant should:
• always take required measures against any disaster or accident,
• when a disaster occurs, immediately perform patrols and inspections to check for abnormality,
• continuously monitor the storage status of materials for emergency recovery and reserve units,
and place the latter in a standby state,
• draw up a mobilization plan and duty list against a disaster or accident, and inform the persons
concerned thereof, and
• make plans for reporting, liaison, temporary action, and recovery.
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10.4 LATRINE / TOILET
10.4.1 Pour Flush Water Seal Latrine
• The squatting pan should be sprinkled with a small volume, about 500 mL of water and scrubbed
daily with a long handle bamboo piece or strong wood gently crushed to the shape of a brush at
one end. This shall be done preferably immediately after the morning usage when the pan is wet
to scour the sticky organics.
• After scrubbing, again a small volume of water should be poured and simultaneously the
scrubbings can be pushed into the pit using the same make shift brush, or by other means
by the householder.
• Ablution water shall be kept in a plastic container and covered with a lid and kept ready inside the
latrine enclosure. The volume shall not be less than the needs of the number of persons in the
household for a morning usage. For example, if a person can manage with 2 litters per usage and
if there are four persons in a household, the water required is 8 litres. It will be prudent to store 10
litres of water. The mug which is used for taking the water from the stored plastic container shall
be hung on the wall on a strong nail and shall not be immersed for long time inside the container
because of growth of slime over the mugs.
• Storm water should not be let into the pan.
The Technology Advisory Group and World Bank have stipulated the procedure for switching from
one pit to another as under.
A. Only one of the two pits is to be used at a time. After about three years when the first pit is full
(the indication being back flow when flushed), the discharge from the pan should be diverted to
the second pit and the first pit should not be used. The diversion of discharge to the second pit
can be undertaken by the householder or, if he wishes, he can hire a private agency, which shall
not get into the pit under any circumstances. After the first pit is filled and the latrine is connected
to the second pit, the cover of the first pit should be removed. Thereafter soil should be filled for
150 mm depth in the pit and the cover placed in position. Where earth is not easily available or
there is difficulty in removal of the pit cover, the earth could be added later when emptying the pit
contents for ease of handling. The contents of the first pit shall be removed after two years by the
owner or by a hired agency but no one should enter the pit. Once the cover is removed, the pit
should be left free to ventilate and if it is rainy, a temporary cover shall be provided to prevent rain
water entering the pit. Long handle spades, shovels or augers alone shall be used to empty the
pit. The contents will then be safe for handling, dry and without any foul smell. In special cases
such as flooded areas, etc., the sludge, after being taken out, should be spread out in a bed for
sun drying during the non-rainy season. It can be utilized as filler in the kitchen garden or fields.
When the second pit is full, the first pit should be used by diverting the discharge from second
to first pit. Thus, one of the two pits is to be used alternately. The householder should keep a
record when each of the two pits is put to use, disconnected and emptied; a card supplied by the
local authority should be used for this purpose. The humus will become the property of the local
authority. Marketing facilities may be developed for the sale and use.
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B. The local authority should provide free service to latrine owners, and attend to their complaints
regarding construction, operation and maintenance. Groups of about 2000 latrines can be
maintained by one skilled person assisted by one unskilled person. In smaller towns of less
than 1500 latrines, at least one trained person should work under the guidance of a technical
employee of the local authority.
However, in the beginning when the number of latrines is less than a thousand, the Junior
Engineer or the Supervisor can attend to complaints by supervising and employing hired labour.
10.4.2 Public Toilet
Public toilets shall be installed in parks, along roads, and in public places. Some of these can be
independent in outdoors and some installed in buildings. The users of toilets in public places are
not well informed and this can result in insanitary conditions. Accordingly, the ULB shall arrange for
frequent cleaning by its staff and maintain the hand-washing units regularly. If a public toilet has
sewage treatment facilities, the local body shall maintain them as well. It is recommended to clean
the toilet at least once a day. There should be a provision for collecting fees from the users and
spending them for cleaning the toilets.
10.4.3 Mobile Toilet
Mobile toilets, which can be delivered by vehicle, are temporarily used for shelters and community
events. These have a storage tank in the lower part to store the sewage, which is extracted and
disposed of at the appropriate time. Some mobile toilets are equipped with a cleaning water tank and
manual flushing to wash the excreta. The tank capacity is limited, so it is necessary to plan a system
for emptying the stored sewage and to maintain a disposal site.
The method of using common toilets applies to public and community toilets. The local authority
should submit a request for regular cleaning and instruct the users not only to follow the guidelines
and cooperate in conserving water.
Mobile toilets need to be kept in stock for emergency use. Therefore, the state and municipal
governments should establish a network with private sectors to construct a system for arranging such
toilets when an emergency occurs.
10.5 ON-SITE METHODS
10.5.1 Conventional Septic Tank / Improved Septic Tank
Septic tanks shall be designed strictly as per BIS 2470. In order to maintain the functions of septic
tanks, the user should:.
• Not use, any chemicals (e.g. acid and alkaline agents) which may have an adverse effect on the
functioning of the septic tank,
• Keep the tank and its surrounding area neat and clean.
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• Never mix oil with discharged water which will upset the digesting function of the septic tank and
generate scum and foul odour. If it is unavoidable, install a gravity baffle chamber for use as an
oil-water separator in the upstream of the septic tank, and
• Monitor the sludge accumulation in the septic tank at the right time to prevent its overflow.
10.5.1.1 Purifying Wastewater and Accumulating Sludge
Organic and solid substances in sewage are digested in the septic tank and converted to digester
gases, scum, and digested sludge, which are gradually accumulated. Meanwhile, the sewage is
purified to change to intermediate water. If the digested sludge and scum in the septic tank
accumulate excessively, they partially flow out with the intermediate water, resulting in degradation in
the quality of treated sewage. If the degraded treated sewage flows into the soak pit, the functioning
of the soak pit is also upset. Therefore, control and regular extraction of sludge from the septic tank
helps in stable performance.
The amount of sludge accumulated in the septic tank varies depending on the type, volume, and
quality of sewage, the tank capacity, the foreign matter mixing ratio, and the liquid temperature.
The amount of sludge can be determined by inserting a transparent vinyl pipe to the bottom of the
tank, blocking the pipe tip with a finger, and pulling it out. When the amount of sludge and scum
reaches about one-half of the tank depth, it is the time to extract the sludges. If the tank is large, it
is recommended to perform sludge surface checks at multiple points and to find the average level.
Accordingly, inspection chambers should be provided at the time of installation of the septic tank.
There shall be a minimum of two chambers in each tank at opposite ends on the longer side.
10.5.1.2 Mechanical Cleaning of Septic Tank
Please refer to Appendix B.10.1 for the details on mechanical cleaning on septic tank.
10.5.1.3 Septage Management
In general, the administrator requests a cleaning contractor to extract sludge from the septic tank.
If a regular extraction system is introduced, the contractor visits the facilities to conduct sludge
extraction work regularly. Sludge extraction is classified into two types according to the sludge
accumulation status: whole and partial. These are used based on the volume of the septic tanks. For
this work, equipment like a septage collection vehicle should be used and not extracting by hand.
The contractor should:
• Not splash sludge on the surrounding area (e.g. the soil surface),
• Take hygienic measures if manual work is unavoidable in case,
• Extract sludge quickly, otherwise offensive odour will spread over the surrounding area, and
• Maintain a record of the work and the amount of sludge extracted.
The sludge extraction frequency is about once every two to three years, which varies depending on
how the toilet is used and the tank capacity. The advisory note on septage management released by
the MoUD is available in http://urbanindia.nic.in/programme/uwss/Advisory_SMUI.pdf
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10.5.2 Advanced Type Treatment Units
10.5.2.1 Pre-treatment Process
A. Screen Facilities
The incoming sewage contains organic as well as other inorganic foreign matter like paper,
wooden pieces, silt and sand. The screening process removes the inorganic floating matter
before the sewage enters the treatment unit. If screening fails for some reason, it clogs or
damages the pipe, waterway, or other equipment.
i. Removing the Screened Materials
The amount of floating matter to be removed by the screen varies depending on the mesh size
of the screen. If foreign matter is not removed, the captured matter increases gradually and the
screen becomes clogged. In the extreme case, the sewage may overflow. Moreover, clogging
stops sewage flow before the screen creating anaerobic conditions and offensive odour.
ii. Sanitary Disposal of Screened Materials
The floating matter is removed and raked into the screen bucket, and then rinsed with water for
sanitary disposal to a location where dewatering equipment is installed. The area where the
screen bucket is placed should be cleaned and disinfected.
B. Flow Equalization Facilities

Stabilizing the function of the biological treatment process (main one) requires making the
flow rate and quality of sewage as uniform as possible and hence a flow equalization facility
may be needed.

i. Control of Transfer Pump

In general, the transfer pump starts, stops, or issues an alert according to the water level of the
flow equalization tank. The level at which the pump starts running varies depending on the varia-
tion in inflow sewage and the margin of the flow equalization tank, but in many cases, it is set at
15 to 30 cm above the pump stop level (also known as the low water level (LWL)).

ii. Controlling the Metering Unit

The metering unit receives the sewage lifted by the pump from the flow equalization tank,
supplies a given amount of sewage to the biological treatment process, and returns the
remainder to the previous tank. The flow rate of the pumped sewage is adjusted by changing the
height of the overflow weir. If sludge and sand accumulate in the unit or foreign matter is caught
in the weir, the flow rate changes.
Therefore, sludge and sand should be removed and the unit should be cleaned regularly.
The metering unit is shown in Figure 10.2. overleaf
10 - 7
Source: Jokasou Standard, 1980

Figure 10.2 Metering unit
iii. Stirring in the Flow Equalization Tank
The stable biological treatment function requires keeping the flow rate and properties of
wastewater constant and uniform, so stirring is necessary in the flow equalization tank. The
stirring method includes liquid circulation, mechanical stirring and air stirring. It is essential to
check whether the stirrer works correctly and whether the resulting stirring effect is sufficient.
10.5.2.2 Main Treatment Process
A. Controlling the Aeration Tank

Refer to Chapter 4. Sec.4.7 “Activated Sludge Process”.

B. Controlling the Sedimentation Method

The contact aeration method is based on treatment principles similar to those for the
activated sludge method, but the contact aeration method is more advantageous in flow rate
and load changes and suitable for the treatment of sewage with relatively low concentration.
Accordingly, the contact aeration method is used in many on-site treatment facilities. However,
it has disadvantages: as the biological film thickness increases and the contact material
becomes clogged. This results in degradation of the treatment function and a fixed amount of
microorganisms can respond to low load but cannot treat load beyond the designed value.
i. Controlling the Contact Aeration Tank
To improve the treatment efficiency of the contact aeration tank, the operator should control it
considering the following points:
• Do not make efforts to change the inflow rate by adjusting it,
• Keep BOD load in the proper range (overload should be avoided)
10 - 8
• Form biofilm that consists of appropriate microorganisms,
• Confirm the performance of the aeration in the tank (the proper dissolved oxygen
concentration is not less than 2 to 3 mg/L and it can be a little higher, lower concentration
degrades the treatment function),
• Pay attention to the thickness of biofilm and activate the back washing unit at the appropriate time
to remove excess biofilm, and
• When the removed biofilm (sludge) increases excessively in the tank, temporarily stop aeration
to settle and extract it with a pump (the sludge causes the contact material to be clogged).
ii. Controlling the Sedimentation Tank

In this treatment method, the amount of microorganisms that contribute to the treatment
depends on the surface area of the contact material; therefore, it does not require adjustment of the
sludge concentration in the aeration tank. Accordingly, all the sludge settled and separated in the
sedimentation tank is not needed, so it should be extracted according to the volume of
accumulation and feed to the sludge treatment process.
C. Controlling the Membrane Separation Method

This is the method of using a membrane separator to divide sewage into solid and liquid
instead of the conventional gravity settlement. The membrane separation method maintains
high MLSS concentration in the aeration tank and it is a compact facility. Many separators used
in on-site facilities employ a membrane immersed in the aeration tank to obtain permeated
liquid. The separator is classified into two types as shown in Figure 10.3: a “flat membrane”
and a “hollow yarn membrane.”
Source: JEFMA
Figure 10.3 Membrane separators
10 - 9
i. Controlling the Aeration Tank
The control of the activated sludge method applies generally. One difference is that it is
necessary to maintain a high MLSS concentration to enable proper functioning of the membrane
separation method. The concentration should be 8,000 to 12,000 mg/L in many cases.
ii. Controlling the Membrane Separator
• Inspecting the treated water (which passes through the membrane)
The water having a transparency of more than one meter alone should be used in
membrane separation processes for successful solid-liquid separation. Therefore, if the results of
inspecting the appearance of the permeated water show haze or suspended solids, it is
likely that the separator will not work. Possible causes include a break in the membrane or a
connector, and the generation of slime in the membrane. In the former case, the broken part
should be replaced or repaired.
In case of generation of more slime, a chemical cleaner, is also used, as described hereunder.
• Differential pressure and water penetration rate
• In the membrane separator, the differential pressure between the front and back of the
membrane is the driving force to filter sewage. Generally, the larger the differential pressure,
the higher the water penetration rate. Continuous operation of the separator gradually forms
sediment and deposit on the surface and in the micro pores of the membrane causing clogging.
Even if the separator runs at the same differential pressure, the filter resistance increases due to
the clogged membrane and the water penetration rate reduces gradually. Conversely, to keep the
rate constant, differential pressure should be increased in proportion to the amount of clogging.
However, there is a limit to increasing the differential pressure. Therefore, the membrane should
be cleaned when the differential pressure reaches a certain level. The level varies depending on
the facilities, so it is necessary to find a control value during trial operation.
Generally the membrane needs to be cleaned when the pressure rise is 5 to 10 kPa for the flat
type or 20 to 30 kPa for the hollow yarn type
• Checking the aeration state
The tank in which the membrane separator is installed (immersed / kept out) should be aerated at
a constant rate. Accordingly, it is necessary to check whether the aeration rate is appropriate and
whether the whole membrane separator is uniformly and consistently aerated. The separation is
by filtration through membranes.
• Cleaning the membrane
As mentioned earlier, the continuous operation of the membrane separator gradually clogs the
membrane and reduces filtering performance. Therefore, the membrane should be cleaned at the
appropriate time.
10 - 10
• Rinsing with water
Activated sludge flocs, microorganism’s metabolites, and other foreign matter that accumulate on
the membrane surface should be removed by rinsing with water or by other physical means such
as taking out the membrane module and cleaning and reassembling.
• Cleaning with chemical liquid
When the membrane pores are clogged with refractory organic substances in sewage or with
scale derived from inorganic substances in sewage, it is not possible to remove them only by
physical means. In this case, it is essential to use chemicals to decompose such adherents.
Sodium hypochlorite is used as a cleaner to decompose stains derived from organic substances.
To decompose inorganic scale, organic acid such as acetic acid is used.
10.5.2.3 Advanced Treatment Process
A. Controlling the Flocculation Sedimentation Treatment
• The control of sewage treatment facilities mentioned in section 4.7 Activated Sludge Process is
applicable here.
B. Controlling the Sand Filter
• The control of sewage treatment facilities section 4.7.1 Sand Filtration is applicable here
C. Controlling the Activated Carbon Adsorption Unit
• The activated carbon adsorption unit has the property of adsorbing soluble and
non-biodegradable organic matter (COD) and inorganic matter included in sewage and their
removal. Fixed bed activated carbon adsorption tower has practically the same construction as
a sand filtration tower, and it requires periodic back washing, but it can also be automated. In
the fixed bed tower, back washing may be performed at a frequency of once in one to two days.
If the activated carbon layer gets deposited with suspended solids, combined washing using
water and air is an effective method. The adsorbing performance of activated carbon degrades
as water passes through; therefore, the replacement of activated carbon if desired is decided by
taking COD as a control indicator and in some cases, the iodine value which is desirable at not
less than 600 when in use.
10.5.2.4 Controlling the Disinfection Unit
There are some disinfection methods, such as chlorination, ultraviolet (UV) light treatment, and ozone
treatment. These are popular methods used by field engineers.
A. Coliform Bacteria as a Pollution Index
Escherichia coli that lives parasitically in the intestinal tract of human beings and animals is
discharged with faeces outside and can be used as an index that shows the degree of pollution
with excreta. Detecting coliform bacteria is a means of a possibility of pollution with many other
bacteria that causes alimentary infectious diseases.
10 - 11
The lifespan of such pathogenic bacteria in water varies depending on the living environment,
such as water temperature and pH. It is generally said that the lifespan of Salmonella typhi, Vibrio
cholera, and dysentery causing organisms in a river are 10 to 30 days, 20 to 30 days, and 7 to
10 weeks, respectively.
B. Handling Disinfectants
Sodium and Calcium hypochlorite are frequently used as disinfectants in water treatment
practices. They can be handled easily by wearing protective eye goggles, hand gloves
and masks.
C. Controlling the Contact Tank
Adjusting the disinfectant injection rate requires measuring the residual chlorine
concentration at the outlet of the contact tank. Too high a chlorine concentration is not good from
the viewpoint of effect on the ecosystem in the effluent area. On the other hand, absence
of residual chlorine indicates a possibility of insufficient disinfection. Therefore, the residual
chlorine concentration at the outlet of the contact tank should be not too high or too low.
In general, the control value is 0.1 to 0.3 mg/L.
10.6 SEPTAGE TREATMENT UNIT
The principles of Screen, Grit, Centrifuge, Activated sludge respectively shall apply here also.
10.6.1 Collecting and Delivering Sludge
The collection and delivery efficiency varies depending on the volume, the distance between
facilities or distance to treatment plants, and the truck size.
In general, 4 kilolitre trucks are used for a small-scale facility, and 6 to10 kilolitre trucks for medium
to large-scale facilities.
Manual sludge extraction causes inhuman activities and pollution due to splashing during
transportation. Accordingly, a mechanical method (e.g. a truck mounted pump or vacuum tanker)
should be used as per the guidelines.
When the tank truck extracts sludge, the suction unit may sometimes emit offensive odour, which
requires control measures. For example, a deodorizer (e.g. an activated carbon adsorption unit) is
sometimes attached to the outlet.
The tank truck is likely to be insanitary, so it should be cleaned regularly. In addition, water used to
clean the tank inside should be treated hygienically.
If the distance from the collection point to the vehicle is large or the difference in level between
the two is large, it is necessary to install a suction pump or to use a high-power vacuum tanker.
The vehicle carries corrosive matter. Therefore, it is essential to clean internal parts of the tank and
change the lubricating oil at certain intervals depending upon the vehicle age and upkeep.
10 - 12
10.6.2 Basics of Sludge Treatment
There are various sludge treatment methods, including treatment in a special facility, common
treatment along with sewage in a STP, and solar drying on a paved floor.
It is necessary to select an optimal method considering the local conditions. The following
summarizes the common and basic points for planning sludge treatment and disposal:
• Sludge includes worm eggs and pathogenic bacteria and hence so a sanitary treatment method
should alone be used.
• The organic concentration of sludge is more than 100 times higher than that of sewage.
Discharging it into the environment without treatment causes pollution. Hence, treatment as per
the advisory on septage treatment http://urbanindia.nic.in/programme/uwss/Advisory_SMUI.pdf
is required.
• Water accounts for a major part of sludge, so selection of technology for efficiently separating the
water from the sludge is necessary.
• The O&M of a sludge treatment system require the development of human capabilities.
• It is necessary to introduce a resource recycling system so as to ensure a safe treatment of

sludge for agricultural use.
10.6.3 Operational Control of Sludge Treatment
10.6.3.1 General
In the case of sludge treatment units, the solid liquid separation activity shall be carried out only in
the day shift. The characteristics of sludge collected from septic tanks vary depending on the volume,
extraction frequency, and load condition.
Accordingly, the owner of the treatment facility should hold prior discussion with the collecting
contractor. The following points must be considered in sludge treatment.
• In a medium- or large-scale STP, a large amount of sludge is extracted at once. Therefore, the
administrator should ask the vendor to distribute the work over several days to mitigate changes
in the amount of sludge.
• The contractor shall not concentrate sludge delivery in a limited time slot.
• Sludge collected from restaurants includes large amounts of oil. Accordingly, the ULB should ask
the owner of the restaurant to install oil removal units as directed by the local PCB.
• Industrial effluent sludge interferes with the biological treatment function significantly, so the
owner should ask the contractor to adopt measures against these sludges.
In the sludge treatment facility, the main process is solid-liquid separation. The maintenance of the
facility requires expertise in the solid-liquid separation technology of sludge. The sludge treatment
facility is shown in Figure 10.4 overleaf.
10 - 13
Figure 10.4 Flow chart of sludge treatment
10.6.3.2 Controlling the Pre-treatment Unit
A. Pre-treatment
The collected sludge includes foreign substances, such as cloth, paper, wooden pieces, soil,
and sand, which should be removed, because they cause clogging of pipes or equipment failure.
A pre-treatment unit consisting of screen and sedimentation tank is shown in Figure 10.5.
Figure 10.5 Flow chart of a pre-treatment unit
Extracting the foreign matter including sand is insanitary work, so it is recommended that such
work should be automated.

The automatic raking screen rakes and places garbage into a bucket automatically, but it is
necessary to clean the screen and remove the garbage at regular intervals.

