borda dewats handbook

8/6/2019 BORDA Dewats Handbook

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Decentralised Wastewater Treatment

in Developing Countries

DEWATS

Ludwig Sasse1998

BORDA


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Decentralised Wastewater Treatment

in Developing Countries

DEWATS

Ludwig Sasse1998

Bremen Overseas Research and Development AssociationBremer Arbeitsgemeinschaft fr berseeforschung und EntwicklungAssociation Brmoise de Recherche et de Dveloppement dOutre MerIndustriestrasse 20, D-28199 Bremen

BORDA


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The Author:

Ludwig Sasse, civil engineer, responsible for biogas and wastewater projects of BORDAsince 1980, editor of the BORDA BIOGAS FORUM, wrote several books and articles on

biogas and wastewater technology and dissemination.

This publication of BORDA was prepared with the financial assistance of

The European Commission, Directorate - General IB/D4, Environment and

Tropical Forest Sector, Rue de la Loi 200, B - 1049 Bruxelles, Belgium

andThe Free Hanseatic City of Bremen, Senator of Ports, Transport andForeign Trade, State Office for Development Cooperation, Martini Str. 24,D - 28195 Bremen, Germany

The views expressed in this publication are those of the author and do not represent the

official views neither of the European Commission nor the State Government of Bremen

Printed in Delhi 1998


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CONTENTS

1 FOREWORD

2 DEWATS: PROPERTIES,

PERFORMANCE AND SCOPE

2.1 Properties of DEWATS

2.2 Performance

2.3 Scope

2.4 Implementation

3 DISSEMINATION

3.1 The Need for Active

Dissemination of DEWATS

3.2 Preconditions for

dissemination

3.3 The Social Aspect

3.4 The Economic Aspect

3.5 The Technical Aspect

3.6 The Legal Aspect

3.7 Dissemination Strategy

4 ECONOMICS

4.1 Economy of

Wastewater Treatment

4.2 Treatment Alternatives

4.3 Parameters for Economic

Calculation

5 PROCESS OF WASTEWATER

TREATMENT

5.1 Definition

5.2 Basics of Biological

Treatment

5.3 Aerobic - Anaerobic

5.4 Phase Separation

5.5 Separation of Solids

5.6 Elimination of Nitrogen

5.7 Elimination of Phosphorus

5.8 Elimination of Toxic

Substances

5.9 Removal of Pathogens

6 ECOLOGY AND SELF PURIFICATION

EFFECT

6.1 Surface Water

6.2 Groundwater

6.3 Soil

7 CONTROL PARAMETERS

7.1 Volume7.2 Solids

7.3 Fat, Grease and Oil

7.4 Turbidity, Colour and Odour

7.5 COD and BOD

7.6 Nitrogen

7.7 Phosphorus

7.8 Temperature and pH

7.9 Volatile Fatty Acids

7.10 Dissolved Oxygen

7.11 Pathogens

8 DIMENSIONING PARAMETERS

8.1 Hydraulic Load

8.2 Organic Load

8.3 Sludge Volume


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9 TECHNOLOGY

9.1 Grease Trap and Grit

Chamber

9.2 Septic Tank

9.3 Imhoff Tank

9.4 Anaerobic Filter

9.5 UASB

9.6 Baffled Septic Tank

9.7 Fully Mixed Digester

9.8 Trickling Filter

9.9 Constructed Wetlands

9.10 The Horizontal Gravel

Filter

9.11 Vertical Sand Filter

9.12 Ponds

9.13 Hybrid and Combined

Systems

9.14 Unsuitable Technologies

10 SLUDGE DISPOSAL10.1 Desludging

10.2 Sludge Drying

10.3 Composting

11 REUSE OF WASTEWATER AND SLUDGE

11.1 Risks

11.2 Groundwater Recharge

11.3 Fishponds

11.4 Irrigation

11.5 Reuse for Process and

Domestic Purposes

12 BIOGAS UTILISATION

12.1 Biogas

12.2 Scope of Use

12.3 Gas Collection and Storage

12.4 Distribution of Biogas

12.5 Gas Appliances

13 COMPUTER SPREAD SHEETS

13.1 Technical Spread Sheets

13.1.1 Usefulness of Computer

Calculation

13.1.2 Risks of Using Simplified

Formulas

13.1.3 About the Spread Sheets13.1.4 Assumed COD / BOD

Relation

13.1.5 Wastewater Production per

Capita

13.1.6 Septic Tank

13.1.7 Imhoff Tank

13.1.8 Anaerobic Filters

13.1.9 Baffled Septic Tank

13.1.10 Biogas Plant13.1.11 Gravel filter

13.1.12 Anaerobic Pond

13.1.13 Aerobic Pond

13.2 Economic Computer Spread

Sheets

13.2.1 General

13.2.2.Viability of Using Biogas

13.2.3 Annual Cost Calculation

13.3 Using Spread Sheets withoutComputer

14 APPENDIX

15 LITERATURE

16 KEYWORDS


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This handbook is an outcome of a projecttitled

Low Maintenance WastewaterTreatment Systems - LOMWATS;

Development of Technologies andDissemination Strategies.

The project had been financed by the Com-

mission of the European Union, with sub-stantial contribution by the State Office forDevelopment Co-operation of the FreeHanseatic City of Bremen from October 1994until April 1998.

The following organisations participated inthe project:

CEEIC (Chengdu) and HRIEE (Hangzhou) fromChina; SIITRAT (New Delhi), MDS (Kanji-

rapally) and CSR (Auroville) from India, andGERES (Marseilles) from France. BORDAfromGermany co-ordinated the project.

This book aims at a target group which istypical for decentralised technology imple-mentation. This group consist of people whoare aware of the general problem and knowsomething about possible solutions. How-ever, their knowledge is too general on theone hand, or too specialised on the other

to master the very typical problems whichgo together with decentralisation. This bookwants to provide enough basic knowledgeabout the technology to non-technicalproject managers in order to enable themto adapt the technology locally. The bookwants also to help the technical specialistto understand where technical simplifica-tion is required in order to disseminate thetechnology in its typical decentralised con-

text - and provides tables for dimensioningof treatment plants on the computer. Lastbut not least, the book will assist seniordevelopment planners who need to under-stand the specifics of decentralised waste-water treatment technology sufficiently inorder to select or approve appropriate strat-egies for its dissemination.

Consequently, this book cannot and will notprovide additional information to any of thespecialists in his or her own field. On thecontrary, a specialist may be irked by cer-tain simplifications. This may make goodfor the fact, that practical people are oftenirritated by academic specialists, of boththe technical and non-technical field.

There will be always a need for decentral-ised wastewater treatment in Developing

Countries. The only realistic approach forthe time being is the use of low mainte-nance technology. However, the abbrevia-tion for it, namely LOMWATS, carries un-

justly an image of low standard which couldbecome counter productive to dissemina-tion. Therefore, the name DEWATS will beused, which stands for DecentralisedWastewater Treatment Systems. DEWATSincludes only such systems which are con-

sidered suitable for decentralised applica-tion and dissemination in the case thatqualified maintenance and operation can-not be expected. Nevertheless, DEWATStechnologies may also be suitable for largecentralised applications. On the other handmay sophisticated technology of consider-able maintenance and steering requirementalso be appropriate in certain decentralisedcases.

1 FOREWORD


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However, even the rather simple DEWATS -technologies are generally not mastered at

the place of decentralised pollution. Thisindicates the biggest disadvantage of de-centralisation, which is the need for know-how and expertise at each of the decentral-ised location. This book intends to improvethe situation. Nonetheless, centralised guid-ance and supervision of decentralised ac-tivities is required which is extremely costly,and therefore, dissemination of DEWATSneeds active promotion.

Acknowledgement

I would like to express my sincere thanksto a ll who enabled the writing of this book,either through providing funds or throughsharing their rich experience. I want to thankespecially those who made mistakes in thepast and saved me from falling into theditch myself. Unfortunately, it would beunfair to mention their names, however, Iwould like to encourage everybody to openlyreport about own failures, because whenthey have been sincerely analysed they arethe best teaching material for others.

The book in your hand can only be an entrypoint to the wide field of wastewater treat-ment technology. Fortunately, there are otherbooks which describe the various sectorsof the technology more profoundly. You find

a long list of books and articles in the an-nex whos authors deserve my gratitude,however, I would like to mention three booksof quite different type which were of par-ticular help to me:

My favourite is Biologie der Abwasser-reinigung (Biology of Wastewater Treatment)by Klaus Mudrack and Sabine Kunst, be-

cause it explains the biochemical subject insuch a manner that even civil engineers

like myself can follow. I hope the book inyour hand has something of this clarity.

Another book indispensable for a Germancivil engineer is Taschenbuch der Stadt-entwsserung (Pocket book of Sewerage)by the famous Imhoffs, in which one findsgeneral guidance on simply everythingconcerning sewage and wastewater treat-ment. The book has been translated intoseveral languages under various titles and

parts of it have been included into booksby local authors.

