urban wastewater projects - a layerperson's guide.docx

8/12/2019 urban wastewater projects - a layerperson's guide.docx

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Production managed and edited by Stephen D. Myers (EWPCA President, 1996-97)and coordinated byGunnar Fr. Aasgaard and Harsha Ratnaweera (Norwegian Institute for Water Research, NIVA)

European Environmental Agency in collaboration

with European Water Pollution Control Association e.V.

This Report was prepared for the EEA by

the European Water Pollution Control Association e.V. European Environment Agency (1998)

The European Environment AgencyKongens Nytorv 6DK-1050 CopenhagenPhone: + 45 33367100

Fax: + 45 33367199

Published byThe European Water Pollution Control Association e.V.Theodor-Heuss-Allee 17D-53773 HennefPhone: +49 2242872189Fax: +49 2242872135

Printed in Germany by Mocker Merkur Druck GmbH, Cologne

Acknowledgements

The preparation of this Laypersons Guide to Urban Wastewater Projects has only been possible through thecombined efforts of many individuals and organisations and their respective contributions are gratefully

acknowledged.

The European Water Pollution Control Association (EWPCA) first discussed the initiative with the EuropeanEnvironment Agency (EEA) in 1995. Thanks are due to the EEA for providing funds towards the preparationof the Guide and in particular, to the Executive Director of the EEA, Domingo Jimz-Beltrand the ProjectManager, Dr Niels Thyssen. Thanks are also due to the Norwegian Government who provided supplementaryfunds in the early stage when the concept was being developed. The Norwegian Institute for Water Research(NIVA) is thanked for providing with supplementary funds during the final editing stage.

A great debt of gratitude is due to all those who actively participated in the development of the project and tothe drafting of the Guide, as they all devoted far more time to the project than was covered by the verynominal renumeration accorded them. Their respective involvement in the work, all gratefully acknowledged,were as follows:

Mr Stephen D. Myers (UK), managed the production overall, edited the Guide, wrote Chapters 1, 2, 4 (part),5 and 9 and permitted Annex C to be reproduced;

Mr Gunnar Fr. Aasgaard and Dr Harsha Ratnaweera (Norway) co-ordinated production and preparation ofthe Guide, jointly wrote Chapter 3 and contributed to Chapter 7;

Dr John Hawkins (UK), who wrote Chapters 6 and 7, and Mr David Musco (UK) who wrote much of

Chapter 4;


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Dr Peter Matthews (UK), who acted as Technical Editor and who arranged his organisation, Anglian Waterplc, to produce Chapter 8;

Mr Fetter Wang (Norway), who produced cartoons at the head of each Chapter and Mrs Kathleen Soupilas,

who reviewed the text;

the members of the Panel which reviewed the Guide at all stages of its production - Mr Athanasios Soupilas(Greece), Mr Jorge S. Santos Temido (Portugal), Mr Henri Barthalan (France), Mr Zeljko Telisman (Croatia)and Mr Miroslav Kollar (Slovak Republic).

In addition, an advanced draft of the Guide was circulated to the EEAs 18 National Focal Points, members ofthe EEAs Scientific Committee, Directorate General XI of the European Commission, each of the 24 nationalmember organisations of the EWPCA, and a broad range of organisations involved in the wastewater sectorthroughout Europe. The many comments received were invaluable in the revision and completion of the finaltext.

The assistance of the following organisations, which supplied photographs for illustrating the text is gratefully

acknowledged:

Vlaamse Milieumaatschappij (Belgium), Alfa Laval (Denmark); I/S Avedloakv (Denmark); Krystems A/S(Denmark); Lyonnaise des Eaux (France); Endress + Hauser (Germany); Lurgi GmbH (Germany); AziendaPo Sangone (Italy); Biovac AS (Norway); Kaldnes Miljologi AS (Norway); Kemira Water (Sweden); AnglianWater (UK); Biwater Ltd (UK); McDowells (UK); Southern Water (UK); Water Research Centre (UK).


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Chapter 1. The Guide - Its Purpose, Structure and Use

Figure

1.1 Purpose of the Guide

Figure

Figure


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Figure

The primary purpose of the Guide is to provide persons who do not have a technical background, includingthe general public, with information on aspects and issues that arise when planning and implementing anurban wastewater project.

The Guide is principally aimed at employers and politicians involved in local, regional and nationalgovernments in Member States of the European Union and neighbouring countries. It has also been designedand written to be of interest to persons at all levels of government who have a technical background and who,

for the first time, are to be involved in the management of wastewater.

The objectives underlying the production of the Guide, with respect to urban wastewater management, are to:

provide a readily understood guide to related EU legislation;

enable options to be identified and to describe the principal characteristics, issues and consequencesassociated with choosing between them;

provide a bridge of communication between non-technical persons and their technical colleagues andprofessional advisers;

provide laypersons with the basic principles sufficient to understand the proposals for the projects, productsand services put to them by their advisers and commercial entities.

1.2 The Guides Structure

Chapter 2 provides an introduction to urban and rural wastewater management through responses to questionscommonly raised on the subject.

Chapter 3 outlines the EU directive concerning Urban Wastewater Treatment and other legislation, the impactof wastewater treatment on the environment and introduces the concept of integrated planning of wastewatermanagement.

Chapter 4 explains the decision making issues in urban wastewater projects, the necessary resources to bemanaged and matters that relate to project phasing and institutional arrangements.

Chapter 5 describes sewerage systems, sewer networks, and their construction and management.

Chapter 6 outlines the issues, solutions and process options involved in planning an urban wastewater and

sludge treatment works.


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Chapter 7 covers key points of technical detail associated with wastewater and sludge treatment but with eachof the technical points explained only in summary form.

Chapter 8 deals with revenue and user charges.

Chapter 9 explains the options for implementing urban wastewater projects.

All sector-specific terms, or technical terms that a layperson might not be expected to understand, are includedin an Annex B, which contains a glossary of terms used in the Handbook.

1.3 The Use of the Guide

The Guide has been structured to meet the needs of different levels of understanding of the subject. It is

essential to recognise that it is a Guide for the use of laypersons and that, even though it is as technicallyaccurate as is possible given that context, it is not a textbook on wastewater projects and as such is unlikely tosatisfy technical purists in every respect.

As far as has proved practical, each of the chapters has been written to be self-contained. If time does notpermit a complete reading of the Guide, it is therefore possible to dip into chapters of particular currentinterest to the reader. Further, in order to speed reference to the Guide, technical and institutional details have

been removed to the annexes.

In order to minimise the material to be read, and where appropriate, options, issues and the ramifications ofchoice have been reported in a summarised tabular form. Use has been made of charts, diagrams andphotographs, to convey the main points in each chapter.

The main chapter headings are as follows:

Chapter 2 An Introduction to Urban and Rural Wastewater Management

Chapter 3 Environmental and Legislative Context

Chapter 4 Planning Issues

Chapter 5 Wastewater Networks

Chapter 6 Wastewater and Sludge Treatment and Disposal - General

Chapter 7 Wastewater and Sludge Treatment and Disposal - Details

Chapter 8 Revenue and User Charges

Chapter 9 Project Implementation

It is recommended that Chapter 2 be read by all persons using the Guide as this deals with a number of keyconcepts.


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Chapter 2 - An Introduction to Urban and Rural Wastewater Management

Figure

Fig. 2 No caption

2.1 Chapter Content

The purpose of this chapter is to provide an introduction to the subject of urban wastewater and the issues it

raises with respect to its management in the best interests of the public and the environment in which it lives.

A list of questions commonly asked by those embarking upon the planning of an urban wastewater project forthe first time has been compiled. Many of the topics are dealt with in greater detail in later chapters.

