Borda Wedc Decentralised Wastewater Treatment Systems Dewats and Sanitation in Developing Countries 2009
Borda Wedc Decentralised Wastewater Treatment Systems Dewats and Sanitation in Developing Countries 2009
Borda Wedc Decentralised Wastewater Treatment Systems Dewats and Sanitation in Developing Countries 2009
Published by
BORDA
A Practical Guide
Editors: Andreas Ulrich, Stefan Reuter
and Bernd Gutterer
Please note that views expressed in this publication are not necessarily
those of WEDC, Loughborough University.
ISBN: 978 1 84380 128 3 Editors of the publication are:
© BORDA, 2009 • Andreas Ulrich (BORDA Director)
Designed and produced by Bremen Overseas Research • Stefan Reuter (BORDA Vice Director)
and Development Association (BORDA), Germany • Bernd Gutterer (PhD, International Consultant)
Phone: +49 (0) 421 137 18 Fax: +49 (0) 421 165 53 23 E-mail: office@borda.de Authors of the publication are:
• Bernd Gutterer (PhD): Chapters 1–7
Published by the Water, Engineering and Development Centre (WEDC), • Ludwig Sasse: Chapters 7–10, Sections 11.4–11.5
Loughborough University, UK • Thilo Panzerbieter Sections 11.1–11.3
Postal address: WEDC, The John Pickford Building, Loughborough University, (Section 11.3 in collaboration with Andreas Schmidt)
Leicestershire, LE11 3TU, UK Thorsten Reckerzügl has provided substantial documentation.
Phone: +44 (0) 15 09 22 28 85 Fax: +44 (0) 15 09 21 10 79 Editorial contributions: Mary Breen and Michael Smith
Email: wedc@lboro.ac.uk http://www.lboro.ac.uk/wedc
WEDC is one of the world’s leading education and research institutes for Acknowledgements
for developing knowledge and capacity in water and sanitation for low- and This publication is a collective effort. Since the early 1990s BORDA has
middle-income countries. Education and training programmes at postgraduate- collaborated with a multitude of individuals and institutions throughout Europe
level include Water and Waste Engineering and Water and Enviromental and Asia to develop the DEWATS approach. The first DEWATS Handbook was
Management. published by Ludwig Sasse in 1998. It served as an instruction manual focusing
WEDC research and consultancy is directed towards the study of aspects on the technical design. A wealth of experience in demand-oriented technology
of infrastructure and services (especially related to water and sanitation) in adaptation and dissemination has evolved since then, including public health and
low- and middle-income countries. community-based sanitation. This book presents the collaborative efforts made
by a wide range of professionals from local and central authorities, from private
BORDA was founded in 1977 in Bremen Germany as a non-profit professional businesses and international donors, NGOs, community-based organisations and
organisation with the goal of developing new methods of using renewable academia. Therefore, this publication could not have been realised without the
energy to alleviate poverty and, through the implementation of development pro- generous contribution of the many individuals and organisations who shared their
grammes, to improve the living conditions and social structures in disadvantaged experience and expertise. In particular the editors would like to express their
communities abroad. gratitude to following partner organisations and individuals:
• Indonesia: LPTP (Surakarta); BEST (Tangerang); BaliFokus (Denpasar)
Unlike other organisations, in the struggle against poverty BORDA focuses on • India: Consortium for DEWATS Dissemination Society (CDD, Bangalore)
the facilitation of basic needs services in the sectors of water, wastewater, solid and the associated partner network
waste and energy. To achieve this, partner structures, with the participation of all • China: Sustainable Development Strategy Institute (SDSI) at
stakeholders, are advised and assisted in the stablishment and organisation of Zhejiang University of Technology (ZUT), Hangzhou
innovative basic needs services (BNS); this occurs during all phases of planning • BORDA's Regional Programme Co-ordinators Frank Fladerer (BORDA –
and construction up to the stages of operation and maintenance. South-East Asia), Pedro Kraemer (BORDA – South-Asia) and Andreas Schmidt
(BORDA – Southern Africa)
• Prof. Chris Buckley (Pollution Research Group, University of KwaZulu-Natal,
South Africa) and Ludwig Sasse (retired, pioneer of BORDA's Biogas and
DEWATS solutions)
4 5
TABLE OF CONTENTS
6 7
6.5 Implementation phase 118 9.2.7 Planted soil filters 195
6.5.1 Task planning 118 9.2.7.1 Horizontal gravel filter 197
6.5.2 Quality management 120 9.2.7.2 Vertical sand filter 207
6.5.3 Construction 121 9.2.8 Ponds 211
6.5.4 Pre-commissioning test 123 9.2.8.1 Anaerobic ponds 212
6.5.5 Parallel training measures 123 9.2.8.2 Aerobic ponds 216
6.6 Operation phase 124 9.2.9 Hybrid and combined systems 221
6.6.1 Start operation 124 9.3 Non-DEWATS technologies 223
6.6.2 Operation & maintenance 126 9.3.1 UASB 223
6.6.3 Use of biogas 129 9.3.2 Trickling filter 225
6.6.4 Monitoring and evaluation 131 9.3.3 Aquatic-plant systems 228
8 9
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11 Project Components: sanitation and wastewater 12 System malfunction – symptoms, problems, solutions 336
treatment – technical options 282 12.1 Insufficient treatment of wastewater 336
11.1 Toilets 283 12.2 Reduced flow at the outlet of the facility 344
11.1.1 Common practices to be discouraged 284 12.3 Other problems and nuisances 349
11.1.2 Closed pit toilets 286
11.1.3 Composting toilets 289 13 List of abbreviations 350
11.1.4 Dry, urine-diversion toilets 290
11.1.5 Pour-flush toilets 292 14 Appendix 352
11.1.6 Community toilet blocks 296 14.1 Geometric formulas 352
11.2 Collection systems 297 14.2 Energy requirement and cost of pumping 352
11.2.1 Rainwater drains 297 14.3 Sedimentation and flotation 353
11.2.2 Conventional gravity sewerage 298 14.4 Flow in partly filled round pipes 354
11.2.3 Simplified gravity sewerage 299 14.5 Conversion factors of US-units 355
11.2.4 Vacuum sewerage 303
11.3 Sludge accumulation and treatment 306 15 Bibliography 356
11.3.1 Sludge removal 307
11.3.2 Sludge treatment 308
11.3.2.1 Small-scale application – drying and composting 309
11.3.2.2 Large-scale application – sludge and septage-treatment facility 313
11.4 Reuse of wastewater and sludge 318
11.4.1 Risks 318
11.4.2 Groundwater recharge 321
11.4.3 Fishponds 321
11.4.4 Irrigation 324
11.4.5 Reuse for process and domestic purposes 324
11.5 Biogas utilisation 325
11.5.1 Biogas 325
11.5.2 Scope of use 327
11.5.3 Gas collection and storage 328
11.5.4 Distribution of biogas 333
11.5.5 Gas appliances 334
10 11
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1 Introduction
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Water is a key feature of public concern worldwide. Inappropriate use and poor Based on the experiences and “good practice” of numerous programmes and
management of water resources have an increasingly negative effect on econo- projects, this book aims to present the most important features for successful
mic growth, on social welfare and on the world’s eco-systems. DEWATS dissemination:
• driving forces and decision parameters for innovative wastewater and
For a long time the need for efficient wastewater treatment was ignored by sanitation strategies.