The last of the trinity is Wastewater Engi-neering by Metcalf and Eddy. Beside beinga comprehensive and voluminous handbookfor engineers that is based on theoreticalknowledge and practical experience, it isalso a textbook for students with examplesfor dimensioning and planning.

I would also like to thank the participantsof a workshop held in Auroville, India inNovember 1997, whom I used without theirknowledge to check the general concept ofthis book. I am further indebted to those towhom I have sent the draft version for com-ments. I am grateful for remarks and infor-mation given by D.P. Singhal, Deng Liangwei,Andreas Schmidt, Gilles B., Dirk Esser andChristopher Kellner. I would also like tothank Mr. Siepen who compiled mountainsof literature for me while working as a vol-unteer for BORDA. My special thanks goesto Mrs. Anthya Madiath who tried hard toclean the text from the most cruel Ger-manisms without hurting my ego too much.

Ludwig Sasse

Bremen, March 1998

1 FOREWORD


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This chapter gives a general overview onDecentralised Wastewater Treatment Systemstechnology (DEWATS) and may be consid-ered being a summary of its essentials. It ismeant for development planners or politi-cians, especially, who tend to not to go

deep into technical details before makingtheir decisions.

2.1 Propert ies of DEWATS

2.1.1 DEWATS

J DEWATS is an approach, rather than justa technical hardware package.

J DEWATS provides treatment for waste-water flows from 1 - 500 m3 per day, fromboth domestic and industrial sources.

J DEWATS is based on a set of treatmentprinciples the selection of which has beendetermined by their reliability, longevity,tolerance towards inflow fluctuation, andmost importantly, because these treatmentprinciples dispense with the need for so-phisticated control and maintenance.

J DEWATS work without technical energy,and thus cannot be switched off inten-tionally (see Fig. 1.).

J DEWATS guarantees permanent and con-tinuous operation, however, fluctuation

in effluent qua lity may occur temporarily.J DEWATS is not everywhere the best so-

lution. However, where skilled and re-sponsible operation and maintenancecannot be guaranteed, DEWATS technolo-gies are undoubtedly the best choiceavailable.

2.1.2 Treatment Systems

DEWATS is based on four treatment sys-tems:

J Sedimentation and primary treatment insedimentation ponds, septic tanks orImhoff tanks

J Secondary anaerobic treatment in fixedbed filters or baffled septic tanks (baf-fled reactors)

J

Secondary and tertiary aerobic / anaerobic treatment in con-structed wetlands (subsurfaceflow filters)

2 DEWAT S

PROPERTIES, PERFORMANCE AND SCOPE

Fig. 1.One of too many non-aerating aera-tors [photo: Sasse]


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J Secondary and tertiary aerobic / anaero-bic treatment in ponds.

The above four systems are combined inaccordance with the wastewater influent andthe required effluent quality. Hybrid systems

or a combination of secondary on-site t reat-ment and tertiary co-operative treatment is

also possible.

The Imhoff tank is slightly more compli-cated to construct than a septic tank, but

septic tanklongitudinal section

inlet outlet

baffled septic tank

provision for principal longitudinal sectiongas release outlet

inlet

settler

baffled reactor

anaerobic filter

septic tank gas release anaerobic filterinlet outlet

horizontal fil ter (constructed wetland)

longitudinal section

plantation, preferably phragmites

inlet outlet

rizomes

Fig. 2.Treatment systems considered to be suitable for decentralised dissemination

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provides a fresher effluent when de-sludgedat designed intervals. The Imhoff tank isused preferably when post-treatment takes

place near residential houses, in openponds or constructed wetlands of verticalflow type.

2 DEWATS

Pros and Cons of DEWATStype kind of

treatment

used for type

of wastewater

advantages disadvantages

septic tank sedimentation,sludgestabilisation

wastewater ofsettleable solids,especiallydomestic

simple, durable, little spacebecause of beingunderground

low treatment efficiency,effluent not odourless

Imhofftank

sedimentation,sludgestabilisation

wastewater ofsettleable solids,especiallydomestic

durable, little spacebecause of beingunderground, odourlesseffluent

less simple than septictank, needs very regulardesludging

anaerobicfilter

anaerobicdegradation ofsuspended anddissolvedsolids

pre-settleddomestic andindustrialwastewater ofnarrow

COD/BOD ratio

simple and fairly durable ifwell constructed andwastewater has beenproperly pre-treated, hightreatment efficiency, little

permanent space requiredbecause of beingunderground

costly in constructionbecause of special filtermaterial, blockage of filterpossible, effluent smellsslightly despite high

treatment efficiency

baffledseptic tank

anaerobicdegradation ofsuspended anddissolvedsolids

pre-settleddomestic andindustrialwastewater ofnarrowCOD/BOD ratio,suitable forstrong industrialwastewater

simple and durable, hightreatment efficiency, littlepermanent space requiredbecause of beingunderground, hardly anyblockage, relatively cheapcompared to anaerobic filter

requires larger space forconstruction, less efficientwith weak wastewater,longer start-up phase thananaerobic filter

horizontalgravel

filter

aerobic-facultative-

anaerobicdegradation ofdissolved andfine suspendedsolids,pathogenremoval

suitable fordomestic and

weak industrialwastewaterwhere settleablesolids and mostsuspended solidsalready removedby pre-treatment

high treatment efficiencywhen properly constructed,

pleasant landscapingpossible, no wastewaterabove ground, can becheap in construction if filtermaterial is available at site,no nuisance of odour

high permanent spacerequirement, costly if right

quality of gravel is notavailable, great knowledgeand care required duringconstruction, intensivemaintenance andsupervision during first 1 - 2years

anaerobicpond

sedimentation,anaerobicdegradationand sludgestabilisation

strong andmediumindustrialwastewater

simple in construction,flexible in respect to degreeof treatment, littlemaintenance

wastewater pond occupiesopen land, there is alwayssome odour, can even bestinky, mosquitoes aredifficult to control

aerobicpond

aerobicdegradation,

pathogenremoval

weak, mostlypre-treated

wastewater fromdomestic andindustrialsources

simple in construction,reliable in performance if

proper dimensioned, highpathogen removal rate, canbe used to create an almostnatural environment, fishfarming possible when largein size and low loaded

large permanent spacerequirement, mosquitoes

and odour can become anuisance if undersized,algae can raise effluentBOD


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Deep anaerobic ponds and shallow polish-ing ponds are also considered being DEWATS.

Special provisions may have to be madefor industrial wastewater before st andard-ised DEWATS designs can be applied.These for example include, an open set-tler for da ily removal of fruit waste from acanning factory, buffer tanks to mix vary-ing flows from a milk processing plant,grease traps or neutralisation pits to b al-ance the pH of the influent. In these cases ,standard DEWATS are applicable only af-

ter such pre-treatment steps have beentaken.

Despite their reliability and impressive treat-ment performance, such well-known andproven systems as UASB, trickling filter, ro-tating discs, etc. are not considered as be-ing DEWATS as these systems require care-ful and skilled attendance.

Most of the treatment processes which are

used in large-scale treatment plants despitetheir proven efficiency do not meet theDEWATS criteria and therefore, cannot beincluded. The activated sludge process, thefluidised bed reactor, aerated or chemicalflocculation and all kinds of controlled re-circulation of wastewater are part of thiscategory. Regular or continuous re-circula-tion is partly acceptable under the condi-tion that the pumps that are used cannotbe switched off easily, i.e. separately fromtransportation pumps.

Well designed conventionaltreatment plants may not meet

DEWATS requirements

Admittedly, this self-imposed restraint overtechnical choices in DEWATS could in prac-

tice impact upon the quality of the effluent.However, inferior quality need not to be

when there is sufficient space for the plant.There are certain measures at hand to dis-charge effluent of acceptable quality:

J provision of sufficient space at the sourceof pollution

J pre-treatment at source and post treat-ment where sufficient land is available

J pre-treatment at source and post treat-ment in co-operation with others

J accepting an effluent with higher pollu-tion load

J restricting wastewater producing activi-ties at this particular site

J connection to a central treatment plantvia sewage line.

Permanent dilution of wastewater or theinstallation of a mechanised and highly ef-ficient treatment plant remain theoreticaloptions, because experience shows that suchprocesses are chronically afflicted by irregu-lar operation.

2.1.3 Kinds of Wastewater

Septic tanks are used for wastewater with ahigh percentage of settleable solids, typi-cally for effluent from domestic sources.

Anaerobic filters are used for wastewaterwith low percentage of suspended solids(e.g. after primary treatment in septic tanks),and narrow COD/BOD ratio; biogas utilisa-tion may be considered in case of BODconcentration >1.000 mg/l. (BOD = biologi-cal oxygen demand, COD = chemical oxy-gen demand; both are the most commonparameters for pollution).

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Baffled Septic Tanks are suitable for all kindsof wastewater, however, preferably for such

of high percentage of non-settleable sus-pended solids and narrow COD/BOD ratio.

Constructed wetlands are used for waste-water with low percentage of suspendedsolids and COD concentration below 500 mg/l.