Soil and sand accumulated at the bottom of the sedimentation tank should be removed to the
outside by a high-powered suction vehicle.
B. Stirring Storage Tank

The stirring storage tank is used to make the quality and quantity of sludge uniform. The
stirring method may be classified into sub-surface mixing and pump circulation methods. The
sub-surface method is better and less troublesome. A given amount of the treated sludge moves
from this tank to the sludge thickening tank through a transfer pump and a metering regulator.
The operation control of mini package plants (Section 10.3.2.1) applies to each unit.
10 - 14
C. Controlling the Solid-liquid Separation Tank
i. Sludge Thickening Tank
An important point for running the sludge thickening tank is the adjustment of the extraction
time according to the sludge accumulation status. Therefore, it is essential to observe the
concentration of the extracted sludge. There are some sludge extraction methods, such as a
manual pump and a combination of a timer and a pump. The daily control of the thickening tank
includes removing scum on the surface and cleaning the area around the overflow weir.
ii. Sludge Storage Tank
The sludge storage tank emits hydrogen sulphide and causes lack of oxygen because of its
anaerobic state. Accordingly, safety measures should be adopted while cleaning the tank
inside and outside.
iii. Flocculants
The purpose of adding a flocculant is to change the nature of sludge particles to improve
dewaterability. The flocculant is classified into organic and inorganic (polymer) types, which
are used independently or in combination. In many cases, the organic flocculant is a powder,
which is diluted to attain a specified concentration. The sludge thickening method is classified
into two types: one uses a condensing tank with a stirrer, and the other employs a centrifugal
separator in which a flocculant is injected directly into the sludge supply pipe. The proper
flocculant shall be selected based on laboratory jar tests and sometimes a combination of
flocculants may also be required.
iv. Sludge Dehydrator
Refer to Chapter 5. Sec.5.4 “Sludge De-watering”.
D. Controlling the Activated Sludge Treatment Unit
Refer to Chapter 4. Sec.4.7 “Activated Sludge Process”.
10.7 SUMMARY
On-site sewage treatment has so many features, such as treatment carried out near the source or
away from the source. Its volume is mostly small because the treatment applies to individual houses
and a variety of technologies are adopted according to the surrounding conditions. Accordingly, there
are cases where the administrator itself or a private special contractor conducts operational control
of on-site facilities. In the operational control of a septic tank, it is important to extract accumulated
sludge properly in order to keep the function stable.
Therefore, the State Governments and ULBs need to draw management plans based on the
“Advisory note on Septage Management” (MoUD, 2012). The optimal treatment technology is
selected in consideration of the local conditions and it is necessary to conduct operational control
according to the selected treatment technology.
10 - 15
APPENDICES
Part B: Operation and Maintenance APPENDIX
Appendix Title of Appendix Page
B 1.1 Monitoring Through Information Control Technology ............................................B-1

B 1.2 Database for Effective O&M.....................................................................................B-3
B 1.3 Evaluation of O&M of STPs....................................................................................B-5
B 2.1 Troubleshooting in Sewers.....................................................................................B-10
B 2.2 T.V. Inspection Report ..............................................................................................B-12
B 3.1 Detailed Troubleshooting for Horizontal Centrifugal Pump Sets............................B-13
B 3.2 Possible Causes and Corrective Actions to Check for Pumps...............................B-18
B 3.3 Troubleshooting in Sewage Pump Stations............................................................B-22
B 4.1 Troubleshooting in STPs........................................................................................B-24
B 4.2 Operational Parameters.........................................................................................B-53
B 4.3 Calculations........................................................................................................B-58
B 5.1 Troubleshooting in Sludge Treatment Facilities.....................................................B-63
B 6.1 Typical Ledger and Records...................................................................................B-68
B 6.2 Preventive Maintenance........................................................................................B-72
B 6.3 Troubleshooting for Electrical Facilities..................................................................B-75
B 7.1 Minimum Laboratory Equipments Needed for Tests..............................................B-85
B 7.2 Suggested Laboratory Service Infrastructure for Monitoring Water Quality.........B-87
B 9.1 Health and Safety Policy.........................................................................................B-88
B 9.2 Characteristics of Common Gases Causing Hazards.............................................B-94
B 9.3 Confined Space Entry Procedure...........................................................................B-97
B 9.4 Confined Space Pre-entry Checklist......................................................................B-99
B 9.5 First Aid................................................................................................................B-101
B 9.6 Sewage Treatment Plant Accident Report.........................................................B-105
B 10.1 Mechanical Cleaning of Septic Tanks..................................................................B-106
APPENDIX B.1.1 MONITORING THROUGH INFORMATION CONTROL TECHNOLOGY
1.1.1 OUTLINE
Understanding the condition of sewage to be treated is very important for efficiently operating a
STP. In this manner, the condition of sewage to be treated can be grasped simultaneously by
making use of systems for monitoring through information control technology. This can be done by
centralized monitoring using systems such as SCADA (refer to Sec. 6.6 of Part B manual), that helps
to determine operating methods.
Items to be measured include DO, SS, pH, ORP, COD, influent flow rate, effluent flow rate, and
return flow rate. Measuring equipments include equipment for measuring single items to those
that can make several kinds of measurements simultaneously. Equipments that can make several
measurements simultaneously, are described below.
1.1.2 EXAMPLES OF MEASURING EQUIPMENT
Features
• Monitors the environmental water quality of rivers, lakes, other water bodies and the water quality
of effluents, etc.
• Built-in automatic cleaning and calibration functions greatly reduce maintenance work.
• Integrated sensors are employed to reduce unit size and save space.
• Measurement items are water temperature, pH, electrical conductivity, turbidity,

dissolved oxygen
A typical equipment is shown in Figure B1.1-1
Source: DKK-TOA CORPORATION

Figure B1.1-1 Automatic Water Quality Monitor
MONITORING EXAMPLE FROM JAPAN
1.1.3.1 Sewerage (Public Works Bureau) in the City of Osaka
• Operation and Maintenance (O&M) of Sewerage System
B-1
It is important to properly operate and maintain facilities such as sewers, pumping stations and
sewage treatment plants so that these facilities play their roles effectively.
• Operation and Maintenance (O&M) of Sewage Treatment Plants
STPs are operated on a 24-hour basis in order to treat wastewater continually for ensuring
effective operation of sewage treatment plants in response to varying inflow rates.
Various water quality examinations are conducted at plant laboratories to monitor the quality of
the final effluent. A typical laboratory is shown in Figure B1.1-2 and Figure B1.1-3
Figure B1.1-2 Water Quality Analysis Figure B1.1-3 Central Control Room
1.1.3.2 Bureau of Sewerage Tokyo Metropolitan Government
Sewage Reclamation Centre
• Sewage reclamation centres must process sewage as it flows non-stop, 24-hours per day. If the
centres do not function properly, pollution would spread quickly to rivers and the sea.
• In order for microorganisms, which are the main players in the treatment process, to function
properly and discharge sewage debris as sludge, the water quality of influent and effluent is
tested and maintenance, inspection, and monitoring of equipment are performed constantly.
A typical centre is shown in Figure B1.1-4
Figure B1.1-4 Main Monitoring Room in Water Reclamation Centre

Note: Tokyo Metropolitan Government calls a “sewage treatment plant” a water reclamation centre.
B -2
APPENDIX B.1.2 DATABASE FOR EFFECTIVE O&M
Effectively collecting, analyzing, reporting, distributing, storing and archiving data irrespective
whether electronic, paper, audio, image, or video have become key aides to effective and
efficient operations.
In recent years, raw data is being increasingly managed by computers.
A computerised maintenance management system (CMMS) {also called a computerised work

management system (CWMS) or a work management system (WMS)} enables utilities to manage
maintenance work and minimise equipment downtime cost-effectively. The system is designed to
plan, schedule, and manage maintenance activities; control parts inventories; coordinate purchasing
activities; and help prioritise long-term asset investment needs.
A CMMS typically consists of the following six components:
• Work management (corrective, preventive, predictive maintenance scheduling, activities

and procedures);
• Equipment inventory (an inventory and description of equipment and support systems
requiring maintenance, along with other technical or accounting information); Electrical
equipment of ledger is shown in the next page.
• Inventory control, tools and materials management (materials, tools, spare parts management,
scheduling and forecasting);
• Purchase or procurement (maintenance-related requisition, procurement, and accounting);
• Reporting and analysis (standard and ad hoc reports); and
• Personnel management (staff skills, wages, and availability).
If a database containing the items mentioned above can be used, costs can be easily managed, and
the data can be used to prepare budgets.
A typical sample ledger for electrical equipment is shown in Table B1.1-1 overleaf.
B-3
Table B1.1-1 Ledger for electrical equipment
Source: JICA, 2011
B -4
APPENDIX B.1.3: Evaluation of O&M of STPs in India – CUPS/68/2007

Conclusions and Recommendations
1. Mostly influent to the STP was found to contain lot of solid wastes including plastics,
pouches etc. that may cause wear and tear of pumps and machinery and reduce deficiency
of treatment, specially in case of UASB process where the feeding pipes and overflow weirs/
V-notches in division boxes/effluent gutters, are chocked/obstructed, thus, also resulting in
reduced STP capacity. It is, generally, observed that mechanical screens installed in STPs/SPS
are out of order, mainly because these are not regularly sun and also due to poor maintenance.
Comprehensive scheme for providing soid waste management in all the towns including public
awareness, institutional strengthening, etc. need to be implemented. As an immediate solution
to the problem, specially in UASB process, fine/mesh screens can be put in place of ordinary bar
screens. Larger size of feeding pipes with more frequent cleaning can also solve this problem.
2. Staff/officers/engineers engaged for O&M at some STPs are not fully familiar and aware of
the subject of sewage treatment. They are not trained in the O&M of the STPs. Proper training
programme needs to planned and implemented for all the engineering level staff/officers, who
are deputed for O&M of STPs. This should be followed by training for operators as well as
chemists, who perform sampling/testing work.
3. At most of the STPs, either O&M manual is not prepared or it is not available/used, or it is not
comprehensive enough to include various steps/procedures to be followed in day-to-day O&M of
the plants as per design, so as to have desired quality of treated effluent. O&M manual should
spell out the procedure of reporting and recording of all the data/parameters including quality of
wastewater in various units of the plants.
4. Polishing ponds (in case of UASB process) and Waste Stabilisation Ponds (WSPs) are mostly
found accumulated with sludge resulting in reduced capacity/detention time in the tank. This also
effects the quality of treated effluent due to sludge flowing out with it. Sludge levels should be
checked regularly and the ponds should be cleaned off deposited sludge accordingly.
5. In case of polishing ponds or WSPs, it is found that single unit of these ponds have been
provided in some STPs. In such cases, it is very difficult to clean the accumulated sludge /silt
without closing the STP. Hence, it is important that at least two units of such ponds are provided
at each STP. Also, in case of big ponds/channels wide and long partition/baffle wall need to be
provided for easy access for inspection/repairs.
6. Sludge in UASB reactors are not withdrawn regularly based on its level and concentration in
the reactors which results in sludge flowing with the effluent in polishing ponds and thus poor
quality of treated effluent. Regular checking of sludge level and its concentration in the reactors
is essential for proper sludge withdrawal.
7. Due to improper removal of filtrate from sludge drying beds, subsequent removal/withdrawal of
sludge from sludge drawing beds/reactors is not possible in a desired manner, as the capacity of
sludge drying beds is reduced. Hence, filtrate from the beds and sludge from the reactors/sludge
drying beds need to be taken out regularly in a proper way.
B-5
8. It is important to prepare daily status report to record occurrence of problems in respect of

running, functioning, repair, maintenance etc. of all the equipments, units, facilities etc.
installed in each STP, so that the problems, if any, can be solved as and when applicable. This
will also serve as feed back for future planning and execution as well as tool for monitoring the
performance of STPs at a higher level.
9. Some of the STPs don’t have sufficient baffle walls and also, sufficient length of overflow weirs
at their final outlets in case of UASB polishing ponds and WSPs, resulting in poor effluent quality.
Baffle walls should be constructed for the whole length of the pond width so that scum/sludge
does not flow out with the effluent. Similarly, longer overflow weirs will ensure less approaching
velocity of flow and subsequently, efficient solid liquid separation.
10. In view of frequent rusting/damage of iron/MS parts/accessories installed in STPs/SPSs due

to sulphur action, such items e.g. railings, screens, platforms etc., as far as possible, should
be manufactured in stainless steel, as seen in case of STPs being constructed/renovated in
Tamil Nadu, Maharashtra etc. Moreover, small electric installations such as motors, flow meters,
starters, etc put up for operation of aerators, screens, grit removal mechanism, gates etc. should
be covered with temporary sheds (PVC) to protect against rain water, dust etc.
11. It is observed that in most of the towns specially, in UP, Bihar and even Delhi, where there is acute
shortage of power supply, a standby arrangement during power cut/failure does not generally exists
to meet the power requirement for running the plant. Frequent and long power cuts and subsequent
sudden discharge into the STP also causes shock load to various units of STP, even in UASB and
WSP processes, thus adversely effecting the efficiency of treatment. Hence, alternative standby
arrangement in the form of generators along with sufficient funds for fuel need to be provided to
ensure continuous operation of STPs. Intermittent operation of STPs will not help in achieving
the desired quality of treated effluent and thus minimising the river water pollution. In addition,
unless continuous power supply is available effluent quality parameters specially, BOD, etc,
cannot be tested accurately.
12. Majority of State Govts/implementing agencies are not able to provide sufficient and regular
funds for O&M of STPs resulting in their unsatisfactory performance. The annual cost of O&M
of sewerage system and STPs in a town varies from 5 to 10 %, depending on the quantum of
pumping (stations) and type/size of STP. It is also observed that the revenue from STPs is
negligible or far less than the expenditure required to be incurred for proper O&M of
the STPs in all cases. In case of STPs constructed with central funding under NRCP
by MoEF, O&M cost is to be borne by the State Govts. If the amount for O&M of STPs
cannot be provided on regular basis by the State Govts. then the matter needs to be looked into
at the highest level, whether further new works should be taken up under the programme.
13. Sometimes, the staff/engineers engaged in O&M of the STPs are frequently transferred so that
their experience and know-how does not get transferred to their successors and is thus not
available for O&M of the STP. So the O&M staff/engineers should be deputed at a plant for
sufficient number. of years and their experience and knowhow transferred to their successors in
a planned and systematic manner.
B -6
In case O&M is being conducted privately through an annual contract, the agreement should
be such that the same contractor continues after the initial period of one year, subject to its
satisfactory performance. As a matter of fact, O&M of a STP should be included in the main
construction contract for a period of at least five to 10 years. This arrangement has been
giving good results in some of the STPs, namely at Channai, Panji, Nasik etc. where this practice
has been adopted.
14. Mostly the result of tests for effluent quality being carried out by various independent agencies
are not fed back to the staff managing the O&M of the STPs. As a matter of fact the results of the
tests, especially, if they are adverse, should be informed to the operating staff as soon as possible
so that corrective measures can be taken at site accordingly. Also, testing of effluent for fecal
coliform is not being conducted in most of the plants which is one of the most important indicator
in abatement of pollution of rivers.
15. In some of the states, specially in UP, O&M of the STPs in some towns is being done by local
bodies which do not have qualified, experienced and knowledgeable staff who can supervise the
O&M of the STPs. Local bodies have engaged private agencies on contract for O&M of these
STPs but their performance is very much unsatisfactory. This arrangement of O&M of STPs
by local bodies, where competent staff is not available, may not last long. In such cases, if it is
essential for O&M to be done by local bodies only, staff / engineers with experience in O&M
of STPs should be transferred / appointed from the implementing agency, namely UPJN
who have constructed the plant.
16. A holistic approach for abatement of pollution of rivers need to be adopted, as on one hand
population and other human activities are increasing and on the other hand the problem
further gets compounded due to declining minimum flow, as a significant quantity of water is
abstracted upstream of a town for irrigation/drinking purposes. This is specifically applicable
in case of Yamuna in Delhi, where all the water is withdrawn from the river
upstream of Wazirabad barrage.
17. It is estimated that out of 3267 MLD of sewage generated in Delhi, treatment capacity exists
for only 2376 MLD, but only 1530 MLD of total sewage generated is treated at the STPs. Thus
only 64.37% of treatment capacity of STPs is utilised. Under utilisation of capacity of treatment
is on account of (i) deficiency in sewerage not work (settlement/silting of trunk sewers) and
(ii) improper O&M of conveyance system and pumping stations. Also, it is important to note
that treated sewage is mostly discharged into storm water drains (17 nos), which carry
untreated sewage and join river Yamuna. Storm water drains carry sewage from unsewered
areas, overflow from manholes/pumping stations and treated/untreated industrial wastewater.
In order to have desired quality of river water in Yamuna at Delhi, the following immediate
measures have to be taken :-
a. Rehabilitation/desilting of trunk sewers.
b. Provision of sewerage net work in unsewered areas.
c. Augmentation of treatment capacity of STPs as per requirement.
B-7
d. Use of treated effluent for irrigation and other purposes.
e. Proper O&M of the sewerage system and STPs.
18. Sewage treatment with WSPs (anaerobic, facultative and maturation ponds) is most economical
in terms of capital as well as O&M cost and is suitable for small towns where sufficient land is
easily available. However, certain basic precautions e. g. providing proper weir length and baffle
wall(s) at the outlet of ponds during construction; and proper O&M in respect of cleaning of sludge
deposited in ponds at suitable intervals (6 to 12 months) and arresting algal/hyacinth growth are
minimum requirements which have to be kept in mind for achieving desired results.
19. Conventional treatment process, namely ASP/trickling filter is very suitable in case of large
towns, where land is scarce, provided there is no shortage of power and funds to meet capital
and O&M costs. In some of the large towns UASB process has been provided under NRCP,
as it is economical in respect of O&M as compared with ASP. It is observed that in some
cases desired results are not achieved as O&M agencies are not paying importance to the
intricacies involved in the treatment process, namely uniform feeding to the plant/reactor, proper
grit removal and withdrawal of sludge from UASB reactors, regular cleaning of accumulated
sludge from polishing ponds etc. Improper O&M of these plants is giving a bad impression about
UASB technology, which otherwise appears to be quite appropriate for sewage treatment for
most of the towns in our country.
20. In places, where land availability is very scarce, sewage treatment using FAB (Fluidized
Aerobic Bed) reactor, in which biomass grows on small elements (media) that move along with the
water in the fluidized bed state, can be the most appropriate choice. The movement is caused by
bubbling air at the bottom of the reactor. The system has been provided in a few towns under
NRCP, but poor O&M might give a negative signal in adoption of this process of treatment.
21. Schemes for providing interceptors with nalah-tapings and main/trunk sewers along with STPs
(down stream works) are being implemented under NRCP by MoEF in various towns which are
situated on the bank of different rivers and are polluting the river waters. Upstream works i.e.
internal / branch sewers including house connections etc. for a town have to be taken up by the
State Governments through their own resources so as to have a holistic approach in abatement
of pollution of rivers. This will also help in solving the problem of weak sewage reaching the STPs
for treatment. Besides, it is also observed that sewerage schemes in various towns are being
sanctioned / implemented by different agencies / departments under different Central / State
plans, e.g. NRCP by MoEF, NURM by MOUD etc. Unless proper coordination exists between
different agencies / departments, implementation of sewerage schemes may lead to defective
planning / execution and duplication of works, without achieving the desired goal. Thus, as far
as possible, all the sewerage schemes for a town should be sanctioned / implemented under
a single funding agency / Ministry.
22. Out of the 68 STPs inspected for their performance evaluation, it is observed that O&M in case
of 40 STPs is found to be poor or very poor for various seasons. There is no mechanism for
physical monitoring of the performance of STPs constructed and commissioned under the NRCP
by MoEF.
B -8
These are seldom visited by higher officers of NRCD in MoEF for their inspection so as to
get first hand information on the status of O&M of STPs by the State Govts./implementing
agencies. Moreover, the scope of work of Project Management Consultants (PMC), appointed by the
Ministry for implementation of YAP - II, includes monitoring of O&M all the STPs constructed
in Delhi, UP and Haryana under YAP – I. But it is understood that no action has been taken
by NRCD in this respect since the appointment PMC two years ago. Regular monitoring of all
the STPs for their performance evaluation at central level (CPCB) twice a year by having own
independent sampling/testing of wastewater need to be carried out for bringing improvement in
O&M of STPs and get the desired quality of treated effluent.
23. It is understood that projects based on generation of electric power from biogas, which is being
produced as a result of digestion of sludge in STPs, are eligible for CDM (Clean Development
Mechanism), as it will help in reducing and stabilising the emissions due to methane which is a
green house gas. Based on the potential of biogas/power generation from STPs, expenditure on
O&M can be offset by earning ‘carbon credits’ on recurring basis. It is, therefore, recommended
that a feasibility study should be done for taking up a CDM project in case of any one of the STPs
by DJB in Delhi as it can be a perennial source of revenue generation.
In view of importance of abatement of pollution and preservation of rivers and other water
bodies, proper sewage treatment, its O&M and subsequently, optimum utilisation of treated sewage for
irrigation and other purposes needs to be given higher priority by Central/State Governments.
urgently. Looking into the overall situation of O&M of the STPs, it can be concluded that sewerage
and sewage treatment is generally not considered a priority item by the State Governments./local
authorities/implementing agencies. So, unless importance/priority is given by them, the situation may
become bad to worse.
B-9
APPENDIX B.2.1 TROUBLESHOOTING IN SEWERS
Table B2.1-1 Troubleshooting in sewers
No. Troubles / Problems Likely causes First stage remedies Second stage remedies
Toilet floor below road elevation Raise the toilet floor Install small lifting arrangement
House sewer pipe broken Relay the sewer Go for new connection
Solids are choking the sewer Use a kraite from the terminal Dig out the sewer and relay
chamber
1 House sewer does not flow Connection is made to public Dig open the junction in road and
Insert a manhole in public sewer
sewer by Y or Tee junctions rectify
House connection may be Dig it out and relay in straight Construct a new sewer in another
passing through bends alignment alignment
Roots of trees might have Expose the pipe and shear off
the roots Dig out and relay the sewer
grown into the sewer
Organic matter has accumulated Raise the vent higher than the
2 Septic tank emits foul smell at the bottom and become roof for free air passage Take a sewer connection if available
concentrated
Septic tank effluent smells This is always the case when Provide a leach pit and then let it
3 Provide trees for evaporating the effluent
bad odour discharged freely out to road drain
The sewer to the next manhole Open out downstream manholes to Use jet rodding machine at the
is choked (or) some other find out where the sewage is not downstream end and jet the sewer at
Sewage overflows from downstream sewer is choked flowing the high end
4 manholes
The sewer has collapsed in the Use a bucket cleaning machine to If established, dig out and provide new
next reach or somewhere else establish the broken sewer or not sewer pipe after temporary blocking
downstream upstream
B - 10
Check the TDS by a pocket meter Provide a bypass to nearby water