many public authorities. As a result the performance of existing treatment • options for a comprehensive technology choice
technologies and the conditions of sanitation facilities are rather poor. At many • planning instruments for wastewater treatment and sanitation mapping
locations the sewage is just drained to surface or ground waters without • presentation of the DEWATS approach and good practices in DEWATS
adequate handling. • basic knowledge about the process of wastewater treatment
• the technical components of DEWATS
Recently, decision makers, planners, engineers and civil society stakeholders • design principles for DEWATS
have launched multiple initiatives to answer the question facing many developing • guidelines for programme development and implementation of DEWATS
countries: How to ensure a good performance and a high coverage of wastewa- based CBS programmes.
ter treatment under rather difficult conditions with financial constraints and limi-
ted human and institutional capacities? Since wastewater treatment and sanitation, with all its implications, is such a
complex subject, the content focuses on providing a basic knowledge that is
In the 1990s an international network of agencies and NGOs drew conclusions relevant for DEWATS dissemination. As a practical guideline it should support
about the deficiencies of existing infrastructure development and produced decision making, planning and implementation activities. For very specific que-
the so-called “DEWATS approach.” DEWATS is designed to be an element of stions, additional literature can be consulted. A selection of books and articles
comprehensive wastewater strategies: not only the technical requirements for can be found in the appendix.
the efficient treatment of wastewater at a given location, but the specific socio-
economic conditions are also taken into consideration.
The international discussion about the conservation of water resources and more
target-oriented poverty-alleviation strategies create a favourable environment for
new sanitation approaches and innovative wastewater treatment solutions.
In many countries a rapidly upcoming market for DEWATS and a demand for
efficient Community-Based Sanitation (CBS) can be observed.
12 13
2 Towards
ersten Ranges,comprehensive wastewater
Absatzformat Headline
and sanitation strategies
Kapitelfortsetzung, Farbe 50% HKS 42
1 Water stress occurs Water is the essential basis for all forms of life. Water is of utmost importance
when the demand for
for human health and dignity. Water is crucial for sustainable social and economic
water exceeds the
available amount development. However, world water resources are under threat. In the past 250
during a certain years the world has seen a tremendous increase both in population and econo-
period or when poor
mic activities. This development process has resulted in extensive social trans-
quality restricts its
use. Water stress formation and a rapidly increasing demand for natural resources. Urbanisation,
causes deterioration industrial development and the extension of agricultural production have a signi- Picture 2_2:
of fresh water ficant impact on the quantity and quality of water resources. Overexploitation of More than half of
resources in terms the world’s major
of quantity (aquifer
water bodies and deterioration of water quality are global trends.
rivers are seriously
over-exploitation, depleted and
dry rivers, etc.) Today one-third of the world’s population lives in countries suffering from mode- polluted
and quality
rate to high water stress.1 Since the mid-1990s, some 80 countries, representing
(eutrophication,
organic matter 40 per cent of the world’s population, have been suffering from serious water Although the threat to water resources is not only a phenomenon in developing
pollution, saline shortages in urban and rural areas – in a lot of cases, the result of the socio- countries, it is particularly the world’s poor that are most affected: worldwide,
intrusion, etc.).
economic development over the recent decades. 0.9 billion people still lack access to safe drinking water and 2.5 billion lack
Source: European
Environment Agency, access to adequate sanitation. While improvements are monitored on the drin-
EEA glossary, 2006 The increasing demand for freshwater sources and rapidly changing production king water side, the challenge on the sanitation side obviously is much bigger
and consumption patterns are directly linked with the pollution of ground and than it was thought to be. Estimates indicate that approximately half the 3 JMP-WHO/
Unicef 2008
surface waters. “More than half of the world’s major rivers are seriously depleted population of the developing world is exposed to polluted water resources,
and polluted, degrading and poisoning the surrounding ecosystems, threatening which increase disease incidence; most of these people live in Africa and Asia.3
2 World Commission
on Water 1997 the health and livelihoods of those who depend on them.2”
Picture 2_1:
Water stress (2000)
in regions around
megacities. This
map is based on
estimated water
withdrawals for
the year 2000, and
water availability
during the ‘climate
normal’ period
(1961–1990). Results
Picture 2_3:
shown in this map
Half the develo-
were calculated on
ping world are still
river basin scale.