This chapter has been divided into the following sections:


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2.2 The Nature of Urban Wastewater

2.3 Sewer Systems

2.4 Industrial Effluents

2.5 Rural Area Sewage

2.6 Wastewater Treatment

2.7 Effluent Disposal and Beneficial Use

2.8 Sludge - Treatment, Disposal and Beneficial Use

2.2 The Nature of Urban Wastewater

2.2.1 What is urban wastewater?

The main component of urban wastewater is sewage from domestic dwellings, offices and other commercialpremises. Liquid effluents from industrial processes and service industries such as laundries are also

commonly discharged into urban sewers together with domestic sewage. Older sewer systems were alsodesigned to receive rainwater, drainage from streets, roofs and other paved and impermeable areas. Although

this practice continues today, it is increasingly common to provide a separate network for rainwater.

2.2.2 What is domestic sewage?

The liquid waste produced by domestic activities has two main components:

Grey water; Water that has been used for baths, showers, in wash-basins and the washing of clothes andfloors, and

Black water; Water and waste from toilets and kitchen sinks. In turn, toilet waste in areas not served bysewer systems may be termed night soil, as it is separately stored and carted away from the house.

Normally both of these components, black water and grey water, are combined and discharged into a singledrainage system and together are referred to as domestic sewage or simply sewage.

2.2.3 Why differentiate between grey water and black water?

Grey water contains very little solid material and under the right circumstances can be considered suitable for

recycling.

If plumbing systems permit the separation of the two components, grey water can be used for wateringgardens in times of drought. However, the adverse influence of increasing amount of detergents in grey wateron gardening should be kept in mind. In very exceptional circumstances, i.e. in chronically water-short areas,grey water may be treated at the place of origin and reused for toilet flushing.

It should be emphasised that the recycling of grey water imposes not only significant additional costs onhousing construction but also its treatment is subject to many problems. Reuse and recycling of grey water isnot yet a common practice.


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2.3 Sewer Systems

2.3.1 Why have we developed a waterborne system for carrying away our waste?

In early urban settlements, waste was dealt with at individual dwellings. The quantity of water used was

considerably less than today. Water would need to be drawn from wells or the nearest watercourse and carriedor hauled to the dwelling. Only rarely was water piped to centres of population and even more rarely toindividual houses. Water used for personal hygiene, the washing of floors and for cooking soaked away into

the ground. Human excreta was at best stored and this nightsoil, as it is sometimes called, was either cartedaway to a tip or watercourse or, as was common in China from early times, used as a fertiliser in agriculture.

As towns grew in size, it became an onerous task to cart away nightsoil from an increasing number of houses.The Romans designed and constructed drains beneath the streets to carry the water and nightsoil mixture awayby gravity to ditches and watercourses.

However, with the passing of the Roman Empire, it appears that its drainage techniques and practices fell intodisuse. Although a few towns could be said to have systematised their water supply and wastewater

infrastructure throughout the ages, in general, most towns and cities grew unplanned and lacked any form ofsystem to carry away waste. Where a system was provided, it generally consisted of open ditches along thecentre of streets into which all manner of domestic waste was thrown. These ditches were occasionallycleaned by the municipal authorities but more often than not were left to fill and fester until a storm carriedaway the accumulated mess. Open, natural watercourses collected the waste from the streets and when theflow in them was sufficient, the wastes were carried away from the city. Crowded cities stank from thesepractices and periodic bouts of dysentery and bubonic plague, which decimated medieval urban populations

from time to time, were a natural consequence of such unhygienic practices.

2.3.2 So what stimulated the inventi on and construction of our modern system of sewers to

carr y away the wastewater that we produce?

With the advent of the industrial revolution in Europe in the late 1700s, there was a considerable migration ofthe rural population to the towns that grew rapidly in size. Local wells and handpumps could no longer copewith the demand for water and, in addition, human waste seeped into the aquifers and contaminated the waterwithdrawn from wells for local use. The invention of steam-driven pumps enabled clean water in considerablequantities to be brought to the cities from sources remote from centres of population. Increasingly, a clean andabundant water supply was made available to cities and towns, initially at public standpipes in the streets andgradually, through a system of pipes, direct into houses and factories.


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Fig 2.1 Small diameter sewer under construction

Fig. 2.2 Effluent-producing factory

From the early 1800s, it became necessary to construct a system of drains to carry away such large quantitiesof water if the streets of towns and cities were not to become continually awash. Industrialised production ofthe water-closet at about this time made its installation in houses more common and further increased the

pressure for sewer systems to be constructed. Quite naturally, drains constructed to carry away water used forlaundering and for personal hygiene were also used to carry away water closet waste.

Although existing open watercourses and storm drains had been used for some time to carry away waste, thesewere now culverted, roofed over, and additions to the system were constructed as closed culverts from theoutset. In time, sewer systems were designed to comprehensively serve all development and where a gravitysystem could not cope alone, pumping stations were constructed.

At first, wastewater was carried away to the edge of developments and discharged untreated intowatercourses, lakes and the sea. As wastewater quantities increased and the link between sewage, disease andhygiene became firmly established in the middle of the 19th century, conditions in rivers, lakes and coastal

waters became aesthetically and hygienically unacceptable. In order to reduce the polluting potential of thewastewater, treatment plants were constructed from about this time. Initially sewage was either subjected to


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settlement or conveyed to farmland on the outskirts of towns and cities. So common and important was thispractice that the public still often refer to modern, sophisticated treatment plants as sewage farms.

Treatment techniques have now been developed to the point that, if necessary, under extreme circumstances,wastewater can be treated and reused as drinking water. However, under most circumstances, it is neither

environmentally necessary nor economic to treat to such a high standard.

2.3.3 What does an urban wastewater system consist of?

An urban wastewater system is composed of a sewer system, a wastewater treatment works and an effluent

discharge pipe. Sewer systems are described in Chapter 5 and wastewater treatment works in Chapters 6 and7.

2.4 Industrial Effluents

2.4.1 What are industrial eff luents?

Industrial effluents are the liquid wastes from industrial processes.

In some cases, industrial effluents are similar in their constituents to domestic sewage, e.g. those from foodprocessing, soft drinks manufacture or laundries, although they are often stronger and produced inconsiderable quantity. In others, they may contain material that would be toxic or corrosive to discharge into a

watercourse or sewer untreated, e.g. those from many chemicals processing plants, refineries, urban gasworks,electroplating factories and metal-pickling and paint workshops. Some wastes may be akin to domesticsewage but are extremely polluting due to high concentrations of organic material such as blood, oils andgrease, e.g. effluents from dairies, slaughterhouses, breweries and distilleries.

2.4.1.1 When should the discharge of i ndustri al eff luents into sewers be permitted?

With the exception of the effluent from largest industrial sites such as petroleum refineries, it is generallyaccepted that, subject to the control of their quality and quantity, most industrial effluents should bedischarged into the public sewer system for treatment at the municipal works. There are a number of reasonsfor this:

Many industrial effluents are readily treated by the same processes normally installed at a municipal

wastewater treatment works and some are more easily treated when mixed with domestic sewage than on theirown.

If required to treat the effluents on site, before discharge into a sewer or a watercourse, the plant will often

be poorly operated and maintained, as effluent treatment is rarely considered an integral part of the industrialprocess. This results in the need for considerable surveillance by the regulatory authorities. Hence theexpertise of the municipal plants can be exploited in ways that may not exist on the factory.

All industrial effluent treatment plants produce sludges and many produce screened material. These musteither be treated at the site of the industry or carried away for treatment. This can cause considerable odourand disruption of traffic and, depending upon the type of industry, can be potentially hazardous.

In some cases, effluent treatment adds considerably to the cost of industrial production and it is not good forthe competitiveness of industry, and thus the local economy, if higher than necessary treatment costs areimposed on industry. The larger the treatment works, the lower the cost of treating a cubic metre ofwastewater. Therefore, to combine industrial effluents with domestic sewage, will result in a lower treatment

cost. The cost of conveying the industrial effluent and of treating it can be calculated and should be chargedback to the industry.


