The Treatment Processes of Sewage and at National Water and Sewerage Corporation (NWSC)

NKUGWA MARK WILLIAM, 17/U/7029/CHE/PE
THE TREATMENT PROCESSES OF SEWAGE AND AT

NATIONAL WATER AND SEWERAGE CORPORATION
(NWSC).
AN INDUSTRIAL TRAINING REPORT
SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR

THE AWARD OF THE DEGREE OF BACHELOR OF SCIENCE IN CHEMICAL AND
PROCESS ENGINEERING
SUBMITTED TO:
DEPARTMENT OF CHEMISTRY
KYAMBOGO UNIVERSITY, UGANDA
SUBMITTED BY:
NKUGWA MARK WILLIAM
REG NO: 17/U/7029/CHE/PE
BACHELOR OF SCIENCE IN CHEMICAL AND PROCESS ENGINEERING
YEAR: II
BASED AT LUBIGI SEWAGE TREATMENT PLANT
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STUDENT DECLARATION.
I NKUGWA MARK WILLIAM, declare this work which is being presented in the Industrial
training Report entitled “THE TREATMENT PROCESSES OF SEWERAGE AND AT
NATIONAL WATER AND SEWAGE COPORATION”, in fulfillment of the requirements
for the award of the Bachelor of Science in Chemical and Process Engineering, and submitted to
the Department of Chemistry of Kyambogo University, is an authentic record of my own
experiences, lessons and work carried out during my industrial training period from 20th May
2019 to 2th July 2018 at National water and sewage corporation in sewage services department
at Lubigi sewage treatment plants.
I also declare that, the matter presented in this Internship Report has been submitted by
me for the award of any other degree elsewhere. It is only prepared for my academic requirement
and not for any other purpose. It should not be used with the interest of opposite party of the
corporation.
Signature of Student ………………………
NKUGWA MARK WILLIAM
11/U/7029/CHE/PE
Bachelor of Science in Chemical and Process Engineering (Year. 2)
Department Of Chemistry
Kyambogo University, Uganda.
nkugwamarkwilliam@gmail.com / 0784906354
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APPROVAL.
The undersigned certify that this Industrial Training Report has been submitted by Nkugwa
Mark William Registration Number – 17/U/7029/CHE/PE, and to the department of
Chemistry, Kyambogo University, in partial fulfillment of the requirements for the award of the
Bachelor of Science in Chemical Engineering. We also certify that the above statement made by
the student is correct to the best of our knowledge. The training was carried out under our special
supervision and within the time frame prescribed by the syllabus. We found the student to be
hardworking, skilled, and eager to undertake any commercial and industrial work related to his
field of study and hence we recommend the award of Bachelor of Science in Chemical and
Process Engineering.
Approved as to the style and content by:
Signature of Internship Manager
MR. GAVA JOB
QUALITY CONTROL OFFICER, LSTP
Date: ………………………………….
Signature & Stamp: …………………………………
Signature of University Supervisor
MR. KIIZA HILLARY
Kyambogo University (Faculty of Science)
Date: ………………………………….
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Signature & Stamp: …………………………………
ACKNOWLEDGEMENTS.
A number of people have helped me in this internship training. First and foremost, I thank The
Almighty God, Who has enabled me to produce this piece of work and to understand the various
things involved in the engineering profession.
I would like to express my appreciation and acknowledgment to all the management and staff of
National Water and Sewerage Corporation especially in the sewage service department for
granting me the opportunity of internship program.
I would like to place on record my deep sense of gratitude to Mr. Deogratius, the human
resource manager-Lubigi sewage treatment plant (LSTP),for his kindness and care he
showed to me during my training at the sewerage treatment plant.
Great thanks to my supervisor at the plant Mr. Andrew Kabuga (the plant manager) for passing
on his technical knowledge of the plant and the process operations. Great thanks to my
supervisors Eng. Kwitonda Angelo and Eng. Ronald (principle engineers at LSTP) for passing
on their knowledge of engineering different processes dealing with the sewage plant. In the same
boat in would also love to thank my senior supervisor Mr. Gava Job the quality control officer
and all the team in the laboratory. Also my network team supervisor Mr. Odongo and all
network team members for their guidance both technical, practical touch during the training and
wellbeing at Lubigi plant.
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Once more I express my sincere gratitude to Mr. Gava Job for his continuous guidance
throughout my internship period, continuous encouragement and full supervision throughout the
course of my internship, His support and effort to compile this report has been key.
I also wish to extend my thanks to Mr. Andrew, plant overseer LSTP, for his insightful
comments and valuable suggestions to improve the quality of this report work.
Finally, yet more importantly, I would like to express my deep appreciation to my mother, Dr.
Sarah Mubiru, my Father Dr. Jackson Mubiru, my sister Miss Namubiru Esther Miriam
for their perpetual support, advice and encouragement that has enabled me reach this level as far
as my Bachelor’s degree, education and life is concerned, may the Almighty God reward them
accordingly.
ABSTRACT.
NWSC is a public corporation owned in full by the government of Uganda, having been
established in 1972 by decree No 34. The corporation‘s legal position was strengthened by
National Water and Sewage Corporation statute No 7 of 1995, which was later incorporated into
National Water and Sewage Corporation act of 2000 under the new legal framework. National
Water and Sewage Corporation’s geographical coverage increased from 23 to 98 towns and
started with three major towns that is; Kampala, Jinja and Entebbe. Kampala metropolitan area
(Kampala water), were I trained has the sewage services department comprising of Lubigi
Sewerage Treatment Plant and did some sampling at Bugolobi Sewerage Treatment Plant
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Lubigi sewage treatment plant (LSTP) is one of the newly constructed plants, constructed
in 2013 and is part of the Lake Victoria Protection Project Phase 1 intended to reduce pollution
of Lake Victoria and improve waste water treatment within the city of Kampala in addition to the
already existing Bugolobi Sewage Treatment Plant.
The Lubigi sewerage Treatment Plant (LSTP) is located in the Lubigi swamp along
the northern by-pass, Hoima road in Namungoona, a Kampala city suburb and it was designed to
treat around 400m3 per day of the fecal sludge and 5000m3/day of the wastewater.
LSTP has the networking section both development and maintenance, the quality
assurance section (at the Lubigi lab), and plant operations section (comprising of the daily
activities done at the plant).Bugolobi sewage treatment works (BSTW) is the biggest sewage
treatment plant, located in the south-east of Kampala and was designed to handle a hydraulic
flow rate of 33,000m3/day.
In both sewage treatment plants, the treatment processes involve the preliminary
treatment and biological treatment and there are three stages, called primary, secondary and
tertiary treatment. The main aim of both plants is to ensure that the final effluent from
wastewater treatment meets the National discharge standards. The difference between the two
plants is that LSTP employs waste stabilization pond system whereas BSTW employs
conventional technology and at the moment is under improvement to start biogas production.
This industrial training report includes the information for both treatment plants including
the clean water treatment process at Gaba but majorly LSTP because it was my base, so that is
the plant where I spent most of my training time.
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TABLE OF CONTENTS
Table of Contents
STUDENT DECLARATION........................................................................................... 2
APPROVAL. ................................................................................................................... 3
ABSTRACT. .................................................................................................................... 5
CHAPTER ONE ............................................................................................................. 13
INTRODUCTION. ......................................................................................................... 13
Company Profile: ............................................................................................................ 13
BACKGROUND INFORMATION OF NATIONAL WATER AND SEWAGE
CORPORATION: .................................................................................................................. 13
GEOGRAPHICAL AND SERVICE COVERAGE. ................................................. 14
HISTORY OF THE URBAN WATER AND SEWAGE SUB-SECTOR. ............... 15
VISION ...................................................................................................................... 15
MISSION ................................................................................................................... 16
QUALITY POLICY .................................................................................................. 16
CORPORATE CORE VALUES ............................................................................... 16
LUBIGI SEWAGE TREATMENT PLANT (LSTP).................................................... 18
Introduction ............................................................................................................... 18
Reasons for constructing the Lubigi Sewage Treatment Plant .................................. 21
Objectives of the plant ............................................................................................... 21
CHAPTER TWO ............................................................................................................ 22
THE SEWAGE TREATMENT PROCESS AT LSTP ................................................ 22
FLOW DIAGRAM ....................................................................................................... 22
ON SITE FECAL SLUDGE ......................................................................................... 24
SCREENING ............................................................................................................. 25
GRIT REMOVAL ..................................................................................................... 36
Flow Measurement .................................................................................................... 39
Flow Distribution:...................................................................................................... 39
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CHAPTER THREE ........................................................................................................ 56

QUALITY CONTROL ................................................................................................. 56
3.1 THE LUBIGI LABORATORY .............................................................................. 58
Table 2: The NEMA Standards for Waste Water Discharge ........................................... 59

PHYSICAL/CHEMICAL PRACTICES IN WASTE WATER ANALYSIS ............... 63
DETERMINATION OF BIOCHEMICAL OXYGEN DEMAND (BOD5) USING AZIDE

MODIFICATION OF WRINKLER METHOD (OXYGEN ELECTRODE METHOD) ............ 64
DETERMINATION OF TOTAL SUSPENDED SOLIDS ....................................... 69
DETERMINATION OF ELECTRICAL CONDUCTIVITY USING A METER .... 70
COLIFORM DETERMINATION BY MEMBRANE FILTRATION METHOD
USING LAUREL SULPHATE BROTH .............................................................................. 72
DETERMINATION OF CHEMICAL OXYGEN DEMAND (COD) USING
CLOSED REFLUX COLORIMETRIC METHOD. ............................................................. 73
DETERMINATION OF PH USING THE PH METER. .......................................... 75
DETERMINATION OF ALKALINITY BY TITRATION. ..................................... 77
CHAPTER FOUR........................................................................................................... 81
THE SEWER NETWORKAND ITS MAINTENANCE.............................................. 81
PLUMBING RODS ...................................................................................................... 87
UNBLOCKING SEWER PIPES .................................................................................. 88
COMMON CAUSES OF BLOCKAGE IN THE SEWER LINES .............................. 89
DESILTING .................................................................................................................. 90
PRECAUTIONS TAKEN DURING DESILTING ...................................................... 90
CHAPTER FIVE ............................................................................................................ 92

ACTIVITIES CARRIED OUT, KNOWLEDGE &SKILLS ACQUIRED AND
CHALLENGES FACED ............................................................................................................ 92
CHEMICAL LABORATORY ...................................................................................... 92
SEWER NETWORK MAINTENANCE. ..................................................................... 92
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LUBIGI AND BUGOLOBI SEWAGE TREATMENT PLANTS ............................... 92
Knowledge Acquired During My Training ................................................................... 92
Skills Acquired During My Training ............................................................................ 93
Challenges Faced During My Training ......................................................................... 94
CHAPTER SIX ............................................................................................................... 95

CONCLUSION, RECOMMENDATIONS, REFERENCES & APPENDICES .......... 95
General Conclusion ....................................................................................................... 95
Recommendations to Kyambogo University ................................................................. 96
References ..................................................................................................................... 97
APPENDIX B ............................................................................................................... 98
NEMA STANADARDS ................................................Error! Bookmark not defined.
Table 2: The NEMA Standards for Waste Water Discharge .......... Error! Bookmark not
defined.
BACKGROUND OF INDUSTRIAL TRAINING

Industrial Training is a course unit with programs or courses specified by universities and
other tertiary institutions, carried out by students in the recess term or holiday time to enable
them relate theoretical work with practical work in the field. It is carried out in reputable firms,
organizations and companies or from within the university, and permits students to get a
considerable vision and awareness of their future professions as well as the working environment
in such careers.
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INTRODUCTION:
I chose to do industrial training at NWSC for my second year, so as to develop a
comprehensive understanding and appreciation of Chemical Engineering and Environmental
engineering concepts and principles as an expanding discipline of a continuous learning process,
in relation to sewage and water treatment process and its quality control.
The services provided at Lubigi Treatment Plant to the people of Uganda are mainly the
treatment of sewage waste water and the proper disposal of grit, the sale of treated manure to the
public, the proper treatment of sewage waste from cesspools from septic tanks from domestic
sites, maintenance of the sewer network in some parts of Kampala such as Kyambogo and
Bugolobi and weekly training and advice to the public on proper waste management.
During my training with NWSC, I was attached to the Lubigi Sewerage Treatment Plant
where I have been able to study all the physical and biological processes of sewage treatment,
the chemical analysis, the design, construction and operation of all the equipment used for
sewage treatment.
The Training at Lubigi was divided into three sections which were the plant, the laboratory and
the sewer network which all had their own special supervisors but I was still under on general
supervisor.
The ultimate goal is the conversion of the raw sewage to the useful product (manure) and that
the final effluent from sewage treatment reaches the standards as set by National environmental
management authority (NEMA).
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Purpose and objectives of industrial training attachment:
 To appreciate and transform the basic knowledge as acquired in the lecture room, to a
more productive and practical bit by physically engaging to the best of my ability in the
real world problems faced in the field.
 To be introduced to the more practical aspects of the engineering field.
 To execute more information judgment at work place and accept the responsibility for it.
 To recognize that financial and economic factors play important role in all engineering
and technology activities.
 To develop own personality and communication skills for future roles as managers and
leaders in the scientific and technological world.
 To develop a sense of responsibility towards society and the community at large.
 To understand the formal and informal relationship in an organization, promoting
favorable human inter-relations and team work.
 To put in practice the skills and knowledge that I have read and learnt.
 To appreciate the science and technology expanding disciplines such as environmental
management and chemistry.
TASKS
The tasks at the organization included: working at the plant, going to the field to collect samples
at different collection points for lab work and analysis from other water stabilization ponds such
as at Naalya and Bugolobi, analysis of the samples at the lab located at the main building of the
plant and unblocking man holes in various places around Kampala again mainly Kyambogo and
Bugolobi.
THE PLANT
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In the plant the main work was mainly filling the operation manual or plant manual which also
lead to other related tasks such as taking measurements of the drying beds where the manure was
drying, to taking the records of the number of tracks that have brought in sewage waste from
outside to then go on to the amount of waste in the sedimentation tank, to taking the time that the
pumps were own and to record if they were any power cuts from how long the generate was on,
the weather condition had to be recorded such as the wind speed , direction , cloud conditions
(whether heavy , light or mild) and the sunlight intensity . We then had to observe the water
stabilization ponds and record there color smell, how many insects the ponds and many others.
The copy of the operation manual is on this report (check the table of contents).
THE LABORATORY
In the lab we were required to go out to field every Monday to collect samples from stream
which are collecting sewerage that is coming into the plant and to also collect samples from other
water stabilization ponds like Naalya , Bugolobi and Nitanda so as to monitor their performance
and to do process control. We the on the next day’s carried out the various test on them which
included BOD5 (which done after five days but must be prepared early), COD, alkalinity, PH
and many others. Every month the team must go on a second field trip on Tuesday to collect
more samples from more streams.
THE SEWER NETWORK
In the sewer network we were not really advice to touch but to do more of observing as there was
too much exposure to sewerage which contacted a lot of human waste and due to the fact that we
were not insured health wise we could not just expose ourselves to such an environment. The
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main type of work at the sewers was mainly unblocking the sewers were blocked through
manholes using long assembly hooked rods which could be sent down far into the system to
removed blocking material. At times when the blockage is to strong a portable generator is used
to spin the rods and hence remove tough material.
CHAPTER ONE
INTRODUCTION.
Company Profile:
BACKGROUND INFORMATION OF NATIONAL WATER AND SEWAGE