Wastewater for treatment in aerobic pondsshould have a BOD5 content below 300 mg/l.

Facultative and anaerobic ponds may becharged with strong wastewater, however,

bad odour cannot be avoided reliably withhigh loading rates.

2.1.4 Area requirement

Depending on total volume, which influ-ences tank depth, nature of wastewater andtemperature, the following values may indi-cate permanent area requirement for set-ting up a treatment plant:

septic tank, Imhoff tank:0,5 m2/m3 daily flowanaerobic filter, baffled septic tank:1 m2/m3 daily flowconstructed wetland:30 m2/m3 daily flowanaerobic ponds:4 m2/m3 daily flowfacultative aerobic ponds:25 m2/m3 daily flow

These values are approximate figures forwastewater of typical strength, however, therequired area increases with strength. Theremight be no waste of land in case of closedanaerobic systems as they are usually con-structed underground. Area for sludge dry-ing beds is not included; this may come to0,1 - 10 m2/m3 daily flow, according tostrength and desludging intervals.

2.2 Performance

2.2.1 Treatment Quality

Treatment quality depends on the nature ofinfluent and temperature, but can basicallybe defined in the following approximate BODremoval rates:

25 to 50 % for septic tanks and Imhofftanks70 to 90 % for anaerobic filters and baffledseptic tanks70 to 95 % for constructed wetland andpond systems.

These values and the required effluent qual-ity decide the choice of treatment systems.For example, septic tanks alone are notsuitab le to discharge directly into receivingwaters, but may suit treatment on land wherethe groundwater table is low and odour isnot likely to be a nuisance. Taking a limit of50 mg/l BOD being discharged, the anaero-bic filter in combination with a septic tankmay treat wastewate r of 300 mg/l BOD with-out further post treatment. Stronger waste-water would require a constructed wetlandor pond system for final treatment.

There are endless possibilities of cheapertreatment solutions based on local condi-tions. What is required is that all options becarefully considered. Whether long-wayopen discharge channels may deliver therequired additional treatment should a lwaysbe taken into consideration. Expert knowl-edge is needed to evaluate such possibili-ties; evaluation should compulsorily includeanalysis of wastewater samples.

Substantial removal of nitrogen requires amix of aerobic and anaerobic treatmentwhich happens in constructed wetlands andponds, only. In closed anaerobic tank sys-tems of the DEWATS-type nitrogen forms to

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ammonia. The effluent is a good fertiliser,but because of that, causes algae growth in

receiving waters and is toxic to fish.

Phosphorus is a good fertiliser, and there-fore dangerous in rivers and lakes. Remov-ing of phosphorus in DEWATS is limited,like in most treatment plants. However, con-structed wetlands could be helpful whenfilter media contains iron or aluminium com-pounds. It should be noted that phospho-rus can be accumulated by sedimentationor fixed in bacteria mass , but can hardly be

removed or transformed into harmless sub-stances.

2.2.2 Pathogen control

Like all modern wastewater treatment plants,DEWAT systems, as well, are not made forpathogen control in the first place. Patho-gen removal rates increase with long reten-

tion times, but all high rate plants workproudly on short retention times.

The WHO guidelines and other independ-ent surveys describe transmission of worminfections as the greatest risk in relation towastewater. Worm eggs, helminths, are wellremoved from effluent by sedimentation butaccumulate in the bottom sludge. The longretention times of 1 to 3 years in septictanks and anaerobic filters provide suffi-

cient protection against helminths infectionin practice. Therefore, frequent sludge re-moval carries a slightly higher risk.

Bacteria and Virus are destroyed to a greatextent, however they remain in infectiousconcentrations in effluent of anaerobic fil-ters and septic tanks. Nevertheless, thestatistical risk of infection is rather limited.High pathogen removal rates are reported

from constructed wetlands and shallowaerobic ponds. This effect is attributed to

longer retention t imes, exposure to UV raysin ponds, and various bio-chemical inter-actions in constructed wetlands. Pathogenremoval rates o f these systems a re higherthan in conventional municipal treatmentplants.

Chlorination can be used for pathogen con-trol. Simple devices with automatic dosingmay be added before final discharge. How-ever, use of chlorine should be limited to

cases of high risk, as it would be for hospi-tals during an epidemic outbreak. Perma-nent chlorination should be avoided be-cause it does not only kill pathogens butalso other bacteria and protozoans whichare responsible for the self purification ef-fect of receiving waters.

2.3 Scope2.3.1 Reuse of wastewater

Effluent from anaerobic units is character-ised by foul smell, even at low BOD values.Irrigation in garden areas should then bet-ter be underground. Effluent from aerobicponds or constructed wetlands is suitablefor surface irrigation, even in domestic gar-dens. However, the better the treatment ef-fect of the system, the lower is the fertilis-

ing value of the effluent.

Although most pathogens are removed inaerobic ponds, domestic or agricultural ef-fluent can never be labelled guaranteedfree of pathogens. Irrigation of crops shouldtherefore stop 2 weeks prior to harvesting.It is best not to irrigate vegetables and fruits,which are usually consumed raw after flow-ering.

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Treated wastewater can be used for fishfarming when diluted with fresh river water

or after extensive treatment in pond sys-tems. Integrated fish and crop farming ispossible.

2.3.2 Reuse of Sludge

Each treatment system produces sludgewhich must be removed in regular intervals,which may reach from some days or weeks(Imhoff tanks) to several years (ponds).Aerobic systems produce more sludge thananaerobic systems. Desludging should com-ply with agricultural requirements becausesludge although contaminated by pathogensis a valuable fertiliser. Consequently sludgerequires careful handling. The process ofcomposting kills most helminths, bacteriaand viruses due to the high temperaturethat it generates.

2.3.3 Use of Biogas

Conventionally, DEWATS do not utilise thebiogas from anaerobic processes becauseof the cost and additional attendance fac-tors. Devices for collection, storage, distri-bution and utilisation of biogas add to thecost to be recovered from the energy valueof biogas. However, under certain circum-stances the use of biogas may actually re-duce the cost of treatment. Biogas utilisa-tion makes economic sense in the case ofstrong wastewater, and especially whenbiogas can be regularly and purposefullyused on-site. Approximately 200 litres ofbiogas can be recovered from 1 kg of CODremoved. A household normally requires2 to 3 m3 of biogas per day for cooking.Thus, biogas from 20 m3 of wastewater

with a COD concentration of not less than1000 mg/l would be needed to serve the

requirements of one household kitchen.

2.3.4 Costs

Total costs, described as annual costs, in-clude planning and supervision costs, run-ning costs, capital costs, and the cost ofconstruction inclusive of the cost of land.As is evident, it is not easy to provide

handy calculations on the total cost ofwastewater treatment. The comparison ofcosts is also made difficult, by the factwhile a particular system may be cheaperit may not necessarily be the most suit-able, while other systems might be expen-sive at one location but cheaper at an-other due to differential land prices. How-ever, in general it can be confidently saidthat DEWATS has the potential of being

more economical in comparison to otherrealistic treatment options. This is true onaccount of the following:

J DEWATS may be standardised for certaincustomer-sectors, which reduces planningcost.

J DEWATS does use neither movable partsnor energy, which avoids expensive butquickly wearing engineering parts.

J DEWATS is designed to be constructedwith local craftsmen; this allows to em-ploy less costly contractors which causeslower capital cost, as well, and later lesserexpenses for repair.

J DEWATS may be combined with naturalor already existing treatment facilities sothat the most appropriate solution maybe chosen.

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J DEWATS has the least possible mainte-nance requirements which spares not only

manpower for daily attendance but alsohighly paid supervisors or plant manag-ers.

No wastewater treatment is profitable in it-self. However, the indirect gains from treat-ing wastewater might be numerous. Whetherdecentralised DEWATS can compete with thefees and creature comforts that people de-rive from of a centralised sewer connectionwould depend on the local situation. The

feasibility of using treated water, sludge orbiogas also differs from place to place. In-tegrated wastewater farming merits consid-eration albeit as a completely independentbusiness.

2.4 Implementation

2.4.1 Designing Procedure

If the planning engineer knows his craftand recognises his limitations, designingDEWATS is relatively simple. Performanceof treatment systems cannot be preciselypredicted and therefore calculation of di-mensions should not follow ambitiousprocedures. In case of small and me-dium scale DEWATS, a slightly oversizedplant volume would add to operational

safety.Based on local conditions, needs andpreferences plants of varying sizes couldbe chosen to become fixed s tandard de-signs. On-site adaptation can then bemade by less qualified site supervisorsor technicians.

Individual caseshave to be calcu-lated and designedindividually; thestructural details ofthe standard plantsmay be integrated.A simplified, quasistandardised meth-od has been devel-oped for calculationof dimensions (seechapter 13.1).

Co-operative plantsystems that re-quire interconnect-ing sewerage mustbe designed indi-vidually by an ex-

Fig. 3.DEWATS anaerobic filter under construction. Planning and supervision by CEEIC [photo: Sasse]

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perienced engineer who is able to placeplants and sewers according to contours

and other site requirements.