without improved
Source:
withdrawal-to-availability ratio Percentage of population using improved sanitation sanitation;
WaterGAP2.1e
Source: JMP-WHO/
by CESR, Kassel, 0 – 0.2 0.2 – 0.4 more than 0.4
low water stress medium water stress severe water stress 91% – 100% 76% – 90% 50% – 75% Less than 50% Insufficient date UNICEF, 2008
Germany
14 15
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3 Ranges,– Absatzformat
DEWATS Headline of wastewater
Sustainable treatment
Kapitelfortsetzung,
at the local level Farbe 50% HKS 42
Private and public entities are faced with the following situations: 3.1 DEWATS – a modular system approach to ensure efficient
• national and regional development plans require the wastewater connection wastewater-treatment performance
of peri-, semi-urban and rural settlements to treatment facilities, which meet
discharge standards “Decentralised Wastewater Treatment Systems” (DEWATS) were developed by
• new housing and real estate developments do not get clearance an international network of organisations and experts. In this handbook, the term
without approved wastewater-treatment systems DEWATS may be applied in singular or plural form, refering to a single specific
• schools, hospitals, hotels and public facilities face public pressure, system, to the modular systems approach or the whole range of systems, as the
due to surface-water pollution case may be. The approach incorporates lessons learned from the limitations of
• small and medium enterprises unable to treat wastewaters adequately conventional centralised and decentralised wastewater-treatment systems,
are closed down by public authorities thereby assisting to meet the rapidly growing demand for on-site-wastewater
solutions. DEWATS are characterised by the following features:
Only a few of the households – well as public and private entities, that require • DEWATS encompass an approach, not just a technical hardware
wastewater treatment can be serviced by conventional sewage and wastewater- package, i.e. besides technical and engineering aspects, the specific
treatment systems. The rapidly growing demand can only be met with the assi- local economic and social situation is taken into consideration
stance of other technical solutions, which should ideally fulfil the following criteria: • DEWATS provide treatment for wastewater flows with close COD/BOD
• suitable for very diverse local conditions and versatile in application ratios from 1m³ to 1000m³ per day and unit
• provide reliable and efficient treatment of domestic and process wastewater • DEWATS can treat wastewaters from domestic or industrial sources. They
• require only short planning and implementation phases can provide primary, secondary and tertiary treatment for wastewaters from
• moderate investment costs sanitation facilities, housing colonies, public entities like hospitals, or from
• limited requirements for operation and maintenance businesses, especially those involved in food production and processing.
• DEWATS can be an integral part of comprehensive wastewater strategies.
It is evident that decentralised wastewater solutions, which fulfil these criteria, The systems should be perceived as being complementary to other
have to become an integral part of comprehensive wastewater strategies, centralised and decentralised wastewater-treatment options
complementing other approaches. • DEWATS can provide a renewable energy source. Depending on the technical
layout, biogas supplies energy for cooking, lighting or power generation
• DEWATS are based on a set of design and layout principles.
Reliability, longevity, tolerance towards inflow fluctuation, cost efficiency and,
most importantly, low control and maintenance requirements
32 33
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3 Ranges,– Absatzformat
DEWATS Headline of wastewater
Sustainable treatment
Kapitelfortsetzung,
at the local level Farbe 50% HKS 42
• DEWATS usually function without technical energy inputs. Independence from 3.2 DEWATS – a brief insight into technical configuration
outside energy sources and sophisticated technical equipment provides more
reliable operation and, thereby, fewer fluctuations in effluent quality. Pumping Typical DEWATS combine the following technical treatment steps in a modular
may be necessary for water lifting manner:
• DEWATS are based on a modular, technical configuration concept. Appropriate • primary treatment – in sedimentation ponds, settlers, septic tanks or bio-
combinations of treatment modules can be selected, depending on the digester
required treatment efficiency, costs, land availability, etc. • secondary treatment – in anaerobic baffled reactors, anaerobic filters
• DEWATS units are quality products. Though they can be constructed form or anaerobic and facultative pond systems
locally available materials and can be implemented by the local workforce, • secondary aerobic/facultative treatment – in horizontal gravel filters
high quality standards in planning and construction have to be met. For sound • post-treatment – in aerobic polishing ponds
DEWATS design a good comprehension of the process of wastewater-treat-
ment is essential fully mixed digester
sedimentation pond
• DEWATS require few operation and maintenance skills. While most operational
tasks can be carried out by the users, some maintenance services might require Sedimentation septic tank
a local service provider. In some cases, both operation and maintenance can
be delivered by a service provider
• DEWATS can reduce pollution load to fit legal requirements. Like all other
wastewater-treatment systems, generated solid waste (sludge) must be
handled, treated and disposed of in accordance with hygiene and
anaerobic baffled reactor anaerobic filter
environmental standards Anaerobic
digestion
• DEWATS consider the socio-economic enviroment of a given location.
Neglecting these conditions will result in the failure of the technology
Post-treatment
Picture 3_1:
DEWATS confi-
guration scheme
34 35
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3 Ranges,– Absatzformat
DEWATS Headline of wastewater
Sustainable treatment
Kapitelfortsetzung,
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The selection of appropriate technical configuration depends on the: 3.3 DEWATS – good practice examples/applications
• volume of wastewater
• quality of wastewater In recent years, DEWATS have been implemented at many different locations
• local temperature by various institutions. Gathered experience shows that each location demands
• underground conditions its own approach. Below, a number of “good practice examples/applications” of
• land availability DEWATS are presented. These are not meant to be exhaustive; they highlight
• costs different aspects of DEWATS implementation.
• legal effluent requirements
• cultural acceptance and social conditions
• final handling of the effluent (discharge or reuse) 3.3.1 DEWATS/CBS – Community-Based Sanitation Programme in Alam Jaya,
Tangerang, Java, Indonesia
DEWATS rely on the same treatment processes as conventional treatment
systems: Alam Jaya is a slum in the middle of an industrial area in Jakarta. Most residents
work in the nearby factories. Due to a high migration rate, social structures are
weak. The level of infrastructure development is low. Housing is poor with
Sedimentation
insufficient water supply.
removal of easily begin of anaerobic fermentation removal of
settleable solids of bottom sludge possible sludge
Sanitation facilities in the settlement are totally insufficient in terms of quality and
quantity. Wastewater is discharged into the environment without any treatment,
posing a permanent threat to human health.