CORPORATION:
NWSC is a public corporation wholly owned by the government of Uganda, having been
established in 1972 by decree No 34. Particularly the National Water and Sewerage Corporation
Act Chapter_317 and the Water Act (General Rates)_Instrument,_2006_SI_30.
The corporation‘s legal position was strengthened by NWSC statute No 7 of 1995, which was
later incorporated into NWSC act of 2000 under the new legal framework. The powers and
structure of NWSC where revised to enable the corporation to operate on a sound commercial
and financially viable basis.
The principal business of the corporation as defined in the NWSC Act is to operate and
provide water and sewage services in areas entrusted to it on sound commercial and financially
viable basis. The NWSC operations have expanded from 3 towns that is ; Kampala, Jinja and
Entebbe in 1972 to 98 major urban centers across the country in 2015.
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In 1988, four additional town of Mbale, Tororo, Masaka and Mbarara were handed over
to NWSC by then water development department now known as Directorate of Water
Development DWD. This was after completion of the International Development Agency IDA
financed rehabilitation program.
In November 1995, the corporation was handed over to NWSC statute. In 1997, the town
of Kasese and Fort Portal were handed over to NWSC following a successful rehabilitation
financed by the German Government.
NWSC’s Sewerage Services Department under Kampala Water: The Kampala SSD
currently operates two Sewage Treatment Plants (STP):
• Conventional Sewage Treatment Works (CSTW) in Bugolobi
• Waste Stabilization Ponds (WSP) in Lubigi
GEOGRAPHICAL AND SERVICE COVERAGE.
NWSC’s geographical coverage increased from 23 to 98 towns, increasing the target
population from 3.8 million people to over 6 million people. The water service coverage in all
the towns including the new towns stands at 76%. In addition, connectivity in the old 23 areas
significantly increased during the corporate plan period 2012-2015, which in turn increased
service coverage from 77% to over 81%
The total number of towns currently served by the NWSC is 98 with 28 old towns and 70
newly added towns which makes a total of 98 towns
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HISTORY OF THE URBAN WATER AND SEWAGE SUB-SECTOR.
The growth of the Urban Water Sub-sector can be summarized as follows: In the 60's, the water
systems were supply driven with plans agreed upon with the municipal councils.
At this time, the investment funds were available and there was relative efficiency with
an optimum population to serve.
The 70's and early 80's were characterized by rundown water and sewage systems with
very little maintenance. From the mid 80's, there was a drive towards the rehabilitation of the
water supply and sewage systems.
The 90's have been characterized by rehabilitation and expansion of both water and
sewage systems. In the later part of the 90's, there was a drive towards efficiency and
performance enhancement of the sector
TOWNS IN WHICH NATIONAL WATER IS OPERATING.
Kampala (including Kajjansi and Nansana), Jinja/Njeru, Entebbe, Mbarara, Tororo,
Mbale , Masaka , Lira , Gulu , Fort Portal, Kasese, Kabale ,Bushenyi/Ishaka ,Arua ,
Soroti , Mukono ,Lugazi ,Iganga , Malaba ,Masindi , Hoima and Mubende
VISION
The vision of National Water and Sewage Corporations is “To be the leading
customer centered water utility in the world”.
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MISSION
The mission of National Water and Sewage Corporations is “To sustainably and
equitably provide cost effective, quality water and sewage services to the delight of all
stakeholders, while conserving the environment”.
QUALITY POLICY
National Water and Sewage Corporations Kampala water shall contribute to national
development by provision of quality water and sewage services to satisfy her esteemed
customers and stakeholders through efficient service delivery, continual improvement and
expansion of infrastructure in an environmentally friendly manner.
CORPORATE CORE VALUES
i) Professionalism. Exude skills and ability in the work environment.
ii) Reliability. The National Water and Sewage Corporations is committed to ensuring
reliability and adequacy of water supply to all its customers.
iii) Integrity. National Water and Sewage Corporations embraces honestly in everything they
do and are determined to adhere to ethical Business principles and good corporate governance at
all times.
IV) Innovation. Continuously develop and apply creative solutions towards improved service
delivery.
v) Team work. The National Water and Sewage Corporations consists of people with many
different skills, knowledge and experience. They value each individual’s contribution to their
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collective effort as they strive to work together for the good of the corporation and the country at
large.
VI) Excellency. National Water and Sewage Corporations looks for and promotes proficiency
and leadership in all aspects of water and sewage services delivery.
vii) Result oriented. They strongly believe in effectiveness in service delivery.
MANAGEMENT AND ORGANIZATIONAL STRUCTURE: NATIONAL WATER AND
SEWAGE CORPORATION STRUCTURE.
Figure 1: Showing the organization structure of NWSC:
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KEY:
MD: Managing Director Sen.: Senior
Mgt: Management KW: Kampala water
LUBIGI SEWAGE TREATMENT PLANT (LSTP)
Introduction
Sewage is a type of wastewater that is contaminated with urine & faeces. Sewerage is the
provision of drainage by sewers or an infrastructure that conveys sewage or runoff using sewers.
As knowledge and understanding of the relationship between waterborne pathogens and public
health has increased, so has the impetus for innovation of new technologies for treatment of
wastewater. In the last century, population growth and industrialization have resulted in
significant degradation of the environment. Disposal of untreated wastes and wastewater on
land or in streams and rivers is no longer an option. Newer regulations are aimed at
protecting the environment as well as public health.
The objectives of wastewater treatment are to reduce:
(1) The level of solids,
(2) The level of biodegradable organicmatter,
(3) The level of pathogens,
(4) The level of toxic compounds in the wastewater, to meet regulatory limits that are
protective of public health and the environment.
SOURCES OF WASTEWATER
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The following are common sourcesor types of wastewater:
1. Domestic or municipal wastewater: this includes wastewater discharged from
residences, Institutions such as schools and hospitals, and commercial facilities such
as restaurants, Shopping malls, etc.
2. Industrial wastewater: wastewater discharged from industrial processes, e.g.
pharmaceutical industry, poultry processing.
3. Infiltration and inflow: this includes water that eventuallyentersthe sewer from
foundation drains, leaking pipes, submerged manholes, and groundwater infiltration,
among others.
4. Storm water: rainfall runoff and snow melt.
5. Municipal wastewater is usually collected in sanitary sewers and trans- ported to the
waste water treatment plant. Storm water may be collected in separate sewer lines called
storm sewers. In some cities, especially older cities, storm water is collected in the
same sewer line as the domestic wastewater. Thistype of system is called a
combined sewer system. Each system has advantages and disadvantages. Industrial
wastewater may be treated on-site, or pretreated and then discharged to sanitary
sewers, after appropriate removal of pollutants. This is also part of Kampala but by
accident not by design.
BACKGROUND INFORMATION OF LUBIGI SEWAGE TREATMENT PLANT.
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The Lubigi plant is part of the Lake Victoria Protection Project (Phase 1) intended to
reduce pollution of Lake Victoria and improve waste water treatment within the city of
Kampala in addition to the already existing Bugolobi Sewage Treatment Plant.
This plant was funded by the World Bank in conjunction with the Government of
Uganda. It is under the Ministry of Water and Environment and it started operating in
2013.
The Lubigi sewage Treatment Plant is located in the Lubigi swamp along the
northern by-pass, Hoima road in Namungoona, a Kampala city suburb (semi-urban
area). It is a reclaimed part of the swamp about eight (8) hectares in size. This plant was
designed to treat around 400m3 per day of the fecal sludge and 5000m3/day of the
wastewater but sometimes the fecal sludge is exceeded. The current flows are as follows;
3000m3/day of Waste water,400m3/day of fecal sludge, the fecal sludge average COD
being 10500mg/l, and the fecal sludge average BOD being 3200mg/l This plant treats
wastewater from the following areas; Makerere, Mulago hospital, Namungoona,
kamwokya, Nansana, Wandegeya, Kawempe, and Bwaise. The plant receives two kinds
of sewage. The wastewater mainly from homes connected to the sewer lines and the fecal
sludge from toilets, septic tanks, ventilated improved pit latrines (VIPS). The fecal sludge
is brought by cesspool trucks whereas the sewage flows by gravity up to the inlet.
However surface run-offs sometimes enter in the open manholes.
The treatment processes at Lubigi Sewage Treatment Plant (LSTP) are natural since they
involve use of stabilization ponds and no chemicals are added, everything occurs
naturally, mainly influenced by the environmental conditions like weather.
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Reasons for constructing the Lubigi Sewage Treatment Plant
 It was constructed to ease the work at Bugolobi Sewage Treatment Plant (BSTP) since it
would be overloaded due to increase in the amount of waste treated.
 Some places such as Makerere (Mulago hospital) were far from BSTP meaning pumps
would be needed to enable the wastewater reach Bugolobi hence the need for a nearer
treatment plant.
 The site also favored the construction of the plant. It is located on a low altitude; this
enables the wastewater to move by gravitational force through the sewer systems instead
of being pumped.
 Since the area itself is a swamp, the effluent is automatically let into the swamp for
further treatment (tertiary treatment).
Objectives of the plant
 To ensure continuous disposal services of fecal sludge and wastewater
 To treat wastewater instead of disposing it to the environment which could pose great
health risks in terms of diseases such cholera caused by bacteria called vibrato cholera,
diarrhea, typhoid caused by bacteria called salmoneratyphae and others. The waste is
also a nuisance to the environment since it smells, and it can cause eutrophication in the
lakes if not properly handled.
 The wastewater is also treated to meet the standards set by the National Environmental
Management Authority (NEMA) for waste disposal.
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CHAPTER TWO
THE SEWAGE TREATMENT PROCESS AT LSTP
Lubigi has a combined capacity to treat 5,400m3 wastewater a day. It receives and treats
wastewater from the piped network as well as fecal sludge that is brought by private cesspool
emptier trucks. The Lubigi catchment area consists of Makerere, Katanga, parts of Mulago,
Kalerwe, Bwaise and areas along the northern by-pass. Lubigi STP has a fully equipped sewage
laboratory for quality monitoring at the various stages of treatment as well as the discharge point
at all sewage treatment plants.
FLOW DIAGRAM
Figure 2: Showing the flow diagram of the sewage treatment process at LSTP.
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PUMP STATION (Screw pump)
The design of the pump station (or lift station) at the WWTP is to a great extent similar
to those placed in the collection system. The major differences are that the building components
are incorporated into the WWTP facility and that an alternative to the no clog centrifugal pump
may be appropriate. The alternative is a screw pump (often called an Archimedes screw). Screw
pumps (Figure 20-1) are high volume, no clog, atmospheric head devices that can pump a variety
of solids and debris in raw wastewater without screening. There are two general types: the open
screw that rotates in a trough and the enclosed screw, in which both the screw and the enclosing
cylinder rotate. A major advantage of these pumps is variable pumping at constant speed,
because the output, up to the design capacity, is controlled by the sump level and equals the
influent flow rate. Operators like screw pumps because the good ones, when properly installed,
are nearly trouble free (Garbus, 2006). The overall efficiency of the pumping system may be as
high as 80 percent at design flow. At approximately 30 percent of design capacity, the efficiency
of the open screw drops to about
60 percent because of friction and backflow (called slippage) of fluid between the flights and the
trough. There is no slippage with the enclosed screw (Garbus, 2006). Major disadvantages of
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screw pumps are the large area (footprint) of the pumping station because of the angle of the
slope of the screw and limited head (about 10 m) that can be achieved. Screw pump selection is
made from manufacturers’ data such as that shown in Table 20-1. The static lift height is
determined based on the difference in elevation between the low flow into the plant wet well and
the required elevation to overcome head losses as wastewater flows through the plant (i.e., the
hydraulic grade line).
At Lubigi there are two Screw pumps each of one flight.
ON SITE FECAL SLUDGE
This onsite fecal sludge is brought by cesspool emptier trucks from different points around the
city. These include latrines, full septic tanks, and other points that have waste water that needs to
be treated. These trucks (cesspool trucks) vary in sizes.
Their sizes include the small with a capacity of about
3m3 commonly known as an Elf is charged 10,000
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Uganda shillings to dump, the medium size with a carrying capacity of about 5m3 commonly
known as an Elf is charged 20,000 Uganda shillings to dump, and the big size which carries a
capacity of about 10m3 commonly known as an Elf is charged 50,000 Uganda shillings to
dump. These trucks are monitored and recorded before they enter to dump, this helps to ensure
that what is received from these trucks does not exceed the plant’s capacity. The truck companies
are all registered with the organization so as to ensure quality. The plant has Closed-Circuit
Television (CCTV) cameras to keep track of every truck that dumps at the plant. Once these
trucks are well monitored and it is found out that what is received is enough for a day, the
remaining trucks are directed to Bugolobi sewage treatment works.
Cesspools dumping at the sedimentation tank.
The equation below can be used to estimate the amount of waste generated from a certain
population:
W = 0.01795S - 0.003761; - 0.003220 + 0.0071P - 0.0002Z + 44.7,
Where: W = waste generated (tons), S = number of stops made by the MSW pickup truck,
F = number of families served, D = number of single family dwellings, P = population, and Z =
adjusted income per dwelling unit (dollars).
SCREENING
A screen is a device with openings for removing bigger suspended or floating matter in sewage
which would otherwise damage equipment or interfere with satisfactory operation of treatment
units.
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Objectives of screening are to removal of coarse solids (pieces of woods, plastics, papers, rags,
leaves, roots, etc.) and protection of pump, valves, pipe lines, impellers. Classification Based on
of screens is based on the Opening size: Coarse, Medium, Fine, Configuration: Bar screens,
Mesh screens, Cleaning Method: Manual, Mechanical, Raked, Water jet, Screen surface: Fixed,
Moving.
TYPES OF SCREENS
Coarse Screens: Coarse screens also called racks are usually bar screens, composed of vertical
or inclined bars spaced at equal intervals across a channel through which sewage flows. Bar
screens with relatively large openings of 75 to 150 mm are provided ahead of pumps, while those
ahead of sedimentation tanks have smaller openings of 50 mm.
Bar screens are usually hand cleaned and sometimes provided with mechanical devices. These
cleaning devices are rakes which periodically sweep the entire screen removing the solids for
further processing or disposal. Hand cleaned racks are set usually at an angle of 45° to the
horizontal to increase the effective cleaning surface and also facilitate the raking operations.
Mechanical cleaned racks are generally erected almost vertically. Such bar screens have
openings 25% in excess of the cross section of the sewage channel.
Medium Screens: Medium screens have clear openings of 20 to 50 mm. Bar are usually 10 mm
thick on the upstream side and taper slightly to the downstream side. The bars used for screens
are rectangular in cross section usually about 10 x 50 mm, placed with larger dimension parallel