2.4.2 Wastewater Data

Data indispensable to the calculation andchoice of the right DEWATS design are:

J daily wastewater flow

J hours of major wastewater flow or otherdata describing fluctuations

J average COD values and range of fluc-tuation

J average BOD values or average COD/BODratio

J suspended solids content, percentage ofsett leable solids

J pH

J ambient temperature and temperature of

wastewater at sourceIn the case of domestic wastewater thisdata is easy to arrive at when the numberof persons and water consumption percapita per day is known. While total waterconsumption might be easy to measure onsite, it is important to consider the amountof water only that enters the treatment sys-tem.

For industrial wastewater other parameterssuch as COD/N or COD/P relation, contentof fat and grease, content of toxic sub-stances or salinity are also likely to be ofconcern. A full analysis may be necessarywhen planning the first such plant. Com-prehensive understanding of the produc-tion process of the industry will help tospecify crucial information required. Cus-tomarily production processes are unlikely

to differ vastly within a defined area of pro-duction, thereby making standardisation

fairly easy.

2.4.3 Construction

DEWATS are relatively simple structures thatcan be built by reasonably qualified crafts-men or building contractors with the abilityto read technical drawings. If this were notthe case, almost daily supervision by a quali-fied technician would be required. The con-struction of watertight tanks and tank con-nections would require craftsmanship of arelatively high order. Control of construc-tion quality is of utmost importanceif biogas is to be stored within the reactor.

Technical details of a design, which hasbeen adapted to local conditions, shouldbe based on the material that is locally avail-able and the costs of such material.

Important materials are:J concrete for basement and foundation

J brickwork or concrete blocks for walls

J water pipes of 3, 4 and 6 in diameter

J filter material for anaerobic filters, suchas cinder, rock chipping, or specially madeplastic products

J properly sized filter material for gravel

filters (uniform grain size)

J plastic foils for bottom sealing of filtersand ponds

Gate valves of 6" and 4" diameter are nec-essary to facilitate de-sludging of tanks regu-

larly.

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2.4.4 Maintenance

The more a standard design has beenadapted or modified to fit local conditions,the greater the likelihood of operationalmodification during the initial phase. It istherefore important that the contractor ordesign engineer keeps a close eye on theplant, until the expected treatment resultshave been achieved. Despite faultless im-plementation, it may be necessary to ex-tend such attendance up to as long as twoyears.

Permanent wastewater treatment that doesnot include some degree of maintenance isinconceivable. DEWATS nonetheless reducesmaintenance to the nature of occasionalroutine work. Anaerobic tanks would needto be de-sludged at calculated intervals (usu-ally 1 to 3 years) due to the sludge storagevolume having been limited to these inter-vals. Treatment is not interrupted duringde-sludging. Normally, sludge is drawn fromanaerobic digesters with the help of port-able sludge pumps, which discharge intomovable tankers. Direct discharge into ad-

jacent sludge drying beds may be possiblein the case of Imhoff tanks with short de-sludging intervals.

Anaerobic filters tend to clog when fed withhigh pollution loads, especially when ofhigh SS content. Flushing off the biologicalfilm is possible by back washing. This willrequire an additional outlet pipe at the in-let side. In practice, what is usually done isto remove the filter media, wash it andclean it outside and put it back after thiscleaning. This may be necessary every fiveto ten years.

Constructed wetlands gradually loose theirtreatment efficiency after 5 to 15 years, de-pending on grain size and organic load.

The filter media would need to be replaced.The same media may however be re-used

after washing. During this exercise unlessseveral filter beds were to be provided, treat-ment would have to be suspended. Sur-face plantation has then to be replacedalso; otherwise regular harvesting of coverplants is not required.

Pond systems require the least maintenance.De-sludging may not be necessary for 10 to20 years. Normally, an occasional controlof the inlet and outlet s tructures should be

sufficient. Control of wastewater flow maybe required when a foul smell occurs dueto overloading in the hot season. Such prob-lems can be avoided through intelligentinflow distribution and generous sizing ofponds.

2.4.5 Training for Operation

DEWATS is designed such that maintenanceis reduced to the minimum. Daily attend-ance is limited to certain industrial plants.However, there should be someone on-sitewho understands the system. It would bebest to explain the treatment process tothe most senior person available, as he islikely to be the one to give orders to theworkers in case of need. In case the educa-tional qualifications of the on site staff islow, the engineer who designed the plantor the contractor who constructed the plantshould provide service personnel, who maycome to the s ite once a year or at t imes ofneed.

Extensive training of staff at the lower levelis generally not necessary and in most casesnot effective due to fluctuation of workers.Hiring professional manpower for after careservice may then be considered the better

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solution. The case might be different forhospitals or housing colonies that usually

have a permanent staff.

If a large number of DEWATS are to be im-plemented the aim should be to standard-ise the maintenance service. This is likelyto be possible because of local standardi-sation of plant design, with similar charac-teristics for operation.

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3.1 The Need for Active Disseminationof DEWATS

Planning and implementat ion of DEWATS isnot a very profitab le business for engineersand building contractors. Therefore, dissemi-nation of decentralised wastewater treat-ment systems will need to be pushed bypolitical will and administrative support.

The treatment units are relatively small, nev-ertheless complicated and are usually spreadover a scattered area. The required exper-tise for their realisation is truly remarkable.Resultantly, general planning must be cen-tralised and designing standardised in or-der to reduce the overall cost per plant andto maintain the required expertise. On theother hand, any centralisation will involvethe setting up of a superstructure with its

build-in tendency to create an expensiveofficers pyramid. To achieve implementa-tion of a large number of plants, a strongand omnipresent superstructure seems to berequired. The dog bites in his own ta il. How-ever, this superstructure becomes relativelyless expensive if the scale of implementa-tion is large. Therefore, a reasonable, afford-able and sustainable dissemination strategyis essential to balance the desired environ-

mental benefits with acceptable social costs.Short-term economic viability of the super-structure cannot necessarily be the yardstickfor choosing a dissemination strategy.

3.2 Preconditions for Dissemination

There are some preconditions commonlyrequired for dissemination of any decen-

tralised technology or technical hardware.These preconditions have to be fulfilledbefore one may start thinking about a dis-semination strategy:

J The hardware to be disseminated is tech-nically sound

J In principle it is feasible to operate and

maintain the hardware on the spot.

J The technology in general is economi-cally and/or environmentally useful.

J The technology is suitable and useful inthe particular local situation.

Dissemination would make sense only ifthese pre-conditions are fulfilled.

There will be no improvedwastewater treatment withouttechnical expertise

DEWATS, as a decentralised technology willalways need local adaptation. Even fullystandardised designs are constructed lo-cally; for example, they have to be con-nected to the source of pollution and haveto be set at proper level to allow free flow

of effluent to the receiving water. Implicitin the de centralisa tion of technology is thedecentralisation of know-how and exper-tise. Centralised guidance and supervisionof decentralised activities is extremelycostly. These services would the refore haveto be kept to the minimum. This would bepossible, only if basic knowledge and aminimum of expertise were locally avail-able.

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Local adaptation of DEWATS is influencedby:

J the technical requirements and solutions,

J the geographical or physical environmentand

J the social and socio-economic circum-stances.

On the other hand, dissemination has tochoose a strategy which observes severalaspects:

J the social aspect,

J the economic aspect,

J the technical aspect and

J the legal aspect

The dissemination strategy that is ultimatelychosen has to include all these aspects.

3.3 The Social Aspect

3.3.1 The Status of Waste Disposal inSociety

The public is growing in its awareness ofwastewater treatment as a result of increas-ing damage and pollution to the environ-ment from wastewater. However, public in-terest appears to be confined to the harm-ful effects of pollution, only. In other words ,

there is no particular public interest in hav-ing a wastewater treatment plant - and thereappears to be definitely even less interestin maintaining it. The general attitude isone of somebody must do something .

The public needs to realise that that some-body is they, if nobody else really caresabout their problem. The question then iswith regard to the preferred treatment con-

cept. It is unlikely that individual DEWATSwhich must be taken care of by the indi-

vidual will be very popular. Even if DEWATSwere to be the only possibility, public will-ingness to participate in the programmewould still be limited. Therefore, concepts,which require the participation of the gen-eral public, are not likely to work too well,and consequently should be avoided when-ever possible.

Throughout the ages anything related towastewater seems to have had very low

priority. Even in olden times it was alwayspeople of the lowest social status who wereput in charge of waste disposal. Unlike car-penters, masons or other professionals, thesescavengers as they were called were neverreally interested in upgrading their discrimi-nated skills. Understandably, the knowledgeof wastewater disposal lagged behind otherbasic civic techniques. Strangely that miss-ing interest was found even among royalty

whose otherwise impressive castles had allbut a primitive toilet outside. The well-de-signed and elaborate p lace of Versailles forinstance, did not have a toilet. Similarly,the genius engineer Leonardo da Vinci de-veloped weapons, bridges, air planes; butin his model city of 1484, treatment of wastewas relegated to just one low-level waste-water canal.