Sewage level does not go The sewage pump sets are very every hour to find out abnormalities
down at all in the sewage course in the night hours and arrange
5 old and worn out (or) ground in nights. If TDS is much less in
pumping station for higher capacity pump sets to nearby
water is infiltrating into the nights ground water is seeping STP or next higher pumping station.
sewers through defective sewers or joints Launch a study to locate the infiltration
6 Sewer manhole keeps The sub surface soil is defective Insert new manholes on each side Interconnect by a CI or DI sewer pipe
sinking into ground (or) the foundation has given at a reasonable distance to be away laid on proper venteak piles
way
Use temporary bypass pumping of sewage from upstream manhole to
downstream by diesel pump sets and flexible hose till the above remedy is
completed. Connect the house service connections to the upstream manhole
The sewers are choked and Pull out the column and seal the Try to ensure sewers flow freely and
Public do not want ventilating anaerobic conditions have set
7 connecting pipe to the public sewer not over 80 % of its depth at all times
columns near their property in resulting in foul smelling
Hydrogen Sulphide gas
Sewage pump sets require The pump is horizontal and its Replace by wet submersible pumps Redesign the pumping station fully
8 priming and take a long time axis is higher than the sewage
elevation in the well
Sewers do not let out sewage The sewer has collapsed in Similar to the troubleshooting of item 1 above
9 at downstream manhole between and sewage is going
into the ground
The underground portion is safety equipments such as

barricade, signs or security lights Dig out the sewer and re-backfill or
Road collapse occurs hollowed because sand has
10 should be installed immediately relay. As other methods, soil
been drawn into the pipe due to
around the collapsed road to prevent stabilization is required
breakage or step displacement
secondary disaster
B - 11
APPENDIX B.2.2 T.V. INSPECTION REPORT
Table B2.2-1 T.V. inspection report
Book No.____________________Page No.______________________Date:_________________
Camera Direction M.H. No.____________to M.H.No.__________________Viewer_____________
B - 12
APPENDIX B.3.1 DETAILED TROUBLESHOOTING FOR HORIZONTAL CENTRIFUGAL PUMP SETS
Table B3.1-1 Type of troubles
No Type of Trouble Probable causes as per conditions indexed in Table below
a. Pump does not deliver water 1,2,3,5,6,7,9,10,15,18,21,23,26,28,29,30,31,33,40,41,42
b. Insufficient discharge 2,3,4,5,6,7,8,9, 10,13,16,17,18, 20,21,23,24,27,28,29,30,31,33,39,40,41
c. Insufficient pressure is developed 2,3,4,21,23,24,26,27,28,33, 39
d. Pump loses prime after starting 22,25,28,33,37,38,49,53,54, 55,56,58
e. Pump requires excessive power 22,25,28,33,37,38,49,53,54, 55,56,58
f. Stuffing box leaks excessively 34,36,44,45,46,47,48,50,51, 52
g. Gland packing has short life 11,12,34,36,44,45,47,48,49, 50, 52
h. Bearing has short life 17,20,32,34,35,36,37,39,41, 44,48,51,54,55,56,57,58,59, 60,61,62,63
i. Pump vibrates or is noisy at all flows 10,17,19,20,22,33,34,36,37, 38,40,41,43,45,46,47,48,51, 52,53,55,56,57,58,59,60,61,62, 63, 65
j. Pump vibrates or is noisy at low flow 1,2,3,9,10,17,20,21,27,39
k. Pump vibrates or is noisy at high flow 25,28
l. Pump oscillates axially 38
m. Coupling fails 34,36,38,60,62
n. Pump overheats and /or seizes 1,2,3,11,12,17, 2 0,24,26,27, 31,34,36,37,38,44,45,47,48, 49,50,53,54,55,56,57,58
o.
Pump rotates in reverse direction on 14,64
shutdown or after power failure or tripping
B - 13
Table B3.1-2 Probable causes
No Probable Causes
1. Pump not fully primed
2. Pressure at eye of impeller has fallen below vapour pressure, causing cavitation (check for clogging on suction side)
3. Suction lift too high. (Reduce suction lift after calculating permissible suction lift from NPSHA and NPSHR)
4. Excessive amount of air in liquid
5. Air pocket in suction line (Check whether any point in suction line is above center line of pump, and if so, lower the line)
6. Air leaks into suction line
7. Air leaks into pump through stuffing boxes or mechanical seal
8. Net opening area of foot valves is small
9. Foot valve/strainer partially or fully clogged or silted up
10. Suction bell mouth or foot valve insufficiently submerged
11. Water-seal pipe clogged
12. Seal cage improperly mounted in stuffing box, preventing sealing and allowing fluid to enter space to from the seal
13. Circular motion in suspended suction pipe observed (The problem indicates occurrence of vortex)
14. Foot valve leaks
15. Flap of foot valve jammed
16. Concentric taper in suction line causing air pocket (Replace with eccentric taper)
17. Occurrence of vortex in intake, sump or well (Check whether all parameters for vortex-free operation are satisfied; take remedial measures)
B - 14
No Probable Causes
18. Casing not air-tight and therefore breathing in
19. Short bend/elbow on suction side
20. Inadequate clearance below suction bell mouth (Raise bell mouth to achieve recommended bottom clearance for vortex-free operation)
21. Speed too low for pump driven by diesel engine
22. Speed too high for pump driven by diesel engine
23. Wrong direction of rotation
24. Total head of system higher than design head of pump
25. Total head of system lower than design head of pump
26. Static head higher than shut off head of pump
27. Pump characteristics unsuitable for parallel operation of pumps
28. Burst or leakage in pumping main
29. Pumping main partially or fully clogged
30. Air trapped in pumping main
31. Malfunctioning of line valve causing partial or full closure
32. Capacity of thrust bearing inadequate
33. Foreign matter in impeller
34. Misalignment
B - 15
No Probable Causes
Foundations not rigid, or broken/loose foundation bolts, or supporting structural member (RCC/ structural steel beams) not rigid (Dismantle existing
35.
foundation and cast new foundation. Strengthen supporting RCC/ structural steel beams)
36. Pump (impeller) shaft bent
37. Rotating part rubbing on stationary part
38. Pump shaft bearing (bush bearing or anti-friction bearing) worn
39. Wearing rings worn
40. Impeller damaged
41. Impeller locking pin loose
42. Pump shaft or transmission shaft broken
43. Transmission shaft bent
44. Shaft or shaft sleeves worn or scored at the packing
45. Gland packing improperly installed
46. Incorrect type of gland packing for operating conditions
47. Shaft running off center because of worn bearing or misalignment
48. Rotor out of balance, causing vibration
49. Gland too tight, resulting in no flow of liquid to lubricate gland
50. Failure to provide cooling liquid to water cooled stuffing boxes
51. Excessive clearance at bottom of stuffing box between shaft and casing, causing interior packing to be forced into pump
B - 16
No Probable Causes
52. Dirt or grit in sealing liquid, leading to scouring of shaft or shaft sleeve
53. Excessive thrust caused by mechanical failure inside the pump or by the failure of the hydraulic balancing device, if any
54. Excessive grease or highly viscous oil in anti- friction bearing housing or lack of cooling, causing excessive bearing temperature
55. Lack of lubrication causing overheating and abnormal friction in anti-friction bearing, bush bearing or transmission shaft bearing
56. Improper installation of anti-friction ring (damage during assembly, incorrect assembly of stacked bearings, use of unmatched bearings as a pair, etc)
Dirt in bearings
57.
58. Rusting of bearing from water in housing
59. Mechanical seal worn out
60. Coupling bushes or rubber spider worn out or wear of coupling
61. Base plate or frame not properly levelled
62. Coupling unbalance
63. Bearing loose on shaft or in housing
64. Reflux valve (NRV) does not close tightly during shut down, after power failure or after tripping
65. Critical speed close to normal speed of pump
Source: JICA, 2011
B - 17
APPENDIX B.3.2 POSSIBLE CAUSES AND CORRECTIVE ACTIONS TO CHECK FOR PUMPS
Table B3.2-1 Corrective actions
(1) Pump won’t start or run

Check to see if float ball is stuck. If so, remove obstacle. If required,
Float switch is not being raised reposition pump or remount switch in new position so it does not get
high enough stuck. Fluid level might not be high enough to engage switch. Raise
float manually or add water until float is at activation height to test
switch
Check outlet to ensure that it has power. If not, replace fuse or reset
breaker in fuse/breaker box.
Plug pump directly into an outlet without using an extension cord.
If extension cord MUST be used, ensure that it is made of adequately
Pump is not receiving adequate heavy gauge wire to support the length of cord and horsepower
power of pump being used. Check that wire providing power to the outlet
where pump is plugged in is adequate.
Pump should be plugged into an outlet that is fed by its own circuit
breaker (or fuse).If circuit breaker feeds power to other outlets or
appliances, use an outlet that is fed by its own breaker
Remove screen from bottom of pump and make sure no

Impeller is jammed with debris obstruction is preventing the impeller from moving freely. Remove
any obstructions
Bypass the float switch. Unplug pump cord from the piggyback plug
of float switch. Plug the pump’s plug directly into outlet to test. If
Float switch is defective
pump runs, float switch is defective. Replace float switch. (Do not
leave pump plugged in too long or it will burn out)
If all items above check out OK, then pump is defective and needs
Pump is defective
to be replaced
(2) Motor hums but little or no fluid is ejected from pit
Motor is just humming but does

Follow diagnostics above for “Pump won’t start or run”
not run
Drill 1/16” to 1/8” anti-airlock hole in pipe just above pump’s
Pump is air-locked
discharge and just below check valve
Check valve usually has an arrow on it indicating water flow.

Check valve is stuck or closed, or Ensure it is pointing up towards the discharge, not towards pump.
installed incorrectly Inspect to see if check valve is stuck or closed.We recommend
check valves be installed horizontally in sewage applications so
solids cannot settle onto the flapper valve and hold it shut
Inspect impeller for worn or missing blades.

Impeller is damaged
Replace impeller if needed
B - 18
Check for blockages at discharge of pipe. If in cold area, see if pipe

Discharge pipe is partially or fully is frozen closed.
blocked Discharge pipe has too many 90-degree elbows which restrict flow.
Using more than 3 or 4 elbows can restrict flow considerably.
Consider using 45° elbows instead of 90° elbows
Inspect impeller area of pump for debris that has jammed the impeller.
Impeller is jammed
Remove as needed
Suction intake screen is partly or Inspect suction screen at bottom for debris blocking it.
fully blocked Remove debris
Volute (bottom of pump) is cracked Inspect bottom section of pump for cracks or holes that would allow
allowing water to leak out water to escape
Inspect discharge pipe and joints for any location where water can
Discharge pipe is leaking
leave the pipe and return to the sump pit
(3) Pump runs for a short time and ejects some fluid, but shuts off before pit is empty. (Bear in mind a few
inches will remain at bottom of pit. This is normal)
Be sure that pump is plugged directly into outlet. It is
recommended that the outlet be fed by its own circuit breaker (or
fuse). If the breaker (or fuse) sends power elsewhere, the pump
Pump is overheated and shut off by may be short of voltage when it starts. Make sure proper pump has
thermal overload been chosen for your application. A sewage or effluent pump is
designed to empty a sump, sewage or effluent pit. Using this pump
where it can run for extended periods (waterfalls, pond circulation,
etc.) can cause overheating
Check if pump shuts off before float ball is all the way down. If it
Float switch is out of adjustment shuts down too early, adjust float switch according to instructions in
the owners’ manual
If adjustment above did not resolve problem, or no adjustment is
Float switch is defective
possible, replace the float switch
(4) Pump runs continuously
Pump cord and float switch cord Plug pump cord into piggyback connector on back/side of float
are plugged in separately switch plug. Place the combination in a single receptacle of an
outlet
Inspect pit for debris that can cause the float ball to get stuck and
Float switch is stuck not settle at its OFF position. Remove debris or relocate pump or
switch to avoid it
For tethered style float ensure there is minimum of 5cm of cord be-
Float switch is out of adjustment tween float ball and cord mounting bracket. Make sure cord is not so
long that float can settle on floor of pit and not hang straight down
Fluid is not being discharged See item above labelled “Motor hums but little or no fluid is
from pit ejected from pit”
B - 19
(5) Pump starts and stops too often
A very small pit or basin will simply not hold as much water.
Sewage pit or basin is very small Enlarging the pit or basin (if possible) would be wise
For tethered style float ensure there is minimum of 5cm of cord
Float switch is out of adjustment
between float ball and cord mounting bracket
Fluid is coming back into pit from After pump has run, inspect to see if fluid is coming back into pit
discharge pipe through the pump. If so, the check valve has failed. Replace the
check valve
(6) Pump is noisy
Place insulating foam between pipe and wall and/or joists. Try
Discharge pipe is rattling or bang- hanging the pipe with an exhaust hanger from an auto parts store.
ing against wall and/or floor joists Install a section of flexible rubber hose (like radiator hose) between
the pump discharge and the discharge pipe for insulating vibrations
Install a section of flexible rubber hose (like radiator hose) between

the pump discharge and the discharge pipe for noise insulation. You
Check valve slams shut with a
may be using a pump that is higher in horsepower than you need.
bang just after pump shuts off
It may cause the water to move too fast in the pipe. After the pump
shuts off, the fluid column keeps moving upward for a moment, then
slams down
Pump is sucking air at end of its Adjust float switch according to the owners’ manual so that it shuts off
cycle before it starts sucking air
Inspect impeller for broken or missing blades, or debris stuck to

Pump itself is vibrating blade. Clean / replace impeller or pump to rectify but also inspect
sump pit to eliminate debris that could damage new impeller
(7) Fuse or circuit breaker feeding the outlet where pump is plugged in trips or blows when pump activates
Water entered cord and/or float Separate pump plug from switch plug use hair dryer to dry them out.
switch connector (especially Remove cord connector from top of pump and dry out with cloth or
possible if your breaker is a hair dryer
GFCI type breaker)
Impeller is stuck or jammed with Remove screen from bottom of pump and make sure nothing
debris prevents the impeller from moving freely. Remove any obstructions
Using an extension cord or wiring to Check to make sure the wire supplying power to the pump is
outlet which is of inadequate appropriate for the horsepower and amp draw of the pump in place
capacity
We recommend that the pump be plugged directly into an outlet and

Shared circuit breaker (or fuse) that the outlet is the only item being powered by the circuit breaker
that feeds it. If the breaker is powering other items, the additional
draw of the pump starting can pop the breaker (or blow the fuse)
B - 20
Plug pump directly into outlet (without plugging into float’s piggyback
plug) to see if pump runs without popping breaker or fuse. If it does,
Float switch is defective but it pops fuse/breaker when plugged in through float switch, the
float switch is defective. Replace float switch
Pump motor has a shorted winding If all the items above check out OK, then the motor may be defective
and it will be necessary to replace the pump
B - 21
APPENDIX B.3.3 TROUBLESHOOTING IN SEWAGE PUMP STATIONS
Table B3.3-1 Troubleshooting in sewage pump stations
The rated current Check the current drawn If it exceeds rated current,
has been exceeded and compare value with stop the pump & report to
because of worn out that in the manual for competent officer
motor pump set
Sewage pump set starts Cavitation has Check for unusual If so, stop the pump
pumping and changed the dynamic gurgling sounds from the &report to the competent
1 automatically trips after balance of the impeller pump volute officer
some time
The pumping mains Verify the outlet end of If a pipe seems to be
has been choked and the pumping main if it is clogged, close the valve,
there is back pressure a free discharge remove a pipe length and
check
Sewage pump motor Use an appropriate If heating is excessive,
heats up beyond flap type thermometer. Verify with the manual of stop the pump & report to
2
permissible limit Do not use bare hands the pump set competent officer
Sewage pump set Bearings have worn Use a hand held decibel If noise level exceeds 80
3 makes a lot of noise out or cavitation has level meter and verify dB, stop the pump and
loosened parts of from 1-m distance report to the competent
impeller officer
A constant and steady

drip is beneficial in Most probably, the
Stop the pump and rectify
gland packing of packing rope has
Sewage pump has the same from fresh
4 horizontal foot softened and has
continuous gland leak supplies
mounted pump sets, given way
but a steady flow is a
source of trouble
Most probably the Install a new foundation Make an adaptor frame
5 Sewage pump vibrates foundation bolts have
outside the footprint of old and remount the base
noticeably given way or cavitation foundation plate
has occurred within
The pump delivery head Remove the pressure

The non return valve may be in the shut off gauge, fit a standby
Pump seems to be
may have tripped and range. This should be calibrated pressure gauge
drawing current, but
discharge pressure is verified from the pump and reconfirm that the
6 flow meter does not
not able to open the curve and delivery pump is at the shutoff
record any flow
flap of the non return pressure gauge range
valve. The same thing
may occur with a gate
Immediately shut down the pump set and arrange
valve also
for opening and inspection of the non return valve
and gate valve, and rectify the same. Allow the raw
sewage to go through emergency bypass to identified
water course
B - 22
If it is lower by 5% stop
Pump may not be Check the voltmeter the pump and report
receiving the reading to competent officer or
designated voltage switch over to genset
if the timing is morning
peak flow
Pump delivery line Check the air valve If the air valve is
Pump makes a may be having an position and release any defective, replace the
humming noise when air lock trapped air by opening it ball inside
7 switched on, but there
If the pump is The pump has to be If crack is detected, take
is no discharge
submersible, the switched off and pump out of service and
bottom casing may physically raised above send it to the pump
have cracked and the water level and manufacturer
sewage may be inspected
escaping there itself
Allow the well to flood.

The suction opening Stop the pump set. Use Chances are the sheet
may be blocked by another pumpset if or rag may float up and
some sheets or rags available can be removed by a
long pole and hook
Circuit breaker for the Pump motor may This is to be verified by a qualified operator. If true,
8 pump trips when pump have shorted winding take the pump out of service and do not install
is switched on unless it comes back fully repaired and with all
correct records
B - 23
APPENDIX B.4.1 TROUBLESHOOTING IN STPs
Table B4.1-1 Manual bar screens
Velocity of approach Take a branch air line Reconstruct the

and velocity of exit are and fix it to agitate the approach and exit
Grit settles in less than 0.6 m/s sewage at entry and channels appropriately
1 screen chamber exit. This will at least and maintain at least 4
The flow is not entering
the screen help in buoyancy times the width in each
perpendicularly and location
forms a swirl before it
Screen rods get Place a flow deflector

2 Same causes as in 1
clogged with plastic arrangement in water
above
sachets, rags, resistant ply upstream
sanitary napkins like the turnstile used in
etc horse racing
Hand rake rod The rods might have
cannot be been welded to a cross Fabricate a new screen set of rods, which are
3 “ploughed” freely rod before the sewage individually fixed in the concrete floor and the walking
through the full enters the screen platform
length of the screen
Operator feels The width of platform is

Add extra width of platform with handrail at the
4 insecure to stand too small and there is
upstream end
and rake no handrail behind him
Operator is Provide a light roofing arched cover and fix

5 uncomfortable in There is no roof appropriate light on the roof edges so that the
sun and rain operator is not subjected to glare
Operator is not able There is no Make arrangement for hanging the rod on the outer
6 to carry the raking arrangement to keep air side of the sidewall at waist height while standing
bar with him while the raking bar near on the platform
climbing up the platform
Unusual or Increase in sewage Verify flows and verify If gravity does not
7 excessive quantity or higher peak that bypass peak flows permit and flows are
screenings sewage flows or back to inlet chamber very high, demand
industrial effluents may during peak hours of additional screen
occur flow if gravity permits chambers
B - 24
Table B4.1-2 Mechanical bar screens
1 Same as items 1 and 2 above
Screenings drop The flap plate at the Should not be attended by the operator. Call the
2
back into the top requires equipment supplier
sewage channel resetting
The moving raker The mechanical
3 drops back with a arrangement is faulty
loud noise
Shear pin may be
broken, or rope over the
4 Motor is running but
pulley may be loose, or
raker does not move
rack & pinion are not
in mesh Should not be attended by the operator. Call the
Alignment of stationary equipment supplier
Marks of metal
5 made on metal in and moving parts are
screen rods not in order and these
parts have moved away
Screen starts Motor torque power is

6 moving and not adequate
suddenly the
motor trips
The screen may be
Sewage overflows clogged (or) the If choking is not the problem, refer to the design
7 screen chamber hydraulics and department
channel dimensions are
not matching
Increase in sewage Verify flows and bypass If gravity does not
Unusual or quantity or higher peak peak flows back to inlet permit and flows are
8 excessive sewage flows or chamber during peak very high, demand
screenings industrial effluents hours of flow if additional screen
may occur gravity permits chambers
B - 25
Table B4.1-3 Detritors
Try to reduce the flow If this solves the

Sewage is flowing too through the detritors problem construct
fast across the detritors by opening the bypass additional detritors as
valve? and watch for needed
improvement
Grit classifier is not Try to screed the Get the channel made
meshing with the grit inclined floor to match in SS and fix correctly
Detritors and evacuation channel the rakes
1 classifiers do not floor in the case
bring out any grit of scrapers
The screw is not

meshing with the Change the arrangement to raker type. This is
curved portion in which economical considering overall aspects
it is moving
The sewage may not Take a sample in a beaker, allow it to settle and
have grit at all watch for grit load in raw sewage. If there is no grit,
bypass the grit chamber and remove the mechanical
equipment to stores
The grit washing Install organic return pump to lift the sewage to the
2 The grit has foul mechanism is top of the grit washer rake (or) screw and wash down
smell not working the organics
Add extra classifiers to Trace the locations in

Road washings, ash, or the existing ones by collection system and
3 Excessive grit material from building additional SS troughs rectify the connections
sites may be entering and screws
the collection system
Increase speed of scrapper as well as
frequency of removal of grit
This can occur when Install additional organic Try to recirculate outlet
4 Excessive the flow is small and return pumps in flows to attain the
organic matter in velocity through classifiers velocity
the grit detritors is less than
design velocity
For all other mechanized systems refer the problem to the equipment supplier.
5 The operator should not attempt repairs
B - 26
Table B4.1-4 Velocity controlled grit removal channels
Grit gets washed Velocity varies widely

1 Refer the problem to the design department
away in the channels between average flow
and peak flow conditions
Usually traveling
platform with trip
switches at end and
vacuum pump set with
Never enter the grit
Grit removal facilities hanging hoses are
2 Do not attempt any channel. Demand a
do not exist provided to discharge rectification mechanized grit removal
into dedicated channel
system
along the length of grit
chamber. This probably
is not provided or it is
not working
The grit delivered
The system design does
by the grit removal Construct a grit washing hydro cyclone facility
3 not permit rinsing of
vacuum system has
the grit
foul smell
This can occur when Reduce the number of Install temporary pump
Excessive the flow is small and parallel grit channels in sets to recycle outlet
4 organic matter in velocity through use flow
the grit detritors is less than
design velocity Insert planks or brickwork along the length to reduce
the width of flow and increase the velocity
Velocity is too high and Add more channels or

Carryover of grit Increase grit removal
5 detention period is too introduce equalization
frequency
short basin for raw sewage
B - 27
Table B4.1-5 Oil & grease removal unit - gravity type
The required facility of Do not try to skim by Arrange for spraying an

a slit pipe rotatable at any other means. The insecticide mildly once
the surface of the oil layer is best left as it is a day on the scum
has not been provided
The required operating
platform with handrails Demand the platform
Oil and grease floats is not provided
on the surface before
1
the downstream Try to loosen it by
baffle and cannot be blowing hot air around
skimmed The slit pipe is not its housing at the ends.
If this does not work,
rotating This can be done by
call the equipment
using a hair drier. Stand
supplier
on the outside on a
ladder and not on the
oil trap
In hot summer fumes The oily scum becomes Immediately place a non Install a non flammable
2 are seen above the hot and starts emitting flammable light roof on light roof with 4.5 m
unit fumes the unit headroom
Table B4.1-6 Mechanized oil & grease removal unit
Whatever the reasons, the operator shall not attend to the problem and shall
1 All problems
call the equipment supplier
B - 28
Table B4.1-7 Primary clarifiers circular mechanical sludge scraper type
Install a circular platform
with handrails on the
Scum flows over Scum baffle is not Use a long wire brush
1 land side. The platform
outlet weirs provided to scrape out the
shall be preferably RCC
biological growths if
supported independent
there is a circular
of the clarifier foundation
walkway with handrail.
If there is no walkway,
do nothing Demand installation of
a scum baffle all round
and a scum removal arm
If discharge is by gravity, Even after these
open the valve fully and measures, if the sludge
watch for sludge. does not drain, divert the
If no sludge drains out, sewage from the clarifier,
pump compressed air empty out by temporary
if a “Tee” flange joint is diesel pump set. Then
available. If there is no hose, inspect and
“Tee” joint, bring a sewer rectify. Invariably, sludge
jet rodding machine and pipelines are of CI or DI
jet the line at mild and they do not collapse.
pressure for not more However, if it has
Sludge solids start Choked up sludge than a minute and again collapsed, major repair is
2 floating withdrawal pipeline after an hour called for especially after
ensuring that dewatering
If it discharges by direct the groundwater is done
suction and if no sludge to below the floor level of
drains out, pump the clarifier
compressed air if a “Tee”
flange joint is available.
If there is no “Tee” joint,
bring a sewer jet rodding
machine and jet the line
at mild pressure for not
more than a minute and
again after an hour
Higher HRT generates

gas bubbles, which 1. Spray water on sludge lumps
reduces density of 2. Increase sludge removal frequency
sludge solids, leads to
floating of sludge lumps
Sludge scraper arms Jamming of motor, Check whether electrical If both the connection
3 gearbox unit (or) supply is available at the and switch are in order,
do not rotate
breakage of motor terminals. call the equipment
transmission Check the local push manufacturer
mechanism button switch with
megger
B - 29
Scraper arms rotate, Scraper blades have Guide a remote operated video camera on the sides
4 but the sludge lost the squeegees of the wall at three or four locations. Inspect the film
coming out is merely at the floor level. This footage and perform repairs
sewage and sludge means the sludge is
is occasional not moving towards
the center for
withdrawal
Excess growth of Indicates aerobic

5 Same procedure as in item 1 above
bio mass on the V organisms growing in
notches in weirs the grooves
If it is a horizontal foot Verify electrical

mounted centrifugal connections, and switch Even after these
pump set, the gland off the motor. measures, if pump does
packing may be Remove the gland not work, call the pump
too tight packing and set supplier
Sludge pump runs
6 re-fit it properly
for few minutes and
stops suddenly If it is a positive
displacement
stator- rotor pump set, Call the pump set supplier
the stator and rotor
might have jammed
Sludge does not Grit has entered the Install air lift pumps on Try to increase the
7 drain easily by tanks and has choked the top of tanks and efficiency of grit
gravity in hopper the drain pipe of the evacuate the grit removal equipment
bottom tanks hopper tank content periodically
Surges occur in the The incoming raw Usually settling tanks can absorb a peak flow of
8 settling tank sewage is probably about 2.5 times during morning hours but if the raw
overflows on being pumped directly sewage itself is pumped intermittently, then an
the weirs from the equalization tank is needed
collection system
Settling tank effluent Typically, the thickener