to the flow.
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Fine Screens: Fine screens are mechanically cleaned devices using perforated plates; woven
wire cloth or very closely spaced bars with clear openings of less than 20 mm. Fine screens are
not normally suitable for sewage because of clogging possibilities.
Here, screens of 10mm bar spacing are installed and fixed in one place hence cannot
move to remove bigger rags that come with the fecal sludge. Fecal sludge comes with a lot of big
solids since some people use their toilets as the dumping sites. Waste water flows to the
sedimentation tank.
Velocity
The velocity of flow ahead of and through the screen varies and affects its operation. The
lower the velocity through the screen, the greater is the amount of screenings that would be
removed from sewage. However, the lower the velocity, the greater would be the amount of
solids deposited in the channel. Hence, the design velocity should be such as to permit 100%
removal of material of certain size without undue depositions. Velocities of 0.6 to 1.2 mps
through the open area for the peak flows have been used satisfactorily. Further, the velocity at
low flows in the approach channel should not be less than 0.3 mps to avoid deposition of solids.
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Head loss: Head loss varies with the quantity and nature of screenings allowed
accumulating between cleanings. The head loss created by a clean screen may be calculated by
considering the flow and the effective areas of screen openings, the latter being the sum of the
vertical projections of the openings. The head loss through clean flat bar screens is calculated
from the following formula:
h = 0.0729 (V2 - v2)
Where, h = head loss in m
V = velocity through the screen in mps v = velocity before the screen in mps
Another formula often used to determine the head loss through a bar rack is Kirschmer's
equation:
h = K (W/b) 4/3 hv sin θ
Where h = head loss, m
K = bar shape factor (2.42 for sharp edge rectangular bar, 1.83 for rectangular bar with
semicircle upstream, 1.79 for circular bar and 1.67 for rectangular bar with both u/s and d/s face
as semicircular). W = maximum width of bar u/s of flow, m
b = minimum clear spacing between bars, m hv = velocity head of flow approaching rack,
m = v2/2g θ = angle of inclination of rack with horizontal the head loss through fine screen is
given by h = (1/2g) (Q/CA) where, h = head loss, m Q = discharge, m3/s.
C = coefficient of discharge (typical value 0.6).
A = effective submerged open area, m2.
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The quantity of screenings depends on the nature of the wastewater and the screen
openings.
THE SEDIMENTATION TANK
Particle that will settle within a reasonable period of time can be removed in a sedimentation
basin (clarifier). The basin is divided into 4 zones: inlet, settling, outlet and sludge storage. In the
design of an ideal sedimentation tank, one of the controlling parameters is the settling Velocity
(v s) of the particle to be removed. For the purpose of discussion and illustration, the settling
properties of particles are categorized into four classes: (1) discrete particle settling, (2)
flocculent settling, (3) hindered settling, and (4) compression settling. By convention these
categories have been labeled Type I, Type II, Type III, and Type IV settling, respectively. In
actual settling tanks, it is not uncommon to see all of these types of settling. The value of
separating the discussion into these categories is that it provides a means of understanding the
relationship between variables in the design of the sedimentation basin.
Settling: Solid liquid separation process in which a suspension is separated into two
phases that are: clarified supernatant leaving the top of the sedimentation tank (overflow) and
concentrated sludge leaving the bottom of the sedimentation tank (underflow).
Purpose of Settling: To remove coarse dispersed phase, to remove coagulated and flocculated
impurities and to remove precipitated impurities after chemical treatment. To settle the sludge
(biomass) after activated sludge process / tricking filters.
Principle of Settling
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Suspended solids present in water having specific gravity greater than that of water tend to settle
down by gravity as soon as the turbulence is retarded by offering storage. Basin in which the
flow is retarded is called settling tank. Theoretical average time for which the water is detained
in the settling tank is called the Detention period.
Types of Settling
Type I: Discrete particle settling - Particles settle individually without interaction with
neighboring particles.
Type II: Flocculent Particles – Flocculation causes the particles to increase in mass and
settle at a faster rate.
Type III: Hindered or Zone settling –The mass of particles tends to settle as a unit with
individual particles remaining in fixed positions with respect to each other.
Type IV: Compression – The concentration of particles is so high that sedimentation can
only occur through compaction of the structure.
Type I Settling
 Size, shape and specific gravity of the particles do not change with time.
 Settling velocity remains constant.
If a particle is suspended in water, it initially has two forces acting upon it:
Force of gravity: Fg =ρpgVp,
Buoyant force quantified by Archimedes as: Fb=ρgVp
If the density of the particle differs from that of the water, a net force is exerted and the particle
is accelerated in the direction of the force: Fnet= (ρp-ρ) gVp. This net force becomes the driving
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force. Once the motion has been initiated, a third force is created due to viscous friction. This
force, called the drag force, is quantified by: Fd=CDAp ρv2/2
CD= drag coefficient.
Ap = projected area of the particle.
Because the drag force acts in the opposite direction to the driving force and increases as the
square of the velocity, acceleration occurs at a decreasing rate until a steady velocity is reached
at a point where the drag force equals the driving force: (ρp- ρ )gVp = CDAp ρv2/2
For spherical particles,
Vp=∏d3/6 and Ap= ∏ d2/4 Thus, v2= 4g (ρp - ρ) d /3CDρ
Expressions for CD change with characteristics of different flow regimes. For laminar, transition,
and turbulent flow, the values of CD are:
CD = 24 (laminar) /Re. CD= 24 / Re + 3/Re 1/2 +0.343 (transition) .CD= 0.4(turbulent)
where Re is the Reynolds number: Re= ρvd/ μ Reynolds number less than 1.0 indicate laminar
flow, while values greater than 10 indicate turbulent flow. Intermediate values indicate
transitional flow.
Stokes Flow: For laminar flow, terminal settling velocity equation becomes:
v= (ρ p- ρ) gd2 /18μ
Which is known as stokes equation.
Transition Flow: Need to solve non-linear equations:
v2= 4g (ρp - ρ) d /3CD ρ
CD= 24/ Re + 3/ R 1/2+0.34 Re= ρ vd/ μ
 Calculate velocity using Stokes law or turbulent expression.
 Calculate and check Reynolds number.
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 Calculate CD.
 Use general formula.
 Repeat from step 2 until convergence.
Types of Settling Tanks
Sedimentation tanks may function either intermittently or continuously. The intermittent tanks
also called quiescent type tanks are those which store water for a certain period and keep it in
complete rest. In a continuous flow type tank, the flow velocity is only reduced and the water is
not brought to complete rest as is done in an intermittent type. Settling basins may be either long
rectangular or circular in plan. Long narrow rectangular tanks with horizontal flow are generally
preferred to the circular tanks with radial or spiral flow. These are the same type at Lubigi
sewage treatment plant.
Long Rectangular Settling Basin
Long rectangular basins are hydraulically more stable, and flow control for large volumes is
easier with this configuration.
A typical long rectangular tank has length ranging from 2 to 4 times their width. The bottom is
slightly sloped to facilitate sludge scraping.
A slow moving mechanical sludge scraper continuously pulls the settled material into a sludge
hopper from where it is pumped out periodically.
Drag of sedimentation tank
A long rectangular settling tank can be divided into four different functional zones: Inlet zone:
Region in which the flow is uniformly distributed over the cross section such that the flow
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through settling zone follows horizontal path. Settling zone: Settling occurs under quiescent
conditions. Outlet zone: Clarified effluent is collected and discharge through outlet weir. Sludge
zone: For collection of sludge below settling zone.
Inlet and Outlet Arrangement
Inlet devices: Inlets shall be designed to distribute the water equally and at uniform velocities. A
baffle should be constructed across the basin close to the inlet and should project several feet
below the water surface to dissipate inlet velocities and provide uniform flow;
Outlet Devices: Outlet weirs or submerged orifices shall be designed to maintain velocities
suitable for settling in the basin and to minimize short-circuiting. Weirs shall be adjustable, and
at least equivalent in length to the perimeter of the tank. However, peripheral weirs are not
acceptable as they tend to cause excessive short-circuiting.
Weir Overflow Rates
Large weir overflow rates result in excessive velocities at the outlet. These velocities extend
backward into the settling zone, causing particles and flocs to be drawn into the outlet. Weir
loadings are generally used up to 300 m3/d/m. It may be necessary to provide special inboard
weir designs as shown to lower the weir overflow rates.
Inboard Weir Arrangement to Increase Weir Length.
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Circular Basins
Circular settling basins have the same functional zones as the long rectangular basin, but the
flow regime is different. When the flow enters at the center and is baffled to flow radially
towards the perimeter, the horizontal velocity of the water is continuously decreasing as
the distance from the center increases. Thus, the particle path in a circular basin is a parabola as
opposed to the straight line path in the long rectangular tank. Sludge removal mechanisms in
circular tanks are simpler and require less maintenance.
Settling Operations
Particles falling through the settling basin have two components of velocity:
1) Vertical component: vt= (ρp- ρ) gd2 18μ
2) Horizontal component: vh=Q/A
The path of the particle is given by the vector sum of horizontal velocity vh and vertical settling
velocity vt.
Assume that a settling column is suspended in the flow of the settling zone and that the column
travels with the flow across the settling zone. Consider the particle in the batch analysis for type-
1 settling which was initially at the surface and settled through the depth of the column Z0, in the
time t0. If t0 also corresponds to the time required for the column to be carried horizontally
across the settling zone, then the particle will fall into the sludge zone and be removed from the
suspension at the point at which the column reaches the end of the settling zone.
All particles with vt > v0 will be removed from suspension at some point along the settling zone.
Now consider the particle with settling velocity < v0. If the initial depth of this particle was such
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that Zp/vt=t0, this particle will also be removed. Therefore, the removal of suspended particles
passing through the settling zone will be in proportion to the ratio of the individual settling
velocities to the settling velocity.
The time t0 corresponds to the retention time in the settling zone.
T / Q = V/ Q =LZ0W
Also, t0=Z0 /v0
Therefore, Z0/ v0 = LZ0W/ Q and v0= Q/ LW
Or v0=Q/ AS
Thus, the depth of the basin is not a factor in determining the size particle that can be removed
completely in the settling zone. The determining factor is the quantity Q/As, which has the units
of velocity and is referred to as the overflow rate q0. This overflow rate is the design factor for
settling basins and corresponds to the terminal setting velocity of the particle that is 100%
removed.
Design Details
1. Detention period: for plain sedimentation: 3 to 4 h, and for coagulated sedimentation: 2 to
2.5h.
2. Velocity of flow: Not greater than 30 cm/min (horizontal flow).
3. Tank dimensions: L: B = 3 to 5:1. Generally L= 30 m (common) maximum 100 m. Breadth= 6
m to 10 m. Circular: Diameter not greater than 60 m. generally 20 to 40m.
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4. Depth 2.5 to 5.0 m (3 m).
5. Surface Overflow Rate: For plain sedimentation 12000 to 18000 L/d/m2 tank area; for
thoroughly flocculated water 24000 to 30000 L/d/m2 tank area.
6. Slopes: Rectangular 1% towards inlet and circular 8%.
The sedimentation tank
GRIT REMOVAL
Grit Chambers: Grit chambers are basin to remove the inorganic particles to prevent damage to
the pumps, and to prevent their accumulation in sludge digesters.
Types of Grit Chambers
Grit chambers are of two types: mechanically cleaned and manually cleaned. In
mechanically cleaned grit chamber, scraper blades collect the grit settled on the floor of the grit
chamber. The grit so collected is elevated to the ground level by several mechanisms such as
bucket elevators, jet pump and air lift. The grit washing mechanisms are also of several designs
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most of which are agitation devices using either water or air to produce washing action.
Manually cleaned grit chambers should be cleaned at least once a week. The simplest method of
cleaning is by means of shovel. At Lubigi we have manually cleaned.
Aerated Grit Chamber:
An aerated grit chamber consists of a standard spiral flow aeration tank provided with air
diffusion tubes placed on one side of the tank. The grit particles tend to settle down to the bottom
of the tank at rates dependent upon the particle size and the bottom velocity of roll of the spiral
flow, which in turn depends on the rate of air diffusion through diffuser tubes and shape of
aeration tank. The heavier particles settle down whereas the lighter organic particles are carried
with roll of the spiral motion.
Principle of Working of Grit Chamber:
Grit chambers are nothing but like sedimentation tanks, designed to separate the intended heavier
inorganic materials (specific gravity about 2.65) and to pass forward the lighter organic
materials. Hence, the flow velocity should neither be too low as to cause the settling of lighter
organic matter, nor should it be too high as not to cause the settlement of the silt and grit present
in the sewage. This velocity is called "differential sedimentation and differential scouring
velocity". The scouring velocity determines the optimum flow through velocity. This may be
explained by the fact that the critical velocity of flow 'vc' beyond which particles of a certain size
and density once settled, may be again introduced into the stream of flow. It should always be
less than the scouring velocity of grit particles. The critical velocity of scour is given by Schield's
formula:
V = 3 to 4.5 (g (Ss - 1) d) 1/2.
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A horizontal velocity of flow of 15 to 30 cm/sec is used at peak flows. This same velocity is to
be maintained at all fluctuation of flow to ensure that only organic solids and not the grit is
scoured from the bottom.
Types of Velocity Control Devices:
1. A sutro weir in a channel of rectangular cross section, with free fall downstream of the
channel.
2. A parabolic shaped channel with a rectangular weir.
3. A rectangular shaped channel with a par shall flume at the end which would also help easy
flow measurement.
Design of Grit Chambers
Settling Velocity.
The settling velocity of discrete particles can be determined using appropriate equation
depending upon Reynolds number.
Stoke's law: v=g (Ss-1) d2 /18μ
Stoke's law holds good for Reynolds number, Re below 1.
Re=ρvd/ μ
For grit particles of specific gravity 2.65 and liquid temperature at 10°C, μ =1.01 x 10-6m2/s.
This corresponds to particles of size less than 0.1 mm.
Transition law:
The design of grit chamber is based on removal of grit particles with minimum size of 0.15 mm
and therefore Stoke's law is not applicable to determine the settling velocity of grit particles for
design purposes.
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v2=4g (ρp-ρ) d /3CDρ
Where, CD= drag coefficient Transition flow conditions hold good for Reynolds number, Re
between 1 and 1000. In this range CD can be approximated by
CD=18.5/ Re 0.6=18.5/ (ρvd/ μ) 0.6.
Flow Measurement
Flow measurement is carried out to know the amount of waste water to be treated and this
measurement is carried out using two methods either ruler measurement or automatically using a
machine directly connected to a computer. This instrument is known as the venturi meter.
Figure 7: The instrument used to measure flow of sewage