Wastewater engineers areprobably the only ones who love

handling wastewater

Nonetheless, the taboo on faeces that ex-ists over centuries is perhaps the most effi-cient sanitary measure, and still is from ahealth point of view a beneficial habit. How-soever, the phenomenal population growth

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the world over has increasingly demandedprofessional attention to wastewater and

its disposal in response to which, today wehave a new breed of wastewater engineerswho are not ashamed of their profession.

3.3.2 Organising People

For wastewater treatment to take place in aco-operative context, it is important thatpeople are organised. The objectives of or-

ganising people may be manifold:J collecting investment capital,

J contributing land,

J giving permission for trespassing of sew-ers over private land,

J collective operation and maintenance

J collective financing of services for op-eration,

J use of effluent for irrigation, sludge forfertiliser or biogas for energy.

There are numerous ways in which peoplecan come together. The framework of ac-tion may be the general community admin-istration, a development project, or an NGO,which supports self- help activity. Howso-ever, the local tradition of self organisationand co-operation and the particular imageof the subject wastewater will influencethe organisational structure.

How to organise people is a well-researchedsubject. The results and suggestions of allthose books and concepts cannot be pre-sented here in detail. However, great careis necessary to check any proposed methodwhether it is suitable and promising in caseof wastewater treatment and disposal. Mostexperiences of community involvement in

sanitation are related to water supply orlow cost toilet programmes for individual

households, programmes which meet im-mediate felt needs. It must be rememberedthat this is not so with wastewater disposal- and even less so with wastewater treat-ment. People do not want to be botheredwith it. In general, people expect that anony-mous authorities should take care of thisproblem. Public willingness to get involvedin treating their wastewater is low and canonly be expected to increase in case of

severe crises, or in the likelihood of sub-stantial economic benefit as in the case ofre-using wastewater for irrigation, for in-stance.

3.3.3 Partners for Dissemination

The logical partners in dissemination of waste-water treatment systems beside the pol-luter as customer, are the government ad-ministration at one end, and private enter-prise such as engineering companies, atthe other. In an ideal scenario, the govern-ment would announce a set of by-laws andthen oversee the implementation of thesebylaws. Thereupon, polluters by socialagreement or threat of punishment wouldbe obliged to contact private engineers andcontractors to implement an adequate treat-ment and d isposal system. The investment

capital would come from the individual,from bank loans, and perhaps as a subsidyfrom public funds. This scenario is typicalto industrialised countries.

In developing countries, the scenario mightappear deceptively similar. On the contrary,the comparison is not likely to go beyondthe introduction of bylaws, which are sel-dom enforced, as a result of which pollut-

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ers may not even be aware of their exist-ence. The service of private engineers is

also likely to be far too expensive for thesmall polluter. Altogether, this leads to asituation of complete in-action or to one ofarbitrary abuse of power by some officials.As a result of the failure of the governmentor the private sector, informal or registeredself-help groups step in to carry out thevarious tasks that are normally not theirs.

Public awareness towards the problem ofwastewater pollution has grown tremen-dous ly in recent years. Politicians and gov-ernment administrations welcome any ini-tiative to help solving the problem throughdecentralised measures. Money is often notthe biggest problem, at least for pilot ordemonstrat ion projects. However, the re is ageneral helplessness when it comes to in-dividual implementation, and more so whenit comes to active and well organised dis-semination of DEWATS.

Marketing experts , development consultantsor socially oriented NGOs are the first to

present themselves as partners for dissemi-nation. Other business organisations andcontractors more suited to wide scale dis-semination are rare diamonds in a heap ofsand. The logical consequence of this di-lemma is to find new local partners for de-centralised dissemination at each place.Since these partners will play the key rolein implementation, dissemination conceptsmust necessarily be shaped to suit them.

Dissemination concepts must suitthe local partners

3.4 The Economic Aspect

3.4.1 Decentralisation

Whether decentralised wastewater treatmentis better than centralised treatment is basi-cally a question for theoretical or ideologi-cal discussion. In practice, there is alwayslikely to be a mix of centralised and decen-tralised solutions.

Cost-benefit analyses are help-ful as general policy considera-tions and for choosing themost economic treatment sys-tem in individual cases. How-ever, the problem of a cost-benefit analysis of DEWATS liesin the parameters influencingthe calculation, which are of-ten difficult to project a priori.A time frame of 20 to 30 years- the normal lifetime of a treat-ment plant - should constitutethe basis for calculation. Whileconstruction costs are relatively

Indian National Discharge Standards

discharge into

parameter unitinland

surfacewater

publicsewers

land forirrigation

marinecoastal

areaSS mg/l 100 600 200 100pH 5.5 to 9 5.5 to 9 5.5 to 9 5.5 to 9

temperature C < +5C < +5CBOD5 mg/l 30 350 100 100COD mg/l 250 250oil and grease mg/l 10 20 10 20total res. chlorine mg/l 1 21NH3-N mg/l 50 50 50

Nkjel as NH3 mg/l 100 100

free ammonia as NH3 mg/l 5 5nitrate N mg/l 10 20diss. phosphates as P mg/l 5sulphides as S mg/l 2 5

CPCB

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Tab. 1.Indian discharge standards


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easy to calculate, an estimate of realisticrunning costs would need an in-depth

study of the technical requirements of thesystem as well as the prevailing social en-vironment.

Further, it would need a fairly precise read-ing into future management structures. Over-heads in form of salaries for the manage-ment, expenditure for the logistic require-ments of operation and maintenance areextremely difficult to foresee, especially inthe case of co-operatives. The cost of trans-porting sludge, for example, can increasemanifold if the neighbouring farmer decidesnot to take the sludge. Anew drying or dump-ing place could be so far away so that truckswould have to be hired instead of oxcarts asplanned, sending calculations awry.

Atotally centralised systemwould result inthe lowest plant construction cost pertreated volume of wastewater. On the other

hand, connecting individual sources to thetreatment unit may result in up to five timesthe cost for the required sewerage. Man-agement costs are comparatively low be-cause one highly qualified manager caresfor a large volume of wastewater, respec-tively a large number of users. Maintenancecosts are quite high, instead, because so-phisticated mechanised equipment requirespermanent care.

Asemi-centralised systemconnects severalsmaller treatment units to sewerage ofshorter overall-length. Construction costs arerelatively low, but qualified managementmay be needed for each plant, thus push-ing up the cost.

A ful ly decentralised systemwould need anatural environment that is capable of ab-sorbing the discharged wastewater of each

individual plant on-site. Structural costs arelikely to be the lowest for fully decentral-

ised systems, especially if slightly sub-stand-ard treatment is accepted . Safe s ludge dis-posal must also be possible at site, other-wise the cost of transportation for sludgecollection and disposal must be included.Maintenance and management costs aredispensed with when the user of the plantalso attends to it. However, if proper op-eration on a more sophisticated level is tobe secured, the need for qualified supervi-

sion and service structures may arise, whichto a certain extent would need to be or-ganised centrally (for example for collec-tion and disposal of sludge). Regular efflu-ent control is particularly costly in decen-tralised systems.

3.4.2 Treatment Quality

The kind of environmental pollution thatexists tends to justify the strict dischargestandards that prevail. However, standardsthat are extremely high, paradoxically mayworsen, not improve the situation.

The nature of treatment is first of all afunction of the area, for which one mayallow a certain degree of environmentalpollution. If the area where pollution oc-curs is infinite, there may be no necessity

for treatment. Similarly, when pollution isinfinitely small the polluted area is zero.Situations between these two extremesshould be open for setting priorities, mean-ing that the final choice should be opento negot iation. Economic, social and envi-ronmental aspects would each merit dueconsideration to reach the most accept-able compromise with regard to the re-quired treatment quality.

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Permitted discharge quality will also dependon the location of pollution. Transport of

wastewater to sites further away instead ofon-site treatment had been practised sinceman developed settlements. Today, waste-water transportation to remote land or wa-ters is still common. While this is may beacceptable today, the damage to the envi-ronment may become irreversible and intime, the legacy of pollution could hit backat the polluter. In the case of DEWATS dis-semination, the decision to treat wastewater

on-site and not just send it away is a lreadymade.

In most countries national pollution stand-ards allow for higher pollution loads in ef-fluents of smaller plants, and effluent stand-ards are softer when the discharge is ontoland and into waters that are little used.

Discharge standards in developing countrieshave often been borrowed from industrial-

ised countries, which are based on highlydiluted municipal sewage. DEWATS in de-veloping countries are meant for public toi-lets, hospitals, schools or smaller commu-nities where it is likely that lesser water isused for household and toilet purposes thanin industrialised countries. The high con-centration of wastewater from wate r savingtoilets leads automatically to higher BODconcentration of the effluent, even when

BOD removal rates are within the technicalrange of an adequate treatment system. Insuch case, as saving of water is crucial tosustainable development it would not bereasonable to dilute the effluent artificiallyin order to achieve an administratively im-posed concentration. Standards which re-late to absolute pollution loads (instead ofconcentrations) would be more reasonable,at least for small units.