9 is darker than overflow may be darker There is nothing to be done; this can be allowed to go
raw sewage than sewage and can on and will automatically be rectified after
cause this problem aeration tank
Bubbles are noticed Too much detention in Increase sludge removal Recirculate the outlet
in the tanks and the settling tank frequency to contain flow back to inlet to
sludge spreads after introduces septic the problem increase the flow and
10
the bubbles conditions and reduce detention
anaerobic activity. This
releases methane
and hydrogen
sulphide bubbles
B - 30
Table B4.1-8 Activated sludge plants
If the plant has been Simultaneously, in the
constructed in at least other module, remove the
two parallel modules, air diffuser facilities, motors
shut down flow to one and gearboxes in other
module. This applies to units and store them
all units like clarifiers, carefully in the store. Do
aeration tanks, thickeners not disturb piping
and digesters and valves
The clarifiers may be Simultaneously, verify
hydraulically under whether it is possible to
loaded causing serious install a lower air
problems like septicity compressor of the required
and foul odour. Try to air capacity calculated by
install temporary pump pro rating the same to the
set and return 100 % of flow and same head
treated sewage back to
screen chamber
This is a common
Raw sewage flow If there is VFD facility for
1 problem, and it seriously If possible install a new
is much less than the existing air compressor,
affects the performance air compressor without
design flow changing the motor try to adjust the output
causing huge waste in
prorated to the flow
the electrical energy for
aeration The sludge withdrawal Consult a process design
from primary clarifier will person before operating
give thin sludge and the the dilution water pump set.
thickener may not need Too much water into thick-
separate dilution water ener is not recommended
In the secondary clarifier, Simultaneously, verify the
operate the return pump MLVSS in the aeration
set as designed. The tank. If the concentration
excess sludge wasting is too low compared to the
time and volume may design value, throttle and
have to be adjusted pro reduce recirculation in the
rata to the sewage flow treated sewage
versus design flow recirculation pump set
The digester may not be The dewatering machines
working efficiently due to will have facilities for
smaller organic load and polyelectrolyte addition.
Check the proper dosage
possibly smaller solids
in the lab. Do not add
concentration. Do not
more polyelectrolyte than
take any action
actually needed
The dewatering Construct required
machines will have facilities to store the first
facilities for time dewatered sludge
polyelectrolyte addition. and the required pump
Check the proper sets to pump it back
dosage in the lab. Do not again to the
add more polyelectrolyte dewatering machine
than actually needed
B - 31
In STPs of industrial Even after these
clusters where the work measures, if microbes do
is only in day shifts, the not develop, supplement
sewage is actually mostly commercially available
urine and no night soil enzymes as per
as the nature’s call is manufacturer’s guidelines.
finished by the Also add micro nutrients
A balanced population in their once a week. The Excel
Microorganisms do availability of organic houses itself before sheet for calculating the
2
not develop material, nitrogen and coming to the industry. micro nutrients quantity
phosphorous must be Locally available cow is given in Appendix-B.
available otherwise dung has to be Procure the chemicals,
organisms will not grow dissolved in water, prepare a solution and
filtered to remove straw add to the aeration tank
etc and added to aeration slowly over an hour so that
tank. Dosage should be it mixes well with the tank
determined to obtain at contents. The addition is at
least 50 mg/l of BOD the inlet end
Same as above for batch type reactors like SBR
In case of sewage First apply physico - chem-
Toxic Material may be coming from one SPS, ical treatment to a stream
present in raw sewage first off identify the line carrying toxic material and
at inlet and divert it then let it be allowed for
further treatment
Raw sewage flow
This can be adjusted to Make sure the hydraulics If not, bypass after
3 is much higher than
about 15 % is adequate grit removal
design flow
4 MLSS develops but A peculiar problem may Verify the design TDS Locate the source and
does not survive be the TDS of and actual TDS avoid it in the
the sewage collection system
White coloured New plants usually have Try to spray the treated By adopting these
5 foaming of such problems because sewage using a measures, the problem
aeration tank the sludge is young and temporary pump set should be controlled within
not aged. The foam twice in a day time shift a month at the maximum
may be removed to break the foam
without any worries
If possible attach a
greenhouse nylon net to
strong anchor nails on
the side walls handling
it carefully
F/M ratio is too high Do not waste sludge from either secondary
clarifier or aeration tank
Increase sludge
If the problem persists
Older plants may have wasting and verify
Dark brown foaming provide a raw sewage
such problems due to whether MLVSS has
6 of aeration tank equalisation tank and
very little sludge wasted increased to about
ensure uniform raw
in secondary clarifier, 70 %. If air supply is
sewage flow to the
available, increase it by
aeration tank
using the VFD
B - 32
Most probably, Nocardia to be checked Check and correct oil,

Greasy very dark filamentous organisms under a microscope by grease & fat in raw sewage
7
foaming of such as Nocardia might a microbiologist
aeration tank have come into the Increase sludge wasting by 10 % day till the desired
MLSS level of MLSS is achieved
If possible increase
Insufficient oxygen has
Very dark foam and caused anaerobic Check the DO in the aeration air by VFD. If this
8 aeration tank is not available, report the
mixed liquor is black conditions in the
matter to all including the
aeration tank
plant in charge directly to
supplement the aeration
Unequal flow distribution
MLSS
or unequal return sludge Check the flow rates and adjust the valves of return
9 concentration varies
to the aeration tanks or sludge lines to each aeration tank or division weirs in
between the parallel
both can cause this flow division boxes before entry into aeration tanks
aeration tanks
problem in both surface
and diffused aeration
Small amount of
10 whitish foam This is actually a sign of a plant operating well
at corners
Verify F/M ratio. Most If the aeration tank is step
probably this would aeration type, send the
have increased to a raw sewage to the second
Sludge rises almost Toxic contents in raw higher value than the compartment
11 all over the clarifier sewage may be causing design value
weir and overflows dispersed growth
Verify the DO in If the aeration tank is a
bulking in plug flow type, try to divert
aeration tank. This
aeration system the raw sewage at least
might be very low
or absent about 20 % of the
distance away from
the inlet
Verify the MLVSS. Its If the tank is a complete
value might be very mix tank with uniform
low compared to the entry of sewage all along
designed value one side, try to cut off
raw sewage for one hour
every shift
Verify the raw sewage If the plant has facilities
pH for any sudden to add a coagulant, try to
drop due to use a non ionic
acidic effluents polyelectrolyte for
some time
Microscopic examina- Check nitrogen, Distribute the raw
tion by a microbiologist phosphorous, BOD sewage along the length
shows a large number of ratio and adjust N and of aeration tanks in plug
filamentous organisms P by adding commercial flow reactor so that initial
NPK fertilizers zones can recover
B - 33
If the STP is not Check for nitrification and Assemble 50 mm SS crib

designed for reduce oxygen supply to mesh with lockable clasps
denitrification and if aeration tank by reducing of size equal to cross
excess oxygen is given the air output of blowers / section of launders and
in aeration tank, there compressors, but without of cubical shape, fill with
can be nitrification of affecting mixing energy loose foam and stack along
ammonia, this nitrate requirement, which are the launder at intervals to
will be denitrified in the also equally important in trap the solids. Periodically
sludge zone of diffused aeration systems remove, wash and restack
secondary clarifiers and If the aeration is by If this is not possible,
the rising bubbles will surface aerators adjust follow the foam
carry over the sludge the submergence to filled cribs as
solids from the reduce the mentioned above
sludge layers oxygen transfer
Sludge return rate is Check return sludge concentration and solids level
too high (balance) around final clarifier and settleability test
Check micro biota, DO, pH and nitrogen

Sludge concentration
Filamentous growth concentration; raise Do and pH, supplement
12 in return sludge is low nitrogen and add chlorine
(<8,000 mg/L)
Actinomycetes Check micro biota and dissolved iron content; if
predominant present, supplement nitrogen feed
Collector mechanism
Adjust speed of collector mechanism
speed is inadequate
B - 34
Table B4.1-9 Biological nitrification-denitrification systems
Check for DO in the If there is still no
mixed liquor as it enters nitirification, the problem
the secondary clarifier may be elsewhere. Hence,
This can be due to go to the next step as
and find out if it is the
insufficient oxygen given below
Nitrification does same as in the design of
supply, absence of
not occur the STP. If it is less, try
1 required bicarbonate
to increase by using the
alkalinity and hindrance
VFD on the compressor
from toxic chemicals
Check the bicarbonate If the alkalinity is less,
in sewage
alkalinity and nitrogen supplement it by adding
ratio. The alkalinity sodium bicarbonate to
expressed as CaCO3 the extent required. The
shall not be less than quantity is to be
7.5 times of nitrogen calculated by the
expressed as N chemist
Check the nitrate in the If everything appears
influent to and effluent normal, check whether
from the denitrification the bottom floor level
tank and compare with mixer is functioning in
the design values. If it is the anoxic tank portion
This is due to much lower, check the N and rectify the
inadequate contact time in the raw sewage and equipment, if necessary
between raw sewage, clarifier effluent to find
Denitrification does return mixed liquor and out the nitrification
2
not occur return sludge and also
due to inadequate Check if the BOD in If this is the case, in
nitrification itself raw sewage has gone reality there is no
up compared to design immediate solution in a
value. If this is the case, plant already constructed
the oxygen supplied is and in use. The best
consumed by possible solution would
BOD reducing be to restrict the raw
micro-organisms sewage volume
proportionately
Table B4.1-10 Secondary clarifier problems
1 Problems in primary clarifier sludge issues as discussed earlier are equally applicable here also
The better form of MLSS Check for nitrification and If the problem persists,
Pin type of flocs in
settling in clarifier is BOD removal in kg / day. the only method is to
clarifier are seen
2 “blanket settling.” The If the nitrification fraction add a non-ionic polymer
and these flocs
settling flocs trap any is higher then such a pin to the mixed liquor
do not educe the
suspended matter and pull head floc formation can before it enters
turbidity of effluent
it down along with settling. occur. Increase the return the clarifier
completely
The effluent may not sludge ratio to the
appear very clear extent possible
B - 35
Table B4.1-11 Rotating biological contactors
Check for pH variations If the problem persists
in raw sewage every even after taking these
four hours for a week. If measures, toxic
variation is large, , try to chemicals are probably
identify the source in the entering the sewage
Very large bio mass This can be due to pH collection system and
sloughs off from the variations and / or correct it
1
discs all of a sudden sudden toxic chemicals If the problem continues
Check for metals in the
while rotating in raw sewage even after taking these
raw sewage and detect
any unusual increase. measures, the only remedy
Trace the problem to its is to introduce an
source and correct equalization tank for
it there raw sewage
Typical streaks of The presence of Check the raw sewage An optional method is to
whitish bio mass hydrogen sulphide in the for hydrogen sulphide introduce coarse bubble
2
over the discs raw sewage and odour, estimate the aeration in the first 25 % of
observed frequently associated septicity can concentration and try to the RBC drum by releasing
lead to this problem pre-aerate in the compressed air through a
collection tank pipe with perforations. This
has been found to be
very effective
Check the BOD loading Even after this if the
as per design and adjust problem continues, verify
it suitably by limiting the as hereunder
sewage volume
Verify whether raw
sewage SS are much
In the meantime insert
Solids build up in the The initial BOD higher than the
3 coarse bubble aeration in
RBC drums concentration is higher designed SS and try to
the drum as
than the designed value rectify the problem at
discussed earlier
the source in the
collection system
Sometimes, a mild non If the problem continues in
ionic polyelectrolyte can spite of these measures,
be added to the influent introduce primary settling
end to precipitate before RBC and take the
coagulant from primary sludge to
BOD load aerobic digesters
After a period of When the power outage Ask the equipment
power outage, when occurs, the biomass on Check alignment before
supplier to verify and
the RBC is re-started, the disc has water trying anything else. If
match the torque
it refuses to rotate, the content. This water adds alignment has
rating of the motor and
motor creates a to the weight of the disc changed, call the
4 the torque enforced by
humming noise and and initial torque of the equipment supplier
the wet disc assembly
the disc assembly motor is not adequate to which is measured by the
needs an external overcome the inertia rope and weight method
push to set it rolling
B - 36
A simple method is to Also, reversing the
This is an associated
temporarily increase the direction of feed and
phenomenon of RBS
5 Growth of snails RPM of the disc outlet about once a month
systems. Strictly
in discs assembly to just about helps build up bio mass
speaking, they do not
double the designed growth to uniform weight
affect the BOD removal
value for a few minutes along the length of
efficiency
at a time and use a long the shaft
pole to dislodge the
snails back into the
sewage drum
Table B4.1-12 Biological phosphorous and nitrogen removal
Check the anaerobic The air supply to aeration
The phosphorous zone for DO. It should tank can be reduced if
Treated effluent removal occurs in the be zero or less than there is a VFD attached to
1 contains more anaerobic zone. If it is 0.2 mg/l. If DO is high, the air compressor motor.
phosphorous than not removed fully, it can reduce the aeration air If it is not there, demand
designed cause eutrophication in supply to hold the DO for it
receiving water bodies in aeration tank to not
more than 1 mg/l. This
is the root cause
Check the raw sewage Instead of supplemental
Treated effluent has This condition is possible
BOD and if needed, air compressor, a high
low phosphorous if raw sewage BOD is
2 install supplemental air duty compressor can also
content but the BOD higher than the
compressor to meet the be installed
is high at over design value
extra oxygen needed for
20 mg/l
the higher BOD
Treated sewage Nitrogen removal and Confirm the raw sewage If all parameters are as
meets phosphorous phosphorous removal nitrogen and BOD and per the design, raw
3 removal occur in two separate the air actually pumped sewage has nitrate
requirements, but the zones and not together. by the air compressor to inhibitors. Conduct lab
nitrogen content is Hence, understanding be according to design. studies and control
much higher the respective problem If the air supply is less, the source in
than required is necessary increase it collection system
B - 37
Table B4.1-13 Facultative ponds
Weeds do not grow if If sludge depth has built
water is more than 1 m up and reduced the water
depth. Check the outlet depth, remove the weeds
Weeds attract and
level and the
promote growth of
Weeds grow inside sludge depth
1 insects like flies,
the pond sewage
mosquitoes and so on. If there are two Thereafter allow the
They can also become a parallel ponds, take out sludge to sun dry and
nuisance as reptiles may one pond at a time from then till it by a tractor.
be found hidden in sewage flow at start of Leave as-is for a week
the weeds summer and pump out and then remove the
the top liquid using a sludge taking safety
portable diesel pump set precautions
into the other pond
Scum forms in the Scum promotes insect Do not try to remove Once it breaks up, the
corners and insects growth and the scum out of the gas bubbles propping
2
grow over it propagation, particularly pond. Take a long thin the scum are released.
flies and mosquitoes. It pole and beat the scum The scum mat will sink
can cause insect borne gently so that it breaks into the pond
epidemics if up at the surface
not removed
Bunds are overgrown The greatest risk of Physically shear off the It is dangerous to stand
3 with weeds, small such growth is that growths. Do not pull on top of a tree and cut
plants or even trees someday this growth the roots from the bund the tree branches. Use
will break the bund and as this will loosen and a crane and make the
suddenly the sewage break the bund. The labourer sit inside its
will flow out and fall into sheared material must bucket. The cut weeds,
all wells or rivers in the not fall into the pond twigs etc., can be placed
zone causing a major into a netting tied to the
health hazard or water bucket and taken
borne epidemic out safely
Overhanging tree This is to be avoided Identify the trees and

branches drop leaves because the pond mercilessly cut the
4 on the pond and requires sunlight to branches overhanging
this causes shadow function and the the pond. Do not cut the
region on the blocking sunlight will tree as the cut roots will
pond surface cause septicity, and topple the bund
BOD removal will suffer
Pond turns Accept it; this should Leave it as it is and it If the density is high
5
dense green in not be taken as will disappear on its own recirculate the pond
summer months a problem when monsoons set in effluent by pumping
DO level in pond This need not Raw sewage BOD may If DO is present in the pond
water is very low and necessarily be a problem be very low and this may effluent, do not disturb it
6 even at mid day it as long as effluent BOD cause low DO level
does not go above is under control
2 mg/l
B - 38
This is risky. It blocks the Check the raw sewage Demand the construction
solar heat energy from for oil & grease regularly. of a gravity oil & grease
Oily sheen and shine
penetrating the pond, Sometimes, automobile removal unit for raw
slowly increases on
which prevents algae service stations and sewage before the raw
the pond surface
growth. This in turn stops industries will suddenly sewage is allowed into
7
oxygen production by discharge waste oils into the pond This is a must
algae, so removal of the collection system.
BOD from the pond is Trace the source and
affected adversely control it
A temporary and very effective method is to sink

country wood poles around the inlet zone, tie fishing
net and place straw inside this zone. The straw will
absorb the oil & grease and should be left there until
the oil & grease removal unit is built
Table B4.1-14 Aerobic ponds
Minimum 1 m liquid Check and correct the Simultaneously verify

depth is needed to sewage depth by whether the minimum
Weed grows inside adding an elbow or bend
1 prevent weeds freeboard is 0.5 m. If not,
the pond in the liquid to the outlet pipe to get 1
from growing the bund should be raised
m sewage in pond. Inlet all round
pipe may remain
submerged
Too much of algae in This is inherent in As long as receiving water course has flow, algae are
2 the pond sewage aerobic ponds and not a problem and the ecological system need not be
cannot be avoided disturbed
Receiving water Algae are aquatic The immediate remedy The final remedy is to
course is dry, algae organisms. This is a is to bypass the aerobic use chemical treatment
3 dangerous situation as pond and avoid growth instead of aerobic ponds
die there and foul
odour is present algal toxins may enter of dense algae
soil and ground water
Foul odour of dead One possible reason is Try to erect a temporary The final remedy is to
algae from ponds very small flow as rock fill bund like a construct a regular cross
4 compared to design flow, “coffer dam” and reduce bund, switch the flow into
especially in high
summer months and thus very high the area of the pond pro it and remove the rock fill
detention time in rata to flow as compared
the pond to the design flow
B - 39
Table B4.1-15 Anaerobic ponds
This is an inbuilt The only practical method is to use aromatic trees
Foul odour of
1 mechanism when like Eucalyptus as live fence in two successive rows
hydrogen sulphide
sulphate is reduced in with first row at least 3 m away from the toe of the
(rotten egg)
anaerobic action bund
Oily scum with This is also an inbuilt Try to install a simple Engage a licensed
shiny appearance is mechanism of such gravity type underflow re-refiner to collect and
2
floating on the pond ponds baffle tank at the inlet take away the oil
surface and trap the oil periodically
Bubbles rise from This is a good sign that This is part and parcel of the anaerobic pond system
the pond sewage the anaerobic system and no action need be taken to control it. However,
and burst at the pond is functioning well. The if the sludge in the pond has built up to leaving only
surface, which throws end product of sulphide about 30 cm of liquid depth, start desludging
up black sludge and methane gas lifts a procedures as described in Section 4.1.13
3
column of sludge equal Facultative ponds. If the pond is a single pond,
to its diameter and construct a rock fill bund in the middle and proceed
when bubble escapes to desludge one after the other
to the air, the sludge
disperses back into the
pond
Table B4.1-16 Maturation ponds
1 These are to be dealt with similar to Section 4.1.14-Aerobic ponds
Table B4.1-17 Land irrigation systems
This promotes flies,
mosquitoes and may Check the ground water Stop irrigating and divert
Applied sewage is
1 cause water borne level. Sometimes, this the sewage to a natural
ponding on land
epidemic; therefore, may be the problem drainage course
it should be
controlled quickly
If sodium is high, it will Check the sodium If it is too high, stop
Sewage is running enter the soil and content and verify irrigation for a prolonged
off over land instead exchange the calcium whether it is within the period and wait for
2
of going in and magnesium. Slowly permitted values monsoon rains to slowly
the soil becomes hard as application measured wash out the sodium by
a rock and permeability as Sodium Absorption dissolution in rainwater
is lost Ratio (SAR) or
Exchangeable Sodium
Percentage (ESP)
B - 40
Irrigated crop has The root zone may be Free up the soil by tilling Drain the stagnating
suddenly become flooded and air entry it ensuring that it sewage by cutting
3 weak and dies to soil is sealed. This can breathe ditch drains
creates foul odour and
results in water pollution
Nitrate Nitrogen is applied as Check whether raw Verify the permissible
4 concentration nitrate and is not being sewage nitrogen is being loading rate and correct it
in ground taken up by plant. This nitrified in the if necessary
water increases can cause nitrate treatment plant
pollution in ground water
Suspended solids in Removal of suspended A well constructed soil

Sprinklers do applied sewage have solids is very important filter can help instead of
4 not sprinkle blocked the pores and before application to a mechanized system
organisms may have sprinkler systems
grown in the
sprinkler end
Table B4.1-18 Chemical treatment systems
1 Flocs do not form in Flocs form from The raw sewage does The added chemical
rapid mixer & chemical reactions in not have the required may have impurities
flocculator rapid mixer and build up acidity or alkalinity to which prevent floc
in flocculation. react with the formation. Examples
However, initial flocs chemicals. Check the are lime powder and
do not develop due to plant O&M manual and commercial alum
organics and SS the actual chemicals
being used
The added chemical Carry out lab test on
may be actually different the chemicals
than what is indicated
on the label
Hydraulic shear of the Install vertical radial If the first stage of remedy
raw sewage is needed baffles for half the does not work, change
in the mixer. If the tank radius to break the the tank to a
is a circular one, vortex vortex and bring up square shape
alone will form and not the shear
shear
Flocs are formed in The speed of the Take the rapid mixed If the lab test proves
2 the flash mixer but flocculator has to be sample in a glass floc can build up but the
these are broken up slow enough to allow beaker and slowly flocculator fails in the
in the flocculator the flocs to be built rotate it clockwise and plant, then the
up to a bigger size then counter clockwise flocculator needs to
with a glass rod and be changed
watch the flocs
Chemicals settle The mixing energy is Increase the speed of If this does not work,
3 down in the important to keep the rapid mix impeller introduce additional
flash mixer chemicals in suspension and watch compressed air
B - 41
4 Flocs overflowing in The flocs are unable to The detention time may The detention time may
the sedimentation settle down be too short. Check the be too short. Check the
tank time needed by allowing time needed by allowing a
a sample to settle in a sample to settle in a glass
glass beaker and verify beaker and verify the
the detention time in detention time in the plant
the plant
The shape of the tank In small plants, the best

also plays an important arrangement will be a
part. Horizontal flow square shaped tank
rectangular tanks are with conical hopper
usually not preferred. bottom at 60 degrees to
Circular tanks with horizontal
conical hopper
are better
The flow pattern carries
over the flocs and the Refer the problem to the equipment supplier
inlet baffle is not effective
The flow through the unit Check the design If needed, ask for one
may be much higher than manual of the plant and more unit to manage
what is designed rectify the same the flows
The water in the sludge Add lime powder to the