Flow Distribution:
Because rectangular tanks are typically constructed side-by-side to take advantage of common
walls, the distribution of wastewater is by a single channel that runs perpendicular to the flow
through the tanks. The channel is covered with removable grates that allow access for cleaning.
The design velocity of the channel should be a minimum of 0.3 m/s to prevent deposition of
organic matter and a minimum of 0.75 m/s to prevent deposition of mineral matter at 50 percent
of the design flow. The width also affects the flow distribution.
LUBIGI SEWAGE STABILIZATION PONDS
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Stabilization Ponds
The stabilization ponds are open flow through basins specifically designed and constructed to
treat sewage and biodegradable industrial wastes. They provide long detention periods extending
from a few to several days.
Pond systems, in which oxygen is provided through mechanical aeration rather than algal
photosynthesis, are called aerated lagoons.
Lightly loaded ponds used as tertiary step in waste treatment for polishing of secondary effluents
and removal of bacteria are called maturation ponds.
Classification of Stabilization Ponds
Stabilization ponds may be aerobic, anaerobic or facultative.
Aerobic ponds are shallow ponds with depth less than 0.5 m and BOD loading of 40- 120kg/ha.d
so as to maximize penetration of light throughout the liquid depth. Such ponds develop intense
algal growth.
Anaerobic ponds are used as pretreatment of high strength wastes with BOD load of 400-3000
kg/ha.d such ponds are constructed with a depth of 2.5-5m as light penetration is unimportant.
Facultative pond functions aerobically at the surface while anaerobic conditions prevail at the
bottom. They are often about 1 to 2 m in depth. The aerobic layer acts as a good check against
odour evolution from the pond.
Mechanism of Purification
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The functioning of a facultative stabilization pond and symbiotic relationship in the pond
are shown below. Sewage organics are stabilized by both aerobic and anaerobic reactions. In the
top aerobic layer, where oxygen is supplied through algal photosynthesis, the non-settle able and
dissolved organic matter is oxidized to CO2 and water. In addition, some of the end products of
partial anaerobic decomposition such as volatile acids and alcohols, which may permeate to
upper layers, are also oxidized periodically. The settled sludge mass originating from raw waste
and microbial synthesis in the aerobic layer and dissolved and suspended organics in the lower
layers undergo stabilization through conversion to methane which escapes the pond in form of
bubbles.
The SSP are a low cost Sewage Treatment System that uses bacterial activity to remove organic
matter, nutrients and microbes in sewage.
Most of the WSP used by NWSC are usually three in series comprising of anaerobic, facultative
and maturation ponds in the same order. The sewage treatment occurs through anaerobic
digestion in the 1st pond followed by aerobic degradation in the 2nd pond, and finally algal
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activity and microbes death in the 3rd pond. The ponds are occasionally, 2-3 years, de-sludged
when there is sludge accumulation.
Anaerobic, facultative and maturation ponds
Anaerobic Treatment Ponds: primary BOD removal.
Anaerobic ponds are the smallest units in the series. They are sized according to their
"volumetric organic loading", which means the quantity of organic matter, expressed in grams of
BOD5 per day, applied to each cubic metre of pond volume. Ponds may receive volumetric
organic loadings in the range of 100 to 350 g BOD5/m3 day, depending on the design
temperature. The main function of anaerobic ponds is biodegradable organic material (BOD)
removal, which can be reduced 40 to 85 %. As a complete process, the anaerobic pond serves to:
– Settle undigested material and non-degradable solids as bottom sludge
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– Dissolve organic material
– Break down of BOD material
It acts as open septic tanks that rely on the sedimentation of settable solids and
subsequent anaerobic digestion in the resulting sludge layer. During anaerobic
digestion, biogas is produced which could be collected can be collected for energy
production.
Anaerobic settling pond
These high loadings produce a strict anaerobic environment throughout the pond volume (i.e.,
there is no dissolved oxygen present and the redox potential is negative). The depth of anaerobic
ponds is in the range 2−5 m; the precise value depends on the ground conditions and local
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excavation costs (which increase with depth) − depths are often 3−4 m. Anaerobic ponds work
extremely well in warm climates: for example, a properly designed pond will achieve around 60
percent BOD5 removal at 20°C and over 70 percent at 25°C and above. Organic matter removal
in anaerobic ponds is governed by the same mechanisms that occur in all other anaerobic
reactors (Mara et al., 1992; Peña, 2002). A retention time of one day is sufficient for
wastewaters with a BOD5 ≤300 mg/l at temperatures above 20°C.
Odour nuisance from anaerobic ponds, typically due to hydrogen sulphide, has always been a
concern for design engineers. However, odour is not a problem provided that the anaerobic pond
is properly designed and the sulphate concentration in the raw wastewater is less than 500 mg
SO42-/l.
Aerobic Facultative Treatment Ponds: secondary BOD removal
These ponds are of two types: primary facultative ponds that receive raw wastewater (after
screening and grit removal) and secondary facultative ponds that receive settled wastewater from
the primary stage (usually the anaerobic ponds effluent). Facultative ponds are designed for
BOD5 removal based on their "surface organic loading”. The term refers to the quantity of
organic matter, expressed in kilograms of BOD5 per day, applied to each hectare of pond surface
area; thus the overall units are kilograms of BOD5 per hectare of facultative pond surface area
per day − i.e., kg BOD5/ha d. A relatively low surface organic loading is used (usually in the
range of 80−400 kg BOD5/ha d, depending on the design temperature) to allow for the
development of an active algal population. The depth of facultative ponds is in the range 1−2 m,
with 1.5 m being most common.
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The maintenance of a healthy algal population is very important as the algae generate the oxygen
needed by bacteria to remove the BOD5 (see Figure1). The algae give facultative ponds a dark
green color. Ponds may occasionally appear red or pink, due to the presence of anaerobic purple
sulphide-oxidizing photosynthetic bacteria (Mara and Pearson, 1986). This change in facultative
pond ecology occurs due to slight BOD5 overloading, so color changes in facultative ponds are a
good qualitative indicator of pond function. The concentration of algae in a well-functioning
facultative pond depends on loading and temperature. It is usually in the range 500−1000 μg
chlorophyll-a per litre (algal concentrations are best expressed in terms of the concentration of
their principal photosynthetic pigment). The photosynthetic activity of the algae results in a
diurnal variation of dissolved oxygen (DO) concentration and pH. The DO concentration can
rise to more than 20 mg/l (i.e., highly supersaturated conditions) and the pH to more than 9.4
(these are both important factors in the removal of fecal bacteria and viruses; Curtis et al., 1992).
BOD5 removal in primary facultative ponds is about 70 percent on an unfiltered basis and more
than 90 percent on a filtered basis (filtering the sample before BOD5 analysis excludes the
BOD5 due to the algae in the sample; this "algal BOD5" is very different in nature to ordinary
wastewater BOD5 or "non-algal BOD5"). Some regulators specify effluent BOD5 requirements
for WSPs in terms of filtered BOD5 − for example, in the European Union WSP effluents are
required to achieve ≤25 mg filtered BOD5/l (Council of IRC International Water and Sanitation
Centre 5 the European Communities, 1991). Other regulators should be encouraged to apply
similar standards.
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The facultative pond serves to: Further treat wastewater through sedimentation and aerobic
oxidation of organic material, Reduce odour, reduce some disease-causing microorganisms if pH
raises and Store residues as bottom sludge
Simplest of all WSPs and consist of an aerobic zone close to the surface and a deeper, anaerobic
zone.
The algal production of oxygen occurs near the surface of aerobic ponds to the depth to which
light can penetrate (i.e. typically up to 500 mm). Additional oxygen can be introduced by wind
due to vertical mixing of the water.
Aerobic BOD digestion
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Aerobic / Maturation Ponds (MPs)
Maturation or polishing ponds are essentially designed for pathogen removal and retaining
suspended stabilized solids. The principal mechanisms for fecal bacterial removal in facultative
and maturation ponds are high temperature, high pH (> 9), and high light intensity. If used in
combination with algae and/or fish harvesting, this type of pond is also effective at removing the
majority of nitrogen and phosphorus from the effluent
Additional Waste Stabilization Ponds: NWSC also operates and maintains satellite Waste
Stabilization Ponds in Bugolobi, Naalya estates and Ntinda Ministers’ village. These areas have
their separate sewer networks which collect sewage from the various premises.
Maturation ponds
Maturation ponds receive the effluent from the facultative ponds and their size and number
depends on the required bacteriological quality of the final effluent. They are shallower than
facultative ponds with a depth in the range 1−1.5 m, with 1 m being optimal (depths of less than
1 m encourage rooted macrophytes to grow in the pond and so permit mosquitoes to breed).
Because of the lower organic loadings received by maturation ponds, they are well oxygenated
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throughout their depth. The algal populations are much more diverse than that in facultative
ponds; algal diversity increases from pond to pond along the series.
The main mechanisms of fecal bacterial and viral decay are driven by algal activity along with
photo-oxidation. Further details on the removal mechanisms in maturation ponds can be found
in Curtis et al. (1992). Maturation ponds are designed for E. coli removal.
Maturation ponds only achieve a small additional removal of BOD5, but they make a significant
contribution to nitrogen and phosphorus removal. Total nitrogen removal in a whole WSP
system is often above 80 percent and ammonia removal is generally more than 90 percent (these
figures depend on the number of maturation ponds included in the WSP system). Phosphorus
removal in WSPs is lower (usually about 50 percent).
Algal Growth and Oxygen Production
Algal growth converts solar energy to chemical energy in the organic form. Empirical studies
have shown that generally about 6% of visible light energy can be converted to algal energy.
The chemical energy contained in an algal cell averages 6000 calories per gram of algae.
Depending on the sky clearance factor for an area, the average visible radiation received can be
estimated as follows:
Avg. radiation= Min. radiation + [(Max. radiation - Min.radiation) x skyclearance factor]
Oxygen production occurs concurrently with algal production in accordance with following
equation:
106C02 + 16NO3 + HPO4 + 122H2O + 18H+ C106H263O110N16P1 + 138O2
On weight basis, the oxygen production is 1.3 times the algal production.
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DESIGN EQUATIONS FOR WSPS
Anaerobic ponds. The volumetric BOD loading (λv, g/m3 d) is given by:
λv = LiQ/Va
Where Li is the BOD5 of the raw wastewater (mg/l = g/m3),
Q is the wastewater flow (m3/d) and Va is the anaerobic pond volume (m3). The permissible
range of λv is 100 g/m3 d at temperatures ≤10°C, increasing linearly to 300 g/m3 d at 20°C, and
then more slowly to 350 g/m3 d at 25°C and above. The design temperature is the mean
temperature of the coldest month. Once the temperature is known, the value of λv is determined
and the value of Va calculated. The anaerobic pond area is then determined by dividing Va by
the pond depth (e.g., 3 m). BOD5 removal is 40% at temperatures ≤10°C, increasing linearly to
70% at 25°C and above.
Facultative ponds. The surface BOD5 loading (λs, kg/ha d) is given by: λs = 10LiQ/Aaf where
Li is the BOD of the anaerobic pond effluent (mg/l) and Aaf is the facultative pond area (m2). The
value of λs depends on the design temperature (T, °C), as follows: λs = 350(1.107 –
0.002T)T−25 The value of λs is determined for the design temperature and the value of Aaf
calculated.
Minimum retention times: The mean hydraulic retention time (θ, days) in an individual WSP is
given by: θ = V/Q (or AD/Q) where V is the pond volume (m3), Q the wastewater flow through
the pond (m3/d), A is the pond area (m2) and D is the pond working liquid depth (m). The
minimum design retention time is one day in anaerobic ponds, four days in facultative ponds,
and three days in maturation ponds. If the calculated value of θ in the latter is less than this
minimum value (θmin), then the pond volume or area is recalculated from:
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V = Qθmin
A = Qθmin/D
Maturation ponds: These are designed for E. coli and helminthes egg removal or removal of
human intestinal nematode eggs .
The design equation of Ayres et al. (1992) is used:
R = 100[1 − 0.41exp (−0.49θ + 0.0085θ2)]
where R is the percentage egg removal in a single pond, and θ is the retention time in the pond
(days).
The equation is applied first to the anaerobic pond, then to the facultative pond, to calculate the
number of eggs per litre of the facultative pond effluent, as follows: Efac = Erw (1 − ran) (1 − rfac)
Where Efac and Erw are the number of eggs per litre of facultative pond effluent and the raw
wastewater, respectively, and r = R/100 with the subscripts 'an' and 'fac' referring to the
anaerobic and facultative ponds.
If Efac is >1 (or >0.1 if children under 15 are exposed), then the facultative pond effluent requires
further treatment in a maturation pond (usually a single 3-day maturation pond is sufficient, but
this must always be checked).
Removal of E. coli
The equations of Marais (1974) are used:
Nfac = Nrw / [(1 + kB (T) θan) (1 + kB (T) θfac)]
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where Nfac and Nrw are the number of E. coli per 100 ml of facultative pond effluent and the raw
wastewater, respectively; and kB(T) is the value of the first-order rate constant for E. coli removal
at T °C (day−1), given by:
KB (T) = 2.6 (1.19) T−20
If Nfac is >105 per 100 ml, then further treatment in one or more maturation ponds is necessary.
where Nfac and Nrw are the number of E. coli per 100 ml of facultative pond effluent and the raw
wastewater, respectively; and kB(T) is the value of the first-order rate constant for E. coli removal
at T °C (day−1), given by:
KB (T) = 2.6 (1.19) T−20
If Nfac is >105 per 100 ml, then further treatment in one or more maturation ponds is necessary.
The main routine maintenance activities are:
• Removal of screenings and grit from the preliminary treatment units • Periodically cutting the
grass on the pond embankments
• Removal of scum and floating macrophytes from the surface of facultative ponds and
maturation ponds. This is done to maximize the light energy reaching the pond algae, increase
surface re-aeration, and prevent fly and mosquito breeding
• If flies are breeding in large numbers on the scum on anaerobic ponds, the scum should be
broken up and sunk with a water jet • Removal of any material blocking the pond inlets and
outlets
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• Repair of any damage to the embankments caused by rodents or rabbits (or any other
burrowing animals)
• Repair of any damage to fences and gates.
NOTE: there are no maturation ponds at Lubigi due to the fact that the swamp acts like
one and the water will not be for domestic use but they are present at the Naalya
stabilization ponds.
Residual Management
In all biological waste treatment processes some surplus sludge is produced. The objective of
residual management is: Reduction of water content, Stabilization of sludge solids, Reduction
in sludge solids volume.
In facultative type aerated lagoons and algal waste stabilization ponds, the surplus sludge settles
out in the unit itself and is removed only once in a few years after emptying the unit, exposing
the wet sludge to natural drying, and carting away the dried sludge for agricultural use or land
filling. In extended aeration process where aerobic digestion of surplus sludge is done, the
sludge can be taken directly for dewatering and disposal. In case of activated sludge and
trickling filter plants, the sludge is taken (along with the primary sludge) to sludge digester for
further demineralization and thereafter it is dewatered.
52 | P a g e
Sludge Dewatering Methods
Natural: sludge drying beds, sludge lagoons
Mechanical: sludge thickeners, centrifuges, vacuum filters, filter press
Physical: heat drying, incineration
Disposal of Sludge
Final disposal of sludge is to land and sometimes to the sea, in one of the following ways:
 Agricultural use of dried or wet sludge.
 Use of dried sludge as landfill in absence of agricultural demand.
 Spreading wet sludge on eroded or waste land, contouring the field, so as to gradually
build up a top soil of agricultural value.
 Disposing of wet sludge along with solid wastes for (i) composting, or (ii) sanitary
landfill.
 Transporting and dumping into the sea.
Sludge Characteristics
For the rational design of sludge drying systems, it is essential to know a few characteristics of
sludges, such as moisture content as affected by the nature and extent of organic and other matter
contained in them, their specific gravity, weight and volume relationships, their dewatering
characteristics, etc. The specific gravity of sludge is very close to that of water itself,
for biological sludge and 1.02 from alum sludge.
53 | P a g e
Sludge source Moisture content Weight, g/person-day