Anaerobic digestion
settling of
mineralisation of mineralised
removal of easily suspended or particles, removal of
degradable organic dissolved organic collection and sludge
solids compounds, ventilation of
biogas production biogas
Post-treatment
Picture 3_2: removal of settling of finest retaining of removal of
Typical succession of suspended digested suspended living and sludge
solids and active solids, removal
treatment processes dead algae
bacteria mass of algae
within DEWATS Picture 3_3:
Housing in
Alam Jaya
36 37
4 Mainstreaming
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Ranges, Absatzformat – strategic planning
and implementationFarbe
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50% HKSinfrastructure
42
Nowadays public authorities are challenged to provide sanitation and wastewater- • Community Sanitation Centres (CSCs) are appropriate in areas where financial
treatment services on a large scale. Mainstreaming decentralised wastewater- resources are very limited and most residents live in rented rooms or huts,
treatment solutions is one of the key elements for sustainable infrastructure leaving no space for in-house sanitation. The centre is established at a central
development. location within the settlement and offers different services as requested by
the community. Services can include water points, toilets, bathrooms and
4.1 Strategic planning of sanitation programmes laundry areas. Each CSC is connected to a DEWATS, usually located under-
ground below the Centre. CSCs are usually guarded and operated by paid
Comprehensive wastewater strategies may consider different options for the staff.
treatment and discharge of wastewater:
• treatment in a centralised plant, which is connected to a combined or The experience gathered in multiple efforts to create efficient and cost-effective
separate sewer system sanitation and wastewater-treatment strategies clearly shows that, without com-
• treatment in several medium-sized treatment plants, which are connected prehensive legal frameworks and efficient law enforcement, without institutional
to a combined or separate sewer system capacities within public and private services, without relevant financial resources,
• primary and secondary treatment in decentralised plants, which are connected and without awareness at the household or enterprise level, the hoped-for health
to a sewer line, leading to a common plant for final treatment and environmental standards cannot be achieved.
• completely decentralised treatment with final discharge, reuse, or connection
to communal sewerage
• controlled discharge without treatment (ground percolation, surface- Shared Septic Tank
water dilution)
The final decision, on which treatment option is most suitable for a given water
pollution problem, should be based on a number of different considerations,
which are discussed in greater depth later in this book. Different options may be
considered for residential areas: Simplified Community
Sewerage
• Simplified community-sewerage systems with household-based sanitation
systems are preferred in areas where the residents have sufficient financial re-
sources and households have sufficient space. On average, 20 to 100 families
are connected to one system. The system consists of toilets and bathrooms
within each household. The wastewater is directed to a DEWATS by shallow,
narrow sewer lines. Community
Sanitation Centre Picture 4_1:
• Shared septic tanks present a simpler version of the household-based sanitation Different treatment
system with off-site treatment. A smaller cluster of about 10 to 50 households options within a
is connected to a community septic tank. The system treats toilet and bathroom CBS programme
effluent from each household. Wastewater is channeld to the septic tank by
shallow small-diameter sewer lines. The wastewater cannot be discharged
directly to the aquatic environment, due to the low effluent quality of the septic
tank. The system is, usually only applied, therefore where soil conditions allow
the direct infiltration of the effluent without any harm to the groundwater.
58 59
5 CBS
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The profile of each CBS (Community-Based Sanitation) programme has to be 5.2 Responding to basic needs – active involvement of beneficiaries
country, site and situation specific. Nevertheless, in this chapter we will intro- and residents
duce the core elements of successful CBS implementation. The outlined pro-
gramme-implementation steps are based on the project experience of “good CBS programmes respond to the needs of residents in a given area. In most
practice” examples and guide the reader through his or her own programme and cases, the programmes target residents of poorer areas to provide them with
project development. improved in-house toilets or with additional sanitation services, such as toilets,
showers or washrooms in Community Sanitation Centres.
The institutional background has a significant impact on programme initiation.
While organisations experienced in infrastructural development in poor areas The active involvement of communities in the planning and implementation
might be able to develop institutional capacities fairly rapidly, other organisations process is crucial to the success of a sanitation programme because the
might depend on the collaboration with other institutional players. In such a case, residents:
the greatest challenge will be to streamline the process and contributions of all • will use the sanitation facility – the facilities must fit their needs and practices
partners. • have to contribute significantly to the system – financially or in kind
The goal of any sanitation programme should be long-term sustainability with ma- • may have an important role in the operation and maintenance of the sanitation
ximum positive impact. From the preliminary needs assessment in the very early and wastewater-treatment facilities
stage of a programme, up to the disposal and treatment of sludge, a multitude of
tasks have to be completed. The efficient setting-up and implementation of such
a programme requires early identification of the different necessary tasks and
who is responsible for carrying them out.