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In several countries the discharge of treated/untreated industrial wastewater will be allowed only afterthorough assessment, as it can contain constituents that may adversely affect sludge quality, thus affecting its

reuse potential in agriculture.

However, before an industry is permitted to discharge its processed effluents into the public sewer, the public

authority should agree on the conditions for discharge. These will include a limit on the maximum hourly anddaily effluent flow, limits on physical, chemical and bacteriological content and the charges to be levied foraccepting the effluent into the sewers and treating it. The conditions should be expressed in a legally bindinglicence.

It is now common in the EU to practise the precautionary approach. That is to say, an industry is required todemonstrate that effluents whether, untreated or treated will not adversely affect the public wastewatersystem, failing which, permission should not be granted for their discharge into the sewers. In all cases it willbe beneficial to the industry, the community and the environment to encourage processes and practices thatproduce a minimum of waste.

Many sources of information exist on the quality limits to be placed on industrial effluents before they can be

accepted into the public sewer system and on methods for charging for this service in a fair and equitablemanner.

Before an industry is permitted to discharge its effluents into the public sewer system, it should be required todemonstrate that they do not contain substances which, in the sewers, either alone or mixed with sewage orother effluents, could:

produce toxic or explosive atmospheres;

be corrosive to the fabric of the sewers or machinery in contact with the sewage;

have a detrimental effect on the sewers and the treatment processes at the municipal wastewater works;

have a detrimental effect on the use and disposal of the final effluent and sludge by-products;

suddenly or progressively block the sewers, e.g. excessive amounts of oil or grease;

cause flooding by causing pump failures.

In addition, the effluents should be neither excessively hot or cold. It may be that an industry will need toinstall a plant to pre-treat their effluents in order to make them acceptable for discharge into the sewers.

2.4.1.2 When should an industry be refused permission to discharge its eff luentsin to the public sewers?

If an industry cannot comply with the quality or quantity limitations that the authorities wish to set, then itmust make arrangements for treatment at its own site and for the conveyance of the effluent to a watercourse.

However, there are other concerns that may influence a decision to give or refuse permission for an industry to

discharge its effluents into the public sewers.

A town or city normally has a long term existence. Industry is not so permanent. Due to market uncertainties,an industry cannot be sure of its future existence beyond the short term, often less than 2 or 3 years. Sewersystems are designed and built to last for 50 years or more, the structures in Wastewater treatment plants 30years and machinery 10 to 15 years.


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If additional sewer capacity or treatment units have to be provided in order to accommodate an effluent fromindustry, the municipal service provider will need to be certain of recovering the significant investment made,from the industry concerned. It is difficult to be precise as to when additional sewer or treatment capacity willbe needed. However, consideration will need to be given to this when flows and pollution loads from a singleindustry exceed 5% of the municipal wastewater flow and some additional capacity will almost certainly beneeded when this figure exceeds 15%.

In the event that additional capacity would need to be built, there are a number of options:

the industry concerned can pay directly for the additional capacity, or

it can make financial provision to guarantee repayment in the event of closure or change of needs due to areduction in their manufacturing processes or production capacity.

If the industry can satisfy neither of these, discharge of its effluents may be refused and it will need to treat theeffluents on its own site. However, it can be complicated by many economic factors, for example theadditional development of an area may be positively stimulated by various authorities in a particular area

through subsidies or grants or reduced contributions.

2.5 Rural Area Sewage

2.5.1 How is sewage from rural areas treated?

In rural areas, domestic sewage is normally dealt with on individual premises in cesspools and septic tanks.

Cess-pools are tanks without an outlet that are used solely to store the sewage. The stored waste must befrequently removed as the tank is filled. Cess-pools are expensive to operate due to the frequent necessity toempty them. Cess-pools are installed only when the ground is impermeable or the water table rises to near or

above ground level for all or part of the year.

Fig. 2.3 Factory-built treatment plant for small, rural developments

Septic tanks are small underground tanks interred in the ground, away from the houses that they serve andwhich act as small treatment plants with a low efficiency. Solids settle to the floor of the tank and oils andgrease rise to the surface of the tank contents. A clarified effluent is preferably dispersed into the groundthrough a soakaway system. Less acceptably, the effluent may be discharged to a ditch or watercourse but itsquality is such that this may give rise to odour problems or pollute the recipient. Periodically, sludge is suckedfrom the septic tank by a purpose-built road tanker and conveyed to a plant for further treatment and safedisposal.


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For larger premises in rural areas, such as hotels and restaurants, a small treatment plant, often factory-built,will be installed. These plants use the same basic treatment processes as municipal wastewater plants.However, arrangements are normally made to convey the sludges that they produce to a municipal plant fortreatment and safe disposal.

2.5.2 When i s the transiti on made fr om individual on-site treatment to the construction of asewer system to transmit sewage to communal treatment?

A sewer system and communal treatment plant are constructed when it is either cheaper to do so thanconstruct and operate individual on-site facilities, or when the ground on which the development is situated is

insufficiently permeable to absorb the discharges from septic tanks. Under these circumstances, unsanitaryconditions and odour nuisance may result from this practice or the quality of the groundwater may be reducedto an unacceptable level.

2.5.3 Do rural wastewater treatment plants for small populations create particular

problems?

Ideally, a wastewater treatment plant would be served by a short sewer system, receive a constant flow rate ofwastewater and be of a size to justify a full compliment of technical and support staff working on-site. Sewersystems and small treatment plants serving scattered rural populations and villages do not generally satisfythese criteria and so the problems created must be taken into account when planning their design andoperation, viz.:

long lengths of sewer and pumping mains serving small populations have long retention times andwastewater can become septic, creating offensive odours and difficulties in treatment;

the smaller the population served, the more variable is the wastewater flow rate and the pollution load

arriving at the treatment works throughout the day and treatment units must be designed to take this into

account;

it is often difficult to allocate operational staff exclusively to a small treatment works; if there are a numberof such works in an area, the formation of a mobile operations and maintenance team might be justified,otherwise regular visits should be made by the staff from a larger works, suitably trained in the operationalproblems of small units.

2.6 Wastewater Treatment

2.6.1 Why is there a need to tr eat wastewater?

Briefly, the treatment of wastewater is practised to avoid otherwise unacceptable conditions e.g.:

risks to public health

pollution of natural bodies of water into which effluents are discharged -watercourses, lakes and the sea - to

the point where they damage aquatic plant and animal life or prevent their normal economic, social orrecreational use through contamination or deoxygenation

pollution of the general environment by creating offensive odours or sights and the contamination ofgroundwater.

In addition, the provision of wastewater treatment is good social practice, there being a general publicaversion to finding sanitary waste in water bodies of environmental importance.


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The European Communitys Urban Wastewater Treatment (UWWT) Directive requires that all MemberStates pass legislation which ensures that developments having a population above a given figure to treat theirwastewater before discharge into watercourses, lakes or the sea. However, the degree of treatment to beprovided and the date by which such treatment must be operational, depends partly upon the size of thepopulation served and partly upon the sensitivity of the body of water into which the effluent is discharged.This is further detailed in Chapter 3, Section 3.3.

Wastewater treatment is described in greater detail in Chapters 6 and 7.

Fig. 2.4 Medium-sized wastewater treatment plant

2.6.2 What are the detr imental effects of discharging untreated wastewater into a recipient

and what are the benefi ts of wastewater treatment?

Wastewater Constituent Detrimental Effects Benefit of Wastewater

Treatment for CommunityLarge solid material -paper,rags, plastic bags, condoms,etc.