Sludge does not If it does not dewater even
5 may be a “bound water” wet sludge by using a
dewater fully in then, use a polyelectrolyte
and would need a paddle mixer equipment
drying beds in addition to lime
“weighting agent” such before using it on a
as lime powder filter bed
Other chemical such as FeSO4 or FeCl3 or saw dust
may also apply with Lime powder
B - 42
Table B4.1-19 Treated sewage disinfection by chlorination
1 The first aid kit is This is a The plant in charge The old kit if located can be
either empty or it serious problem that shall directly purchase a used as standby
has disappeared can happen in a plant ready kit and install it
and needs emergency
measures to be adopted
bypassing procedures
2 The sodium This again is a major Immediately stop all Call for emergency
hydroxide filled liquid issue of a different chlorination, close all measures to fill the tank
tank is empty kind and needs chlorine containers before re-commissioning
immediate action and open the windows, the chlorination
doors, and ventilators
3 here is no water in This is not an Keep at least three to Connect the shower to two
the shower emergency, but all the four buckets of fresh different water sources so
same requires water and paint the that at any one time, one of
4 There is no water in immediate attention buckets in red colour to these will work
the “eye rinsing indicate it is for use
wash basin” in emergency
situations only
There is no residual Strictly speaking, this is Verify the MPN count of Eventually take up re-ap-
5 chlorine in the the desirable situation inlet to and outlet from praisal of the chlorination
chlorinated effluent if the purpose of chlorine contact tank. If system to deliver higher
chlorination has been the design value is not dosage and augment the
served in MPN count met increase the facilities
chlorine dose after
lab estimation
There is too much This can be because the Check the chlorine in the Request the plant chemist
6 chlorine in the inlet to chlorine contact contact tank outlet and to calibrate the chlorine
sewage coming out tank is not having the compare with the design demand every week and
of chlorine designed demand (or) value. If it is higher by 1 indicate it on a wall board
contact tank too much chlorine mg/l, reduce the for all to see
is being chlorine dosage
applied to the sewage
Testing of joints in the Chlorine gas when in Immediately stop Call the system supplier
7 plumbing lines with contact with ammonia chlorination, close for a complete system
ammonia solution always gives chlorine cylinder check and rectification
swab shows whitish fumes valves and open up all
white fumes windows, doors, and
ventilators. Switch on
exhaust fans
Inadequate chlorination Replace equipment as necessary to provide
equipment capacity treatment based on maximum flow
Coliforms count
8 fails to meet
Short circuit in chlorine Conduct dye test
required standards
contact chamber Install baffles in the chlorine contact chamber
for disinfection
Install mixing device in chlorine contact chamber
B - 43
Solids build up in Clean contact chamber
contact chamber
Chlorine residual is Increase contact time or increase chlorine feed rate
too low
High TSS Reduce TSS in effluent
Inability to maintain Malfunction or

9
adequate chlorine deterioration of chlorine Overhaul pump
feed rate water supply pump
Insufficient number of Connect adequate number of cylinders to system so

10 Inability to maintain
adequate chlorine cylinders connected to that feed rate does not exceed the recommended
feed rate the system withdrawal rate for cylinders
Chlorinator will not Pressure reducing valve Dissemble chlorinator and clean valve stem and seat.
11
feed any chlorine in chlorinator is dirty Precede valve with filter or sediment trap
Table B4.1-20 Treated sewage disinfection by UV
There are no standardized methodologies in this section. Please follow accordingly as prescribed by
1
the system supplier
Table B4.1-21 Treated sewage disinfection by ozonation
There are no standardized methodologies in this section. Please follow accordingly as prescribed by
1
the system supplier
B - 44
Table B4.1-22 Surface aerators

Moisture has entered Have an electrician
the motor or check the motor and Rewind the motor
winding breakdown replace with spare
Motor - high or has occurred motor if available
1
uneven amperage Amperage drawn is Amperage drawn is Call the equipment
higher than the rated higher than the rated supplier
amperage of motor amperage of motor
Excessive friction and Inspect and lubricate
Overhaul, if needed
heat in motor gear bearings and gears
Repair or replace oil If problem persists, call the

pump Change oil equipment supplier
Gear reducer - Lack of
2
bearing or gear noise proper lubrication Remove obstruction in If problem persists, call the
oil line equipment supplier
Cracked coupling Call equipment supplier and replace coupling;

align impeller shaft
Shaft coupling -
3 Call equipment supplier and for torque bolts, use
unusual noise Loose coupling bolts/
and vibration nuts as a result “locking” nuts, align impeller shaft
of vibration
Call equipment supplier and repair torque blade
Loose blades
Aerator impeller - bolts, use lock-washers, align impeller
4
unusual noise
Call equipment supplier and replace torque
and vibration Cracked blades
bolts; align
Table B4.1-23 Air blowers
Coupling misalignment Stop the machine

Unusual noise and realign If difficult, call
1 equipment supplier
and vibration Loose nuts, bolts and Stop the machine
screws and realign
Delivery air is at Bypass valve open, Close the valve and Proceed to check leaks in
2 lower pressure than leaks or breaks in check the pressure pipeline by soap solution
rated pressure distribution piping instantaneously test and rectify
Air system - high Plugged diffusers in the Check the records of Remove, clean and refit
3 pressure aeration tanks pressure at each branch diffusers in the
line and detect abnormal line
abnormalities
Air flow rate is lower Higher ambient
4 than the rated flow temperature than design Check the ambient air temperature and if it is
conditions may be drastically high call the equipment supplier
the reason
B - 45
Oil level too low, oil filter
System oil - low
5 dirty Valve sticks are Drain and refill with proper oil type
pressure
open, incorrect oil
System oil - high

6 Incorrect oil type Drain and refill with proper oil type
pressure
Suction lift too high
7 Oil discharge - low Air or vapour in oil Purge air at filter
pressure Coupling slipping on Secure coupling
pump shaft
8 Low oil temperature Oil cooler water flow Throttle water flow
too high
9 High oil temperature Oil cooler water too Increase water flow
low; incorrect oil type or Drain and refill with proper oil type
insufficient oil circulation Replace oil filter, check oil lines for restrictions
10 Hot bearings Blower speed too high Reduce speed to Call equipment supplier to
Defective bearings recommended RPM check bearings for
Oil cooler water flow Damage: Repair or clearance, hot spots,
rate too low replace. cracks or other damage.
Increase water flow Repair or replace
Increase water flow
11 Motor doesn’t start Overload relay tripped Correct and reset
12 Motor noisy Noisy bearings Check and lubricate
13 Motor temperature Restricted ventilation Check openings and duct

high Electrical abnormality work for obstruction
Check for grounded or If in doubt, call equipment
shorted coils and supplier
unbalanced voltages
between phases
B - 46
Table B4.1-24 Air distribution system

High, low or no Loose movement, out of
1 Clean and correct defects
indication in meters calibration, dirt
Leakage in seals, Loose bolts or fittings
2 gaskets and Blown out Tighten and or replace
flex connections
3 Pipe corrosion Drain traps daily, install additional traps, flush pipes,
Condensate
and remove standing water
4 Sludge inside pipe Vacuum action by Flush pipe, install

If problem still persists,
reverse operation check valve on
remove, clean and refit
of blower blower, repair
check valve
5 Dirt in pipes No or inefficient
Install filters, and clean filters more frequently
air filtration
6 Valves difficult Hardened grease Remove old grease and apply seizing inhibitor,
to operate Corrosion in valves operate valves monthly, drain condensate traps daily
Table B4.1-25 Air diffusers
Some parts of Air is not being released Loosen the joint at the Another option will be
1 aeration tank do not from the diffusers at the walking platform and in situ air purging by a
show release of air floor level of the slowly lift the air drop portable mini air blower.
bubbles at aeration tank pipe till air bubbles can This can be connected
the surface be seen. This means the to the drop pipe by a
diffusers have choked “Tee” and closing the
and cannot get over regular valve to purge
the full sewage depth. the choked organic
Remove the drop pipe matter. This action can
for cleaning also be done routinely
If the air system is Most often this works
designed for doubling very well but the sys-
the air when needed tem should have been
and if more than one air designed for such an
compressor is installed, application. Please
briefly apply the air from check the manual of the
both the compressors plant before
and purge the diffusers attempting the first stage
for about 5 minutes remedy. Take care that
every hour for a this double flow is not
few times continued for more than
five minutes in an hour
B - 47
Compressor shows This may be a serious Switch off the In general, Bourdon
2 full design pressure, gauges are
problem. If the pressure compressor and verify
but there are no air gauge on compressor whether the Bourdon instantaneous
bubbles coming out delivery is of the gauge goes back to its measurement units and
of the aeration tank Bourdon type, most zero position. If it does not permanent reading
probably it has gone into not, replace with a gauges. Change these
permanent set showing new one gauges to proper
the full pressure diaphragm gauges
The gauges are always

best installed with Request for such a
pressure to current change
converter type
transducers or
transmitters
Pressure gauges are If air is not being If pressure gauges are If there is no leak, the
3 in order, compressor released from anywhere available at all locations compressor may be at
is in working in the aeration tank, it before changes of fault. Check the
condition but air causes major leaks in alignment of air amperage. If it is
bubbles do not rise transmission pipelines transmission piping, try negligible then there is a
from aeration tank closing all these and mechanical problem with
open section after the compressor. Call the
section to verify the leaky equipment supplier
section below ground
and rectify
Air escapes in large This may be due to This is a major problem and will require a team of well
4
bursts from a few detachment of the air qualified and properly protected divers to dive and
places instead of header pipe and the fix the problem at site while the service team is on
uniform diffusion all diffuser head at the floor; standby at site. Do not empty the tank because
over the tank hence the bulk of air growing the microbes again is not easy
escapes at the
joint location
The entire contents The MLSS concentration Check the MLSS and If this remedy also fails,
appear viscous and has gone out of control then the MLVSS. If both there is almost surely a
shine like oil and air and become too high. these values deviate very problem of shock loads or
5 escapes at surface They are mostly dead much from the design, toxic substances coming
intermittently in large and cannot abstract the waste fifty percent and let in sewage. Check, identify
exploding bubbles oxygen from the diffused system recover locations in the
air. This causes build up collection system
and sudden exploding of & rectify
air bubbles
B - 48
Table B4.1-26 Power back up
Sudden break/ At least 20-30 %

1
stoppage in Power Failure capacity of aeration
Arrange for Dual power
Air supply to blower should be back
supply (through a separate
Areation Tank by DG (diesel generator)
power supply grid)
sets to ensure minimum
air supply to aeration
tank for duration of
7-8 hours
Table B4.1-27 Interpretation of routine laboratory results
COD value is much If it is only sewage, this Check the N and P also The performance of the
1 should not be the case. and compare with the STP may not be up to the
higher than BOD
However, if there are old records. If the COD designed value. Focus on
large industrial effluents is higher, report the identifying the source and
from chemical matter to locate cutting it off properly
manufacturing the source
industries, this can occur
pH values show
2
sudden increase or
decrease Non biodegradable
organic chemicals enter Pretreatment with chemical coagulation is required
into sewage i.e. wax,
The colour of sewage
3 lignin, cellulose etc.
keeps changing often
The treated sewage This can be the case Take a Whatman number-42 filter paper and filter
4 appears turbid and where the algae present the treated sewage into a test tube of 25 ml and
cloudy but the in the treated sewage check the transparency and clarity. The colour may
laboratory report be that of green algae but there must be clarity. If
records BOD of less the filtrate is still turbid and strong in colour, then the
than 20 mg/l pond is overloaded
Increase quantity of return sludge so as to

increase MLSS
B - 49
Table B4.1-28 Flow measuring systems

Bulk flow meter Any mechanical If there is a channel of If the pump house is within
1 reading appears to equipment may go out at least 10 m straight the plant, find out the
be incorrect of order at any time. length, mark the middle timings of each pump set
The operator must 10 m and conduct a float and calculate the flow from
have the capacity to test. Take the observed the pump name plate
find out the flows from velocity at 0.8 and find
other non conventional out the flow
methods and compare There may be a division It is not at all advisable
the readings box for the raw sewage to go into such locations
to the primary clarifiers. when there is no daylight
Verify the weir length because these locations
and depth of flow over are above ground level
the weir and record the with probably no facilities
readings only in the for night work. An error in
daytime for one shift and day shift means the same
compare with the error occurs at other
meter reading times also
Ultrasonic level The ultrasonic level Try to hold a mirror at If the reading
2 sensor readings seem sensors actually the water surface by actually measured and
to be vastly different measure the depth of tying it to a long stick that obtained with the
from previous the sewage water from and note the reading mirror tally, then there is
recent readings the ultrasonic emitter. It given by the sensor. no problem with the sen-
actually measures the Actually measure the sor. If the depth shown by
time from release to depth from the sen- the sensor is different by
the return signal after sor to the water level more than 5%, the sensor
bouncing back from the if there is safe access, must be serviced
sewage surface, takes without getting
the average and is into sewage
calibrated to the depth
Table B4.1-29 Septic tank and leaching systems where sewerage system is not in place
Sewage backs up The problem is The key point is to minimize the water used for bathing
1
into the house directly related to and washing clothes. This will solve many problems
the leach pit only Open the septic tank outlet Construct a fresh leach pit
because a septic chamber, pour a bucketful if there is space. If there
tank is only a flow of water gently and watch is no space, try to clean
through tank whether it goes into leach up the old leach pit and
pit immediately. If it does construct an up flow filter
not flow, the leach pit and discharge the effluent
has become to the street drain. Some-
saturated. The simplest times gravity will not permit
remedy is to use the this. In such cases, use a
services of septage septage vehicle, which is
clearance vehicle and the only answer to
empty the septic this problem
tank periodically
B - 50
Foul smell comes This is the result of Spray the mosquito net of If the problem continues, a
2
out of the the process in the the cowl with bleaching biological filter consisting
ventilating cowl septic tank, and powder solution daily and of gunny cloth of coir
cannot be stopped, keep it wet wetted with bleaching
but it can be treated powder solution may be
tied
If space is available If the problem continues,
construct a smaller septic the only solution is to
tank and up flow filter only frequently use the septage
for toilets and then allow it clearance vehicle
into the main septic tank
Table B4.1-30 Sequencing batch reactors (SBR)
Raw sewage flow is This is a usual problem If the flow is adequate to If the flow is small even for
1
less than the in some cases in the run one of the modules, this, use the SBR tank as
design flow initial period use that module alone an ASP for 20 hours, then
and leave the other stop the flow and decant.
one unused During this time divert the
flow to the other module.
Once decanting is
completed, start that
module and pump the raw
sewage from the
temporary module to it
If the air compressor Always ensure that the
output air volume is too residual DO in the
much, use the VFD to aeration is not less than
reduce the same to 1 mg/l during aeration
match the raw
sewage flow
Raw sewage flow This type of problem is Try to use all modules The spare module will be
2
is higher than the very rare simultaneously except used to receive the raw
design flow one and run the plant in sewage when the other
continuous mode and modules are in decanting
decanting mode mode and then sewage is
as above pumped
Almost all other issues discussed under ASP shall apply here also
B - 51
Table B4.1-31 Moving biofilm bed reactors (MBBR)
Raw sewage flow is less Almost all other issues discussed under SBR is applicable here
1 than the design flow
Raw sewage flow is

2 higher than the Almost all other issues discussed under SBR is applicable here
design flow
Almost all the media This happens in some Mixing equipment are available as sidewall mounted
3
are floating at the tank geometries and facilities which bring about a circular motion of the
liquid surface only because the specific media in vertical plane. These can be simply fixed
and do not mix fully gravity of the media is on a steel post and anchored to the concrete base.
into the depth just about the same as This is similar to erecting a submersible pump set.
of reactor that of water If anchoring facility is not available, hire a qualified
diver from the fire service.
Media floats in air/ Gas or air trapped in Gas or air trapped in Increase height of
surrounding area with media reduces media reduces side walls
or without foam its density its density
Table B4.1-32 Membrane bio reactors (MBR)
1 Raw sewage flow is less
than the design flow Almost all other issues discussed under SBR is applicable here
2 Raw sewage flow is

higher than the Almost all other issues discussed under SBR is applicable here
design flow
3 Membrane permeate In general, this is Look under the If it does not settle and the
volume is because the MLSS microscope for jar appears cloudy even
reducing slowly cannot be filtered by organisms like Nocardia after an hour, then there is
the membranes. The or Sphaerotilus a need to intervene. The
problem may occur in natans-like filamentous first step is to flush the
both suction type and bacteria. membranes if these are
pressure feed types If Get assistance from a fixed (or) to remove, clean
sludge bulking occurs, qualified microbiologist. and rinse if these are
it is due to If these are detected, removable. In the mean-
the filamentous do not panic. Take a time, identify the bulking
organisms. Usually at sample in a one litre reasons as stated under
high MLSS of 10,000 glass jar and observe ASP and try to solve the
mg/l filamentous the settling. If sludge problem. Do not allow the
organisms do not settles to 30 % in half problem to continue. It will
create any problems hour, it is still OK choke the membrane
4 Membrane permeate May occur when some Try to methodically After identifying the
often brings membranes give way isolate each module module, remove it and
out microbial and the microbes by isolating valves and get it duly serviced before
suspended solids escape through it at study the problem replacing it on line
higher pressure
differences
Almost all other issues discussed under ASP is applicable
B - 52
APPENDIX B.4.2 OPERATIONAL PARAMETERS
4.2.1 PARAMETERS
Typical values of loading parameters for primary and secondary clarifiers and various activated sludge
modifications commonly used in India are furnished in Table B4.2-1 and Table B4.2-2, respectively.
Table B4.2-1 Table parameters for Clarifiers
Overflow rate, Overflow rate, Side water Weir loading,

Type of Settling m3/m2/day m3/m2/day depth, m m3/m/day
Average Peak Average Peak Average Average
Primary Settling only 25 - 30 50 - 60 --- --- ≥ 2.5 - 3.5 125

Clarifiers
Primary
Followed by secondary
35 - 50 80 - 120 --- --- ≥2.5 - 3.5 125
treatment
With activated sludge ≥3.5 - 4.5 125
25 - 35 50 - 60 --- ---
return
Secondary settling for ≥3.0 to 3.5 185
15 - 35 40 - 50 70 - 140 210
Secondary
Clarifiers
activated sludge
Secondary settling for ≥3.0 to 4.0 185
8 - 15 25 - 35 25 - 120 170
extended aeration
Note: Where the mechanized aerobic treatment is used after UASB reactor, the settling tank
design shall be based on conventional activated sludge process as above.
Table B4.2-2 Parameters of Activated sludge systems
MLVSS/ kg O2/
MLSS F/M HRT θC QR/Q BOD
MLSS removal kg BOD
Process Type Flow Regime removed
mg/L ratio Day-1 hrs days ratio % ratio
Conventional Plug flow 1,500-3,000 0.8 0.3-0.4 4-6 5-8 0.25-0.5 85-92 0.8-1.0
Complete mix Complete mix 3,000-4,000 0.8 0.3-0.5 4-5 5-8 0.25-0.8 85-92 0.8-1.0
Extended Complete mix 3,000-5,000 0.6 0.1-0.18 12-24 10-25 0.5-1.0 95-98 1.0-1.2
aeration
4.2.2 LOADING RATE
a. HRT (Hydraulic retention time)
The loading rate expresses the rate at which the sewage is applied in the aeration tank. A loading
parameter that has been developed empirically over the years is the hydraulic retention time
(HRT), , day.
(B4.1)
B - 53
Where,
V : Volume of aeration tank, m3, and
Q : Sewage inflow, m3/day
Another empirical loading parameter is volumetric organic loading which is defined as the BOD
applied per unit volume of aeration tank, per day.
b. Specific substrate utilization rate
A rational loading parameter which has found wider acceptance and is preferred, is specific substrate
utilization rate, U, per day which is defined as:
(B4.2)
Where,
So: Influent organic matter as BOD5, g/m3
S : Effluent organic matter as BOD5, g/m3
V : Volume of aeration tank, m3
X : MLSS conc. in aeration tank, g/m3
c. SRT (Sludge retention time)
A similar loading parameter is mean cell residence time or sludge retention time (SRT), c, day:
(B4.3)
Where,
V: Volume of aeration tank, m3
X: MLSS concentration in aeration tank, g/m3
Qw: Waste activated sludge rate, m3/d
Xs: MLSS conc. in waste activated sludge from secondary settling tank, g/m3
d. F/M ratio

If the value of S is small compared to So, which is often the case for activated sludge systems treating
municipal sewage, U may also be expressed as Food applied to Microorganism ratio.
(B4.4)
Where,
So : Influent organic matter as BOD5, g/m3
V : Volume of aeration tank, m3
X : MLSS concentration in aeration tank, g/m3
B - 54
4.2.3 OXYGEN REQUIREMENTS
Oxygen is required in the activated sludge process for the oxidation of a part of the influent organic
matter and also for the endogenous respiration of the micro-organisms in the system. The total
oxygen requirement of the process may be formulated as herein:
(B4.5)
Where,
f : Ratio of BOD to ultimate BOD
1.42 : Oxygen demand of biomass, g/g
∆ X is biological sludge produced per day.
∆ X = Q × Y observed × (So-S)
Yobs = Y/(1+Kd×θC)
Where Y is 0.5
Kd is 0.06
The formula does not allow for nitrification but allows only for carbonaceous BOD removal. The extra
theoretical oxygen requirement for nitrification is 4.56 kg O2/per kg NH3 -N oxidized to NO3 - N.
The total oxygen requirements per kg BOD, removed for different activated sludge processes are
given in Table B4.2-2. The amount of oxygen required for a particular process will increase within
the range shown in the table as the F/M value decreases.
4.2.4 OXYGEN TRANSFER CAPACITY
Aerators are rated based on the amount of oxygen they can transfer to tap water under standard
conditions of 20°C, 760 mm Hg barometric pressure and zero DO. The oxygen transfer capacity
under field conditions can be calculated from the standard oxygen transfer capacity by the formula:
(B4.6)
Where,
N : Oxygen transferred under field conditions, kg O2/kW/hr
Ns : Oxygen transfer capacity under standard conditions, kg O2/kW/hr
Cs : Dissolved oxygen saturation value for sewage at operating temperature, mg/L
CL : Operation DO level in aeration tank usually 1 to 2 mg/L
T : Temperature, °C
α: Correction factor for oxygen transfer for sewage, usually 0.8 to 0.85
Values of Cs is calculated by arriving at the dissolved oxygen saturation value for tap water at the
operating temperature and altitude as in Table B4.2-3 and Table B4.2-4 and then multiply it by a
factor which is usually 0.95 for domestic sewage without undue industrial effluents and with TDS in
the normal range of 1,200 to 1,500 mg/L.
B - 55
Table B4.2-3 DO saturation vs. temperature in Celsius in tap water at MSL

The relationship between temperature and oxygen solubility
Temperature (degree C) Oxygen solubility (mg/L)
0 14.6
5 12.8
10 11.3
15 10.2
20 9.2
25 8.6
30 7.5
35 6.9
40 6.4
100 (boiling) 0.0
Table B4.2-4 DO correction factor for altitudes

Altitude (feet) Altitude (meters) Factor
0 0 1
500 152 0.98
1000 305 0.96
1500 457 0.95
2000 610 0.93
2500 762 0.91
3000 914 0.89
3500 1067 0.88
4000 1219 0.86
4500 1372 0.84
5000 1524 0.82
5500 1676 0.81
6000 1829 0.80
4.2.5 SLUDGE RECIRCULATION RATE
The MLSS concentration in the aeration tank is controlled by the sludge recirculation rate and the
sludge settle ability and thickening in the secondary sedimentation tank.
(B4.7)
Where,
QR : Sludge recirculation rate, m3/d
Q: Sewage inflow, m3/day
B - 56
X: MLSS concentration in aeration tank, g/m3

Xs: MLSS conc. in waste activated sludge from secondary settling tank, g/m3
4.2.6 EXCESS SLUDGE WASTING
Excess sludge = (A/(0.6 to 0.8)) + B
A is calculated by the following equation and 0.6 to be used for extended aeration and 0.8 is used for
conventional activated sludge.
A = Q×Yobs (So-S)a
Yobs = Y/(1+Kd×θC)
Where Y is 0.5
kd is 0.06
B = Q×inert TSS removal