92 93
6 CBS
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Absatzformat procedure for implementation
Headline
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The success of a CBS programme depends significantly on implementing the The key programme tasks should be identified at an early stage. With these in
steps in the right order. The organisation or the group of initiating bodies, taking mind, the steps of implementation should be defined to enable smooth operation.
the lead in launching a project should be aware of the complexity and usefulness Key tasks include:
of a comprehensive approach. Success depends on the co-ordinated implemen- • overall programme management, including process monitoring
tation of a multitude of tasks and the integration of all stakeholders into the • developing a feasibility study
process. • community preparation, including health and hygiene awareness-raising
campaigns
6.1 First planning activities • construction
• operation and maintenance
• monitoring sanitation and environmental standards
An initial workshop helps to establish a common foundation between key stake- • final sludge management
holders. Members from the leading agency (LA), NGOs – or representatives from
future beneficiary groups – should be invited to form a core team. The following
issues should be addressed:
• targets of the envisaged programme
Sludge Feasibility Overall
• assessment of the current situation in the relevant area, regarding sanitation
management Study programme
and wastewater
management
• key existing problems in sanitation, wastewater and environmental pollution
• existing experiences with relevant projects
• awareness building concerning the tasks to be fulfilled throughout the Community
Maintenance
programme preparation
• identification of relevant stakeholders to involve in the project CBS
programme
Health awareness
Operation
campaigns
100 101
7 DEWATS
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Absatzformat design principles
Kapitelfortsetzung, Farbe 50% HKS 42
DEWATS can be constructed and operated successfully almost anywhere because Treatment consists of a wide range of procedures that relieve the negative effect
they rely on natural wastewater-treatment processes, without special equipment, of the pollutants, by removing or changing harmful substances into a harmless
chemicals, or energy supply. This chapter explains the treatment processes and or less-harmful state. DEWATS treatment depends on natural bio-chemical and
how they apply to different DEWATS components, in order to guide the reader in physical processes including:
appropriate technical selection and design. • degradation of organic matter until the point at which chemical or biological
reactions stop (stabilisation)
The chapter is sub-divided into the following sections: • physical separation and removal of solids from liquids
• basics of wastewater treatment • removal or transformation of toxic or otherwise-dangerous substances (for
• parameters for wastewater-treatment design example, heavy metals or phosphorous), which are likely to distort sustainable
• DEWATS – technical components biological cycles, even after stabilisation of the organic matter
• dimensioning of DEWATS
Most heavy metals are toxic or carcinogenic. They harm the aquatic life of the
receiving water and affect humans through the food chain.
132 133
8 Treatment
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Absatzformat
Kapitelfortsetzung, Farbe 50% HKS 42
DEWATS make use of the natural biological- and physical-treatment processes To protect the “weaker” (slower) micro-organisms, it is advisable to artificially
discussed above to reduce and remove pollutants from wastewater. External separate microbial populations in phases by providing each with its own favourable
energy supply, dosing of chemicals and movable parts are avoided to minimise environment. The characteristics of the wastewater and the desired treatment
both possible flaws in operation and maintenance. results must be identified, before the dimensions of the treatment vessels for the
different phases can be designed.
As the various natural-treatment processes require different boundary conditions
to function efficiently, DEWATS are comprised of a series of treatment units, each In the case of DEWATS, it is often easiest to provide longer retention times, so
providing an ideal environment for the removal of certain groups of pollutants. that the “slow” micro-organisms find their food after the “fast” ones have satis-
Stability of the treatment system is ensured, as each treatment step only remo- fied their demand. This process is easier to manage and, in the case of smaller
ves the “easy part” of the pollution load, sending the leftovers to the following plants, it is cheaper to design certain units this way. In other units, like the
step. baffled reactor, the efficiency of the treatment in subsequent chambers justifies
its higher cost; processes, which require sequencing batch operation involving
technical equipment and process control, are thereby avoided.
Sedimentation Anaerobic digestion Aerobic decomposition Post-sedimentation
removal of easily removal of easily removal of more difficult removal of digested solids Phase separation becomes unavoidable if different phases require either anaerobic
settleable solids degradeable organic solids degradable solids and active bacteria mass
or aerobic conditions. In the case of nitrogen removal, longer retention times
alone do not provide adequate treatment conditions because the nitrifying phase
Picture 8_1: needs an aerobic environment, while denitrification requires an anoxic environ-
Several steps are The term “phase separation” has a double meaning. On the one hand it is used ment. Anoxic means that nitrate (NO3) oxygen is available, but free oxygen is
required for full
treatment for the separation of gas, liquid and solids in anaerobic reactors; on the other hand not. Anaerobic means that neither free oxygen nor nitrate-oxygen is available.
it is used to describe the technical separation of different stages of the treatment Nevertheless, the aerobic phase can only lead to nitrification if the retention
process, either in different locations or in sequences of time intervals. The latter time is long enough for the “slow” nitrifying bacterium to act, as compared to
kind of phase separation becomes necessary when suitable nutrients cannot be the “fast” carbon oxidisers.
provided simultaneously to micro-organisms, which have differing growth rates
and prefer different feeds. Some micro-organisms grow at a slower rate than In the case of the addition of plant material to an anaerobic digester, pre-
others. As not all the enzymes required for degradation are initially found in all composting of plant residues before anaerobic digestion is another example of
substrates, the micro-organisms take time to produce adequate amounts of the simple phase separation. As lignin cannot be digested anaerobically (it requires
missing enzymes. As disscussed previously, enzymes act as the “key which peroxidase enzymes usually produced by fungi), it is decomposed aerobically.
opens the lock of the food box for micro-organisms”. Afterwards, anaerobic micro-organisms can reach the inner parts of the plant
material in the digester.
Substrates, for which enzymes are immediately available, can be readily degraded;
substrates, which first require the microbial production of specific enzymes, are
degraded much more slowly. In an environment which hosts substances that are
both easy and difficult to degrade, the microbial population responsible for easy
degradation tends to predominate.
150 151
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Treatment must remove or reduce pollutants within the wastewater sufficiently Volume
to prevent harm to the environment and humans. Before deciding, what kind of
treatment is necessary and the dimensions of each unit, planners and designers The daily volume or the flow rate of wastewater determines the required size of
must identify the following: the building structure – on which the feasibility or suitability of the treatment
• quality and quantity of the raw wastewater technology is decided. It is essential not to underestimate the peak flow.