Unsightly - accumulate as litter on banksof rivers, lakes and beaches

River banks, lakes and theirsurroundings and beaches are renderedmore pleasant and safer environmentsfor work and for recreation

Can constitute a risk to health on contact Improved economy where based onrecreation and/or tourism

Organic matter - food waste,faecal matter and someindustrial effluent

Oxygen levels in receiving waters arereduced by bacteria and higher orders ofaquatic life consuming the organicmatter - fish and other organisms die and

eventually disgusting odours areproduced -similar to rotten eggs androtten cabbage

Livelihoods dependent upon fishing areprotected as is fishing for sport

More pleasant environment for living,working and recreation

Improved economy where based onrecreation and/or tourism

Oils and greases Unsightly and potentially damaging and

harmful scum formed on water surfacesImpermeable film on water surfacereducing potential for, water to absorboxygen from atmosphere

Improved oxygen absorption into the

water body from atmosphere assistingaquatic life to survive


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Nutrients - nitrogen,phosphorus and tracematerials

Act as fertiliser and stimulates growth ofalgae, seaweed and other aquatic plantschoking watercourses and littering banksof rivers and lakes and beaches with

rotting material, eventually becomingorganic waste

Improved and safer conditions forshellfish cultivation and other aquaticorganisms

Can stimulate toxic algal blooms whichaccumulate in shellfish and can infecthumans who consume them



Disease-causing bacteria andviruses - e.g. cholera, typhoidand salmonella

Contamination of water resources usedfor drinking or irrigation of crops eatenraw by humans or animals

Improved public health Improved andsafer conditions for shellfish cultivationand other aquatic organisms

Contamination of water used forshellfish cultivation


Contamination of water used for watercontact sports

Toxic substances - generally

originating from industrialeffluents

Dependent upon toxicity and

concentrations in receiving water can

Improved conditions for aquatic life

Improved public health

- destroy or damage aquatic life

- accumulate in flesh of fish, shellfishand creatures which feed upon them andeventually affect humans consumingthem

2.7 Effluent Disposal and Beneficial Use

2.7.1 What are the options for eff luent disposal?

Treated effluent from a wastewater treatment plant is normally discharged into the nearest water body capableof accepting it without detrimentally affecting it. This can be a drainage ditch, a river, stream or torrent, a lake

or the sea.


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Fig. 2.5 Agricultural re-use of treated effluent

In some cases, to ensure adequate and effective dilution of the effluent in the receiving water, an underwaterpipeline must be constructed, equipped at its discharge end with a diffuser system. This is particularly so,when treated effluent is discharged into the sea and acceptable bacterial levels are required at the shoreline

and inshore waters without resorting to disinfection. The issue of mixing zones is important and theenvironmental/economic balance of several small discharges versus one large discharge needs carefulassessment.

In addition to providing dilution, a long offshore outfall provides time for natural bacterial die-off to occurbefore the considerably diluted effluent reaches the shoreline. Techniques exist for predicting the dilution,dispersion and die-off that will be achieved.

2.7.2 Under what circumstances is it worthwhi le to reuse treated effl uent for benefici al use?

Recycling treated effluent for further use is unlikely to be either necessary or worthwhile where natural waterresources are sufficient to satisfy all normal demands placed upon them by an area, e.g. satisfactorily servingthe needs of the population, commerce and industry, the public services, landscaping and agriculture.

However, if water resources are either periodically or continually unable to satisfy water demands in the area,the recycling of treated effluent for beneficial use should be considered.

It is generally possible to reuse effluent for use as irrigation water in agriculture, landscaping and forestry,although, unless it has been either disinfected or stored for some time, care should be taken in its use on crops

eaten raw, or where spray irrigation techniques are used.

Treated sewage effluent can be used for secondary industrial purposes such as cooling and quenching withouttreatment other than disinfection and dosing with algaecides.

Some water deficient areas have insisted on dwellings and public buildings being provided with dualplumbing systems for the water supply, one for toilet flushing and the other for all other water uses. It ispossible to use treated effluent in the toilet flushing system as long as suitable precautions have been taken

against cross-connection with the potable supply, e.g. colour coding of pipes and labelling of the effluent,and the effluent has been disinfected and dosed with algaecide.

If other uses are under consideration, such as in industrial processes or for drinking purposes, it will be

necessary to subject the effluent to considerable further treatment as for any other primary quality potablesupply. As effluent is generally of lower quality than natural water sources, this can be very expensive and hasbeen practised in very few locations.

2.8 Sludge - Treatment, Disposal and Beneficial Use

2.8.1 What is wastewater sludge?


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These solid residues are separated from the watery effluent from the process either by physical screening andfiltration or through sedimentation. Because these processes take place in a watery environment and it isdifficult to remove all of the water, the residues are not dry and, in fact, generally contain a high proportion ofwater prior to their further treatment. This mixture of solids and water is termed sludge.

Sludge is, in effect, a concentration of the polluting material in the wastewater, either in its original form ortransformed by the treatment processes. It has a high organic content and, if not treated, rapidly putrefies andgives off objectionable odours. It is therefore subjected to a series of treatments in order to stabilise it and to

remove sufficient water from it to enable it to be disposed of without its causing nuisance or polluting theenvironment.

Depending upon the degree of stabilisation and dewatering required, facilities for the treatment of sludge cancost between 30% and 50% of the cost of the treatment plant.

Sludge is more viscous than sewage and its treatment often poses more problems in operation than wastewater

treatment. However, it is essential to appreciate that:

no treatment plant can operate without producing sludge at some time and normally it is produced insignificant quantities every day

no treatment plant should be built without ensuring that there is a secure means of disposing of the sludge

every wastewater treatment plant must be provided with sludge treatment processing facilities capable ofadequately preparing the sludge for the disposal option chosen.

Sewage sludge utilisation is regulated by the EU Directive 86/278/EEC. The Urban Wastewater Directive91/271/EEC prohibits marine disposal of sludge after 1998. However it should be noted that several countrieshave much stricter national regulations.


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Fig. 2.6 Liquid sludge from wastewater treatment process is stabilised and dewatered prior to disposal or

beneficial use

2.8.2 What are the disposal options for wastewater sludge?

There are not many options for the disposal of sludge. The two most common are disposal into a sanitarylandfill and the beneficial use of sludge in agriculture, horticulture and forestry.

Disposal into a sanitary landfill can either be as dewatered sludge or, following incineration, as ash. Whendisposed into landfill, an especially prepared area, rendered impermeable, should be used, if it is necessary toprotect the groundwater below the site from pollution. Surface water runoff and drainage from the sludge from

this area will need to besubjected to treatment.

The use of sludge in agriculture is the preferable alternative. However it should be appreciated that the sludgecan contain disease-causing bacteria, sometimes in a cyst form resistant to disinfection, as well as organismsthat can harm certain crops. It may well be necessary to carry out some form of pasteurisation of the sludge orlong-term storage to avoid harmful effects. There are a number of processes that convert the sludge into aform of product that is easier and safer to handle in agriculture.

In addition, wastewater sludge contains concentrations of metals where these originate from industrialdischarges. It should be possible to reduce their concentration through controls on the industries concerned, inorder to remain within the acceptable limits for metals in soils.

2.8.3 Are there any other methods of disposal or beneficial uses of sludge?

In the past, disposal of sludge at sea was commonly practised by urban developments at or near the coast. Thispractice is prohibited from 1998 by EU Directive, 91/271/EEC.


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Considerable work has been carried out on beneficial use options. Particularly noteworthy is the recentresearch that has been done in Japan. The use of sludge has been considered for fuel, in ceramic productionand in the formation of building panels. It has even been used to produce decorative brooches, tie-pins andtable mats! At present, these uses are still to be considered experimental and are generally more costly thanconventional disposal or agricultural use. They can only be considered by the very largest of wastewaterplants serving populations in excess of a million.