Inert TSS = Influent TSS – Influent VSS
TSS removal in primary settling tank is 60 percent.
Inert SS removal in primary settling tank is 80-90 percent.
VSS removal in primary settling tank is 20-40 percent.
θC is from Figure B4.2-1 for the lowest operating temperature.
Excess sludge in kg/day = Yobs × BODinlet × Flow MLD
Calculate excess sludge kg/day from the thumb rule in this section.
Adopt the higher value.
Excess sludge volume (m3/day)

= Excess wasted (kg/day) × 1000/MLSS in clarifier underflow
The SRT as a function of aeration basin temperature for 90-95% BOD removal as in Figure B4.2-1
Figure B4.2-1 SRT as a function of aeration basin temperature for 90-95% BOD removal
B - 57
APPENDIX B.4.3 CALCULATIONS
4.3.1 EXTENDED AERATION ACTIVATED SLUDGE TANK
An extended aeration activated sludge tank has the following dimensions for treating the waste with
following characteristics;
Length = 60 m
Width = 20 m
Water depth =5 m
Flow =7,500 m3/day
Influent BOD =200 mg/L
Effluent BOD =10 mg/L
Influent SS =200 mg/L
Influent VSS =150 mg/L
MLSS =4,000 mg/L
SV30 =400 mL
MLVSS =2,800 mg/L
Yobs =0.4 mg VSS/ mg BOD
Kd =0.04 day-1
Determine:
a. Hydraulic retention time, day

b. BOD loading, kg/day
c. BOD volumetric loading, kg/m3.day
d. Microorganisms in aeration tank, kg
e. F/M ratio, kg/kg.day
f. SVI, mL/g
g. Excess sludge generation, kg/day
h. Excess sludge concentration, mg/L
i. Excess sludge volume, m3/day
j. SRT, day
k. Return sludge flow rate, m3/day
l. Oxygen requirement, kg/day
Solution:
B - 58
B - 59
4.3.2 PRIMARY SEDIMENTATION TANK
Characteristics of influent to and effluent from primary sedimentation tanks are as follows;
Flow rate =10,000 m3/ day

Influent BOD = 200 mg/L
Influent SS = 300 mg/L
Effluent BOD = 140 mg/L
Effluent SS = 100 mg/L
B - 60
Find:
a. The BOD removal efficiency of the primary sedimentation tank, %
b. SS removal efficiency of the primary sedimentation tank, %
c. Dry sludge generated, kg/day
d. Volume of sludge generated, m3/day if sludge concentration is 40,000 mg/L.
Solution:
4.3.3 CIRCULAR SECONDARY SEDIMENTATION TANK
A circular secondary sedimentation tank has the following dimensions for treating the waste with
following characteristics;
Diameter =20m
Depth =3.5m
Inflow =10,000 m3/day
Return sludge flow =5,000 m3/day
MLSS =4,000 mg/L
B - 61
Find:
a. Surface overflow rate,
b. Detention time,
c. Solids loading rate, and
d. Weir overflow rate.
Solution:
B - 62
APPENDIX B.5.1 TROUBLESHOOTING IN SLUDGE TREATMENT FACILITIES

Table B5.1-1 Sludge thickening by gravity thickeners
No. Troubles / Likely causes First stage remedies Second stage remedies
Problems
1 Typical septic Any thickener will Check the per day total of If this fails to solve the
odour invariably produce a sludge volumes and problem, investigate a
of hydrogen typical odour. Do not try dilution water pumped into sludge flocculation system
sulphide to disturb the system the thickener. Compare like the picket fence, etc.
because of this alone with per day total of sludge This may have given way
withdrawn and thickener below the liquid level. If
overflow. Check for volume the ampere of the motor
balance If the outlet is lesser, is very low compared to
sludge stays longer and is design consumption, call
likely to choke and become the equipment supplier to
septic. Withdraw more attend to the system. Do
sludge not attempt it by yourself
2 Thickened Typically a minimum Check volumes of sludge Even after this, if the
sludge is not detention time is and dilution water problem persists, the
what is needed for sludge entering the tank from their reason lies with the type of
designed for solids to break free flow meters. Reduce the sludge and not the
of bound water and flows so they do not exceed thickener. Proceed to
thicken at the bottom. design values. Check clarifier sludge sections
If this is not occurring, flocculator also
the thickened sludge
will be very weak
3 Biological This is related to the The simplest remedy is a Even after this, if the
growth over the escape velocity over daily scrubbing of the weir problem persists, remove
outlet weir the weir length and surface by a wire brush and the V notch plate and
surfaces temperature conditions. a long handle while walking level the weirs as shown in
becomes Do not alter the along the outer platform Part-A , Figure 5-29
very dense process conditions
if they are as per the
design
4 Sludge solids As long as the inflow Proceed to the sections on Even after this, if the
are overflowing and outflow rates are clarifiers. Sludge from problem continues, add
the outlet weirs not exceeding the secondary clarifier may be polyelectrolyte to the
design values, this very loose and not settling thickener feed well
problem has nothing to down. Follow the remedy temporarily
do with the thickener.
Do not alter the
process
5 Drive motor Too much of sludge at Try increasing the Even after this, if the
trips often the bottom or a foreign sludge withdrawal problem continues, check
object is obstructing the frequency temporarily for the gearbox visually for
free movement of the a day. Most probably this any broken teeth and call
flocculator paddles will solve the problem the equipment supplier
6 Chocking of Top Layer may become
sludge pump dry as a result of Roof may be provided to protect from direct sunlight
direct sunlight
B - 63
Table B5.1-2 Anaerobic sludge digesters
This is an identified high risk unit operation for any person trying to look into this unit or enter it. Sometimes
strobe lights are installed inside the digester to light up the inside so that it can be seen through a fixed
glass plate on the cover slab and viewed from outside. This shall not be allowed, as a simple spark at the
cable terminal can blow up the digester by igniting the methane gas inside it. All investigations of digester
performance should be made indirectly by observing the performance parameters and never by directly
entering the digester. Persons smoking near the digester or while standing near the top dome are likely to
cause severe accident. There is at least one case of the operator and the dome getting blown up because
of smoking. In actual practice, there is not much an operator can do to correct the digester mechanism if it
is not functioning because work on such equipment is a highly specialized task requiring high skills in
explosive zones. The operator can attend only to the pump and motor of externally circulated sludge
mixing type digesters, in which standard horizontal foot mounted centrifugal pumps are coupled to motors.
All other types of equipment are prohibited from being repaired by the operator and shall be attended to
only by the equipment supplier or his service personnel.Hence troubleshooting of digesters will be confined
only to process control in this section
Gas production is a If the feed VSS is too low, If the conditions are as
function of the VSS and then gas production will per the design, it is a clear
detention time and mixing surely be very small. If case of mixing system
efficiency in the digester. the feed VSS is too high, failure. Call the equipment
Measure the VSS in feed then also gas production supplier. Do not correct it
sludge in the lab and verify will suffer. First check the except in case of
loading rate from feed flow. value of VSS externally re-circulated
Compare with design pumped sludge
values
Gas production
1 is less than the Sometimes, the pH of the Raising the pH to Even after these
designed output digester may be less due 6.8 - 7.2 is required. measures, if the problem
to too much of Though lime solution is persists, the reason is not
acidification. This can the easier option, the with the process, but with
be checked in the lab use of sodium hydroxide either the mixing
and compared with past is preferable because it equipment in the digester
records does not create or the sludge quality
problems of precipitates coming out of the
in the digester or the clarifiers. First check on
sludge pipelines the sludge quality as per
The feeding of the earlier sections. If the
solution shall be by a quality is in order, call the
solution tank and equipment
acid-alkali proof dosing supplier to inspect the
pump mounted at ground mixing equipment and
level. The delivery bring it to maximum
pipeline shall be thick efficiency. This shall not
walled UPVC pipeline be attempted by operator
discharging into the
sludge suction sump
B - 64
2 Sometimes there is an Check the sulphate The way to reduce this

auto toxicity problem content of the digester toxicity is to prevent the
when high TDS waters feed and digested outlet. sulphates from getting
are used by the Estimate the sulphide reduced to sulphide in the
habitation. The produced as one third of first place, but this is not
sulphate in the water the sulphate. Estimate possible inside a digester.
gets into sewage. 40 % of this value as A higher degree of mixing
This gets into digester unreacted sulphide. Also usually expels the
liquid. The sulphate estimate sulphide in the hydrogen sulphide gas
reduces to sulphide. digested liquid by titration faster and thus, promotes
This is partly converted in the laboratory. Consult more formation in the di-
to hydrogen sulphide a process specialist on gester liquid. This reduces
gas. The unreacted this further to establish the unreacted sulphide
sulphide is toxic to sulphide toxicity as the remaining in the digester
digesters in the range reason
50 mg/l in dispersed
sludge and 250 mg/l
in granular sludge. In
digesters, it is usually
dispersed sludge
3 Foul or sour odour Usually, a well digested Follow the procedure for raising the pH of the digester
sludge does not smell by lime or preferable sodium hydroxide as
offensive. If the described earlier
digested sludge smells
sour and foul, the
digester has probably
become sour and the
pH may have dropped
4 Smell of hydrogen Apply soap solution
sulphide when to all piping joints to
walking around the verify any leaky joints
base of the fixed or cracked pipes. It can
dome on the digester also be the digester
sidewalls, which are
above the sludge level,
but usually this is not Erect a sign board in local Do not try to fix the
the case language and all familiar problem by yourself. Call
languages that gas is the equipment supplier to
5 Smell of hydrogen Floating dome covers leaking and persons shall attend to it
sulphide when are usually fabricated not go to the top of
walking around the from steel or synthetic digesters
base of the floating materials. The joints
dome on the digester are the sources of the
leak. It can also be
the digester sidewalls
which are above the
sludge level but usually
this is not the case
B - 65
6 Smell of hydrogen Usually these are The simple soap solution Do not try to fix the
sulphide when inflatable gas balloons test will help in problem by yourself. Call
walking around the made of synthetic identifying the leak. If this the equipment supplier to
base of the inflatable material and are of is the case, the fasteners attend to it
gas holder on the multi layered are to be fixed
digester construction. Unless
there is an external
puncture, these do
not leak. The actual
leak may occur at the
base where the gas
cover is jointed with
the digester which
again is through a
piping. Thus, the
fastening around the
joint piping should be
checked
7 Floating gas dome The holding down Try small adjustments Once it becomes vertical,
on the digester is not weights on the rim are at a time by adding or record the work in the site
truly vertical but is not properly adjusted removing the weights register
tilted
8 Gas pressure in the Gas is not being

gas line from digester withdrawn regularly Use the flame trap to release and burn off the required
is higher than the or gas production is volume of the gas
design value more than the design
9 Gas pressure in the Gas production is not Take no action but attend to the sludge section as
gas dome is less adequate discussed earlier
than the design value
10 Mixing systems Get an authorized agency to inspect, service and leave a report at regular
intervals which can be monthly intervals
Table B5.1-3 Mechanical sludge dewatering devices
1 Metallic noise in May be due to worn Lubricate moving parts Refer bearing problems to
moving parts out bearings or equipment supplier
absence of lubrication
B - 66
Table B5.1-4 Sludge drying beds
1 Fires occur in This is due to methane This is due to methane Erect a warning board
drying beds gas in high summer gas in high summer that cell phones should be
months ignited by a months ignited by a spark switched off for a distance
spark from an electrical from an electrical line or of about 10 m from the
line or due to due to somebody edges of the drying beds
somebody smoking smoking nearby
nearby
2 Wet sludge is The drying bed might Cut off the sludge flow If the F/M ratio is higher
ponding for a long have choked or the to the bed and allow it to than 0.2 in biological
time and does sludge applied filter through slowly. Till aeration, demand that a
not filter without digestion it lightly by a long boom digester be provided. If
crane from all sides F/M is less and tilling does
and restart not help, scrap out
and restack
3 Drying beds are full Nothing that can be

of water from rains done about this. If
Nothing that can be done about this. If rainfall is
rainfall is frequent,
frequent, demand mechanized dewatering facility
demand mechanized
dewatering facility
B - 67
APPENDIX B.6.1 TYPICAL LEDGER AND RECORDS
Table B6.1-1 Operational record: Power Receiving and Transforming Equipment
Note: These Appendices are only Indicative and the STP Operator has to develop their own reports and ledger sheets , based on the equipments installed
B - 68
Table B6.1-2 Monthly Report: Electric Power Receiving
B - 69
Table B6.1-3 Ledger for Electrical Equipment
B - 70
Table B6.1-4 Electrical facility ledger (Distributing board)
B - 71
APPENDIX 6.2 PREVENTIVE MAINTENANCE
6.2.1 MOTOR
a. Daily
• Check air draft through motor

• Check bearing temperatures
• Check for any undue noise or vibration
b. Monthly
• Observe presence of oil, grease in bearings from the type of noise when it is in operation.
If necessary top up
• Nothing special other than the daily checks
c.Quarterly
• Blow away dust and clean any splashes of oil or grease
• Check wear of slip ring and brushes; smoothen contact faces or replace, if necessary. Check
spring-tension. Check brush setting for proper contact on the slip-ring.
• Check cable connections, terminals and insulation of the cable near the lugs: clean all contacts;
if insulation is damaged by overheating investigate and rectify. All contacts should be fully tight.
d. Semi-annual
• Check condition of oil or grease; and replace if necessary. While greasing avoid excessive
greasing.
• Test insulation by megger.
e. Annual
• Check Coupling and pins for excessive/unequal wear/damage. Replace if necessary and realign
• Examine bearings for flaws, clean and replace if necessary.
• Check end-play of bearings and reset by lock-nuts, wherever provided.
f. Bi-annual
• Same as annual
6.2.2 PANEL, CIRCUIT BREAKER, STARTER
a. Daily
• Check the phase-indicating lamps.
B - 72
• Note readings of voltage, current, frequency, and others.
• Note energy-meter readings.
b. Monthly
• Examine contacts of relay and circuit-breaker. Clean, if necessary.
• Check setting of over-current relay, no-volt coil and tripping mechanism, and oil in the
dash-pot relay.
c. Quarterly
• Check fixed and moving contacts of the circuit- breakers/switches. Check and smoothen
contacts with fine glass-paper or file.
• Check condition and quantity of oil/liquid in circuit-breaker, auto-transformer starter and

rotor-controller.
d. Semi-annual
• Nothing special.
e. Annual
• All indicating meters should be calibrated.
f. Bi-annual
• Same as annual.
6.2.3 TRANSFORMER SUBSTATION
a. Daily
• Note voltage and current readings.
b. Monthly
• Check the level of the transformer oil.
• Confirm that the operation of the GOD (ground operated disconnection) is okay.
• Check temperatures of the oil and windings.
• Clean radiators to be free of dust or scales.
• Pour 3 to 4 buckets of water in each earth-pit.
c. Quarterly
B - 73
• Check condition of the H.T. bushing.

• Check the condition of the dehydrating breather and replace the silica-gel charge, if necessary.
Reactivate old charge for reuse.
d. Semi-annual
• Check di-electric strength and acid test of transformer oil and filter, if necessary.
• Test insulation by megger.
• Check continuity for proper earth connections.
e. Annual
• Check resistance of earth pit/earth electrode.
f. Bi-annual
• Complete examination including internal connections, core and windings.
Note: These Appendices are only Indicative and the STP operator has to develop their own reports and
ledger sheets , based on the equipment’s installed
B - 74
APPENDIX B.6.3 TROUBLESHOOTING FOR ELECTRICAL FACILITIES
Table B6.3-1 Electric motors
Trouble Cause Remedy
Bent or sprung shaft Straighten or replace shaft
Excessive belt pull Decrease belt tension

Misalignment Correct coupling alignment
Bent or damaged oil rings Replace or repair oil rings
Use recommended oil. Use of oil of
Oil too heavy or too light very light grade is likely to cause the
bearings to seize
Insufficient oil level Fill reservoir to proper level when
motor is at rest
Badly worn bearings Replace bearings
Hot bearings Bearing loose on shaft or in bearing Re-metal shaft / housing or replace
housing shaft or bearing housing
Maintain proper quantity of grease in
Insufficient grease
bearing
Remove old grease, wash bearings
Deterioration of grease or lubricant
thoroughly with kerosene and replace
contaminated
with new grease
Reduce quantity of grease. Bearing
Excessive lubricant should not be filled more than the
two-third level
Broken ball or rough races Clean housing thoroughly and replace
bearing
Ventilation passage blocked. Windings Dismantle entire motor and clean all
coated with fine dust or lint (dust may windings and parts by blowing off dust,
Motor dirty be cement, sawdust, rock dust, grain and if necessary, varnish
dust and the like)
Bearing and brackets coated inside Clean and wash with cleaning solvent
Rotor winding coated with fine dust / Clean and polish slip ring. Clean rotor
cement and varnish
Check for excessive rubbing or
Motor over loaded
clogging in pump
Low voltage Correct voltage to rated value
Fuses blown, check overload relay,
Motor stalls Correct voltage to rated value starter and push button
Mechanical locking in bearings or at Dismantle and check bearings. Check
air gap whether any foreign matter has
entered air gap and clean
No supply voltage or single phasing or

Motor does not start open circuit or voltage too low Check voltage in each phase
B - 75
Start on no load by decoupling. Check

Motor may be overloaded
for cause for overloading
Examine starter and switch/ breaker
Starter or switch/breaker contacts
for poor contact or open circuit. Make
improper
sure that brushes of slip ring motor are
making good contact with the rings
Rotor defective Check for broken rings
Examine overload relay setting.
Motor runs and Ensure that the relay is set correctly
then stop Overload replay trips to about 140-150% of load current.
Check whether dashpot is filled with
correct quantity and grade of oil
Consult manufacturer on suitability for
design duty and load
Motor does not Voltage too low at motor terminals Check voltage, change tapping on
accelerate to rated because of line drop transformer
speed
Broken rotor bars Look for cracks near the rings
Reduce load. (Note that if motor is

driving a heavy load or is starting up a
Excess loading
long line of shafting, acceleration time
will increase)
Reduce load. (Note that if motor is
Motor takes too long to
driving a heavy load or is starting up a
accelerate Timer setting of starter is incorrect
long line of shafting, acceleration time
will increase)
Correct the voltage by changing tap on
Applied voltage too low transformer. If voltage is still low, take
up the matter to power supply authority
If overloaded, check and rectify cause
of over load. Overloading may be due
Check for overload to system fault, for example, if pipeline
bursts, the pump may be operating at
low head causing overload of
motor. Vortices in sump also may
cause overload
End shields may be clogged with dust,
Blow off dust from the end shields
preventing proper ventilation of motor
Check to make sure that all leads are
Motor overheats while Motor may have one phase open
well connected
running
Check for faulty leads or faulty
Unbalanced terminal voltage
connections from transformers
Check insulation resistance, examine
Weak insulation
and re-varnish or change insulation
Replace worn bearings
High or low voltage Check for true running of shaft
and rotor
B - 76
Motor misaligned Realign
Weak foundations or holding down Strengthen base plate/ foundation;

bolts loose tighten holding down bolts
Coupling out of balance Balance coupling
Motor vibrates after
connections have Defective ball or roller bearings Replace bearing
been made Bearings not in line Line up properly
Single phasing Check for open circuit in all phases
Excessive end play Adjust bearing or add washer
Resonance from supporting structure
or foundation or vibration of adjoining Consult expert
equipment
Fan rubbing air shield or striking Check for cause and rectify
insulation
Scraping noise
Loose on bed plate Tighten holding down bolts
Motor may be over loaded Reduce the load
Brushes may not be of appropriate Use brushes of the recommended

quality and may not be sticking in the grade and fit properly in the brush
Motor sparking at slip
holders holder
rings
Clean the slip rings and maintain its
Slip ring dirty or rough smooth glossy appearance; ensure
they are free from oil and dirt
Slip rings may be ridged or out of Turn and grind the slip rings in a lathe
turness to a smooth finish
Clean the spilled oil on winding.

Thrust bearing oil seal damaged
Replace oil seal
Leakage of oil or grease Reduce quantity to correct extent.
Excessive oil, grease in bearing
on winding Grease should be filled up to
maximum half space in bearing
housing
B - 77
Table B6.3-2 Capacitors
Leaking welds & solders Repair by soldering

Leakage of heclor*
Broken insulators Replace insulators
Arrange for circulation of air either by
Poor ventilation reinstalling in a cool and ventilated
Overheating of unit place or arrange for proper ventilation
Over voltage Reduce voltage if possible, otherwise
switch off capacitors
Abnormal bulging Gas formation due to internal arcing Replace the capacitor
Cracking sound Partial internal faults Replace the capacitor
Short external to the units Check and remove the short
Over-current due to over voltage and Reduce voltage and eliminate

harmonics harmonics
HRC Fuse blowing Short circuited unit Replace the capacitor

Replace with bank of appropriate
kVAR rating high kVAR
Correct or replace the discharge
Capacitor not discharging Discharge resistance low
resistance
Unbalanced current Insulation or dielectric failure Replace capacitor unit
*Leakage of Heclor from terminals, insulators or lid etc. is not a serious trouble. After cleaning, the nuts should be tightened
carefully, araldite shall be applied if necessary and the capacitor should be put into circuit. If the leakage still continues,
refer the matter to manufacturer.
Table B6.3-3 Starters, breakers, and control circuits

Non availability of power supply to the
starter / breaker Check the supply
Starter/breaker not
switching on Over current relay operated Reset the relay
Relay not reset Clean and reset relay
Relay contacts are not contacting
Starter / breaker not Check and clean the contacts
properly
holding on ON-Position
Latch or cam worn out Readjust latch and cam
Check and reset to 140-150 % of
Over current relay setting incorrect
normal load current
Starter/breaker tripping Moderate short circuit on outgoing Check and remove cause for short
within short duration due side circuit
to operation of over
Check overcurrent setting
current relay
Sustained overload Check for short circuit or earth fault
Examine cause of overload and rectify
B - 78

Loosen connection Clean and tighten
Inadequate lubrication to mechanism Lubricate hinge pins and mechanisms

Adjust all mechanical devices such as
Mechanism out of adjustment toggle stops, buffers, springs as per
manufacturer’s instructions
Examine surface, clean and adjust
Failure of latching device
latch. If worn or corroded, replace it
Relay previously damaged by short
Starter / breaker not Replace overcurrent relay and heater
circuit
tripping after
Review installation instructions and
overcurrent or short Heater assembled incorrectly
correctly install the heater assembly
circuit fault occurs
Relay not operating due to: -Replace fuse
-Blown fuse -Repair faulty wiring; and ensure that
-Loose or broken wire all screws are tight
-Relay contacts damaged or dirty -Replace damaged contacts
-Damaged trip coil -Replace coil
-C.T. damaged -Check and repair / replace
Contacts burnt or pitted. Clean the contacts with smooth

polishing paper or if badly burnt /
pitted, replace contacts. (Contacts
should be cleaned with smooth
Overheating polishing paper to preserve faces.
File should not be used)
Loose power connection Tighten the connection
Sustained overcurrent or short
Check cause and rectify
circuit / earth fault
Poor ventilation at location of starter /
Improve ventilation
breaker
Overheating of auto Winding design improper Rewind

transformer unit Replace transformer oil in auto-
Transformer oil condition poor
transformer unit
Check voltage condition. Check
Low voltage
momentary voltage dip during starting.
Low voltage prevents magnet sealing.
Check coil voltage rating
Contacts chatter Poor contact in control circuit Check push button station, (stop
button contacts), auxiliary switch
contacts and overload relay contacts;
test with test lamp
Poor contact in control circuit Replace coil. Rating should

compatible for system nominal voltage
Check for grounds and shorts in sys-

Contacts welding Abnormal inrush of current tem as well as other components such
as circuit breaker
B - 79