• local conditions and their influence on treatment processes
• standards to be fulfilled in final use or discharge Surprisingly, the determination of flow rate is often rather complicated, due to the
fact that flow rates change throughout the day or with the season, and that volumes
Laboratory analysis is used to determine the quantity and quality of the pollution have to be measured in “full size”. It is not possible to take a representative
load, the feasibility of treatment, the environmental impact under local conditions sample. In the case of DEWATS, it is often easier and more practical to measure
– and whether a particular wastewater is suitable for biogas production. Some or enquire about the water consumption (per capita consumption of water from
parameters can even be seen and understood by experienced observation. taps and/or wells) rather than try to measure the wastewater production. The flow
of wastewater is not directly equal to water consumption, since not all the water
As the quality of wastewater changes according to the time of day and from that is consumed ends up in the drain (for example, water for gardening), and
season to season, the analysis of data is never absolute. It is far more important because wastewater might be a mix of used water and stormwater. If possible,
that the designer understands the significance of each parameter and its “nor- stormwater should be segregated from the treatment system, especially if it
mal” range than to know the exact figures. Ordinarily, an accuracy of ±10% is is likely to carry substantial amounts of silt or rubbish. Rainwater drains should
more than sufficient. never be connected to the treatment plant, however, ponds and planted gravel
filters will be exposed to rain (and evaporation). The volume of water in itself is
This chapter gives a concise overview, introducing: normally not a problem as hydraulic loading rates are not likely to be doubled and
• control parameters, essential for characterising wastewater and a certain flushing effect might even be advantageous. Soil clogging (silting) could
• dimensioning parameters, utilised in DEWATS design become a problem, however, if stormwater reaches the planted gravel filter after
eroding the surrounding area.
Textbooks on the analysis of wastewater should be consulted for laboratory
techniques or comprehensive handbooks on wastewater, such as Metcalf and For high-rate reactors, like anaerobic filters, anaerobic baffled reactors and UASB,
Eddy’s “Wastewater Engineering”. the flow rate could be a crucial design parameter. If exact flow data are not
available, the hours of the day, which account for most of the flow, should be
determined and used. Hydraulic retention-time calculations should take into
account the flow rate fluctuation.
The flow rate is calculated by collecting and measuring volumes per time period.
Possible measurement techniques include monitoring the rise in level of a canal
that is closed for a period of time, or the number of buckets filled during a given
period. Another good indicator of the actual flow rate is the time it takes, during
initial filling for the first tank of a treatment plant to overflow.
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This chapter introduces the technical-treatment components of DEWATS, which Septic tanks are the most common form of treatment. The robust system provides
correspond to the DEWATS criteria defined in chapter 7. a combination of mechanical treatment through sedimentation and biological
degradation of settled organic solids. Septic tanks are used for wastewater with
After a brief overview and comparison of the different technologies, detailed a high percentage of settleable solids, typically effluent from domestic sources.
sections on each component explain the specifics of design, applied-treatment
processes, and start-up considerations as well as operation and maintenance Fully mixed digesters provide anaerobic treatment of wastewater with higher
procedures. organic load, while serving as a settler in a combined system. In the process,
biogas is produced as a useful by-product.
9.1 Overview of DEWATS components Imhoff tanks are slightly more complicated to construct than septic tanks,
but provide a fresher effluent when de-sludged frequently. Imhoff tanks are
DEWATS is based on four treatment systems: preferred when post-treatment takes place near residential houses, in open
• sedimentation and primary treatment in sedimentation ponds, septic tanks, ponds or constructed wetlands of vertical flow type.
fully mixed digesters or Imhoff tanks
• secondary anaerobic treatment in baffled reactors (baffled septic tanks) or Anaerobic baffled reactors or baffled septic tanks function as multi-chamber septic
fixed-bed filters tanks. They increase biological degradation by forcing the wastewater through
• secondary and tertiary aerobic/anaerobic treatment in constructed wetlands active sludge beneath chamber-separating baffles. All baffled reactors are suitable
(subsurface flow filters) for all kinds of wastewater, they are most appropriate for wastewater with a high
• secondary and tertiary aerobic/anaerobic treatment in ponds percentage of non-settleable suspended solids and narrow COD/BOD ratio.
Components are combined in accordance with the wastewater influent and the Anaerobic filters combine mechanical solids-removal with digestion of dissolved
required effluent quality. Hybrid systems or a combination of secondary on-site organics. By providing filter surfaces for biological activity, increased contact
treatment and tertiary co-operative treatment is also possible. between new wastewater and active micro-organisms results in effective
digestion. Anaerobic filters are used for wastewater with a low percentage
The following treatment components are discussed in further detail in the ensuing of suspended solids (for example, after primary treatment in septic tanks), and
chapters: narrow COD/BOD ratio. Upstream Anaerobic Sludge Blanket (UASB) reactors
Grease traps and grit chambers are beneficial for wastewater from canteens and utilise a floating sludge blanket as a biologically active filter medium.
certain industries. Short retention times prevent the settling of biodegradable solids.
Grit and grease must be removed frequently.
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Trickling filters treat wastewater aerobically by letting it trickle over biologically Most treatment processes applied in conventional, large-scale treatment plants
active filter surfaces. do not meet the DEWATS criteria. The activated-sludge process, the fluidised-bed
reactor, aerated or chemical flocculation and all kinds of controlled re-circulation of
Horizontal gravel filters are sub-surface, flow constructed wetlands, which wastewater fall within this category. Regular or continuous re-circulation might be
provide effective, facultative treatment and filtration, while allowing for appealing acceptable if the pumps that are used cannot be switched off because they also
landscaping. Constructed wetlands are used for wastewater with a low percen- act as transportation pumps.
tage of suspended solids and COD concentrations below 500mg/l.
Pond systems are the ideal form of DEWATS treatment – if the required space is
available. Anaerobic ponds are deep and highly loaded with organics. Depending
on the retention time, digestion of sludge only or the complete wastewater is
possible. Facultative and anaerobic ponds may be charged with strong waste-
water, however, bad odour cannot be avoided reliably with high loading rates.
Aerobic ponds are large and shallow – they provide oxygen via the pond surface
for aerobic treatment. Wastewater for treatment in aerobic ponds should have a
BOD5 content below 300mg/l. Pond systems can be combined with certain
types of vegetation, creating aquatic plant systems with additional benefits.