% by weight Solids Water Total
Initial moisture 99 30 2970 3000

content
After thickening 96 30 720 750
After other 90 30 270 300

mechanical
process
After natural or 60 30 45 70
physical drying
It is evident that the bulk of the water is removed in the thickener. Thereafter, the bulk of the
remaining moisture is removed in free drainage. Evaporation removes the least but, in fact, takes
the longest time. The final "dried" sludge still has considerable moisture in it, but the sludge is
now "handle able".
Sand Beds for Sludge Drying
Sand beds are generally constructed as shown in the typical cross-sectional view.
Sludge is generally spread over the sand which is supported on a gravel bed, through which is
laid an open-joint earthen pipe 15 cm in diameter spaced about 3 m apart and sloping at a
gradient of 1 in 150 towards the filtrate sump. The drying beds are often subdivided into smaller
units, each bed 5-8 m wide and 15-50 m long. The drying time averages about 1-2 weeks in
warmer climates, and 3-6 or even more in unfavorable ones.
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There e are mainly two types of beds the covered and uncovered and at Lubigi both are present.
55 | P a g e
CHAPTER THREE
QUALITY CONTROL
The state of the water both in and out of the plant is of great importance as we have seen
in the design of the water stabilization ponds it is of great need to know the state of the water
entering the ponds and also leaving ponds so as to know whether the pond is functioning well.
Even in the design of the sedimentation tank it has been observed that we must know the type of
suspended particles so as to know the volume and dimensions or sizing needed for the tank.
Not just in the design of process equipment but also the fact that we must put into
considerations other organisms in the environment and must ensure that we do not affect their
habitats but changing the conditions such as PH. And even people can affected if we detect some
really nasty chemicals.
Adverse Effects of Impurities
Problems Constituents Responsible
Aesthetically not acceptable and Palatability Clay, Silt, Humus, Color
decreases
Health related problems pH
affect mucous membrane Hardness, TDS, Ca, Mg, SO4
gastro-intestinal irritation
Dental and skeletal fluorosis Fluoride
Methaemoglobinemia Nitrate
Encrustation in water supply structure Hardness, TDS
56 | P a g e
Adverse effects on domestic use Ca, Mg, Cl
Eutrophication of the water body Zoo & Phyto, Phosphate, Nitrate
Taste, discoloration and corrosion of pipes Iron, Mn, Cu, Zn, Alkalinity
fittings and utensils
Promotes iron bacteria Fe & Mn
Corrosion in water supply system pH, Cl
Carcinogenic effect Cr, As
Toxic effect Cd, Pb, Hg
Formation of chlorophenols with chlorine Phenols
Imparts unpleasant taste and odour after Oil & grease
chlorination
Water-borne diseases Bacteria & viruses
The quality and sewerage services department consists of a quality control section which ensures
that all sewerage effluent is satisfactory and meets the required standards. According to the
section, after the various sewage treatment processes have been completed (preliminary, primary
and secondary) the final sewerage effluent has a BOD range of 20-90mg/l and a TSS range of
30-60mg/l, values not far off the National Environmental Management Authority (NEMA)
standards of BOD and TSS of 50mg/l and 100mg/l respectively considering the high dilution
factor of the receiving water in the Nakivubo Channel and later to Lake Victoria.
57 | P a g e
WHY MONITOR SEWAGE
 Facilitate plant optimization.

 Gain early warning of plant failure.
 Assess the effectiveness of the sewage treatment plant.
 Ensure compliance with local authority requirements.
 Demonstrate compliance with applicable standards.
3.1 THE LUBIGI LABORATORY

For my 3rd week I was at LSTP, I worked in the quality assurance section which was headed by
Mr. Job Gava as my supervisor. The section at LSTP is under water quality management
department that has an obligation of monitoring all the effluent of NWSC waste water treatment
plants and stabilization ponds to ensure they comply with National discharge standards hence
ensuring environmental protection.
Under the quality assurance laboratory at LSTP, we used to regularly monitor the satellite ponds
of Ntinda, Bugolobi, and Naalya and plant ponds with also BSTW. The inner Murchison bay of
lake Victoria was also monitored with some industries for example Mukwano, Sadoline paints,
House of Eden and Fresh Diary that discharge in NWSC-Kampala water sewer lines. The mode
of monitoring would be regular sampling and analysis of the samples both on site and in the lab
to check on the quality of treated sewage before discharging into the environment, ensuring that
it met the required standards. Collection of samples was done every Tuesday and sampling of
Lake Victoria was done once every month and during the analysis, the following parameters
were tested; electrical conductivity (EC), Total suspended solids(TSS), Alkalinity, PH,
Chemical oxygen demand (COD), Biological Oxygen Demand (BOD), Temperature, Dissolved
Oxygen(DO), Color, Turbidity, Ammonia, Phosphates.
Parameters that were tasted immediately onsite are; DO, Temperature, TSS, and the rest
of the parameters were tasted in the lab.
THE STANTARDS AT NWSC ARE BELOW GIVEN BY NEMA
NATIONAL STANDARDS FOR WASTEWATER DISCHARGE – NEMA
STANDARDS
58 | P a g e
National Standards
4 effluents discharge.
Parameters Units
(Maximum
Permissible)
O
Temperature C 20-35
Ph -- 6.0 – 8.0
Electrical Conductivity S/cm 1500
Colour PtCo 500
Turbidity NTU 300
Total Dissolved Solids mg/L 1200
Total Suspended Solids mg/L 100
Alkalinity: total as CaCO3 mg/L 800
Orthophosphate mg/L 5.0
Sulphide mg/L 1.0
Total Phosphorus mg/L 10.0
Sulphate mg/L 500
Ammonia-N mg/L 10.0
Total Nitrogen mg/L 20.0
Nitrate: NO3- mg/L 10.0
BOD5 mg/L 50
COD mg/L 100
Faecal Coliforms CFU/100m 5,000
Total Coliforms CFU/100m 10,000
L
L
Table 2: The NEMA Standards for Waste Water Discharge
THE EQUIPMENT USED IN THE LABORATORY
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Henson Spectrophotometer: This works at a wavelength of 630nm

by using the light absorption to give the
light intensity amount for different
chemical parameters. Especially
ammonia, COD, phosphates (both ortho
and total),turbidity and TSS
This works by dipping the probe

in a given sample after the saturation
point and then switching it on to take
the readings. It is used to measure the
electrical conductivity of the samples.
EC PH Meter
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Oven For drying different samples
COD reactor used at LSTP Before the absorbance and

concentration are determined using the
spectrophotometer, the samples are first
reacted for 2-3hours in the reactor and
then analyzed.
Water still For distilling water
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DO meter This meter uses electricity to

determine the amount of dissolved
oxygen in a given sample. This meter is
used in the measurement of BOD by
determining DO1 and DO5.
Autoclave For sterilization ofTP (Total

phosphates).
BOD INCUBATOR For keeping BOD samples at a

particular temperature.
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PHYSICAL/CHEMICAL PRACTICES IN WASTE WATER ANALYSIS
By weight is 99.9% water and It is the 0.1% that we have to remove. That 0.1% contains Organic
matter – Microorganisms (a few of which are pathogenic), Inorganic compounds.
Major Measures of are: Oxygen Demand, Biochemical oxygen demand, Chemical oxygen
demand, Indicator organisms: Fecal coliform and Escherichia coli (E Coli 0157:H7 is the really
bad), Solids content: Total suspended solids and Total dissolved solids.
Chemical analyses: Ammonia & nitrate, Total & reactive phosphorus and pH Alkalinity: Volatile
compounds and Dissolved gases – Odors
Oxygen Demand
Indictor of mass of dissolved oxygen needed by microorganisms to degrade organic and some
inorganic compounds – High BOD/COD is indirect indicator of the organic content – Ammonia
is inorganic and creates an oxygen demand .As it is converted to nitrate.
Aerobic Biotransformation: Dissolved oxygen is consumed in the process of convert organic

matter into inorganic matter.
Organic Matter
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Contains more than – Carbon, hydrogen, and oxygen and Can also contain Nitrogen,
Phosphorus, Sulfur and Many other compounds.
Degradation of Organic Matter : Releases these other compounds typically in an inorganic
form for example Nitrogen becomes ammonia/ammonium which then Creates an additional
oxygen demand and Phosphorus becomes ortho-phosphate.
Nitrogen Cycle: Nitrogen is a component of protein and as proteins are degraded, nitrogen is
released and nitrogen converts to ammonia/ammonium in the Process of ammonification.
Organic-N + Microorganisms → NH3/ NH4+
Biological Nitrification: Ammonia/ammonium is then converted to nitrite and nitrate through
Nitrification which then creates an Oxygen demand. Nitrification is a two-step autotrophic
process (the conversion from ammonium to nitrate)
Nitrosomonas, Step 1:NH4+ + 3/2O2 → NO22- + 2H+ + H2O
Nitrobacter, Step 2:NO2-+ 1/2O2 → NO3-
DETERMINATION OF BIOCHEMICAL OXYGEN DEMAND (BOD5) USING AZIDE

MODIFICATION OF WRINKLER METHOD (OXYGEN ELECTRODE METHOD)
Introduction
All living organisms depend upon oxygen to maintain the metabolic processes that
produce energy for growth and reproduction .Dissolved oxygen is important in precipitation and
dissolution of inorganic substances in water Need. To assess quality of raw water .To check on
pollution .Determination of biological changes by aerobic or anaerobic organisms. D.O. is the
basis of BOD test to evaluate pollution potential of wastes. All aerobic biological wastewater
treatment processes. It is also an important factor in corrosion.
Principle
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Oxygen present in sample oxidizes the divalent manganous to its higher valency which
precipitates as a brown hydrates oxide after addition of NaOH and KI.
Upon acidification, manganese reverts to divalent state and liberates Iodine from KI equivalent
to D.O. content in the sample. The liberated Iodine is titrated against standard (N/40) solution of
Sodium thiosulphate using starch as an indicator.
Interference
Interference with the degradation process: To provide optimum conditions for the bacteria
community, the pH of sample should be adjusted by adding NaOH or HCL to fit the range 6.5 to
8.5 Some samples may be sterile, and will need seeding. The purpose of seeding is to introduce a
microbiological community capable of oxidizing the organic matter .Where such microorganism
are already present as in surface waters. For domestic sewage or chlorinated effluents, seeding is
not required .For seeding, whenever necessary use settled domestic sewage which has stored at
20oc for 24 hours or use fresh raw sewage . For seeding use 1 to 2mls of settled seed to each liter
of dilution
The microorganisms doing the materials may experience a lack of the diluted sample, which may
slow the process of degradation down.
The presence of heavy metals or other toxic material such as residual chlorine is other sources of
interference in this test.
Interference with the measurement of dissolved oxygen : The compounds which are interfering
in the BOD test are the same as those interfering in the determination of dissolved oxygen
Reagents
Phosphate buffer solution
To prepare this, 0.85g KH2P04, 2.18gK2HPO4, 3.34g NaHPO4.7H2O and 0.17g NH4CL were
dissolved in 50mlof distilled water and diluted to 100ml. The pH of this solution was kept at 7.2.
Magnesium Sulphate solution
3.64 g of MgSO4.7H20 was dissolved in 50ml of distilled water and made to 100 ml.
Calcium Chloride solution
3.64 g of CaCl2 .H20 was dissolved in distilled water and diluted to 100ml
Ferric Chloride solution
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0.025g of FeCl3.H20 was dissolved in distilled water and diluted to100ml