Where sufficient landfill space is not available and when the sludge is not suitable for use in agriculture,

incineration will have to be considered. Ash resulting from incineration, which will be far smaller in volumecompared to the original sludge, must also be properly disposed of according to the same restrictions assludge.

2.8.4 What happens to screened material as well as grit and sand removed in the

prelimi nary treatment uni ts?

A very important aspect is the removal of sanitary litter e.g. sanitary towel strips, condoms, cotton and sticks.Very unsightly, blocks equipment, major PR problem in sludge use.

Paper, rags, pieces of timber, etc. arriving through the sewers at the wastewater treatment works can blockpipes and damage machinery and processes. This material is removed by screens at the inlet to the works.Frequently contaminated with sewage solids, screenings should be separately stored, preferably after awashing process and strained of excess water. They should either be burnt on site in an appropriately designedincinerator, or carted into the sanitary landfill used for the disposal of solid refuse.

Sand and grit enter sewers principally from roads and can damage machinery and accumulate in processpipework. In order to avoid this, and to protect the works, sand and grit, are removed in one of the firsttreatment units. Sand and grit should also be disposed of to a sanitary landfill. If units removing the sand andgrit are operating correctly, the material should be inoffensive to handle but, if not, washing prior to disposalmay be necessary.

Fig. 2.7 Grit and sand is disposed of to sanitary landfill


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Chapter 3. Environmental and Legislative Context

Figure

3.1 Chapter Content

This chapter explains the background and driving forces behind the current water legislation, and indicates

additional factors to be considered, based on local conditions, when setting effluent standards for wastewatertreatment plants.

The chapter has been divided into the following sections:

3.2 Why Treat Wastewater?

3.3 Environmental Legislation

3.4 The impact on the Environment

3.5 Success through Integrated Planning


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3.2 Why Treat Wastewater?

Fig. 3.1 Protecting user interests

Protection of the environment from the adverse effects of urban wastewater discharges is the objective of the

current EU Directive concerning Urban Waste Water Treatment (UWWT), which was adopted in 1991(91/271/EEC). This directive concerns the collection, treatment and discharge of urban wastewater and thetreatment of wastewater from certain industrial sectors. Additionally there are a number of EU Directivesaddressing related specific issues that require consideration, viz.:

Drinking Water (75/440/EEC)

Bathing Water (76/160/EEC)

Fish Farming/Aquaculture (78/659/EEC)

Shellfish Waters (79/923/EEC)

Sewage Sludge Disposal (82/278/EEC)

Discharge of Dangerous Substances (76/464/EEC)

Other relevant Directives are listed in Annex A.

All wastewater management in the European Union is expected to be based on these Directives. Many other

European countries are also implementing them. However, when planning urban wastewater projects, otherEU, national and local legislation must be taken into consideration. These will address the issues of the impactof all wastewater discharges that affect public health, the economy, aesthetic qualities and the sustainability ofenvironmental water use, as important driving forces.

The impact of a wastewater discharge on the local environment will vary, depending on the location and theexisting environmental status of the recipient. The need to attain and maintain acceptable local environmentalconditions may often exceed general requirements and hence require special attention. Thus the design of a

wastewater treatment plant should take into consideration both existing legislation and the present conditionof the environment.

An overall view of the legislation and the factors to be taken into account when initiating a wastewater projectis presented in Figure 3.2.

3.3 Environmental Legislation

The principal objectives of environmental legislation are to protect the environment, satisfy aesthetic criteria,protect public health and safeguard legitimate interests related to the use of water. Regulatory authorities mustestablish discharge standards for a given wastewater treatment plant, based on the relevant legislation and on

local and external environmental conditions. The EU Member States are free to adopt legislation in theabsence of EU legislation. However, where the Community has acted, EU legislation is supreme and binding,


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taking precedence over both past and future Member State actions. Thus the Member States must at least,fulfil the requirements of the EU Urban Wastewater Treatment Directive (UWWT).

Fig. 3.2 Elements and evaluations when initiating a wastewater project

3.3.1 What is the EU Urban Wastewater Treatment Directive?

The EU Directive on Urban Wastewater Treatment establishes a comprehensive system controlling the qualityof urban wastewater treatment and effluent discharge from most population areas, including industrial

wastewater discharged by industrial sectors to sewage systems and urban wastewater treatment plants.

The UWWT Directive sets minimum standards, which may be improved upon in local circumstances if theenvironment requires it. It seeks to combine the principle of quality objectives (with local emission standards)and uniform emission standards. Table 3.1 lists the principal requirements of the UWWT Directive withrespect to sewage treatment.


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Fig. 3.3 Sampling effluent from wastewater treatment plant

Table 3.1 Principal Technology needs of the EU Directive on Urban Wastewater Treatment

Population

EquivalentDischarge Location Technology

2 000 Inland rivers, lakes Full secondary treatment

> 2 000 Sensitive inland rivers, lakes Full secondary treatment and nutrient removal

> 10 000 High dispersion marine waters Primary treatment

> 10 000 Low dispersion marine waters Full secondary treatment

> 10 000 Low dispersion marine waters whichare sensitive

Full secondary treatment with nutrient removal

> 150 000 High dispersion marine waters - same -

Table 3.2 Major Deadlines, by 31 of December of the given year

> 15 000 p.e.10 000 - 15 000 p.e.2000 - 10 000 p.e.

Urban Wastewater

Collection System

sensitive areas 1998 1998 -

all areas 2000 2005 2005

Secondary treatment

sensitive areas 1998 1998 -

all areas 2000 2005 2005(if discharges are to freshwater and estuaries)

By certain dates, varying according to the size of the agglomeration and the location, as shown in Tables 3.1and 3.2, the following degrees of treatment must be provided for municipalities of 2 000 population equivalent(p.e.) or more, discharging into fresh water and estuaries and municipalities of 10 000 p.e. or more,

discharging into coastal waters:


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Standard treatment

Secondary treatment must meet with a certain standard of biochemical oxygen demand (BOD) - 25 mg/lwithout nitrification - chemical oxygen demand (COD) - 125 mg/l - and total suspended solids (SS) - 35 mg/l,the latter being optional. Minimum values for SS, BOD and COD removals are also specified as percentages.

The sampling frequency and acceptable number of samples not meeting the requirements are also specified.

For high altitudes, the provision of biological treatment may not be appropriate or practical but its omission isonly permitted subject to a study demonstrating that there will be no adverse environmental effects. In suchconditions, BOD must be reduced by a minimum of 40% and suspended solids must be reduced to 60 mg/l forpopulations from 2 000 to 10 000 and to 35 mg/l for populations in excess of 10 000.

Sensitive Areas (particularly those vulnerable to eutrophication)

The Directive sets minimum standards that may be improved upon locally, if environmental circumstanceswarrant it. Standard treatment is to be given as a minimum, but in addition phosphate and total nitrogen mustbe reduced to specified levels as necessary. Sensitive areas were to have been defined by national

governments by December 1993, although some countries did not comply with the legislation by the due date.The need for treatment at an individual work in a catchment may be assessed against an overall requirementfor at least 75% reduction in nutrients.

Less Sensitive Areas

Where comprehensive studies indicate that a discharge of less than standard treatment quality would notadversely affect a coastal, marine or estuarine environment, then primary treatment can be accepted for thosewaters for defined sizes of discharges. Primary treatment is defined as settlement or other processes in whichBOD is reduced by at least 20% and solids by at least 50%. These areas were also to have been designated byDecember 1993. Discharges are to be treated unless it can be demonstrated that there would be no

environmental benefits from the provision of such treatment.

Provision of Facilities

Sewage collection systems should be provided in accordance with the best practicable techniques not entailingexcessive costs and should be designed to limit pollution from storm sewage. Treatment works must bedesigned for a loading of 60 grams of BOD per person per day. Discharges of lesser size than that definedabove should have appropriate treatment by the end of 2005.