Special provisions are usually required for the treatment of industrial wastewater
before standardised DEWATS designs can be applied. These may include open
settlers for the daily removal of fruit waste from canning factories, buffer tanks
for mixing varying flows from milk-processing plants, or grease traps or neutra-
lisation pits to balance the pH of the influent. In these cases, standard DEWATS
components are applicable only after such pre-treatment steps have been taken.
Picture 9_1:
Treatment systems
considered to be
suitable for decen-
tralised dissemi-
nation
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If the planning engineer knows his or her craft and recognises his or her limita- Computerised calculations can be very helpful, particularly if the formulas and the
tions, designing DEWATS is relatively simple. Treatment-system performance input data are correct. Flawed assumptions or wrong data, on the other hand,
cannot be precisely predicted and, therefore, calculating of dimensions should will definitely result in worthless results. Nevertheless, assuming the input data
not involve ambitious procedures; in the case of small- and medium-scale is correct, spreadsheets provide a quick impression of the plant’s space require-
DEWATS, a slightly oversized plant volume adds to operational safety. ment and what treatment performance can be expected. Ready-to-use computer
spreadsheets are especially helpful to those who do not design DEWATS on a
Based on local conditions, needs and preferences, plants of varying sizes can daily basis and would otherwise need to recollect the entire theory for sizing a
be chosen as standard designs. On-site adaptations can then be made by less- plant before starting to design.
qualified site supervisors or technicians.
Please bear in mind that DEWATS provides a set of approaches. The equations
In the case of specific demands, calculations and design must be carried out used in the technical spreadsheets do rely on certain assumptions. Because of
individually; the structural details of the standardised plants can be integrated. the very different parameters that are relevant for the performances of a plan
In this chapter we introduce a simplified, quasi-standardised method of calculating (temperature, materials to be used, composition of the wastewater etc.) there is
dimensions using spreadsheets. not a “right way” to calculate dimensions. It is the experience and understanding
of the planner that is crucial to create the designs most appropriate to local condi-
Co-operative plant systems that require interconnecting sewerage must be de- tions – i. e. the wastewater problem.
signed individually by an experienced engineer, who is able to place plants and
sewers according to contours and other site requirements.
10.1.2 Risks of using simplified formulas
10.1 Technical spreadsheets – background The formulas applied in the spreadsheets have been developed by practitioners,
who are not overly concerned with theoretical knowledge. But the formulas are
10.1.1 Usefulness of computer calculation based on scientific findings, which have been simplified in the light of of practical
experience.
The purpose of this chapter is to provide the engineer with tools to produce his or
her own spreadsheets for sizing DEWATS in any computer programme that he or Even if the formulas were to be 100% correct, the results would not be 100%
she is familiar with. The exercise of producing one’s own tables will compel engi- accurate, as input data is not fully reliable. But the accuracy of the formulas is
neers to deepen their understanding of design. likely to be greater than the accuracy of wastewater sampling and analysis. There
are many unknown factors influencing treatment efficiency and “scientific” hand-
The curves that have been used as the basis for calculation in the formulas books provide a possible range of results. But this book, although “scientifically”
applied in the computer spreadsheets may also be of interest to those who do based, is written for people who have to build a real plant out of real building
not use a computer (these are found in this chapter). As these curves visualise materials. The supervisor cannot tell the mason to make a concrete tank “about
the most important relationships between various parameters, they will enhance 4.90m to 5.60m long”; he or she must say: “The length should be 5.35m”. The
understanding of the factors that influence the treatment process. It should be following spreadsheets were designed in this spirit. Anyone who already uses
noticed that the graphs have been developed on the basis of mixed information; more variable methods of calculation and who is not the target reader of this
the methods of calculation, therefore, do not always follow the same logic. book is free to modify the formulas and curves according to his or her experience
and ability (the authors welcome any information that would help to improve the
spreadsheets).
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As the formulas represent simplifications of complex natural processes, there 10.1.3 About the spreadsheets
is a certain risk that they do not reflect reality adequately. However, the risk of
changes in the assumed reality is even greater; for example, expanding a factory The spreadsheets presented in this handbook are in Microsoft EXCEL; other
without enlarging the treatment system is obviously more significant than an suitable programmes may also be used.
assumed BOD of 350mg/l, when in reality it is only 300mg/l.
There might be differences in the syntax of formulas, for example 3² (3 to the
Listed below are some examples of incorrect assumptions and their consequences: power of 2) may be written as =POWER(3;2) or =3^2, square root of 9 could
• underestimating sludge accumulation in septic tanks, sedimentation ponds, be =SQRT(9) or =9^1/2, cubic root of 27 would be =power(27;1/3) or =27^1/3.
Imhoff tanks and anaerobic reactors results in shorter desludging intervals Some programmes may accept only one of the alternatives.
• in the case of anaerobic reactors, severe under-sizing could lead to a collapse
of the process, while over-sizing may require longer maturation time at the The spreadsheets are based on data which is normally available to the planning
beginning engineer within the context of DEWATS. For example, while the measurement
• incorrect treatment performance of primary or secondary treatment steps of BOD5 and COD may be possible at the beginning of planning, it is unlikely that
could be the cause of over- or undersized post-treatment facilities. This may the BOD5 will be regularly controlled later on. Therefore, calculations are based on
result in unnecessarily high investment costs or having to enlarge the post- COD or the results of BOD-based formulas have been set in relation to COD, and
treatment facilities vice versa. In the following, the term BOD stands for BOD5.