Acid and alkali solutions
This solution was required for neutralization of acidic or caustic waste water sample prior to any
analysis.
Acid
28 ml of conc. sulpuric acid was slowly and carefully added while stirring to 500ml of distilled
water. It was then diluted to 1000ml.
Alkali
40 g of sodium hydroxide was dissolved in distilled water and diluted to 1000ml
Others
 2-chloro – 6-[trichloromethyl] pyridine [TCMP] (Nitrification inhibitor).
 Sodium sulphite solution[ used to destroy chlorine in chlorinated samples]
 Ammonium chloride solution.
 Glucose – glutamic acid solution.
Procedure
1. Preparation of the dilution water. 500ml of distilled water was transferred in a
container. The water was saturated with dissolved oxygen (DO) by aerating with organic free
filtered air.
1 ml of each of, phosphate buffer, MgSO4, CaCL2 and FeCL3 solutions /l of saturated
water was added. The solution was mixed thoroughly before starting to use.
2. Preparation and measurement of initial DO. 5ml of the sample was added to the
individual BOD bottles whose volume was 300ml.The bottles were filled up to the brim with
enough dilution water so that when a stopper was inserted, air could be displaced leaving no
bubble.
3. Preparation of blank sample. The blank was made by filling the BOD bottle with un-
seeded dilution water. The samples were then incubated at 200c for 5days
Determination of final BOD
After 5 day incubation the residual DO was determined in the samples.
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Calculation
BOD=(DO1-DO5)X(300/sample volume)
Where; DO1 is Dissolved Oxygen immediately after preparation
DO5 is Dissolved Oxygen after 5 days
(300/sample volume) is the dilution factor.
DETRMINATION OF TOTAL PHOSPHATE BY PERSULPHATE METHOD
Principle
Organically combined phosphorus and all phosphates are first converted to orthophosphate. To
release the phosphorus as ortho – phosphate from organic matter , a digestion or wet oxidation
technique is applied .The least tedious method , based on wet oxidation with potassium per-
sulphate, is adopted .The same procedure for orthophosphate determination is followed .
Interference
This method is relatively free from interference. Arsenates produce a blue color similar to
that formed with phosphate. They interfere in concentration as low as 0.1mg/L. In most waters,
however, arsenates are present. If necessary, their concentration can be subtracted from the
result. Interference of sulfide can be removed by adding several milligrams of potassium
permanganate and shaking of 1 to 2 minutes; after that, 1ml of ascorbic solution is added and the
standard procedure continued. Hexavalent chromium interferes to give lower results; to remove
this influence 1ml of ascorbic solution is added before the standard procedure. Changes in
temperature of ±10 ºC do not affect the results.
Sampling and Preservation

Sample should be collected in plastic polythene narrow mouth containers at 0.4 m below the
surface in the main water body. Preserve with 2ml of concentrated H2SO4 to pH<2 cool it at
4ºC. Maximum allowable holding limit until analysis of sample is 24 hours. Ammonia in water
sample if not chemically preserved, will slowly be degraded by microbiological activity to
Nitrate. The rate of conversion is variable. It is important to inhibit bacterial activity by
acidifying the water sample with conc. H2SO4.
67 | P a g e
Reagents
4M Sulpuric acid, H2SO4,
100 ml conc. H2SO4was carefully diluted with distilled water up to 500ml (for preservation).
0.04M Sulpuric acid, H2SO4,
10ml H2SO4, 4M was diluted up to 1000 ml (for blank) and digestion bottles were cleaned.
Sulpuric acid, H2SO4.5N.
70 ml of conc. H2SO4was diluted to 500ml using distilled water
Potassium persulphate; K2S2O8, 50g/L
5 g potassium persulphate were dissolved in distilled water and diluted to 100ml.
Potassium antimonyl tartrate solution
1.37 g potassium antimonyl tartrate, K (SbO) C4H4Owhere dissolved in 400ml of distilled water.
Ammonium Molybdate solution
20 g (NH4)6MO7O24.4H2O were dissolved in 500ml of distilled water.
Others
Ascorbic acid
Standard phosphate solution
Equipment and Apparatus
 Autoclave
 Spectrophotometer, HENSON 530 reading at 630nm
 Acid –washed glassware
Procedure
1. 25.0ml of sample was diluted and acidified with 1ml H2SO4, 0.04M, and then to it, 5ml
digestion reagent was added and mixed well.
2. 25 ml distilled water was taken to prepare the blank and phosphate standard by taking 25ml of
known standard concentration. Both blank and phosphate standard were treated in the same way
as the sample.
3. Heating for 30 minutes was done in an autoclave at 120ºC and cooled at room temperature.
4. For the color reaction made in the destruction bottles, 3ml of combined reagent which
comprised (50 ml of 5N H2SO4 +5ml potassium antimonyl tartrate +15ml ammonium Molybdate
only) was added and, mixed well.
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5. Finally, 1ml of ascorbic acid was added to each sample, Swirled to mix.
6. It was left to stand for 20 minutes for blue color development
7. The concentration in mg/L at 630 nm wavelength was measured using the spectrophotometer
Henson 530 and the reading was multiplied by the dilution factor.
8. Results were recorded straight in the workbook.

Calculations.
To derive the concentration in mg/L of TP in the sample, the following formula was applied
Sample TP conc. mg/L = mg /TP x 1000 .

Sample Vol. (ml)
Phosphorus concentration determines the level of eutrophication (increased plant and algal
growth due to an excess of nutrients such as phosphorus and nitrates),
High levels of phosphates result in; eutrophication, increased biochemical oxygen demand due
to increased algal growth and also, decreased dissolved oxygen.
Low levels of phosphate limit plant and algal growth.
DETERMINATION OF TOTAL SUSPENDED SOLIDS

Principle
Total Suspended solids refer to Portion of Solids that passes through a filter of 2.0 µm or smaller
pore size. Total suspended matter has two methods namely; photometric method and gravimetric
method. Photometric method of determining suspended solids is a simple direct measurement
which does not require the filtration or ignition and weighing steps that gravimetric procedures
do.
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Interference
Dirty or scratched sample cell can cause high reading.
Gas bubbles in the water may affect the results removed by swirling or tapping the bottom of the
cell on a table.
Samples were collected from different points as listed earlier, in clean plastic bottles and samples
were analyzed as soon as possible after collection.
Reagent
Distilled water.
Apparatus / Equipment
 DR 3900 at 630 nm
 Sample Cell
 Beaker
 Measuring cylinder
Procedure
Each sample was shaken vigorously so as to attain a complete mixture.
The machine reading was directly recorded in the workbook for each sample after placing the
TSS meter in each of the samples.
Since the total suspended solids (TSS) was measured directly from undiluted samples, no
calculations were needed.
DETERMINATION OF ELECTRICAL CONDUCTIVITY USING A METER

Principle
Conductivity is measure of water’s capacity to convey electrical current and is directly related to
the concentration of ionized substance in the water.
Interference
Atmospheric gases such as dissolved carbon dioxide or ammonia increases conductivity without
increasing the mineral content. To minimize these effects, the sample can be boiled and then
placed in a covered container for cooling.
If the sample is to contain significant amounts of hydroxide it can be neutralized to avoid
erroneously high reading. Adding four drops of phenolphthalein indicator solution to 50 ml of
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sample and then adding Gallic solution drop-wise until the pink color completely disappears
does this.

Samples were collected in clean plastic bottles. The samples were analyzed as soon as possible
after collection.
Reagents
Distilled Water
Equipment /Apparatus
 Conductivity meter (probe / sensor)
 Soft tissue
 Beaker, (50 ml)
Water sample containing oil greases or fats will coat the electrodes and affect the accuracy of the
readings. Should this occur, the probe should be cleaned with a strong detergent solution and
then thoroughly rinsed with dematerialized water. Mineral build up on the probe can be removed
with 1:1 hydrochloric acid solution.
Procedure
The probe was immersed in a beaker containing the sample solution. The probe was agitated on
the beaker to free any bubbles from the electrode area.
Reading on the conductivity of the sample in S/cm was made
Since several samples of different conductivities were to be measured, carry over from one
sample to the next was minimized by rinsing the probe thoroughly with distilled water, followed
by the sample to be measured before immersing in the sample.
The sensor was read directly and the results were expressed in micro-Siemens per centimeter
(S/cm) at an exact temperature of 25 C
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COLIFORM DETERMINATION BY MEMBRANE FILTRATION METHOD

USING LAUREL SULPHATE BROTH
Principle
A measured volume of 100ml or its equivalent is filtered through a membrane filter composed of
cellulose esters which retains all the bacteria on the surface of the membrane, which is then
incubated with the girded side upon a selective medium.
Caution
Sample with high level of suspended solids have interference with colony growth enumeration
hence have to be diluted using dilution water.
Sampling and preservation
Samples were collected in clear, clean, plastic bottles each with a stopper. Aseptic method of
sample collection was used to avoid sample contamination. It was ensured that the sampling
point or sample was such that it was representative of the batch or area it represented. Samples
were analyzed after distant travel and before analysis was done, were preserved in a fridge for
not more than 36 hours to avoid alteration of the bacteriological status of the sampled water.
Reagents and nutrients
Laurel Sulphate broth
38.1g of anhydrous broth powder was weighed and dissolved in 500ml of water
It was dispensed in 100ml volumes in screw capped bottles.
It was then Sterilized in an autoclave for 15min at 121oC 15bars.
It was then stored in dry pace.
Equipment and apparatus
Filtering unit, Membrane filter pads, autoclave, Incubator, Petri dishes, forceps, pipettes
(graduated ), transfer pipette, digital counter, water still, measuring cylinders, sterilizing burner,
hot plate, disinfectant (ethanol 70%), weighing balance, thermometer.
Procedure
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The membrane filter was picked and placed using a sterile forceps ascetically.
2.5 ml of laurel Sulphate broth was transferred on to the absorbent pad in the Petri dish so that it
was socked just to leave a film of broth round the absorbent pad.
Filter membrane was placed with the gridded face up and the filter jar was replaced.
100ml of the diluted sample was poured and filtered into the filtration jar and all of it was filtered
through the filter paper. For raw sewage samples, a dilution factor of 105 was used whereas for
final effluent samples, a dilution factor of 103 was used.
Then filtering membrane was removed and placed on to the absorbent pad that was earlier
socked with the broth (The gridded side of the filter membrane had to face up).
The petri dish was covered with the lid upper most and placed on to the petri dish carrier then
placed in the incubator. The incubator was set at 44oC for fecal coliform test (while for total
coliform it should be set at 35oC for 30min before the sample was incubated).
After incubation, the carrier plus the petri dish were removed and allowed to cool for 10min, to
allow false yellow color to lose color and ensure that the yellow was only for the typical
colonies.
A magnifying glass and a counting pen were used to count the colonies. The number of colonies
was then multiplied by the respective dilution factor.
DETERMINATION OF CHEMICAL OXYGEN DEMAND (COD) USING CLOSED

REFLUX COLORIMETRIC METHOD.
Principle
COD is definedas the oxygen equivalent of organic matter that can be oxidized by a strong
chemical oxidizer in an acidicmedium. COD measures bothbiodegradable and no
biodegradable organicmatter. The results can be obtained in a few hours.
The chemical oxygen demand determines the amount of oxygen required for oxidation of
organic matter using a strong chemical oxidant such as potassium dichromate under reflux
conditions. The test is widely used to determine the same types of pollution as the BOD
73 | P a g e
The limitation of the test lies in its inability to differentiate between the biologically Oxidisable
and biologically inert material.
COD determination has an advantage over BOD test in that the result can be obtained in
less than 5 hours whereas BOD determination requires 5 days. Further the test is relatively easy
and precise. Also there are not much interference as in case BOD.
Volatile organic compounds are more completely oxidized in the closed system because
of longer contact with the oxidant. Most types of organic matter are oxidized by boiling mixture
of chromic Sulpuric acids. A sample is refluxed in strongly acid solution with a known excess of
potassium dichromate (K2Cr2O7). The amount of dichromate consumed is proportional (1:7) to
the oxygen required to oxidize the Oxidisable organic matter. Usually a sample of 50 mls volume
is used; however when other volume are used, keep ratios of reagent weights, volumes and
strength constant. The standard 2 hours reflux time may be reduced if it has been shown that a
shorter period yields the same results.
Sampling and preservation
Samples were collected in clear plastic bottles and the samples were well mixed before taking
aliquots for reflux.
Reagents
Digestion solution
To 500 ml distilled water, was added 10.216 g K2Cr2O7 and primary standard grade, previously
dried at 103oC for 2 hours, 167 ml conc. H2SO4and then 33.3 g HgSO4. It was then dissolved and
cooled to room temperature and diluted to1000mL.
H2SO4/ Ag2SO4
10 g Ag2SO4 was added to 1 L conc.H2SO4, and left to stand overnight to dissolve. It was then
mixed carefully after dissolving.
Stock KHP
Equipment and apparatus
a. Digestion vessels
b. Heating block, cast aluminum, 45 to 50 mm deep. with holes sized for close fit of culture
or samples
c. Oven , to operate at 150oC
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d. Ampule sealer
e. Henson 530 Spectrophotomer
Procedures
The digestion tube and caps were washed with 4M H2SO4 before first used to prevent
contamination.
2 mls of the sample was transferred to the digestion tube and 2.0 mls of digestion solution were
added.
2.0 mls H2SO4 / Ag2SO4 were carefully rundown inside of tube, so an acid layer was formed
under the sample – digestion solution layer. Tubes were tightly capped and swirled several times
to mix completely.
The tubes were placed in a preheated oven of 150oc during 2 hours
They were allowed to settle, the content were left to settle.
The following day, the content was gently transferred and without mixing, the concentration at
620nm was measured against blank.
The concentration of the samples were read and recorded in the work form.
Calculation
COD as mg O2/l = mg O2 in final volume x 1000mL
ML sample
Result expressed in mg/L COD as O2
DETERMINATION OF PH USING THE PH METER.
Principle
The pH is the negative logarithm of the hydrogen-ion concentration in moles per litre. In water
samples it is determined by the measurement of a voltage produced between an electrode
responsive to hydrogen ions (glass electrode) and a reference electrode (usually a calomel
electrode) when both are immersed in the sample. A difference of 1 pH unit produces a potential
charge of 58.16 mV at 25 C
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The pH of natural water is controlled by the carbon dioxide / bicarbonate equilibrium and usually
ranges from 4.0 to 9.0. The majority of waters are slightly basic (pH > 7) due to the presence of
bicarbonates and carbonates. Acidity affects chemical and biological processes taking place in
water in the following ways;
 Dissociation of organic and inorganic molecules, thereby changing toxicity.