Industrial Discharges

Industrial discharges with pollution loads of BOD, COD or suspended solids equivalent to sewage from apopulation greater than 4000 should be specified and require a discharge permit.

Sewerage

A collecting system for municipal wastewater must be provided by the end of 1998 - 2005 for agglomerations

larger than 2000 p.e., as indicated in Table 3.2.

Sludge

The Directive also requires that the disposal of sewage sludge to the sea should have ceased by December1998. In the interim there is to be no increase in volume and a progressive reduction in any toxic persistent

and bio-accumulative constituents of sludge discharged to sea.


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Sewage sludge used in agriculture must conform with the provision of the EU Directive 86/278/EEC passed in1986. It should also be noted that several countries require much stricter standards in this respect.

Other Requirements

There are several other requirements. Industrial discharges into sewers should have been authorised by acompetent authority by December 1993 and be reviewed regularly. Criteria for identification of sensitiveand less sensitive areas are defined in the Directive. The list of sensitive areas must be reviewed every 4years.

National Legislation and Multinational Agreements

As rivers can flow through more than one European country and lakes and aquifers (groundwater reservoirs)can be transboundary, individual states affected in this way are working together to harmonise their policies

and actions by establishing multinational agreements. EU water legislation includes aspects related to theabove.

Both multinational agreements and national legislation must be considered when defining the treatmentrequirements for any urban wastewater treatment project.

3.4 Impact on the Environment

3.4.1 User i nterests must be defined

The state of the local water environment -the receiving water quality - may require a greater degree oftreatment from a wastewater treatment plant, than that set down by legislation. This will, in part, be due to the

user interests in the water resource, both now and anticipated for the future. This leads to the concept of waterquality objectives being used to determine discharge standards. Such objectives can be integrated into

environmental protection through integrated river catchment and river basin management plans that take aholistic view of the combined impact of all discharges.

The required quality of a water resource is related to current or future user interests. Such interests might be:

drinking water

agricultural use

recreation

shellfish and fish farming/aquaculture

commercial and hobby fishing

industrial use

nature protection area, etc.


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Fig. 3.4 User interests in a watershed

Some of these user interests are described in other EU Directives (see Section 3.2 and Annex A), whileseveral others are defined within national legislation.

An illustration of various user interests is presented in Figure 3.4.

A governmental authority should define the water uses, for each recipient; either for a part, or for the whole of

it. These must be considered when the treatment efficiencies for a wastewater treatment plant are designed.

3.4.2 How can the acceptable pol lution load to a receiving water be establi shed?

The difference between the water quality criteria defined for a water body and its existing water qualityindicates the extent of the need for a reduction in the pollution load of an effluent. Existing water quality cannormally be analysed by a local laboratory, as most of the parameters defined in water classifications arecommon.

When the quality of a receiving water is better than the levels required by the defined water qualityclassification it is an indication that it is able to accept a certain amount of pollutant load. Armed with this

information, the pollution load which may be discharged without lowering the classification of the water bodyor hindering its accepted use can be derived. The degree of treatment efficiency required of the effluent tomeet this limitation can then be calculated.

The acceptable pollution load resulting from the legislative requirements should be compared with the actualpollution loads to the selected recipients of sectors. Keeping in mind that industrial developments andpopulation expansion may occur in the future and given a choice, the regulatory authority should select themost suitable body of water to receive the effluent from the municipal wastewater treatment plant. Both atechnical and an economical evaluation must be carried out together with an environmental impact assessment

(EIA), see Section 4.6, to determine the most appropriate system of sewers and wastewater treatment plant or

plants that will achieve this objective. This is explained in greater detail in Chapter 4.


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3.4.3 How can the actual polluti on load to a recipient be estimated?

When estimating the pollution load which will enter a municipal wastewater system prior to treatment,account should be taken of the population to be treated, permanent and transient, industrial effluent and anypollution from municipal runoff permitted to the sewers. Calculation of pollution loads must also estimate

increases which will take place within the design life of the treatment plant. When calculating pollution loadto surface waters, account should be taken of effluents from wastewater treatment plants, industry notdischarging to the municipal system and agriculture. Households which do not discharge their sewage to a

sewer system may pollute groundwater with discharges from septic tanks.

Fig. 3.5 Sampling of effluents and rivers

If a treatment plant or a sewer system already exists in the area, it is recommended that the calculatedpollution load, should be based on the results of a sampling and analysis campaign.

Where it is not possible to sample the effluents to be treated, typical values for the average daily pollutionload generated per person and for several types of public institutions are available in the literature. Anestimation of pollution loads from industrial units producing significant quantities of polluting effluent shouldpreferably be made by a direct monitoring of the quantity and quality of their wastewater. Alternatively, if aneffluent sampling is either impractical or not possible, pollution loads should be estimated by a qualifiedconstancy or environmental institution.


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Fig. 3.6 No caption

3.5 Success through Integrated Planning

3.5.1 How can poll uti on loads be minimised?

Where industry has not previously been concerned with the treatment of its effluents, there is frequently scope

to reduce both volume and polluting load. Environmental audit procedures are used to analyse industrialprocesses which give rise to effluent production and it may prove economically beneficial either to modifyoperation of installations or consider alternative production processes which lead to effluent and pollution

load reduction. Many industries have achieved a reduction in pollution by improved housekeeping and

through increased awareness among their operational personnel. Introducing Clean Technology will furtherreduce adverse environmental impacts of industrial production processes.

There is increasing interest in demand management, i.e. the encouragement of reduction in water usage byhouseholds and, where successfully introduced, this leads to a reduction in wastewater discharged to thesewers. Examples of savings that can be usefully made are in limiting the size of toilet cisterns andencouraging manufacturers of water-consuming domestic appliances - washing machines, dishwashers andpower showers - to produce equipment which consumes less water. It should be recognised that sink units

which grind up solid kitchen waste considerably increase the load of pollution which must be expensivelytreated at the municipal works. The disposal of kitchen waste in its solid state -as solid refuse - is much less

costly and less harmful to the environment.

3.5.2 What i s the sustainable use of water?

Sustainable Development has been defined as development that meets the needs of the present withoutcompromising the ability of future generations to meet their own needs (WED, 1987). Development isinevitably related to the use of water and sustainability is a key principle in maintaining the developmentprocess both now and for future generations. Exploitation of water can go beyond the limits which nature cantolerate, endangering sustainability. This is evident from the impaired state of the water quality seen in many

bodies of water today. To ensure that common interests are safeguarded, various means can be used locally,regionally, nationally and internationally:

Regulatory: Permits,

Standards, LiabilityTechnical: Source control,


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Treatment,

Impact reduction

Economic: Charges, Levies, Subsidies

Details of the items mentioned in the above groups will be discussed in later chapters. The foundations of aneconomic, environmentally-friendly and responsible policy for the use of water can be established by use ofone or a combination of the above means. Integrated approach to the management of water quality puts thesemeans into practice.

3.5.3 What is integrated urban water qual ity management?

The fresh water source, waterworks, distribution system for potable water, sewer system, wastewatertreatment plant, sludge treatment and disposal and the recipient water body to which effluents are discharged,are interrelated components in the water and wastewater management of a municipality or a region. Thesecomponents are further linked through their economical, ecological and technological aspects.

An integrated approach to the management of water and wastewater will necessarily result in economic,ecological and technological benefits. An integrated approach would result in optimum design and operationof sewer systems and wastewater treatment plants, whilst minimising adverse impacts on receiving waters.Many advanced simulation methods have been developed and are now applied to increase efficiency of theentire sewerage system at a lower cost. This approach should be the basis for the satisfactory execution ofintegrated river basin management.


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Chapter 4. Planning Issues

Figure

4.1 Chapter Content

The process of planning a sustainable urban wastewater system requires the consideration and management ofa number of resources - financial, land, energy, human and environmental.