This point is especially important, becauseone of the great advantages of decentrali-

sation and on-site treatment is that wastetransport in short sewer pipes does not re-quire highly diluted wastewater. Despitehigher concentrations, the absolute pollu-tion load remains the same. Water savingpolicies could easily accept higher concen-trations at the outlet when other environ-mental factors being favourable; for exam-ple when there is enough land available orthe receiving river carries enough water the

year round.Furthermore, it makes little sense to installDEWATS of a high treatment quality, whentheir effluent joins an open sewer channelwhich receives other untreated wastewater.In this case, simple, individual septic tanks,which cost less but are albeit less effectivein their performance, would be appropri-ate, because treatment of the main waste-water stream would in any case have to be

done.

3.4.3 Treatment Cost

Thirty to fifty percent of the pollution loadmay be removed with simple technology,such as the septic tank. Another thirty toforty percent might be removed with thehelp of units such as baffled septic tanks

and anaerobic filters that a re yet s imple butfar more effective. Any further treatmentwould require post treatment in ponds orconstructed wetlands (conventional systemsusing artificial oxidation do not belong tothe DEWATS family). The higher the relativepollution removal rate, the higher are theabsolute treatment costs per kg BOD re-moved. Additional treatment devices for re-moval of nitrogen, phosphorous or other

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toxic substances are likely to be unusuallyexpensive.

Technically spoken, DEWATS are able to meetany discharge standard. However, since selfsustainable dissemination of DEWATS islikely to be strongly influenced by invest-ment and operational costs, the choice ofan appropriate treatment standard will notonly determine the dissemination strategybut may be vital for the total success ofDEWATS.

Treatment efficiency of DEWATSmay be as high as that of anyconventional treatment plant

Environmental experts and experiencedwastewater engineers would need to deter-mine appropriate treatment s tandards. It iscrucial that authorities that administrate

pollution control have a understanding ofthe issue and can be flexible in acceptingand legalising deviations from general stand-ards, so long as these deviations are eco-logically acceptable.

3.4.4 Investment Capital

As there is generally no financial return onwastewater treatment there is little genuine

economic interest to invest in it. Apart fromthe few persons who act out of a sense ofresponsibility for the environment, there israrely anybody who invests in wastewatertreatment voluntarily. Only if and until pol-luters are compelled by law to pay for thepollution they cause will investment capitalbecome available to wastewater t reatment,because investment in wastewater treatmentwill be viable compared to imposed fines.

Construction budgets for new buildings andente rprises are likely to include wastewater

treatment costs. Existing units, apart fromthe problem of having the space for con-struction may not be able to raise funds forinstalling a treatment unit at one time. Dis-semination programmes must therefore nec-essarily ensure the availability of creditschemes to polluters for wastewater treat-ment.

A sustainable dissemination strategy musttake into account the time it may take a

polluter to allocate the required capital (forexample, to wait until the next board meet-ing decides on the matter). Practically thiscould translate into a time lag of a year ormore between the time when the planningengineer invites the contractor to see thesite and make a realistic estimate for con-struction and the availability of funds forthe purpose. Besides the inflation factor thisalso implies that a contractor cannot afford

to rely solely on DEWATS for his survival.Under these circumstances it may be diffi-cult to recruit contractors who are perma-nently available to a DEWATS dissemina-tion programme.

3.5 The Technical Aspect

3.5.1 Decentralisation

From an economic point of view, decen-tralisation requires a simplified technologyfor the reason that it will be prohibitivelyexpensive to permanently maintain the nec-essary expertise for sophisticated technol-ogy on a decentralised level.

It may be possible to actualise decentral-ised solutions with the help of completelystandardised designs based on local con-

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struction techniques; in other words, byplacing black-box hardware packages on

the market. In both cases expertise willbe needed for choosing the right design orthe suitable black-box. Expertise will alsobe needed to advise the user in properoperation and adequate maintenance. Suchadvice must have a stable address, whichmight be difficult in case certain operationsbecome necessary after one or two yearsonly, for example in the case of de-sludging.This could also mean that the constructing

enterprise would need to be contracted formaintenance and operation on behalf of thecustomer. The expertise available for on-site operation and maintenance would de-cide on the nature of required plant man-agement.

Invaluable experience gained from ruralbiogas dissemination programmes over aspan of 30 years in India, China and sev-eral other countries confirms that each such

project or programme had first to developan appropriate local design notwithstand-ing the availability of standardised designsfrom other projects /countries. Interestinglyneither India nor China have been able tosustain the dissemination of their small-scale rural biogas programme from a tech-nical point of view without the support of asuperstructure. In most cases it has beendifficult to ensure that the user has suffi-cient expertise to maintain the biogas plantsproperly. None of the programmes have beenable to do without a subsidised after salesservice. This scenario is bound to be trueto other areas of technology disseminationas well.

DEWATS is far more complicated than ruralbiogas plants. The bio-chemical and physi-cal properties of wastewater especially incase of wastewater from industrial sources

are far from uniform. Consequently, the ex-pertise required for design, construction and

operation of DEWATS become all the moreindispensable as compared to rural biogasplants. One of the crucial points is to de-cide whether a standard des ign is suitable,or how it should be modified.

The availability of the right expertise is ir-replaceable in DEWATS dissemination. It isdecisive for a dissemination programme ofdecentralised plants to clarify the nature ofthe expertise that is to be maintained, atwhat level and for which technology. Miss-ing knowledge and expertise cannot be con-signed to the insignificance of a so-calledsocial matter. Professionals and techni-cians are duty bound to ensure that thegoods or structures they provide are tech-nically sound and appropriate. The breakdown of a technical system is not neces-sarily the fault of the customer. It is theduty of the technician to deliver the right

design for a given situation.

It is the duty of the technician todeliver an appropriate designwhich will be realised with an

appropriate technology

A division of labour between different ex-perts is e ssential. It is the duty of the non-

technical social staff to feed the techni-cian with information about social mattersand the technician to feed the social ex-perts with information about the technicalnecessities. What is required is collabora-tion between the disciplines, not role con-fusion. It is a known fact that techniciansas a rule do not give enough informationabout technical necessities to social experts.This in all likelihood happens for two rea-

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sons: the technicians do not know the tech-nology well enough and/or the social ex-

perts are not able to understand the impli-cations of the technical requirements. Theproblem of sub-standard technical knowl-edge is likely to be true of most potentialDEWATS constructors - and promotors.

3.5.2 Construction

The local availability of hardware is a pre-

condition for decentralisation. In case of mainstructures, appropriateness of local buildingmaterial plays a decisive role in executingthe construction. The kind of filter materialavailable for instance influences the choiceof the treatment principle. Expertise is neededto modify standard designs, or if necessary,make new designs, which can be constructedwith locally available material. It is also im-portant to decide whether traditional con-struction techniques are suitable for waste-water treatment systems, especially if biogasis supposed to be used. The expert has alsoto decide whether the treatment system fitsthe local geography.

At the level of implementation of small-scaletreatment systems, the qualification of crafts-men is usually low. Masons may not be ableto read and write and thus, structural draw-ings are not useful at site. Structural de-signs would therefore have to be simplifiedor supervisors who are properly qualifiedto read the drawing be present regularly.

Familiarity with the design principles apart,a mastery of structural details will be cru-cial to the p roper functioning of the plant.The need for correct execution of the struc-tural details of the design cannot be over-emphasised. Cost or efficiency enhancingmodifications of structural details is ill

advised in the absence of a deep under-standing of the proposed measure. For

example, a dentated sill is of no use if thetop of teeth, instead of the bot tom notches,is kept in level.

3.5.3 Substrate

The quality, quantity and other propertiesof wastewater determine the treatment prin-ciple from a scientific point of view. The

type of treatment system finally chosen willdepend on the geographical, structural andsocio-economic conditions. Expertise toanalyse and evaluate the wastewater, tochoose the most appropriate t reatment sys-tem and to countercheck the design in re-spect to its local suitability will be impera-tive.

In the absence of such expertise at the lo-cal level, standardisation on the basis of

similar wastewate r in the region will be thenext step. The local expert should then atleast be able to distinguish between stand-ard and other wastewater. To do this,there must be somebody in the disseminat-ing organisation that can read laboratoryresults or, at least understands the impor-tance of working with the right data in choos-ing the appropriate structure. Furthermore,someone would be required to collect rep-resentative wastewater samples and inter-pret the laboratory results for the techni-cian.

Low maintenance is demanded of decen-tralised wastewater treatment. If structuralmeasures can improve treatment, chemicalssuch as coagulants are forbidden. How-ever, the use of chemicals may be unavoid-able if bacterial growth is impaired by nu-trient deficiencies, e.g. an unbalanced phos-

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phorous-nitrogen ratio. Bio-chemical exper-tise is required to decide if such measures

are really necessary.