 Changing the water solubility of compounds, also influencing toxicity.
 A lower pH may induce enhanced corrosion.
 Different biological species show optimum performance at different degrees of acidity,
leading to shifts in species consumption.
after collection.
Reagents
Distilled Water
Equipment /Apparatus
 Conductivity meter (probe / sensor)
 Soft tissue
 Beaker, (50 ml)
The probe should be cleaned with a strong detergent solution and then thoroughly rinsed with
dematerialized water. Mineral build up on the probe can be removed with 1:1 hydrochloric acid
solution.
Procedure
The probe was immersed in a beaker containing the sample solution. The probe was agitated on
the beaker to free any bubbles from the electrode area.
Reading on the PH of the sample was made
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Since several samples of different PH were to be measured, carry over from one sample to the
next was minimized by rinsing the probe thoroughly with distilled water, followed by the sample
to be measured before immersing in the sample.
The sensor was read directly and the results were expressed at an exact temperature of 25 C.
DETERMINATION OF ALKALINITY BY TITRATION.
General Discussion: Alkalinity of water is its acid-neutralizing capacity. It is the sum of all the
titratable bases. The measured value may vary significantly with the end-point pH used.
Alkalinity is a measure of an aggregate property of water and can be interpreted in terms of
specific substances only when the chemical composition of the sample is known. Alkalinity is
significant in many uses and treatments of natural waters and wastewaters. Because the alkalinity
of many surface waters is primarily a function of carbonate, bicarbonate, and hydroxide content,
it is taken as an indication of the concentration of these constituents. The measured values also
may include contributions from borates, phosphates, silicates, or other bases if these are present.
Alkalinity in excess of alkaline earth metal concentrations is significant in determining the
suitability of water for irrigation. Alkalinity measurements are used in the interpretation and
control of water and wastewater treatment processes. Raw domestic wastewater has an alkalinity
less than, or only slightly greater than, that of the water supply. Properly operating anaerobic
digesters typically have supernatant alkalinities in the range of 2000 to 4000 mg calcium
carbonate (CaCO3)/L.1
Principle: Hydroxyl ions present in a sample as a result of dissociation or hydrolysis of solutes

react with additions of standard acid. Alkalinity thus depends on the end-point pH used. For
methods of determining inflection points from titration curves and the rationale for titrating to
fixed pH end points. For samples of low alkalinity (less than 20 mg CaCO3/L) use an
extrapolation technique based on the near proportionality of concentration of hydrogen ions to
excess of titrant beyond the equivalence point. The amount of standard acid required to reduce
pH exactly 0.30 pH unit is measured carefully. Because this change in pH corresponds to an
exact doubling of the hydrogen
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Interferences: Soaps, oily matter, suspended solids, or precipitates may coat the glass electrode
and cause a sluggish response. Allow additional time between titrant additions to let electrode
come to equilibrium or clean the electrodes occasionally. Do not filter, dilute, concentrate, or
alter sample.

after collection.
Reagents and apparatus.

Beakers
Erlenmeyer flask.
Burette
Dropper
Pipette
Tit
Sodium carbonate solution, approximately 0.05N: Dry 3 to 5 g primary standard Na2CO3 at
250°C for 4 h and cool in a desiccators. Weigh 2.5 ± 0.2 g (to the nearest mg), transfer to a 1-L
volumetric flask, fill flask to the mark with distilled water, and dissolve and mix reagent. Do not
keep longer than 1 week.
Standard sulfuric acid or hydrochloric acid, 0.1N: Prepare acid solution of approximate
normality as indicated under Preparation of Desk Reagents. Standardize against 40.00 mL 0.05N
Na2CO3 solution, with about 60 mL water, in a beaker by titrating potentiometrically to pH of
about 5. Lift out electrodes, rinse into the same beaker, and boil gently for 3 to 5 min under a
watch glass cover. Cool to room temperature, rinse cover glass into beaker, and finish titrating to
the pH inflection point. Calculate normality:
Where: A = g Na2CO3 weighed into 1-L flask,

B = mL Na2CO3 solution taken for titration, and
C = mL acid used.
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Use measured normality in calculations or adjust to 0.1000N; 1 mL 0.1000N solution = 5.00 mg

CaCO3.
Mixed bromcresol green-methyl red indicator solution: Use either the aqueous or the
alcoholic solution: 1) Dissolve 100 mg bromcresol green sodium salt and 20 mg methyl red
sodium salt in 100 mL distilled water. 2) Dissolve 100 mg bromcresol green and 20 mg methyl
red in 100 mL 95% ethyl alcohol or isopropyl alcohol.
PROCEDURE
Sample collection
• Collect samples in clean glass or plastic bottles with tight-fitting caps. Completely fill the bottle
and immediately tighten the cap.
• Prevent agitation of the sample and exposure to air.
• Analyze the samples as soon as possible for best results.
• If immediate analysis is not possible, keep the samples at or below 6 °C (43 °F) for a maximum
of 24 hours. If there is biological activity in the sample, analyze the sample within 6 hours.
Select a sample volume and titrant.
Test
1. Fill a 25-mL burette to the zero mark with the titrant.
2. Use a graduated cylinder or pipette 1 to measure the sample volume.
3. Pour the sample into a clean, 250-mL Erlenmeyer flask.
4. If the sample volume is less than 50 mL, dilute to approximately 50 mL with deionized
water.
5. Add the contents of two drops mixed bromcresol green-methyl red indicator solution.
6. Swirl to mix.
7. Put the flask under the burette. Swirl the flask. Add titrant until the color changes to a
light pink color, or the pH is 4.5.
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8. Use a calculator to calculate the concentration. mL of titrant × multiplier = mg/L as
CaCO3 Mixed bromcresol green-methyl red indicator solution.
Data handling and dissemination.
All analytical work done at the Lubigi laboratory accumulates data that is assembled to construct
useful information that describes the specifications in any given sample. All data is recorded in
laboratory work books from where is entered in the network data base to be availed to the senior
analysts, principal analysts and quality assurance managers and any clients to the corporation. A
copy of the results remains in the laboratory as confirmatory and objective evidence of the
analysis.
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CHAPTER FOUR
4.0 THE SEWER NETWORKAND ITS MAINTENANCE
Introduction
Sewer is a pipe or conduit carrying sewage. Sewers are usually not flow full (Gravity Flow).
The full flowing sewers are called force main as the flow is under pressure.
Sewerage: It is the science and art of collecting, treating and disposal of sewage.
There are three types of sewerage system.
Separate system. In this system the sanitary sewage and storm water are carried separately
in two set of sewers.
Combined sewerage system. In this system the sewage and storm water are carried combine
in only one set of sewers to the waste water.
Partially separate sewerage system. This system is the compromise between separate and
combine system taking the advantages of both systems.
Following are types of sewer according to material : Asbestos Cement (AC) Sewer, Brick Sewer,
Cement Sewer ,Cast iron (CT) Sewer, Steel Sewers and Plastic Sewers
1. Asbestos Cement (AC) Sewer: Types of sewer like Asbestos Cement (AC) Sewers are
manufactured from a mixture of cement and asbestos fiber. Asbestos Cement (AC) Sewers
are suitable for carrying domestic sanitary sewage. Asbestos cement sewer is best as vertical
pipe for carrying sullage from upper floors of multistory buildings (in two pipe system of
plumbing).
Advantages of Asbestos Cement (AC) Sewer
1. Smooth and Light in weight
2. Can easily be cut, fitted and drilled
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3. Durable against soil corrosion
Disadvantages of Asbestos Cement (AC) Sewer
1. Brittle cannot withstand heavy loads
2. They are easily broken in handling and transport.
2. Brick Sewers: These types of sewer (Brick Sewers) are made at site and used for construction
large size sewer. Brick Sewers are very useful for construction of storm sewer or combined
sewer. Nowadays brick sewers are replaced by concrete sewer. Brick sewers my get deformed
and leakage may take place. A lot of labor work is required.
Note: To avoid leakage the brick sewer should be plastered.
3. Cement Concrete
i. PCC (Plain Cement Concrete) - for diameter up to 60 cm
Suitable for small storm drains. Not durable.
ii. RCC (Reinforced Cement Concrete) - for diameter > 60 cm
They may be cast in situ or precast, resistant to heavy loads, corrosion and high pressure. These
are very heavy and difficult to transport.
4. Cast Iron (CI) Sewers: These types of sewer are High strength and durability water tight.
Cast Iron sewers can withstand high internal pressure and can bear external load. Cast Iron
sewers are suitable for the following conditions.
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When the sewage is conveyed under high pressure When the sewer line is subject to heavy
external load e.g. under railway line, foundation wall etc, below highways When there is
considerable difference in temperature
5. Steel Sewers: These types of sewer (steel sewers) are Impervious; light, resistant to high
pressure, flexible, suitable when; The sewage is carried under pressure The sewage has to be
carried across a river under water The sewer has to cross under a railway track They are
generally used for outfall and trunk sewers
6. Plastic Sewers : Nowadays PVC sewers are used for carrying sewage. Plastic sewers are
resistant to corrosion. Such types of sewer are light in weight, smooth and can be bent easily. But
these types of sewer (Plastic sewers) are having high co-efficient of thermal expansion and
cannot be used in very hot areas.
Other types of Sewer materials include Wooden Sewers (Rare now) and Stoneware Sewers.
The Kampala sewer networking is comprised of a pipe network of about 135km long with pipe
sizes ranging from 110mm up to 675mm diameter. Pipe materials include; clay, asbestos,
concrete and most recently PVC pipes. 56% of the sewer lines were built in the 1940s with
altogether 86% built within 1940 and 1969 and only 14% installed after 1969.
SEWER HYDRAULICS AND DESIGN
Sewer design begins by selecting a reasonable layout and establishing the expected flows within
each pipe linking the manholes. For large systems, this often involves the use of economic
analysis to determine exactly what routing provides the optimal system. For smaller systems, this
is an unnecessary refinement, and a reasonable system may be estimated and sketched by hand.
The average discharge is estimated on the basis of the population served in the drainage area, and
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the maximum and minimum flows are calculated. Once this is done, the design is a search for the
right pipe diameter and grade (slope) that will allow the minimum flow to exceed a velocity
necessary for conveyance of solids, while keeping the velocity at maximum flow less than a limit
at which undue erosion and structural damage can occur to the pipes. The velocity is usually held
between the following limits:
Minimum = 0.6 m/s.
Maximum = 3.0m/s.
Design of Sewers
The hydraulic design of sewers and drains, which means finding out their sections and gradients,
is generally carried out on the same lines as that of the water supply pipes.However, there are
two major differences between characteristics of flows in sewers and water supply pipes. They
are:
The sewage contain particles in suspension, the heavier of which may settle down at the bottom
of the sewers, as and when the flow velocity reduces, resulting in the clogging of sewers. To
avoid silting of sewers, it is necessary that the sewer pipes be laid at such a gradient, as to
generate self cleansing velocities at different possible discharges.
The sewer pipes carry sewage as gravity conduits, and are therefore laid at a continuous gradient
in the downward direction up to the outfall point, from where it will be lifted up, treated and
disposed of
The velocity in sewers is usually calculated by using the Manning equation, based on the Chezy
open channel flow equation
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v = c (Rs) 1/2
Where
v = velocity of the flow (m/s), r = pipe hydraulic radius, or the area divided by the wetted
perimeter (m), s = slope of the pipe, and c = Chezy coefficient.
For circular pipes, the Manning equation is developed by setting
c= (K/n).R1/6, where n = roughness factor and k = constant, so that
V =k.R2/3.s1/2/n.
If v is in feet per second and r is in feet, k = 1.486. In metric units with v in meters per second
and I in meters, k = 1.0. The slope s is dimensionless, calculated as the fall over distance. The
term n is the roughness coefficient, and its value depends on the pipe material, increasing for
rougher pipe.
Sewer Appurtenances: Sewer appurtenances are the various accessories on the sewerage
system and are necessary for the efficient operation of the system. They include man holes, lamp
holes, street inlets, catch basins, inverted siphons, and so on.
Man-holes: Man holes are the openings of either circular or rectangular in shape constructed on
the alignment of a sewer line to enable a person to enter the sewer for inspection, cleaning and
flushing. They serve as ventilators for sewers, by the provisions of perforated man-hole covers
for gases such as methane, carbon dioxide, carbon monoxide, sulphurdioxide, hydrogen sulphide
and ammonia to escape. Also they facilitate the laying of sewer lines in convenient length.
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Man-holes are provided at all junctions of two or more sewers, whenever diameter of sewer
changes, whenever direction of sewer line changes and when sewers of different elevations join
together.
There are three types of manholes namely; shallow manhole (75-90cm), normal manhole
(150cm) and deep manhole (>150cm)
There are mainly three kinds of maintenance namely;