This chapter first considers the phases through which a wastewater project must pass and gives an estimate ofthe typical duration of each phase. The various principal resources which may require consideration are then

described. The objectives set for the wastewater project may well be satisfied in a number of different waysand therefore this chapter includes an explanation of a number of techniques used to decide between them.Finally, there is an explanation of the value of public consultation.

Fig. 4.1a Construction of a large wastewater treatment plant


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Fig. 4.1b Construction of a large wastewater treatment plant

These topics are addressed under the following headings:

4.2 Wastewater Project Phasing4.3 Costs and Sources of Finance4.4 Land and Energy Requirements

4.5 Reuse - Wastewater and Sludge as a Resource4.6 Environmental Impact and its Assessment4.7 Human Resources - Project Staffing4.8 Techniques to Assist Decision-Making4.9 Public Consultation

4.2 Wastewater Project Phasing

4.2.1 What are the main phases of project implementation?

Project implementation by the conventional route can be divided into a number of phases:

PLANNING

Outlining of the project; planning, production of preliminary designs and cost estimates.

FUNDING

Following initial planning, funding, including any governmental grants, is sought and obtained.

DETAILED DESIGN

Production of detailed designs and cost estimates for the civil, mechanical, electrical and instrumentationworks.

TENDER AND CONTRACT DOCUMENTATION

Production of tender and contract documents consisting of general contract clauses, specifications of materialsand workmanship and bills of quantities.

TENDERING


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Advertisement of the construction contract, application of tenders, assessment and comparison of tenders andnegotiations with and selective of a contractor and agreement and signature of a contractor.

CONSTRUCTION

Supervision of the construction and of the commissioning tests and training of permanent operators.

OPERATION

Operation and maintenance of the completed works.

4.2.2 How long wil l i t take to bring a wastewater project into frui tion?

The funding phase may be carried out in parallel with the planning and design stages. Depending upon thecomplexity of the project being undertaken, i.e. from small extensions to a sewerage system, through to a

major wastewater treatment plant and marine outfall, the time for each phase should lie within the followingtime ranges:

Planning: 2 to 6 months

(It should be noted that if it is necessary first to determine a wastewater management strategy for a whole

region, then it is quite possible for a study phase to be incorporated in the Planning Phase which could takebetween 6 and 18 months to complete, more if extensive investigations such as marine surveys andenvironmental research have to be carried out. The production of an Environmental Impact Statement can also

take between 3 and 12 months to produce depending upon the complexity and sensitivity of the situation.These elements of planning are generally carried out concurrently.)

Detailed design:

2 to 12 months

Contract documentation: to 6 months

Tendering: 3 to 6 months

Construction: 6 to 30 months

Although routine sewer extension work will normally be somewhat shorter in duration, a minimum period ofat least 15 months will be needed for the completion of all the above phases for projects of any size, andperiods of up to 3 years may be required for larger projects - and even more if a substantial and extensivestudy is warranted as noted above.

4.3 Costs and Sources of Finance

4.3.1 What main factors inf luence wastewater project capital and operating costs?

The capital and operating costs of wastewater collection, treatment and disposal will depend on a number offactors.

Civil engineering costs form a large proportion of the capital cost of the project, typically more than 90% ofthe capital cost for sewer construction and between 60 to 70% of the cost of constructing a treatment plant.

Much of the construction requires excavation, pipes laid underground and tanks set into the ground andtherefore the capital cost of a wastewater scheme is influenced to a significant extent by ground conditions -

the bearing capacity of soils and whether construction is above or below groundwater level. Groundconditions have a high variability depending on the location. Weaker soils may require the bearing capacity to


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be increased through piling and high groundwater levels may require expensive methods to render anexcavation dry by dewatering or freezing.

There is a basic cost which a contractor must incur when setting up on a site. The smaller the project, thegreater the effect of these basic costs on the unit cost, for example the cost per person served.

The greater the wastewater flow to be conveyed by a sewerage system and the larger the pollution load thatmust be treated at the plant, the lower will be the unit cost of treatment. Other factors which contribute to the

size of a project include the relative contributions made to the pollution load to be treated, by industrial anddomestic effluents, the quality of effluent that must be achieved and the sludge disposal or reuse route for the

sludges and the treatment that they must be given to render them suitable for the chosen route.

The factors that influence operating costs for wastewater treatment are the same as those that influence theircapital cost. For a sewerage system, operating costs are dependent upon the length of the system, as thisinfluences maintenance, and the amount of pumping which is dependent upon the average wastewater flow

and the difference in the levels through which it must be pumped. Whether on the system itself, or just at thetreatment plant, it is difficult to avoid pumping wastewater, as most of the wastewater networks are based on

gravity flow. It is the maximum wastewater flow rate which dictates the cost as this, together with the lengthof the collection system and the nature of the terrain, influences the amount of pumping involved.

Fig. 4.2 Tunnel boring machine for large diameter sewer construction

4.3.2 Is it possible to provide typical costs for wastewater projects?

The foregoing factors, and their understandable variability from location to location, all combine to make it

extremely difficult to provide firm guidance as to both the capital and operating costs to be expected of awastewater project. Therefore, it is essential at this point to stress that each project will need to be individually

assessed in order to determine its capital and operating costs. This should be done at the outset of the project,during at the planning stage, and then revised at each stage of the projects progress as greater accuracy ofprediction will be possible when the details of the factors influencing cost become known.

This said, typical unit costs can give an indication of the order of magnitude of the costs of systemconstruction and operation. Unit cost information has therefore been collated from Europe and the US and ispresented in this chapter. However, for the reasons previously explained, this information should be seen as

being indicative only and should not be used for detailed cost estimates.


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Additional information on European capital costs, based on data from the UK, France, Italy and Portugal,reveal that for secondary treatment with population equivalents (p.e.) of works between 10 000 to 30 000 p.e.,the cost ranges between 70 and 120 ECU/p.e. Facilities greater than 30 000 p.e. range between 60 to 70ECU/p.e. A review of nine sewage treatment plants across the EU, has illustrated that operational costs canrange from 0.1 to 0.6 ECU per cubic metre (m

3), of wastewater treated. Assuming that each person contributes

an equivalent of 30 - 90 m3/year to the system, based on sewage produced per person of between 80 to 250

litres per day per person, then this cost equates to 10 to 60 ECU/person/year.

4.3.3 What costs should be recovered from users?

The underlying rationale of wastewater pricing should be that of full cost recovery from users of the service.Unless there are mitigating socio-economic circumstances or legal restrictions, then all elements of capital andoperating costs, including the cost of financing the work, should be recovered from the users of the service,

i.e. households, industry, commerce and other institutions.

In Europe, wastewater tariffs can range from 0,5 ECU/m3, for primary treatment in an urban area, to over 3

ECU/m3, for tertiary treatment in a rural area. Typically, wastewater tariffs (under full cost recovery) will

range up to 2 ECU/m3. Assuming that a household produces 200 m3 of wastewater each year, and that theincome of that household is 10,000 ECU, a tariff of 1 ECU/m

3will amount to 2% of the household income. A

detailed discussion of tariff setting for wastewater services is provided in chapter 8.

4.3.4 What sources of capital f inance are avail able?

There are five main sources of capital finance:

grants (from regional or central government sources or the various European Union sources such as theStructural and Cohesion Funds);

Municipal Bonds;

long and short term loans from governments and development banks such as the European Investment Bank,the European Bank for Reconstruction and Development and Commercial Banks;

private equity through contractor-financed construction or - more rarely - sale to the public of shares in thewastewater utility;

users of the service, from either capital charges to new users, or capital reserves established withcontributions from existing users.