• undersized anaerobic ponds will develop odour, while slightly oversized ponds
may not develop sufficient scum, also resulting in smells The formulas applied in the spreadsheets are based on curves from scientific
• undersized aerobic ponds can develop an odour; there is no harm in oversizing publications, handbooks and the experience of BORDA and its partners. The
aerobic ponds formulas, therefore, define typical trends. For example, it is well-known that the
• the biggest risk lies in filter media clogging in both anaerobic tanks and removal efficiency of an anaerobic reactor increases when the COD/BOD ratio is
constructed wetlands. However, the risk is more likely to come from inferior narrow. Such curves have been simplified into a chain of straight lines to allow
filter material, faulty structural details or incorrect wastewater data than from the reader to easily understand the formulas – and to adjust their values to local
incorrect sizing conditions if necessary. Although the amount of data on which some of these
curves are based is sometimes too insignificant to be statisticaly relevant, the
In general, moderate oversizing reduces the risk of unstable processes and formulas have been applied successfully and adjusted on the basis of practical
inferior treatment results. experience.
The formulas are simple. Besides basic arithmetical operations, they use only one
logical function, namely the “IF”-function. For example:
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Kapitelfortsetzung, – technical
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The other components of DEWATS and DEWATS/CBS systems along the 11.1 Toilets
sanitation chain before and after the wastewater treatment are:
• toilets When communities use hygiene and sanitation methods that fit their real needs
• collection systems and abilities, they will enjoy better health. In most cases, the toilet component is
• reuse and disposal systems, including sludge treatment the users’ prime concern. There are many reasons why users might prefer one
and biogas applications sanitation option over another, beside, health, better water supplies or improved
• construction management hygiene:
• management of operation & maintenance • Privacy – the need for privacy makes it important for a toilet to have a good
• health and hygiene behaviour shelter. Providing a door or enclosed entrance, or constructing it away from
busy locations, makes the toilet nicer to use
Community-Based Sanitation System • Safety – a poorly constructed toilet can be dangerous to use. If it is far from
To improve health and enviroment of communities the home, women may be in danger of sexual violence. A toilet must be well-
built and in a safe location
• Comfort – people prefer to use a toilet with a comfortable place to sit or
Hygiene behaviour squat, and a shelter large enough to stand up and move around in.
Options Children, the elderly or people with disabilities have special needs to
components
O&M To raise awareness and sustain permit comfortable use
Options
management hygienic behaviour • Cleanliness – no one wants to use a dirty and smelly toilet. Toilet areas should
To maintain the sanitation services operational Construction be well-lit and ventilated. Easy-to-clean surfaces and cleary defined of cleaning
Options
management responsibilities help to ensure that toilets are well-kept
Disposal / reuse To construct the required infrastructure • Respect – a well-kept toilet brings status and respect to its owner; this may
Options
components
be an important reason for people to spend money and effort to build one
To utilise re-use potential and discharge Treatment
Options
cleansed wastewater components
Picture 11_1
To cleanse the wastewater
The following section describes a selection of possible toilets – from common,
Community-Based Collection
Options hazardous models to recommended options. No one toilet design is right for
Sanitation System: component
technical options Toilet every community or household. It is important, therefore, to understand the
To carry the wastewater away Options
along the sanitation components benefits and risks of each and to adapt designs to suit local conditions and
chain To get the wastewater out of the home cultural preferences.
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Open defecation Overhung latrines are usually built from bamboo or wood and sited above the
surface of water bodies (such as rivers, ponds or lakes). Excreta fall directly into
The lacking of sanitation facilities forces large parts of the world’s population to the water, where they are decomposed. Usually it is a public facility, which serves
defecate openly. Depending on the location, refuge is sought in the forest, jungle, an entire or part of a community. This type of latrine pollutes the receiving water
lakes, rivers or the ocean. Apart from lacking privacy and the obvious associated body, which can no longer be used as a fresh-water source (exceptions may
hygienic-health risks, open defecation places humans in a vulnerable situation. include very rural settings with large or fast-moving water bodies). Furthermore,
Women and children can easily become targets of sexual abuse or violence. In the system is usually inconvenient, as it is located away from settlements.
many cases, parents also worry about the safety of their children, because of The exposed location affords users with little privacy.
poisonous snakes or other potential dangers in the bush or jungle.
Picture 11_4:
Overhang latrine
284 285
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ersten Ranges,malfunction – Headline
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symptoms, problems,
Kapitelfortsetzung, solutions
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13 List of abbreviations
350 351
14 Appendix
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Geometric formulas The performance of a domestic-wastewater settler is sufficient when the effluent
rectangle A=axb contains less than 0.2ml/l settleable sludge after a 2h jar test.
rectangular prism A = 2x (a x b+a x c+b x c) V=axbxc
trapezium A= a+c x h The general formula for calculating the surface area for floatation and sedimentation tanks is:
2
trapeziform prism V = h x h (a x b + c x d + a x b x c x d)
3 Water surface [m²] = water volume [m³/h] /
circle A = π x r² C=2xπxr slowest settling (floatation) velocity [m/h].
cylinder A (mantle) = 2 x π x r x h V = π x r² x h
Settling and floatation velocity can be calculated by observing the settling process
sphere (ball) A = 4 x π x r² V = 4 x π x r³
3 in a glass cylinder. The formula is:
spherical segment A=2xπxrxh V = π x h² x (r- h)
3
cone A (mantle) = π x r x s V = π x r² x h Settling (floatation) velocity [m/h] =
3 height of cylinder [m] / settling (floatation) time [h]
law of pythagoras a² + b² = c² sides of 90° triangle: 3 / 4 / 5
tangent a/b tan 45° = 1 Flocculent sludge has a settling velocity between 0.5 and 3 m/h.
tan 30° = 0.577
The velocity in a sand trap should not exceed 0.3 m/s [1000 m/h].
Table 45: The minimum cross section area is then:
tan 60° = 1.732
Geometric formulas
Area [m²] = flow [m³/s] / 0.3 [m/s], or
Area [m²] = flow [m³/h] / 1000 [m/h]
352 353
15 Bibliography
ersten Ranges, Absatzformat Headline
Kapitelfortsetzung, Farbe 50% HKS 42
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366 367