 Preventive maintenance
 Planned preventive maintenance
 Flashing(with a jetting system)
During my time at the network, my group was operating in Wandegeya, kamwokya, Naalya,
Makerere and Kikoni. We had to report to certain points that had problems of sewage over flow
due blockages and solve them.
These are some of the methods we used to unblock sewer lines.
i) Roding method: This method involves use of rods to unblock the sewer. In case the
blockage is nearer to the manhole where rod starts, the rod wire is rotated by the
person himself holding the rod wire but when the blockage is far and is quite harder,
then the rods are connected to the generator or rod machine which has a motor which
rotates the wires/rod causing them to move further into the piping system to collect
any cloth or rags causing the blockage.
Figure 13: rods used for unblocking manholes
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ii) The jetting /flashing method. This involves flashing of the sewers with water at high
pressure in order to force the blockages to move further down into the network. It is
usually done when unblocking using the Roding method has failed and plays a key
role in the de silting of sewers.
Figure 14: Jetting of water into a blocked sewer pipe
iii) Other maintenance works include replacement of manhole covers as well as

replenishment of the concert manhole benching.
iv) Inspection of different manholes or people with overflows call the management.
4.3 PLUMBING RODS
Plumbing rods are pieces of equipment used to remove most blockages from sewer pipes.
However, when sewer pipes are broken, plumbing rods are not effective and the damaged pipe
must be replaced.
The rods screw together so that they can be made as long as needed. They have different kinds of
endings to help remove the blocking objects
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Figure 15: Plumbing rods
To unblock the sewer pipe, it is important to find an inspection opening (IO) below the blockage
and push the rods up the pipe to the blockage. It is important to remember which way the rods
and endings have been screwed together and always twist the rods in the same direction.
If this is not done, the rods are likely to become unscrewed and be left in the sewer pipe. This
will create a worse problem because the rods will also block the pipe. If this happens it will
probably be necessary to dig up the sewer pipe and break it to unblock the pipe and get the rods
back. This would have to be done by a licensed plumber.
UNBLOCKING SEWER PIPES
The larger sewer pipes have manholes set in them allowing access to the pipe. They are often
about a meter underground and are large boxes which usually have walls made of concrete. The
pipe opens into the box on one side and starts again on another side.
The lids, which are made of metal, can be lifted to allow someone to look down into the sewer to
see if there is evidence of a blockage, for example, wastewater build-up in the manhole.
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Figure 26: Manhole and a blockage
A blockage in the sewer pipe can cause the wastewater to build-up in the manhole.
COMMON CAUSES OF BLOCKAGE IN THE SEWER LINES
Misuse of sewer systems by the general public especially industries or business people
like restaurants who deposit unplanned for substances in the system such as a lot or excess fat.
Toilets and toilet pipes get blocked when people put things that cannot be broken down or
dissolved for example food scraps, paper, rags, cans, bottles, grease and fat. Accumulation of
sand and silt in the sewer.
Wastewater pipes from sinks, basins and laundry tubes can get blocked if people put food waste,
especially tea leaves, fat and other rubbish down them. If hot fat is poured down an outlet pipe, it
will set in the pipe when it cools and cause a blockage.
In addition to blockages caused by these materials, main sewer pipes can get blocked in other
ways, for example, tree roots growing into the pipe joints and cause holes and blockages or they
may wrap around the sewer line and crush it
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Desilting
this involves removal of mainly sand, small aggregates of stones (silt) from manholes. These
usually accumulate as the wastewater flows in those pipes and in the process carry the silt. It is
also as a result of the poor storm drain system that ended up depositing some of the rain water
carrying soil into the sewer system. The silt usually fails to move due to the reduced gradient
(flow) of the wastewater. These if not removed cause blockages in sewer lines causing overflows
which are dangerous to the environment. The process of removing this silt is called desilting. A
well-dressed operator or a desilter enters the manhole and scoops out the silt using a spade and a
bucket.
Figure 17: Desilting
4.7 Precautions taken during Desilting
Extreme care was always taken when opening the lids of sewer pipes as poisonous and explosive
gases could build up in these pipes.
Before attempting to unblock a sewer pipe the following were done
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 Before making an inspection, always, they had to wait several minutes to allow any
poisonous or explosive gases to escape.
 Smoking was always prohibited while doing this work due to the fact that some of the
gases from these chambers are flammable.
 Workers used to work in pairs such that in case of any problem to the one inside the
manhole, he could be easily helped out by the other worker.
 Two manholes connecting the blocked sewer were always opened for proper aeration.
 Wearing of protective gears was always emphasized. These included gas masks among
others
 Use of gas meters before entering the manhole
Sometimes the manholes are below the ground and are not easy to find. To solve this problem, a
metal detector could be used and when it indicated 99.9% then the covered manhole had very
many chances of being found in that place. So it was necessary to dig that particular place to find
them. Before doing all this, a map showing the location of the various manholes in a particular
area was first referred to and the information was transferred from the map to the ground. the
provision of an up-to-date map or GPS system would be helpful as some individuals have
constructed houses over these sewer lines.
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CHAPTER FIVE
ACTIVITIES CARRIED OUT, KNOWLEDGE &SKILLS ACQUIRED AND
CHALLENGES FACED
CHEMICAL LABORATORY
While in the Laboratory at Lubigi, I got involved in collection of samples (sampling) at all the
different places as listed before. This was usually done every Tuesday. I also got involved in
measurement of the parameters that where always dealt with immediately after sampling as listed
earlier. I actively participated in the sample preparation and laboratory analysis of the various
samples and determination of other parameters. Data entrance was also one of the activities I
engaged in while in the lab.
SEWER NETWORK MAINTENANCE.
While in sewer network, I got involved in carrying of the equipment to and from the pickup such
as rod wires, spade, rake, digging up the covered manholes, holding of the rod wires during
unblocking of the sewer. Connecting and disconnecting of the rod wires using a spanner.
LUBIGI AND BUGOLOBI SEWAGE TREATMENT PLANTS.
At Lubigi Sewage Treatment Plant I got involved in some plant operations like recording of the
daily reading done on the plant. At BSTW most of the work done was observation and studying
of the way the plant operates from the inlet until the final discharge points.
Knowledge Acquired During My Training:
I learnt to appreciate the various types of engineering such as civil engineering and
environmental engineering whose work I originally did not understand.
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I have learnt the essence of safety and the precautions to be taken, in any engineering work
environment. Overcoats, a helmet and safety shoes or gumboots must strictly be worn at all times
before setting a foot into the plant. For lab work, gloves and lab coat are essential
I have also learnt the importance of building a collaborative relationship and friendship with
different and various categories of people (staff and workers) in the field and to also understand a
bit of the working environment dynamics and levels in an organization like national water for
future employment opportunities.
I have also learnt the benefits associated with proper team work and co ordination especially in
the lab and in the sewer network as It gets work done much faster by practically being part of it,
at the best of my ability.
I have also been able to understand that some problems encountered in the environmental
engineering industry especially those to do with design and economic and how a future chemical
engineer like me can come in to help.
I have learnt the design of some process structures such as the sedimentation tank, water
stabilization ponds and sewer systems that I found interesting and enlightening in many ways
how knowing the basics of science gives engineers the opportunity to make things work.
I have been able to learn all the chemical and physical processes of sewage treatment, the design,
construction and operation of all the equipment used in the treatment process and I have
appreciated all the knowledge acquired during my studies in a more practical bit.
Skills Acquired During My Training
The use of an overall, lab coat for general work and safety shoes have strictly been worn most of
the time.
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My time management skills improved as was challenged to come very early at about 7:30 for this
training which I did and tried to keep on a daily basis since the end.
Confidence: I have also developed an outstanding ability and confidence to explain all the details
learnt about sewage treatment technologies.
My general understanding of process control increased since we were in the lab doing the test to
determine whether the plant is doing well or not plus my increased understanding of how some
of the plant equipment was designed the factors that had to be considered.
Challenges Faced During My Training:

 Cost of Living was quite high since no form of allowances was given to trainees. All
transport, food, research, and safety working equipment costs, were catered for by me.
 The bad odour and stench from sewage was a very big problem especially during the time of
dumping of the faecal matter and at inlet. This was not so much at Lubigi because the place
has some good aeration but it was worse at Bugolobi sewage treatment plant. Moreover no
milk was provided to the trainees yet it was essential for the neutralization of toxic gases
inhaled. So I had to provide it for me hence more costs.
 Moving of long distances to get to the place where restaurants were to get something to eat
was yet another problem since there was no provision of lunch at the plant.
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CHAPTER SIX
CONCLUSION, RECOMMENDATIONS, REFERENCES & APPENDICES
General Conclusion
Amidst some challenges, my industrial training at NWSC has been a big success. National water
and sewerage Corporation has hardworking, cooperative and trained staff, as well as a very
friendly environment. It has been a big experience in my life, to interact with staff and workers
that are co-operative, social, approachable, caring and competent enough to provide me with all
the necessary information I needed to have obtained. Their efforts provided me a valuable
environment, in which my practical growth occurred.
I am extremely grateful, having trained with NWSC, a large organization I believe that anyone
would wish to train from. I therefore recommend students and other professional personnel to
undergo training at this organization. I also recommend NWSC to continue providing industrial
training placements to students as well as professional personnel from various institutes and
firms.
6.2Recommendations to NWSC
 The management of NWSC should put into consideration, the importance of their trainees to
the organization. Despite trainees benefiting from the knowledge acquired, their research can
also benefit the organization as well or would be motivated to come back and work as
permanent employees. Therefore, I advise the organization to consider some little allowances
for trainees as they strive to survive during their internship training and for motivation. On
the same note, the management should provide protective gears to the trainees.
 The organization should consider the trainees in sewage department by providing for them
milk since they are also subjected to the harmful gases.
 There should be improvement in the design of the pickups used in the network maintenance.
The behind part of the pickup where the workers sit should be covered by a suitable roof to
cater for workers during bad weather.
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 Sensitization of the customers to improve on their ways of using the latrines, toilets and other
waste water disposal systems which end up in sewers to reduce on the many blockages. The
workers in the maintenance section should ensure that the unblocked sewer is totally
investigated to ensure total flow because at times the sewers become blocked after a few days
of maintenance and this brings quarrels to customers.
 The biogas produced from anaerobic digestion should be trapped effectively since it can
produce enough energy to meet most of the energy needs of the sewage treatment plant itself.
Capturing biogas (methane) emission under plastic cover
Recommendations to Kyambogo University

 The university should at-least organize one or two sessions with students to brief them on
what is expected to be done during training and guidance on how to make industrial training
reports. Providing a log book and written guidelines is not quite enough to fully provide the
guidance needed.
 Internship allowances should be provided to students in time, preferably two weeks prior to
training so that students can easily plan for their accommodation especially in urban areas
where costs of living are high.
 Organization of study trips to such organizations especially for those doing engineering, and
other sciences, should be put into consideration as this will benefit many students who
wouldn’t have gotten a chance to train from such a valuable organization for their practical
growth.
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 Likewise, organization of public meetings and exhibitions at the University should be put
into consideration, inviting experienced personnel form NWSC, to share with students more
about waste water treatment and water production technology.
References
Davis, M. L. and D. A. Cornwell (2008) Introduction to Environmental Engineering, McGraw-

Hill, New York, pp. 236–259.
NWSC Magazines.
Mackenzie L. Davis (2010) WATER AND WASTEWATER ENGINEERING, 1st edition,
McGraw-Hill.
Metcalf and Eddy (2003) Wastewater Engineering: Treatment and Revise, 4th edition, McGraw-
Hill, pages. 157–160.
Standard methods for the examination of water and wastewater. 19th Edition. 1995
UNEP /WHO /UNESCO / WMO PROJECT ON Global Water Quality Monitoring GEMS /
WATER OPERATIONAL GUIDE. Chapter III: Analytical Methods. Copenhagen, Denmark.
De Zwart, D. and Trivedi, R.C., 1992. Draft manual on Water Quality Evaluation. The
Netherlands.
Conductivity Instrumental Manual.
ASCE (1990) Water Treatment Plant Design, 2nd ed., American Society of Civil Engineers and
American Water Works Association, McGraw-Hill, NY, pp. 27–56.
NWSC Reports.
Willis, J. F. (2005) “Clarification,” in E. E. Baruth (ed.), Water Treatment Plant Design, A
American Water Works Association and American Society of Civil Engineers, McGraw-Hill,
New York, pp. 7-24–7-25.
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Bernard.B.Berger (1982).Water and wastewater quality control and the public health.Anual
reviews Inc.
Gomez, A, Leschber, R. and L’hermite, (1986). Sampling problems for the chemical analysis of
sludge, soils and plants. Great Britain: Elsevier Applied science Publishers.
Davis, M. L. and D. A. Cornwell (2008) Introduction to Environmental Engineering, McGraw-

Hill, Borton, Massachusetts.
APPENDIX B
LOG BOOKS
OPERATION MANUAL
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The Treatment Processes of Sewage and at National Water and Sewerage Corporation (NWSC)

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The Treatment Processes of Sewage and at National Water and Sewerage Corporation (NWSC)

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NKUGWA MARK WILLIAM, 17/U/7029/CHE/PE

THE TREATMENT PROCESSES OF SEWAGE AND AT

AN INDUSTRIAL TRAINING REPORT

SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR

BASED AT LUBIGI SEWAGE TREATMENT PLANT

training Report entitled “THE TREATMENT PROCESSES OF SEWERAGE AND AT

NATIONAL WATER AND SEWAGE COPORATION”, in fulfillment of the requirements

the Department of Chemistry of Kyambogo University, is an authentic record of my own

at Lubigi sewage treatment plants.

Signature of Student ………………………

NKUGWA MARK WILLIAM

Bachelor of Science in Chemical and Process Engineering (Year. 2)

Kyambogo University, Uganda.

Mark William Registration Number – 17/U/7029/CHE/PE, and to the department of

Approved as to the style and content by:

Signature of Internship Manager

MR. GAVA JOB

QUALITY CONTROL OFFICER, LSTP

Signature & Stamp: …………………………………

Signature of University Supervisor

MR. KIIZA HILLARY

Kyambogo University (Faculty of Science)

Signature & Stamp: …………………………………

things involved in the engineering profession.

granting me the opportunity of internship program.

showed to me during my training at the sewerage treatment plant.

wellbeing at Lubigi plant.

already existing Bugolobi Sewage Treatment Plant.

flow rate of 33,000m3/day.

the plant where I spent most of my training time.

ON SITE FECAL SLUDGE ......................................................................................... 24

CHAPTER THREE ........................................................................................................ 56

3.1 THE LUBIGI LABORATORY .............................................................................. 58

Table 2: The NEMA Standards for Waste Water Discharge ........................................... 59

DETERMINATION OF BIOCHEMICAL OXYGEN DEMAND (BOD5) USING AZIDE

PLUMBING RODS ...................................................................................................... 87

UNBLOCKING SEWER PIPES .................................................................................. 88

COMMON CAUSES OF BLOCKAGE IN THE SEWER LINES .............................. 89

PRECAUTIONS TAKEN DURING DESILTING ...................................................... 90

CHAPTER FIVE ............................................................................................................ 92

LUBIGI AND BUGOLOBI SEWAGE TREATMENT PLANTS ............................... 92

Knowledge Acquired During My Training ................................................................... 92

Skills Acquired During My Training ............................................................................ 93

Challenges Faced During My Training ......................................................................... 94

CHAPTER SIX ............................................................................................................... 95

General Conclusion ....................................................................................................... 95

Recommendations to Kyambogo University ................................................................. 96

NEMA STANADARDS ................................................Error! Bookmark not defined.

BACKGROUND OF INDUSTRIAL TRAINING

I chose to do industrial training at NWSC for my second year, so as to develop a

comprehensive understanding and appreciation of Chemical Engineering and Environmental

engineering concepts and principles as an expanding discipline of a continuous learning process,

management authority (NEMA).

Purpose and objectives of industrial training attachment:

real world problems faced in the field.

 To be introduced to the more practical aspects of the engineering field.

and technology activities.

leaders in the scientific and technological world.