3.6 The Legal Aspect

3.6.1 The Political Environment

The over all political climate is as impor-tant as the administrative framework. It isimportant to know who the movers are and

the different roles each actor plays. It isalso important to be familiar with the regu-latory framework and more specifically theextent to which rules and regulations areactually enforced. To politicians, inefficien-cies of the legal framework are at worst amoral matter, only, whereas to those imple-menting a DEWATS dissemination strategy,inefficiencies of the socio-political environ-ment are essentially a fundamental plan-ning parameter.

Conventionally, policy is formulated on abedrock of relevant facts. Familiarity withscientific or technical facts ensure that theright policy and the right laws and by-lawsare shaped. Decision-makers should knowthat each step in the treatment process re-moves only a portion of the incoming pol-lution load. It is also important that theyknow that DEWATS is premised on the be-lief that wastewater treatment should bepermanent and that permanency can onlybe guaranteed by simple and robust sys-tems. This implies that permanent waste-water treatment is not possible withoutmaintenance. Nonetheless, in DEWATS,maintenance operations are kept to theabsolute minimum - necessarily.

3.6.2 Political Priorities

Political and administrative preferences leanheavily towards large scale, centralisedwastewater and sewerage systems. Giventhe fact that most wastewater is producedby urban agglomerations, this is understand-able. Domestic wastewater from towns andcities is the largest single source of waterpollution. Industrial wastewater from sub-urban areas comes next. In India it has beenest imated that only 50% of the wastewaterthat finally reaches the river Ganges actu-ally passes through urban wastewater treat-ment plants. The other 50% of this waterflows untreated into the environment.Whether this untreated 50% can be actual-ised into a potential demand for DEWATSdepends on policy making and the serious-ness of its application.

Most governments tend to sacrifice envi-ronmental concerns on the altar of fiscaldemand. The industrialised west has beenno different. The history of wastewater treat-ment in Europe and North America reflectsthe tug of war between the economy andthe environment. Earlier and today, the state-of-the-art of treatment technologies andregulatory framework is the outcome of thisdialectic.

The same seems to be happening in devel-oping countries as well, the only differencebeing in the import of advanced treatmenttechnologies from industrialised countries.Today environmental standards, i.e. dis-charge standards for wastewater are beingbased on the treatment technologies thatare available, and not on the prevailing stateof the economy. This is lead ing to a strangesituation wherein the strict discharge stand-ards are hardly followed because their ap-plication is too expensive. Thus, the indi-

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vidual polluter gets away by completely ig-noring the problem or by setting up a fake

treatment system to please the environmen-tal control officer. Either way, the environ-ment is not protected. On the other hand,were environmental standards to be morerealistic and feasible there is greater likeli-hood of adherence to the law by individualpolluters.

Undue haste in adopting standards which are cur-rently too high can lead to the use of inappropriatetechnology in pursuit of unattainable or unaffordable

objectives and, in doing so, produces an unsus-tainable system. There is a great danger in settingstandards and then ignoring them. It is often betterto set appropriate and affordable standards and tohave a phased approach to improving the stand-ards as and when affordable. In addition, such anapproach permits the country the opportunity todevelop its own standards and gives adequate timeto implement a suitable regulatory framework andto develop the institutional capacity necessary for

only 60mg/l unfiltered; two 3-day maturation pondswould be needed to get the BOD down to a 30 mg/l

unfiltered - equal to an increase in retention time of120%! So the filtered, unfiltered question has majorcost implications. Those who might worry about theeffect of pond algae in a receiving watercourseshould remember that they will produce oxygen dur-ing the day but, more importantly, they will be quicklyconsumed by the stream biota,... So maturation

enforcement.

(Johnson and Horan: Institutional Developments,Standards and River Quality, WST, Vol 33, No 3, 1996)

It is also important to apply a law in keep-ing with its original intention. But this isonly possible if the technology is fully un-derstood. It is interest ing to know that Eng-land at the end of the last century consid-ered case by case assessment of individualpolluters but abandoned the propositionfearing administrative snarls and an unten-

able relaxation of discharge standards. Inthe current scenario when decentralisedwastewater treatment is being taken farmore seriously than in the past, such anapproach may still be advisable. In the caseof pond treatment Duncan Mara gives anexample:

If filtered BOD was permissible then a one-dayanaerobic pond plus a 4-day facultative pond couldreduce the BOD from 300 to 30 mg/l filtered, but to

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ponds are not always required.(D. Mara, Appropriate Response in WQI May/June

1997).

Another obstacle to achieving a better de-

gree of treatment are unrealistic and overlyambitious master plans that could neverbe successfully implemented in the giventime and resource frame; whereas moremodest, intermediate solutions would bemore likely to succeed. In all fast growingtowns and cities, municipal boundaries havebeen over run by rapidly expanding urbanagglomeration; a fact, that is perhaps noteven reflected in the master plan. On the

other hand, an over extended master plancould be well beyond the financial andlogistical strength of the municipality. A moregeneral solution, that includes appropriatedecentralised treatment systems could im-prove the environment considerably, al-though this measure would have to bearthe label of being only temporary (tem-porary like slums, which by practice be-came permanent).

3.6.3 Legal Aspects of Some Sectors ofDEWATS Application

3.6.3.1 Human Settlements

Administrative support to disseminateDEWATS must distinguish between low-in-come areas, middle class housing coloniesand high income enclaves. A pragmatic


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approach would be to pass a temporaryby-law (or short-term master plan) for a

specific area, which reflects both, the eco-nomic as well as the environmental situa-tion. Making the ultimate degree of treat-ment the yardstick does not work. A morerealistic benchmark ought to take into ac-count the capacity of the administration -financial and logistical - to enforce the fea-sible standards of those temporary by-laws. Since local conditions vary from siteto site, the prescription of absolute meas-

ures would be self-defeat ing were adminis-trative guidelines would be more befitting.Such guidelines should take into account:

J Items which can immediately be consid-ered, e.g. treatment systems which canbe implemented by the individual pol-luter or the respective group of pollut-ers at the time of constructing the build-ings.

JItems which will remain valid into thefuture, and will not conflict with futuremaster-plans.

J True temporary items which may have ashorter life time or lower performancethan everlasting structures.

The key purpose behind temporary by-lawswould be to prescribe, rather dictate a setof DEWATS measures, than to set stand-

ards of discharge quality which have to becontrolled. Durable, anaerobic rough treat-ment systems such as baffled septic tanksor anaerobic filters may be most suitablein such cases. Smaller sewage diameterscould later be used if these pre-treatmentsystems are kept permanently in operation.A centralised maintenance service or con-trol over a decentralised service would beneeded to guarantee that the system works.

In case of high-income enclaves, individualpost treatment with planted gravel filters

would be appropriate when receiving wa-ters are not located too far away. Other-wise, post-treatment is preferably done insemi-centralised units, e.g. ponds, whichmight be cheaper to construct and operate.Sewage lines cannot be avoided in that case.

3.6.3.2 Hospitals, Schools, Compounds,Army Camps, Hotels, etc.

An institution could sometimes be the onlysubstantial polluter in an otherwise cleanand healthy rural environment. In such acase, permanent on-site wastewater treat-ment is the only solution.

The best approach to achieving the highestdegree of environmental protection wouldbe to let realistic assessment of possibletreatment methods guide administrative

control. The potent ial of the most appropri-ate DEWATS should be the basis for settingdischarge standards and for dictating com-pulsory treatment units. Durability and per-manence should rule over the tendency toset the highest theoretical standards of treat-ment performance.

In the case of new installations, only op-tions which fulfil DEWATS criteria stand achance of providing permanent and viable

service. Systems using artificial oxidationtechnologies should not be permitted, sincethe system can be switched off without nega-tive impact on the polluter himself. Thepollution control authorities have to pro-pose DEWATS if the polluter or his planningarchitect is not familiar with that option. Itshould not be difficult to enforce the nec-essary by-laws, since DEWATS is probablythe most economic alternative.

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3.6.3.3 Industrial Estates

Industrial estates are a conglomeration ofenterprises that produce wastewater ofvarying volume and strength. A commontreatment plant for the whole estate maybe the best solution. However, it may bedifficult to convince all the entrepreneursto pay towards a co-operative treatmentsystem, particularly if only few membersdischarge substantial amounts of waste-water.

A co-operative treatment plantmay be the right solution, but

people forced to co-operate maynot think so

In a decision that favours individual treat-ment systems, the application of generaldischarge standards may turn out to beunjust to certain enterprises, or may even

discourage certain industries from settlingin the esta te. In a scenario where the waste-water output by the majority of the enter-prises is low and only a few industries wouldmerit environmental control, strict dischargestandards enforcement for only those fewmay not lead to an acceptable wastewaterquality at the exit of the estate, since thelarge number of small polluters may havegreater impact than one or two severe pol-luters. A more moderate application of thelaw could be more productive because ofits inherent feasibility. However, it is thedecision of the administration to allow suchexceptions. If discharge standards are strictlyenforced, larger cash rich enterprises mayopt for conventional (non-DEWATS) solu-tions, which are quite likely to succeed ifcontrol and operational management willbe maintained. Fund starved, small-scale

units on the other hand are bound to cheaton pollution control whenever possible due

to financial constrains.