Low voltage preventing magnet from Check and correct voltage
sealing
Short circuit Remove short circuit fault and ensure
that fuse or circuit breaker rating is
correct
Filing or dressing Do not file silver tips. Rough spots
or discolouration will not harm tips or
impair their efficiency
Interrupting excessively high current Check for short circuit, earth fault or
Short push button and / or
excessive motor current
over heating of contacts
Discoloured contacts caused by Replace contact springs, check
insufficient contact pressure, loose contact for deformation or damage.
connections, etc. Clean and tighten connections
Dirt of foreign matter on contact Clean with carbon tetrachloride
surface
Short circuit Rectify fault and check fuse or break-
er rating whether correct
Examine and replace carefully. Do
Mechanical damage
not handle coil by the leads
Coil open circuit
Burnt out coil due to over voltage or Replace coil
defect
Magnets & other Replace part and correct the cause of
mechanical parts worn Too much cycling damage
out/broken
Replace magnet assembly. Hum may

Magnet faces not mating correctly
be reduced by removing magnet
armature and rotating through 180°
Noisy magnet (humming) Dirt oil or foreign matter on magnet Clean magnet faces with carbon tetra-
faces chloride
Low voltage Check system voltage and voltage
dips during start
Low voltage Check system voltage and voltage

dips during start
Wrong coil Check coil voltage rating which must
include nominal voltage and frequency
Failure to pick-up and / or of system
seal Mechanical obstruction With power off, check for free
movement of contact and armature
assembly. Remove foreign objects or
replace contactor
Poor contact in control circuit Check and correct
Gummy substances on pole faces or Clean with carbon tetrachloride
in mechanism
Failure to drop out Worn or rusted parts causing binding, Replace contactor
for instance coil guides, linkages
Improper mounting of starter Review installation instructions and
mount properly
B - 80
Failure to reset Broken mechanism worn parts, Replace overcurrent relay and heater
corrosion, dirt, etc.
Open or welded control Short circuit in control circuit with too Rectify short circuit in general. Fuses
circuit contacts in over large rating of protecting fuse over 10A rating should not be used
current relay
Insufficient oil in breaker/ Leakage of oil Locate point of leakage and rectify
starter (if oil cooled)
Oil dirty Carbonisation of moisture from Clean inside of tank and all internal
atmosphere parts. Fill fresh oil
Moisture present in oil Condensation of moisture from atmo- Same as above

sphere
Table B6.3-4 Panels
Failure to reset Bus bar capacity inadequate Check and provide additional bars in
combination with existing bus-bars or
replace bus-bars
Loose connection Improper ventilation
Improper ventilation Improper ventilation
Insulator cracked --------- Replace the insulator
Table B6.3-5 Cables

Provide a cable in parallel to existing
Over heating cable or higher size cable
Cable size inadequate
Increase clearance between cables
Check size of lug. If not properly
Insulation burning at Improper termination in lug crimpled, correct it
Termination termination Check whether all stands of cable are
inserted in lug. Use a new or higher
size lug if necessary
B - 81
Table B6.3-6 Transformers
Trouble Trouble shooting procedure Cause Remedy

Listen to the noise at A. External Noise: A loose A.Tighten the fixing bolts
Abnormal noise various points of the fixing bolt/nut of the and nuts and other loose
transformer and find out the transformer metallic parts
exact location by means
B. Noise originating from B.In the case of small
of a solid piece of wood or
the inside of the transformer and if such
insulating material placed
transformer: In the case facilities are available,
on body of transformer tank
of old transformer, open the transformer and
at various points. This helps
possibly due to the remove any slackness by
in determining whether the
windings having become placing shim made of
noise is from the inside of
slightly slack insulated board. In case of
the transformer or is only
large transformers, contact
an external one
the manufacturer or
transformer repairer
The temperature rise of a) Transformer is over a) Reduce the load to the

transformer during 10-24 loaded rated load
hours of operation is
b) Transformer room is b) Improve the ventilation
observed. The input
not properly ventilated of the transformer room
current, oil temperature are
c) Certain turns in the to achieve effective air
noted down at intervals of
winding are short cooling
half an hour and tabulated
circuited c) Major repairs are
necessary and should be
taken up in consultation
with an experienced
Electrical Engineer and
transformer repairer
The transformer becomes The transformer has a Take action for major
hot in a relatively short major defect repairs in consultation
High Temperature period; transformer oil with an experienced
escapes from the Electrical Engineer and
conservator or there is even transformer repairer
appearance of gas
Abnormal heating of one Poor termination either a)External contacts should

terminal inside or outside the be checked and put in
transformer order especially those in
the aluminium bus bars
b) If heating persists,
action for major repairs
should be taken in
consultation with an
experienced Electrical
Engineer
a) Short circuit in the Action for major repairs
Tripping of circuit windings should be taken in
breaker or blowing of consultation with an
------------------ b) Damage in the experienced Electrical
fuses
insulation of the winding Engineer and transformer
or in one terminal repairer
B - 82
Frequent change of ---------- a) Breather leakage a) Replace packing

silica gel colour b) Breather oil level low b) Check oil seal.
c) Absorption of moisture Top up oil
c) Remove moisture
completely
Oil leak at joints / ---------- a) Defective packing a) Replace packing

bushing / drain valve b) Loose tightening b) Tighten properly
c) Uneven surface c) Check and correct it
d) Bushing cracked d) Replace bushing along
with washer
e) Drain, valve not fully
tight e) Tighten valve and plug
Low insulation ---------- a) Moisture absorption by a) Heat the windings, by

resistance winding operating transformer on
b) Contaminated oil no-load, and check
whether insulation
c) Presence of sludge resistance improves. If
no-improvement is
observed after operation
for 5-6 hours, filter the oil
b) Replace with proper oil
c) Filter or replace the oil
The transformer becomes The transformer has a Take action for major
hot in a relatively short major defect repairs in consultation with
High Temperature period; transformer oil an experienced Electrical
escapes from the Engineer and transformer
conservator or there is even repairer
appearance of gas
Abnormal heating of Poor termination either a)External contacts should

one terminal inside or outside the be checked and put in
transformer order especially those in
the aluminium bus bars
b) If heating persists,
action for major repairs
should be taken in
consultation with an
experienced Electrical
Engineer
a)Defects in joints a) Rectify the defect

Water inside tank ------------------ b) Moisture condensation b) Drain water and dry the
moisture in winding
c) Oil mixed with water
when topping up c) Heat the winding on
no-load. Recheck dielectric
strength and filter if
necessary
B - 83
Overheating of cable ---------- Loose connections Check and tighten the

ends and cable connections
terminals
Neutral ground a) Loose connections Replace the grounding
conductor (earth ----------
b) Large fault current conductor
strip) burnt
B - 84
APPENDIX B.7.1 MINIMUM LABORATORY EQUIPMENTS NEEDED FOR TESTS
Table B7.1-1 Minimum laboratory equipments needed for tests
Type of Plant
(A) (B)
Equipment
For consent parameter For plant operating
(BOD, SS, pH) parameter
Analytical Balance x x
Autoclave x
Centrifuge x
Chlorine comparator x
Colony counters x
Demineraliser x
Dissolved Oxygen sampler x
Drying oven (hot air) x
Fume cupboards x
Gas liquid chromatograph x
Hot plates x x
Incubator 20°C/27°C (BOD) x x
Incubator 30°C (Bacteriological) x
Kjeldahl Digester Unit x
Magnetic stirrers x
Microscope, binocular with oil immersion and movable stage x

counting cell
Membrane Filter Assembly x
Muffle Furnace x
Orsat or equivalent gas analysis apparatus x
pH comparator (Colorimetric) x x
pH meter with reference & spare electrodes x
pH meter portable x x
Refrigerator x
Sedgwick Rafter funnel x
Sludge sampler x
Soxhlet extraction unit x
Spectrophotometer (atomic absorption) x
Spectrophotometer with or without U-V rage or photo
x
electric colorimeter
B - 85
Type of Plant
(A) (B)
Equipment
For consent parameter For plant operating
(BOD, SS, pH) parameter
Total organic carbon analyser x
Turbidimeter x
Vacuum pump x
Water bath (thermostat controlled) x
Dessicator x
*NB: (1) For plant operating parameters, equipment as needed will also be provided in the laboratory of STP.
(2) Equipment in column B may be in plant laboratory itself or in a regional laboratory to serve multiple STPs.
B - 86
APPENDIX B.7.2 SUGGESTED LABORATORY SERVICE INFRASTRUCTURE FOR

MONITORING WATER QUALITY
Table B7.2-1 Suggested laboratory service infrastructure for monitoring water quality
S.No. Level Minimum Recommended Staff Remarks
1 Basic Laboratory 1. Lab. Assistant /Technician For routine bacteriological and

2. Lab. Attendant physicochemical tests, the
a. Primary Health Centre /
samples should be sent to
Village Level
municipal / district level
laboratory periodically
b. Municipal / District Level 1. Chief Analyst Whenever STP laboratory is

(Plant capacity > 50MLd) 2. Chemist existing
3. Bacteriologist
4. Assistant Chemist
5. Lab. Assistant / Technician
6. Lab. Attendants
7. Driver
8. Helper
2 State / Regional Level 1. Chief Analyst (Higher Scale)
Laboratory 2. Chemist
3. Bacteriologist
4. Biologist
5. Assistant Bacteriologist
6. Assistant Biologist
7. Lab. Assistant / Technician
8. Lab. Attendants
9. Driver
10. Helper
Note: 1. Kindly refer to Manual on Water Supply and Treatment, III Edition, May 1999.
2. The level and the no. of the personnel shall be decided by the respective agencies depending on magnitude of the site.
B - 87
APPENDIX B.9.1 HEALTH AND SAFETY POLICY
The agencies involved in the project development such as the owner, consultant and contractor
jointly or separately shall have a written statement prescribing the health and safety policy of the
organisation.
The health and safety policy conveys the management commitment and intent of the organisation
towards health and safety, its organisation and arrangements to ensure that the set objectives are
met. It also provides a framework for establishing, maintaining and periodically reviewing health and
safety objectives and targets.
Health and safety policy shall meet the requirements of Building and other Construction Workers
(Regulation of Employment and Conditions of Service) Act, 1996 and IS 18001.
The policy shall be communicated to all stakeholders through display and other means. The policy
shall be displayed in local language(s) which may be understood by majority of the workmen.
Guidelines on O&M of sewerage and sewage treatment for operators to help them in practicing
their works in accordance with health and safety requirements specified for sewerage works are
presented below:
9.1.1 APPLICABLE FACTORS
The applicable factors under this important section will be the procedures to be followed by the
operator while working in confined spaces, type of shoes to be worn, personal hygiene and climbing
ladders plus a formal appreciation of first aid.
9.1.2 WORKING IN CONFINED SPACES
This category is the worst location for possible fatal accidents in the STP. A confined space is defined
as (1) Cramped entry and exit, (2) Absence of broad daylight and ventilation and (3) Places meant
for very limited persons like one or two only to get in. The dangers are caused by
• Oxygen less situation

• Flammable situation
• Toxic gas presence
• Engulfment hazards
• Shouts not being heard outside
• Wet and / or slippery surfaces
• Loosely fitted objects that may fall down
The precautions to be taken before entry into these spaces when required are
• Certifying by the plant superintendent in writing that it is free of H2S, CO and Methane
B - 88
• Availability of a portable air compressor which draws free unpolluted air and pumps in
• Personal Respirator with adequate Oxygen cylinder and the Miner’s lamp
• Availability of a strong rope tied to the person and rescue team in position
• The person to have undergone training in safety with St. John Ambulance
• The person to have comfortable and tight fitting garments
• The person to wear only anti-skid shoes.
• The person to have special goggles securely worn over the eyes
• The person to complete his urination and toiletries before entry
• The person to have been in continues duty for at least a week as on that date
• The person not to have returned from medical leave within 7 days of the date of entry
• The person not to a be a known asthmatic or cardiac patient
• The person not to be aged more than 35 years
• Above all, a person who is not mentally scared to get in.
9.1.3 TYPES OF SHOES TO BE WORN
Very often, it is believed that any shoe in the market is good for working in a STP. This is not correct.
There are special anti-skid shoes with metal cladding over the toe portion. These are to be provided
by the employer and the operator should not use it outside the STP.
9.1.4 PERSONAL HYGIENE
The following procedures should be followed by the operator scrupulously in and out of the STP.
• Keep the fingers of the hand away from ears, nose, eyes, mouth and unnecessary scratching
• While handling any equipment, wear gloves or poly bags slipped over the palm and wrists
• When there is an injury to the hand, do not handle any equipment or collect sample
• Before and after food and work wash hands with anti septic solution, soap and fresh tap water
• After the work, take a bath before leaving the STP
• Ensure fingernails are cut properly and there are no deposits
• Insist on two separate lockers one for formal cloths and one for STP cloths
• Ensure you are vaccinated by the employer against Hepatitis, Typhoid, Rubella [for women],
Tetanus, Diphtheria, Pox and Measles.
• Insist on mediclaim to be taken for you by your employer
• Insist on personal accident policy to be taken for you by your employer
B - 89
9.1.5 CLIMBING LADDERS
This is one location of accidents for want of certain simple precautions as follows.
• Make sure the ladder is anchored to the floor securely and not simply resting
• Ensure that the ladder is provided with non conducting shoes and not resting on wet surfaces
• Feel the firmness of each step before you put your whole weight on it
• Tie the top of the ladder to a firm anchor once you climb there
• Ensure that at least 3 steps are rising above the level where you are required to work
• If it is simply resting, call an assistant to stand up and buttress it without slipping
• Verify whether the horizontal clearance is minimum one fifth for one meter length of ladder
• Avoid doing any work by standing on the top 2 or 3 steps of the ladder
• Do not use Bamboo Ladders. They may be weak and suddenly collapse
• Never catch the sides of a ladder. Catch the upper steps
• Do not catch any part of a steel ladder without at least a poly slip on cover over the palm
• Make sure nobody walks below the ladder while you are using it
• Finally, do not climb unless you need to !
9.1.6 ELECTRICAL RELATED SAFETY
• Unless you are qualified for the job, do not undertake it even to replace a fuse or bulb
• Ensure that you have the appropriate gloves, shoes and garments that fit reasonably tight
• Always use local circuit cut-outs before attending to repairs
• Avoid metallic ladders and metallic tape measures near electrical systems
• The best ladder is one made out of teakwood and preserved with anti-termite treatment
• Never work alone and keep an assistant with you all through the work
• Always, de-energize and ground a circuit before venturing any repairs
• Always use approved instruments like tong testers etc and not naked wire and bulb
• Free hanging neck chains are to be removed and kept in pockets while on the job
• All tools shall be insulted in their handles
• Do not latch on to other metallic fittings like piping, etc., while on the job
• If require to use flashlights, use those made of external non-metallic parts
• If wires are found to be dangling, do not attempt to clamp them. Instead, try to reroute them
9.1.7 FIRST AID KIT, SUPPORT FACILITIES & DISPENSATION
The first aid kit should minimally include the following
• A leaflet explaining how to use the kit
B - 90
• Sterilized dressings of assorted sizes

• Plaster casts for waterproof casts
• Bandages of assorted sizes
• Adhesive plasters of assorted sizes and a blunt edges stainless steel long scissors
• Sterilized water of at least 2 liters
• Eye protection pads
• Safety pins of assorted sizes
• Disinfectant lotions
• Unused sealed twin blade razor
• Eyebaths with double showers focussing on the eyes
• An easily identifiable and reachable shower bath with non-slip grip type flooring
• Wall hung charts showing artificial resuscitation in both English and local language
• Wall hung posters showing the telephone numbers, locations and names of medical centers
• Wall hung posters of ambulance centers, rickshaw stands and truck terminals
• Brief history of previous accidents and lessons learned therefrom
• A well ventilated rest room with a cot and mattress of standard height
• A facility for accessing safe drinking water and an instant heater geyser
If the person is having breathing difficulty, check clothing around the chest and neck and loosen
them and then turn him flat on back and chin up and apply artificial resuscitation and later shift his
position sideways to the recovery position. If the person is having a cut wound, apply pressure on the
upper portion of the limbs and tie up the limb reasonable tight to prevent blood loss. If the person
has fainted, just check for breathing and whether he needs artificial resuscitation and administer. In
all cases, rush to a nearest medical center. If the person is frothing in the mouth, do not interfere
and rush to the nearest medical center.
9.1.8 OPERATOR’S RESPONSIBILITIES
The responsibilities of the operator are most important and are as follows.
• Familiarize with the wall charts, wall posters and telephone procedures to medical centers
• Do not go into a work unless you have observed the environment and understood it.
• All water other than from tap water is to be considered as unsuitable for human contact
• Do not operate any equipment unless you are trained in it.
• If you feel something unusual in a moving machinery, do not panic and call
your superintendent
• Do not hide other’s unsafe practices from your employer. Please report discretely
B - 91
• Never hurry up in physical motion when on duty. Be safe and steady in your movements
• Never chit chat in working areas or while standing on structures of the STP
• Never climb up or climb down cat ladders by facing the airside of the ladder. Face the wall
• Always use reasonably and comfortably fitting dresses. Remove neck chains while on duty
• Ensure that you set an example to be followed and not reported upon.
9.1.9 LEPTOSPIROSIS
This is strange disease caused by rats which fall into water source and spread the
respective viruses. The disease is normally noticeable only under advanced conditions and
usually the treatment and recovery is prolonged. Rats are a menace in sludge drying beds in hot
climates as they seek asylum from the heat and find food easier. The drinking water sump should
be checked by you every day in your shift to ensure that there is no ratfall into the sump. If you
detect it, immediately shut off all water connections to the STP and immediately alert your plant
superintendent and the chief executive officer. Also inform the health officer of the local authority.
9.1.10 THE WATCHWORD
The watchword should be your own safety in the first place, so that alertness becomes automatic.
9.1.11 TESTS FOR CHLORINE
Chlorine is not recommended to be used with sewage under any circumstances on a

continued scale. However, under special circumstances, chlorine may be applied for a brief period
like in flood seasons when large quantities of sewage may be bypassed. During these times, some
knowledge of chlorination safety is necessary. The important points are as follows.
• Chlorine gas has specific gravity of 2.49 (Air =1)

• Normally chlorine is got in steel cylinders in gas form and depressurized for use
• The gas may leak sometimes from the joints or the cylinders
• The gas has a pungent smell
• Dip a cotton swab in ammonia solution and move it near the cylinder and joints
• If white fumes are observed, it shows chlorine is leaking there
• The gas will be settling down at the ground level and sink into pits
• As the gas spreads on the ground, the grass will be scorched leaving a tell-tale
• Never bend low while testing for chlorine with a swab
• Stand erect and use an extension twig or stick
• Closing the valve of the cylinder may stop leaks at the joint in the cylinder
• Closing the valve will also help in checking whether the cylinder is leaking
• If the cylinder is leaking, try to douse the cylinder continuously with gentle water shower
B - 92
• This will dissolve the chlorine and help in containing the quick spread of the gas
• Call the supplier or the fire department immediately
• Ensure nobody is working at ground level or in pits near the cylinder
• Do not try to wrap any cloth etc. over the leaking cylinder. Closeness is to be avoided.
• The chlorine smell will anyway make it impossible to be near the cylinder
• If available, locate a nearby pit into which the container can be gently rolled.
• Carry out the rolling using long handled sturdy rods or bamboo ladders
• Once rolled into the pit, do not bend down into it. You are only containing the gas there
• In case someone swoons due to chlorine gas, rapidly remove him to the first floor
• If first floor is not available, use at least an office table to elevate him
• Allow fresh air and avoid crowding around him
• Keep him facing up and the head well back and tongue not in the way
• Apply artificial respiration mouth to mouth
• Voluntarily carry out a monthly drill in artificial respiration
• Always keep a cool head and never get perturbed
• Never try to find out how this leak occurred before you have stooped the leak
• Use common sense
B - 93
APPENDIX B.9.2 CHARACTERISTICS OF COMMON GASES CAUSING HAZARDS
Table B9.2-1 Characteristics of common gases causing hazards
Exposure
SI No Name of Gas Chemical Common Specific Physiological Maximum Explosive Likely
formula properties gravity or effects safe limit % % ppm limit % location of Most common
vapour highest sources
density 60-minutes 8 hours lower upper concentration
1 Carbon CO2 Colourless, 1.53 Cannot be endured 4.0 to 6.0 0.5 5000 --- ---- At bottom Products of
when heated combustion
dioxide odourless when at 10 for more than may stratify at sewer gas
breathed in large few minutes even if points above sludge gas also
quantities may subject is at rest and bottom issued from
carbonaceous
cause odd taste, oxygen content is states
non poisonous normal acts on
respiratory nerves
2 Carbon CO Colour less 0.97 Combines with 0.04 0.005 50 --- ---- Neat top Manufactured
especially if fuel gas, fuel
monoxide odourless, haemoglobin of blood present with gas products
tasteless headache in few illuminating gas combustion
inflammable hours at 0.02%, products of
motor exhausts
poisonous non unconsciousness in fuel almost any
irritating 30 mins at 0.2 % to kind
0.25 %, and total
unconsciousness in
few minutes at 0.1%
3 Chlorine Cl2 Yellowish green 2.49 Irritates respiratory 0.0004 0.0001 1.0 --- ---- At bottom Chlorine
cylinders and
colour tracts. Kills most feed line leaks
detectable in animals in very short
very low time at 0.1 %
concentration,
non-inflammable
B - 94
SI No Name of Gas Chemical Common Specific Maximum Exposure Explosive

Physiological Likely Most common
formula properties gravity or effects safe limit % % ppm limit % location of sources
vapour highest
4 Gasoline C2H2 to C8 Colourless, 3.0 to 4.0 Anaesthetic effect 0.4 to 0.7 0.1 1000 1.3 6.0 At bottom Service
H25 odour noticeable when inhaled rapidly stations,
at 0.03% fatal at 2.4 % garages
inflammable dangerous for short storage
exposure at 1.12 to
2.2 %
5 Hydrogen H2 Colourless, 0.07 Acts mechanically ---- --- --- 4.0 74.0 At top Manufacture
odourless to deprive tissues of fuel gas sludge
tasteless oxygen: does not
inflammable support life
6 Hydrogen H 2S Rotten egg 1.19 Exposure for 2 to 15 0.02 0.001 10 4.30 46.0 Near bottom Coal gas,
sulphide odour in small minutes at 0.01% but may be petroleum,
concentra- impairs sense of smell above bottom. sewer gas,
tion, odour not exposure to 0.07 to If air is heated fumes from
evident at high 0.1% rapidly causes and highly blasting sludge
concentration. acute poisoning humid gas
Colourless, paralyses respiratory
Inflammable centre, death in few
minutes at 0.2 %
7 Methane CH4 Colourless 0.55 Acts mechanically Probably 1.0 1000 1000 15.0 Normally at Natural gas,
odourless to deprive tissues of no limit top extending sludge gas
tasteless highly oxygen does not provided to a certain manufactured
inflammable non support life oxygen depth fuel gas, sewer
poisonous percentage gas in swamps
is sufficient or marshes.
8 Nitrogen N2 Colourless 0.97 Physiologically inert ---- ---- ---- ---- ---- Near top but Sewer gas,
tasteless non may be found sludge gas
inflammable at bottom also issues
principal from some
constituent of air rock strata
(about 79%)
B - 95
SI No Name of Gas Chemical Common Specific Exposure