Small-scale industries that have substantialwastewater production need land for finaltreatment systems, such as ponds or con-structed wetlands which depend on naturaloxygen supply via surface area. The requiredland ought to be provided to the individualenterprise or to the estate as a whole at alower rate. New industrial estates are sel-dom connected to sewer lines immediate ly.

Thus, provision of land for such post-treat-ment systems would need to be made rightat the planning stages. If the pollution con-trol officer could agree to apply the legaldischarge standard at the outlet of the to talestate, instead at the boundary of the indi-vidual enterprise, existing estates could useopen drains as natural oxidation ditches forpost treatment.

3.7 Dissemination Strategy

It would be overbearing, or at least prema-ture to pretend to know the disseminationstrategy for DEWATS without having in minda particular situation. Dissemination strate-gies for decentralised technologies must bebased on local facts and actors, explicitly,however under consideration of general fac-tors, such as:

J the requirements of the technology itself(first of all!)

J the legal framework, and

J the conditions for funding of the neces-sary infrastructure, including a likely su-perstructure.

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3.7.1 Components of Dissemination

3.7.1.1 InformationThe terminology awareness building doesnot appear to do justice to the subject. Whilethere may be a need for awareness build-ing with the administration in some places,the existence of rules and regulations areindicative of awareness in most countries.After becoming aware of their problems,clients want information on solutions. Im-plicit in knowing the technology is knowl-

edge of the limitations and conditions un-der which the potential of the technologycan be put to use. Beside direct customers,administrators, and potential implementers(contractors and engineers, etc.), the gen-eral public also needs to be informed.

Low maintenance does not meanNO-maintenance.

3.7.1.2 Regulation

Regulation of discharge standards play animportant role to create the need for treat-ment and to choose the appropriate tech-nology for it. Regulations should be flexibleenough to allow appropriate alternatives with-out putting at risk the environmental needs.

3.7.1.3 Financing

Wastewater treatment is a cost factor andrepresents a substantial investment tomost polluters. While financial incentivesmay accelerate the introduction of newtechnology, their prescription as a gen-eral instrument for implementation is illadvised . Nevertheless , access to soft bankloans is essential, particularly to small-scale enterprises .

3.7.1.4 Implementation

Characterised by a small building volumeas base for calculating engineering fees,DEWATS understandably does not attractengineers. Engineering companies wouldneed to be seriously persuaded to designDEWATS instead of conventional treatmentsystems of which components can be boughtready made. It may be worth subsidisingengineering fees as a promotion instrumentuntil at least that time when DEWATS be-comes popular. These incentives are social

investments which ought to be calculatedagainst the future gains of a pollution freeenvironment. In the same vein, it may benecessary to pay engineers to train con-tractors in DEWATS construction. One pre-condition for that is that expertise andknowledge about DEWATS is available withthe free-lanced engineers.

3.7.1.5 Operation

Treatment plants that work without a mini-mum of maintenance and supervision arenon-existent. It seems difficult to keep theknowledge about maintenance for sure withthe polluter until maintenance becomesnecessary for the first time. User trainingand professional maintenance would haveto be guaranteed for some years at least,through a contract between the customerand the supplier.

3.7.1.6 Control

Control is the flip side of regulation. If animproved control system cannot be part ofthe dissemination strategy for financial orother reasons, then control must insist onthe implementation of reliable technologyoptions, such as DEWATS.

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3.7.1.7 Reuse of Resources

Treating of wastewater requires a differentexpertise than for the re-use of wastewaterand sludge in agriculture or fishery. Simi-larly the utilisation of biogas also requiresspecial expertise. If the re-use of by-prod-ucts is to be part of the dissemination strat-egy, the engagement of other appropriateagencies or individual experts to attend tothis purpose may become expedient.

3.7.2 The Motors of Dissemination

3.7.2.1 The Government

As governments are primarily responsiblefor environmental protection, by the sameconvention, the responsibility for the dis-semination of DEWATS should essentiallyalso vest with the government. The govern-ments major guiding instrument is reliablecontrol of reasonable discharge standards.

Nonetheless, a suitable legal framework mayalso include tax exemption, the provisionof subsidies - direct or indirect- and suretyfor bank loans. Direct subsidies, which areperceived to distort economic competition,are no longer in vogue. Consequently it maybe necessary to structure indirect financialsupport to activities such as awarenessbuilding, research, training, or infrastructureto non-governmental organisations (NGOs),private enterprise and professional associa-tions to enhance the scope of dissemina-tion. Project ideas would principally haveto come from these agents.

3.7.2.2 Non-Governmental Organisations

Characteristically, NGOs play a variety ofroles foremost of which is their innate sup-port to weaker groups of society to fight

private or governmental abuse of their rightsas citizens. Today a large number of NGOs

are committed to environmental justice. Itis not uncommon to find NGOs protestingagainst the violation of pollution standardsand succeeding in getting the governmentto bring the law to bear against carelessoffenders or to even get the government tochange archaic rules and regulations.

The role of the NGO may be extended toimplementation and technical training aslong as the normal market forces consist-

ing of engineers and contractors have notbecome involved adequately. However, it isimportant to realise that wastewater treat-ment is not a matter of propaganda but amatter of applied natural science. No NGOcan become an implementing agency with-out permanently involving persons of suffi-cient scientific and technical knowledge.

Wastewater treatment does nothappen through propaganda, butthrough applied natural science.

NGOs start traditionally from acute singlecases and then, with growing experienceand knowledge move towards a more gen-eral approach. NGOs have the inherent po-tential to effectively disseminate DEWATSprovided powerful persons and institutionssupport them in overcoming administrativebottlenecks and in access ing the funds thatare needed for their activities.

3.7.2.3 Development Projects

At the one hand, development projects mayeither create a model reality, and try tomanage it well for demonstration purposes,

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or at the other hand, execute and supportmeasures which directly influence the pre-

vailing reality outside and beyond theproject.

For demonstrating a general idea it mightbe effective to create a limited and control-lable model reality wherein everything workswell. However, it would be dangerous tobelieve that the model is a reflection ofreality, because of the expenses involvedthis proposed reality can never come true.

Rural biogas dissemination and other de-velopment programmes have proved thatsuch well-designed projects are not exam-ples of what is really possible. The lavishorganisational structures that such pro-grammes demand are counter productive.The pressure to present a perfect projectsolution has proved not to bring forth asustainable solution for the time after theproject is over.

Decentralised wastewater treatment is a verycomplex subject that is greatly influencedby socio-economic and political circum-stances. A development project is at best amodest contribution towards eliminatingbottlenecks in the overall complex realityof a specific development sector.

Foreign aided development projects that arepartnered by government agencies or localNGOs may be a suitable instrument to over-

come financial and structural shortcomings.The character of the local partner organisa-tion and its need for support determine thenature and character of any aid from out-side.

3.7.3 Approach to Dissemination

3.7.3.1 Individual ImplementationDissemination of DEWATS means first of all,the construction of as many plants as pos-sible. Any private engineer who designs andinitiates the construction of DEWATS for hiscustomers, provided his plants are well de-signed, well constructed, well operated andwell maintained is the perfect disseminator.However, his efficiency depends on the abil-ity to acquire new customers through the

propaganda about his good service.Buildings and other structures, includingestablished treatment systems such as sep-tic tanks are conventionally implementedby individual contractors. Designs for sep-tic tanks of different sizes are easily avail-able and their construction does not requiremore than the usual building practice. Build-ing contractors install septic tanks as ef-fortless ly as they put up buildings. Anaero-

bic filters or constructed wetlands are notthat easy to disseminate. Rigid standardisa-tion tends to jeopardise the economy andthe design principles of these systems. Con-sequently a deeper understanding and ahigher degree of expertise is required atthe level of direct implementation. This couldbe achieved through training or qualifiedsupervision during construction of theseunusual structures. However, both optionswould require a superstructure to execute

and finance these services. Baffled septictanks and pond systems could be dissemi-nated with less specialised expertise.

3.7.3.2 Sector-wise Dissemination

Individual implementation would be the bestapproach to d issemination provided stand-ardised designs were to be available, at least

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Some selected domestic wastewater data

examples COD BOD5COD /BOD 5

SS Flow

g/cap.*d g/cap.*d g/cap*d l/cap*dIndia urban 76 40 1,90 230 180USA urban 180 80 2,25 90 265China pub.toilet 760 330 2,30 60 230Germany urban 100 60 1,67 75 200France rural 78 33 2,36 28 150France urban 90 55 1,64 60 250

BORDA

for those cases that are most common in agiven situation. Any dissemination strategy,

which relies on relatively low professionalstandards for implementation, should bestfollow a sector-wise approach. For exam-ple, there could be standardised treatmentsystems for housing colonies of one city,for rural hospitals in a hilly area or for ho-tels and holiday resorts at a scenic lake.Latex sheet processing plants at small rub-ber farms could as well be standardised, socould plants for wastewater from rice mills

or canning factories.

Tab. 2.Average data of domestic wastewater at variousplaces

tise. The engin

borda dewats handbook

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