Physiological Maximum Explosive Likely
formula properties gravity or effects safe limit % % ppm limit % location of Most common
vapour highest sources
9 Oxygen O2 Colourless 1.11 Normal air contains -- -- -- --- ---- Variables at Oxygen
different levels depletion from
tasteless 21% of oxygen. poor ventilation
odourless Below 16% first signs and absorption
supports of anoxia appears of chemical
combustion of
combustion even in people who available
non poisonous are resting. oxygen
Below 14% anoxia
such as faulty
judgement even with
minimal exertion.
Below 10%
dangerous to life.
Below 6% is fatal.
10 Sludge Gas About 60% May be 0.94 Will not support life Would vary -- -- 5.3 19.3 Near top of For digestion
CH4 and practically widely with structure of sludge
40% CO odourless, composition in Tanks
with small colourless,
amounts inflammable
H2, N2,
H2S, O2
B - 96
APPENDIX B.9.3 CONFINED SPACE ENTRY PROCEDURE
The following steps are recommended prior to entry into any confined space:
• Ensure that all the employees involved in the confined space working have been
effectively trained.
• Identify and close off or reroute any lines that may carry harmful substance(s) to, or through, the
work area.
• Empty, flush, or purge the space of any harmful substance(s) to the extent possible.
• Monitor the atmosphere at the work site and within the space to determine if dangerous air
contamination and/or oxygen deficiency exists.
• Record the atmospheric test results and keep these results at the site throughout
the work period.
• If the space is interconnected with another apace, each space must be tested and the most
hazardous conditions found must govern subsequent steps for entry into the space.
• If an atmospheric hazard is noted, use portable blowers to further ventilate the area;
retest the atmosphere after a suitable period of time. Do not place the blowers inside
the confined space.
• If the only hazard posed by the space is an actual or potential hazardous atmosphere
and the preliminary ventilation has eliminated the atmospheric hazard or continuous
forced ventilation alone can maintain the space safe for entry then only entry into the
area may proceed.
The following must be observed before entry into a permit-required confined space:
1. Ensure that all personnel involved in confined space work have been effectively trained.
2. Identify and close off or reroute any lines that may carry harmful substances to, or through, the
work area.
3. Wear appropriate, approved respiratory protective equipment.
4. Ensure that written operating and rescue procedures are at the entry site.
5. Wear an approved harness with an attached safety line. The free end of the safety line
must be secured outside the entry point.
6. Test for atmospheric hazards as often as necessary to determine that acceptable entry conditions
are being maintained.
7. Station at least one person to stand by on the outside of the confined space and at least one ad-
ditional person within sight or call of the standby person.
B - 97
8. Maintain effective communication between the standby person, equipped with appropriate
respiratory protection, should only enter the confined space in case of emergency.
9. The standby person equipped with appropriate respiratory protection, should only enter the
confined space in case of emergency.
10. If the entry is made through a top opening, use a hoisting device with a harness that
suspends a person in an upright position. A mechanical device must be available to
retrieve personnel from vertical spaces more than five feet (1.5meters) deep.
11. If the space already contains, or is likely to develop, flammable or explosive atmospheric
conditions, do not use any tools or equipment (including electrical) that may provide
a source of ignition.
12. Wear appropriate protective clothing when entering a confined space that contains
corrosive substances or other substances harmful to the skin.
13. At least one person trained in first aid and cardiopulmonary resuscitation (CPR) should be
immediately available during any confined space job.
Source: EPA, 2008
B - 98
APPENDIX B.9.4 CONFINED SPACE PRE-ENTRY CHECKLIST
Table B9.4-1 Confined space pre-entry checklist

CONFINED SPACE PRE-ENTRY CHECK LIST /CONFINED SPACE ENTRY PERMIT
Date and Time issued: Date and time expires:
Job Site space ID.: Job Supervisor:
Equipment to be worked on: Work to be performed:
Standby personnel:
Atmospheric checks:
Time:
Oxygen: %, Toxic: ppm
Explosive: % Carbon Monoxide: ppm
Tester’s signature:
1. Source isolation (No entry): NA Yes No

Pumps or lines blinded, disconnected, ( ) ( ) ( )
or blocked
2. Ventilation modification: NA Yes No

Mechanical ( ) ( ) ( )
Natural ventilation only ( ) ( ) ( )
3.Atmospheric check after isolation and ventilation:

Time:
Oxygen: % > 19.5% Toxic: ppm < 10 ppm H2S
Explosive: % LFL < 10% Carbon monoxide: ppm < 35 ppm CO
Tester’s signature:
4. Communication procedures:
5. Rescue procedures
6. Entry, standby, and backup persons Yes No

Successfully completed required training ( ) ( )
Is training current ( ) ( )
7. Equipment: NA Yes No
Direct reading gas monitor tested ( ) ( ) ( )
Safety harnesses and lifelines for entry and standby persons ( ) ( ) ( )
Hoisting equipment ( ) ( ) ( )
B - 99
Powered communications ( ) ( ) ( )
SCBAs for entry and standby persons Protective clothing ( ) ( ) ( )
*SCBA: Self-contained breathing apparatus
All electric equipment listed for Class I, Division I, Group D
and non-sparking tools ( ) ( ) ( )
8.Periodic atmospheric tests:

Oxygen: % Time: ; : %, : ; : %,: ; : %,
Explosive: % Time: ; : %, ; : %,: ; : %,
Toxic: % Time: ; : %, : ; : %,: ; : %,
Carbon-monoxide: % Time: ; : %, : : %,: ; : %,
We have reviewed the work authorised by this permit and the information contained herein.
Written instructions and safety procedures have been received and are understood. Entry can-
not be approved if any brackets ( ) are marked in the “No” column. This permit is not valid
unless all appropriate items are completed.
Permit prepared by (Supervisor): Approved by (Unit Supervisor):
Reviewed by (CS Operations Personnel):
This permit has to be kept at the job site. Return job site copy to safety office following job
completion.
Source: EPA, 2008
B - 100
APPENDIX B.9.5 FIRST AID
9.5.1 TREATING WOUNDS
a. Caring for a skin tear
• Expose and treat the part with the wound taking care to not move it unnecessarily. Firstly,
start removing clothes with no skin tear below and later, carefully remove clothes with
skin tear below.
• Considering that bacteria may have entered the wound, first wash and disinfect your hands and
apply antiseptic solution over a width of 2 to 3 cm around the wound. Using disinfected tweezers,
apply disinfected gauze, and cover with bandage to prevent infection.
Take the following precautions to prevent infection of the wound:
• Always use paper, towel, cloth or hands that have been disinfected.
• Disinfect the wound and remove debris in the wound using tweezers. Leave debris that cannot
be removed as-is; do not touch it with your finger.
• Do not wipe or wash the wound. If there is slight bleeding, do not try to stop the bleeding
unnecessarily, since bacteria may be removed during initial bleeding.
• Remove the dirt in the wound using aqueous hydrogen peroxide. If the wound has oil or grease,
wipe it off from around the wound to the outside using volatile oil or benzene, etc., and disinfect
the wound using ethanol.
• Wound to the head, chest or stomach is generally a serious matter even if it looks minor from the
outside. Notify the doctor as soon as possible after the patient has rested.
b. Care when there is no skin tear
• Limbs
If the wound is minor, apply antiseptic solution. If swollen, apply cold compress; if there is
suspicion of fracture or dislocation, tie a splint and apply a bandage.
• Head
Even if the injury is minor, treat with care. If the person has headache or nausea, cool the head.
If unconscious, or if there is bleeding from the ear, eye or nose, or if the patient is agitated,
internal wound in the cranium may be a possibility; in such a case, let the patient lie down with
the head kept high and immediately notify the doctor.
• Chest
If the chest pain is unbearable and patient coughs suddenly, or if the patient’s breathing is
laborious, or if blood is mixed with the sputum, allow the patient rest, and then immediately
summon the doctor.
B - 101
• Abdomen
In case of severe pain or swelling in the abdomen, or nausea, there is a possibility of an
internal injury. In such a case, ask the patient to fold his knees and lie down so that the skin on
the abdomen sags. Never give any drink to the patient. Summon the doctor quickly.
c. How to stop bleeding
• Stopping bleeding by applying pressure directly

Place clean gauze or handkerchief on the wound and apply pressure directly with your hand.
If the bleeding is from a large blood vessel, and if bleeding does not stop even after you
apply pressure using one hand, apply pressure with both hands leaning so that your body weight
also exerts pressure.
Take care not to touch the blood to prevent contamination when you try to stop the bleeding.
• How to use a tourniquet

If there is considerable bleeding from a large blood vessel such as an artery in the arm or the leg,
wrap a piece of cloth loosely around the part closer to the heart than the wound, and insert a stick
or similar hard item through the knot.
Insert a backing cloth between the stick and the arm so that the skin is not injured.
Gently rotate the stick until the cloth tightens over the artery and bleeding stops. When the
bleeding stops, fix the stick so that it does not move.
If the arrival of the first aid team is likely to be prolonged, loosen the tourniquet once in
30 minutes to 1 hour so that blood just starts oozing; after blood flows for 1 to 2 minutes,
tighten the tourniquet.
d. Treating electricity-related injury
• When electric current enters from the left hand, it flows through the heart; therefore, the
symptoms are more pronounced when current enters from the left hand.
• The injury is more serious at the part where the electric current leaves the body than where it
enters the body.
The following treatment is recommended:
• Turn off the switch. Wear dry leather shoes or rubber shoes, and dry leather or rubber gloves.
Use bamboo or wood to isolate the person from the electric wire, or use a piece of cloth or wool
to grip the hand and the clothes to pull the person away from the electric wire.
• Do not touch the person with your bare hands or with a wet object or metal.
• Place the person face up at a well-ventilated location; if the person has suffocated, revive with
artificial respiration. If the person is delirious or has cramps, try to cool his head.
B - 102
9.5.2 GAS POISONING
• Occurs when inhaling simple asphyxiant gas (nitrogen, hydrogen, helium, methane, ethane) and
chemical asphyxiant gas (carbon dioxide, cyanide compound)
• If considerable amount of gas has been inhaled, move the patient quickly to a location with
fresh air; if necessary, give fresh oxygen through oxygen supply kit, and immediately
summon a doctor.
9.5.3 CHLORINE
• If chlorine gas has been inhaled

Immediately call for the doctor, follow the doctor’s instructions and take the actions
mentioned below.
Gently move the patient from the gaseous location to a safe place, preferably to a room
of about 20°C. Keep the patient’s head and back high while laying him to rest and cover the
body with a blanket.
If the patient has difficulty in breathing, give oxygen using oxygen supply kit.
If breathing has stopped, give artificial respiration by the prone, face-down method.
• If chlorine has come in contact with the skin
Immediately wash the affected part with plenty of water. Quickly remove clothes wetted by
liquefied chlorine and summon the doctor for further treatment.
• If chlorine has entered the eye
Immediately wash the eye with water keeping the water running for 15 or more minutes and
summon the doctor for further treatment.
• Measures during leakage of chlorine gas
Wear protective gear such as breathing apparatus. Before checking the leakage locations,
wear protective gear and spray ammonia. Leakage is indicated at the location where white
fumes are emitted.
Roll leaking cylinders into the neutralization pit.
Thereafter, request experts to repair the leaking equipment.
• If there is an unexpected leakage and a possibility that the scope of danger may expand.
Contact the relevant department based on the contact system drawing in an emergency
determined beforehand.
If necessary, notify personnel nearby, and evacuate them to the windward side.
At the same time, neutralize the leaked gas.
B - 103
9.5.4 ARTIFICIAL RESPIRATION
Artificial respiration may be carried out to revive a person whose heart has stopped. The procedure
for cardiopulmonary resuscitation (CPR) is given below.
• Check consciousness
• Ensure air passage is satisfactory
• Check breathing
• Start artificial respiration
• Check for signs of circulation
• Heart massage
• Cardiopulmonary resuscitation (CPR)
Source: JSWA, 2003
B - 104
APPENDIX B.9.6 SEWAGE TREATMENT PLANT ACCIDENT REPORT
Table B9.6-1 Sewage treatment plant accident report

SEWAGE TREATMENT PLANT ACCIDENT REPORT
Date of this report Name of person injured

Date of injury Time Occupation
Home address
Age sex Check First aid case or disabling(lost time)injury

Employee or staff injury on duty or Off duty Visitor injury
Date last worked Date returned to work
Person reporting
DESCRIPTION OF ACCIDENT
1. Description of Accident (Describe in detail what happened) (Name machine, tool, appliance,
part, gears, pulley, etc.):
2. Accident occurred where? If vehicle accident, make simple sketch of scene of accident.
3. Describe nature of injury and part of body affected (Amputation of finger laceration of leg,
back strain, etc.):
4. Were other persons involved? (If yes, give names and addresses)
5. Names and addresses of witnesses.
6. If property damage involved, give brief description.
7. Name and address of physician.
8. Treatment given for injures
Source: EPA, 2008
B - 105
APPENDIX B.10.1 MECHANICAL CLEANING OF SEPTIC TANKS
The requirement of suction machines for emptying septic tanks in the towns where septic tanks exists
(full or partial) for a specified population is calculated based on the following assumptions.
1. No. of households in a town having population of 1 Lac (@ 5 persons in an household) - 20000

household i.e. 20000 Septic tanks
2. Septic tanks need to be cleaned once in 2 years. Hence the requirement septic tanks to be
cleaned per year will be about 10000.
3. To clean 10000 septic tanks in a year, the requirement of lorries is 8 numbers
4. Septic tank cleaning is by ordinary vacuum tugs which can hold only 6000 liters maximum. The
regular jet rodding cum suction machines must not be used for septic tank cleaning because the
jet rodding portion of the machine is wasted. As such 10,000 septic tanks to be cleaned means
sewer lorries (not jet rodding cum suction machines) shall alone be used. Cost wise 5 such sewer
lorries can be purchased instead of a single jet rodding cum suction machine.
• Number of septic tanks to be cleaned 10,000

• Size of a typical septic tank 2m * 1m * 1.2m
• Volume to be sucked out 2.5 cum
• Sewer lorry capacity 6 cum
• Number of septic tanks that can be cleaned in one trip 2 numbers
• Time taken for onward, suction and return 4 hours
• Hours available for day shift 8 hours
• Number of trips per day per lorry 2 trips
• Number of septic tanks sucked out per day per lorry 2*2 = 4 numbers
• Lorry maintenance and down time days per year 30 days
• Effective days per year per lorry 365-30=335 days
• Number of septic tanks sucked by lorry per year 335*4 = 1340
• Number of lorries needed per year 10000 / 1340 = 8 lorries
Sewer lorries are to be barred from operating in other than general shifts because the noise
nuisance it will create to the neighbours in the night and the risk of the lorry operator discharging
surreptitiously in the nights at various places plus security concerns.
B - 106
Part B: Operation and Maintenance REFERENCES
REFERENCES
(1) BIS 10533, Part I, Requirement for chlorination equipment, (2007)

(2) BIS 14489, Code of Practice on Occupational Safety and Health Audit, (1989)
(3) BIS 2470, Part1: Code of Practice for installation of septic tank, (1985).
(4) BWSSB correspondences, (2012)
(5) CMWSSB correspondences, (2012)
(6) CMWSSB, Manoharan De, ” O&M of STPs in Chennai”, power point presentation”
(7) Colilert test, http://www.nps.gov/public_health/info/eh/lab/colilert.pdf
(8) CPCB, “Wastewater Generation and Treatment in Class-I Cities and Class-II Towns of India”,.(2009)
(9) CPCB, MoEF, GOI, ”General Standards for Discharge of Environmental Pollutants Part-A : Effluent”, (1986)
(10) CPHEEO, MoUD, “Manual on Sewerage and Sewage Treatment”, (1993)
(11) CPHEEO, MoUD, “Manual on Water Supply & Treatment”, (1999)
(12) CPHEEO, MoUD. “Manual on O&M of Water Supply Systems”, (2005)
(13) CPHEEO. MoUD, “Manual on Municipal Solid Waste Management”, (2000).
(14) Duncan Mara, “Design Manual for Waste Stabilization Ponds in India”, (1997)
(15) Duncan Mara, “Domestic Wastewater Treatment in Developing Countries”, (2003)
http://www.pseau.org/outils/ouvrages/earthscan_ltd_domestic_wastewater_treatment_in_developing_countries_2003.pdf
(16) HIOKI E.E. CORPORATION, http://www.hioki.com/index.html
(17) Hiren Industrial Corporation, http://www.jimtrade.com/hirenindustrialcorporation/plastic_made_first_aid_box.htm
(18) http://inst.bact.wisc.edu/inst/index.php
(19) http://www.mrwa.com
(20) http://www.neutecgroup.com/jartest.htm
(21) http://www.tradeindia.com/fp341764/High-Flow-Rate-Dissolved-Air-Flotation-Clarifier.html
B - 107
(22) JASCOMA, “Sewerage collection system Maintenance Manual”, (2007)

(23) JASCOMA,“Safety measures for Sewer maintenance”, (2012)
(24) JEFMA, http://www.jefma.or.jp/
(25) JICA, “Capacity building project related to O&M of sewerage facilities in India”, (2007).
(26) JICA, “Textbook on Operation and Maintenance of sewerage works”, (2007).
(27) JSWA,“Guideline and Manual for Planning and Design in Sewerage Systems”, (2009)
(28) JSWA,“Guidelines on Operation and Maintenance of Sewerage and Sewage Treatment”, (2003)
(29) Kruger, http://www.krugerusa.com/medias/files/scada
(30) Metcalf & Eddy, Inc., “Wastewater Engineering: Treatment and Reuse”, McGraw-Hill, New York, (2003)
(31) MoLE, GOI, “Sanitation Workers (Regulation of employment and conditions of service) Draft Bill”, (2012)
(32) MoUD, GOI, “Advisory note on Septage Management Guidelines”, (2012)
(33) MoUD, GOI, UNDP, World Bank, “Technical Guideline on Twin Pit Pour Flush Latrine”, (1992)
(34) NISHIHARA Environment Co., Ltd. Nishihara’s technology in SBR process, IC Process, http://www.nishihara.co.jp/
(35) OSHA, Occupational Safety and Health Administration, U S Department of Labor, “ Oxygen-deficient atmosphere requirements in the
Respiratory Protection Standard”, (2008)
(36) PWSSB, Correspondence, (2011)
(37) Rajnarayan R Tiwari, “Occupational health hazards in sewage and sanitary workers”, Indian Journal of Occupational and
Environmental Medicine, Vol. 12, Issue 3, pp 112-115, (2008)
(38) Research, Designs & Standards Organisation, B&S Directorate, Indian Railways, “Guidelines for Non Destructive Testing of Bridges,
BS-103”, http://www.rdso.indianrailways.gov.in/uploads/files/1296882621315-bs_103.pdf, (2009)
(39) Sudo. R, “Biology of Wastewater Treatment”, The Industrial Water Institute, (1977)
(40) Sunil S Rao & R K Jain, “Industrial Safety, Health & Environment Management Systems”, Khanna Publishers, (2011)
(41) The Building Centre of Japan, ”Structural Standards of Johkasou”, (1980)
(42) TNPCB and DANIDA, “O&M Manual of Treatment Plants for Operators”, (2000)
B - 108
(43) USEPA, “Biosolids Technology fact Sheet Belt Filter Press”, EPA Number: 832-F-00-057, (2000)
(44) USEPA, “Development document for proposed effluent limitations guidelines and standards for the landfills point
source category”, (1998)
(45) USEPA, “Exfiltration in Sewer Systems”, EPA/600/R-01/034, (2000)
(46) USEPA, “Operation and Maintenance of Wastewater collection System 6th edition”, (2003)
(47) USEPA, “Operation and Maintenance of Wastewater collection System 7th edition”, (2008)
(48) USEPA, “Operation of wastewater treatment plants 7th edition”, (2008)
(49) USEPA, ”Collection Systems O&M Fact Sheet”, EPA/832-F-99-093, (1999)
(50) USEPA, ”Condition Assessment of washwater collection Systems”, EPA/600/R-09/049, (2009)
(51) Vibgyor Industries, http://www.indiamart.com/vibgyor-industries/safety-products.html
(52) WEF, Manual of Practice No.11, WEF Press, (2008)
(53) WEF, Manual of Practice No.8, WEF Press, (2010)
(54) Ype.C.Wijnia, ”Asset Management for Infrastructures is Fast Developing countries”, (2009)
http://www.nextgenerationinfrastructures.eu/images/Chennai_09_Wijnia/pdf
(55) YSI- http://www.ysi.com/productsdetail.php?ProODO-19, http://www.ysi.com/productsdetail.php?5000-5100-30
B - 109

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In keeping with the advancements in this sector, updates as and when found

necessary will be hosted in the Ministry website: http://moud.gov.in/ and the

All rights reserved

Copy Edited and Published under contract with JICA by

Printed by : Advantage 4U, New Delhi

Part – C on ‘Management’ is a refreshing approach to modern methods of project delivery

The Expert Committee expresses its gratitude to Dr.S.Sundaramoorthy, Consultant, JST,

I am also privileged to express my sincere thanks on behalf of the Expert Committee to

The contribution made by Mr.V.K.Chaurasia, Joint Adviser (PHEE), Mr.J.B.Ravinder, Deputy

I would like to acknowledge all those connected individuals, organizations, institutions,

1. Collection System including house service connections and manholes

1. Most of the towns are only partially sewered.

1.1 NEED FOR O&M

1. Lack of finance and inadequate data on O&M.

1.2 BASIC CONSIDERATIONS OF O&M

1.2.1 Laws and Regulations related to O&M of Sewerage System

1.2.2 Effluent Standards related to Sewage Treatment Plants

1.2.3 Environmental Considerations

1.2.5 Preventive Maintenance

1.2.6 Workmanship and Quality of Equipment

1.3 OUTLINES OF O&M

1.3.1 Overview and Contents of O&M

1.3.2 Management of Facilities

1.3.3 Schedule of O&M

1.3.4 Response to Accidents

1.3.5 Management of Buildings and Sites

1.4 ORGANIZATION OF O&M

1.4.1 Description of O&M Work

Source: Ype C Wijnia, 2009

Figure 1.1 Combined Tasks and Challenges with the O&M

1.4.2 Deployment of Manpower

1.4.3 Outsourcing of O&M

1.4.4 Key criteria for selection of O&M contractor

1.4.6 Monitoring through Information Control Technology

1.4.7 Database for Effective O&M

1.4.8 Problems in Existing O&M

1.5 COMMUNITY AWARENESS AND PARTICIPATION

1.5.1 Public Relations and Public Opinion related to Sewerage Works

1.5.2 Complaint and Redressal

1.5.3 Do’s and Don’ts for Community

1.6 POTENTIAL RISK WITH RESPECT TO SEWERAGE SYSTEM

1.6.1 Provision of Disaster Prevention Systems

1.7 SEWERAGE LEDGER

1.7.1 Preparation of Sewerage Ledger

1.7.2 Management and Use of Sewerage Ledger

1.8 BUDGET ESTIMATION FOR O&M

1.10 RELATIONSHIP BETWEEN PART-A (ENGINEERING), PART-B (OPERATION AND

ii) Part – B on ‘Operation and Maintenance’

iii) Part – C on ‘Management’

CHAPTER 2: SEWER SYSTEMS

A sewerage system consists of the following:

The sewers are the most important part of a sewerage system.

2.1.1 Objectives of Maintenance

2.1.2 Type of Maintenance

2.1.3 Necessity of Maintenance

2.2 INSPECTION AND EXAMINATION OF SEWER

2.2.1 Importance of Inspections and Examinations

• Identify existing or potential problem areas in the collection system,

2.2.2 Guidelines for Inspections and Examinations