Each of the main public and private financing instruments should be compared using the following factors:

the term - the number of years over which the capital is repaid;

the rate - the interest rate at which either the bond is issued or the loan is made;

financing costs - the initial and annual costs which must be added to the bond/loan principal;

delay - the effect of delays in obtaining finance, due to lengthy loan approval and provision procedures, onboth project cost and financing cost;

imposed costs - for example studies such as Environmental Impact Analysis and Cost Benefit Analysis,described in Sections 4.6 and 4.8 respectively, which may be required by the financier;


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ineligibility - that portion of total project costs which cannot be financed through a particular financingprogramme;

coverage - the amount by which the users annual repayments must exceed the annual debt service due.

4.4 Land and Energy Requirements

4.4.1 How much land is requi red for a wastewater treatment plant?

There is a minimum land area required for a wastewater treatment works of approximately 400 to 600 m2as

there is a need to provide some space for access and maintenance around the treatment units serving only avery few properties in a rural area.

However, considering treatment plants serving populations of a few thousand and upwards, a treatment plantbased on conventional activated sludge processes and producing a secondary treatment standard will occupyfrom 0,1 to 0.3 m

2per person served.

In general, the more energy a process uses, the less land area is required, proportionally speaking. The

wastewater processes referred to here are described in greater detail in Chapters 6 and 7 and in Annex A.

Of the conventional, well-tried processes, activated sludge is the most economical in land usage but is a highconsumer of power which is needed in providing air or oxygen for the process and the associated recirculationby pumping of significant flows of active sludge.

Trickling filters use between 2 and 6 times the land area of activated sludge for the biological treatment unitsbut consume less power. Power consumption for this process is largely dependent upon the degree ofrecirculation pumping which is included and on whether pumping can be minimised or avoided altogether ifthere is sufficient fall in the land across the site.

Less intensive treatment processes, such as lagoons without aeration or reed beds, may require between 5 and20 times the land area needed for a plant using conventional processes.

Restrictions on availability of land may well rule out consideration of the less intensive processes for thisreason alone, particularly where it can be used more productively.

When seeking suitable land for siting a wastewater treatment works, proximity to residential developmentsshould be taken into account. In order to avoid complaints of noise or odour nuisance, it is normal to allow an

exclusion zone around a treatment works of 100 to 250 metres. This can be reduced if the works, or its noisyor potentially odorous units, are totally enclosed and air ventilated from them scrubbed. Such measures add

significantly to the cost of constructing and operating a works and are adopted only in exceptionally sensitivesituations.

4.4.2 When would it be appropri ate to establi sh a wastewater treatment facil ity in conjunction wi th one or

more neighbour ing authori ties?

Each of the phases of implementation of a wastewater system require the involvement of skilled professionals

and technicians. It is commonly the case that smaller authorities find it difficult, if not impossible, to justifythe full-time employment of this skilled personnel, particularly as some will only be needed for relatively

short periods.

As an option to the employment of either contracted personnel or consultants, the local authority could

consider joining with neighbouring authorities thereby creating the quantity of users which would justify theemployment of a team which could implement and then jointly operate the project.


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Co-operation of this nature could have other advantages in particular circumstances:

it may well be possible to reduce the number of wastewater treatment works to be constructed bydischarging into a common works

apart from the savings in overhead costs, larger treatment units are more economical both to construct and tooperate and joint management can thus reduce costs

in rural areas with many scattered small developments, it will be easier to justify a mobile treatment worksoperations and maintenance unit.

4.4.3 Why do some towns and citi es adopt unusual l ocations and layouts for their wastewater tr eatment

works?

It is true that some authorities have adopted unusual locations and layouts for their treatment works but thereis often a considerable cost penalty associated with such approaches, with respect both to construction andoperation. Exceptional local circumstances have generally led to these unusual approaches and they should not

be adopted unless such circumstances occur.

Fig. 4.3 Underground wastewater treatment plant

Athens and North West Kowloon in Hong Kong due to shortage of space on the mainland have sited theirtreatment works on islands just offshore and within a reasonable distance of the cities they serve. Siting theplants offshore required undersea outfall sewers to carry sewage to the islands and the shipping of sludge to

the mainland for disposal. In Athens, many millions of tonnes of rock were blasted and excavated to create theflat areas required for the treatment processes and in Hong Kong considerable land area was reclaimed from

the port area.

Several cities in Scandinavia have located their treatment works in rock caverns which avoids the adverseeffects on biological treatment of long periods of extreme cold in winter.

The works to treat the wastewater from the Fylde Coast in North West England, including the coastal resortsof Blackpool, Lytham St. Annes and Fleetwood, is to be completely housed and the air ventilated from thesebuildings is to be scrubbed clean of odours. These expensive measures have been adopted in order to reducenuisance to nearby residential development and to avoid harming industrial processes in nearby food factories.

Treatment plants serving a number of towns on the French Riviera have had to be located under promenade

areas, either in the centre of the towns or in close proximity to high class residential or tourist developments.


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Complex and expensive design approaches have been used to ensure that the impact of these plants isacceptable under these sensitive conditions and operational costs are significantly increased.

Multi-storey treatment works have been installed in Japan, due to chronic shortage of land. Not only isconstruction more costly but the treatment works are also very inconvenient to operate and to maintain.

In general, it is prudent to keep construction of wastewater treatment works as simple as local circumstanceswill permit.

4.4.4 How much energy is requir ed in wastewater tr eatment?

Energy consumed in treating wastewater is generally one of the major factors contributing to operationalcosts.

Energy is consumed in significant amounts when pumping into the plant and satisfying internal processrequirements, in adding air or oxygen to biological treatment units and in pumping and dewatering sludges.

A typical activated sludge plant, producing a secondary process quality effluent and stabilising and dewateringits sludges, will consume between 40 and 80 Wh per person served each day.

This would be considerably reduced (to perhaps less than half of these values) if a biological filter processwere used without recirculation, due to different process requirements.

A treatment works, which stabilises its sludges using the anaerobic digestion process, produces methane gasas a byproduct. At the very least this gas can be used to power boilers which provide all the heat needed tomaintain the anaerobic process and to heat buildings in the winter. However, the energy potential of the gasproduced can be much greater than that needed to fulfil these modest requirements and may satisfy the powerrequirements of a whole treatment works - as long as the works does not have either excessive pumping or

does not need to produce a nitrified effluent or tertiary process standard effluent. For treatment works servingpopulations greater than 50,000 it may be economical to consider the installation of a generation plantpowered by the methane produced on site, in order to reduce power costs.

4.5 Reuse - Wastewater and Sludge as a Resource

4.5.1 What are the main reuse opportuni ties?

During the treatment of urban wastewater, the liquid portion is effectively separated from the solids (i.e. thesludge). Both of these residual streams can be processed into beneficial materials, providing that theundesirable physical, chemical, and biological properties are either reduced to an acceptable level, or

eliminated prior to, or during, wastewater treatment.

Considering the beneficial properties, (wastewater as a source of water and nutrients and sludge as a source ofnutrients and organic matter), the following reuse opportunities can be formed into a list of priorities, ref.Table 4.1.


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Fig. 4.4 Effluent and sludge can be beneficially used by agriculture

Reuse opportunities will depend on local conditions. However, the priorities listed in the table reflect:

the economic importance of agriculture;

the relative contribution of water/nutrients in enhancing the productivity of these sectors;

the specific environmental problems which face coastal regions, which include:

- soil erosion resulting in the formation of desert land;

- seasonal water shortages reflecting the predominance of agricultural water abstractions in those regions;

- salt water intrusion into over exploited coastal aquifers;

The need for additional treatment (thereby increasing the cost) to achieve the required quality levels forgiven reuse opportunity.

Table 4.1 Reuse Opportunities for Wastewater and Sludge

Activity

Reuse Opportunity

Wastewater Sludge

Agriculture Crop Irrigation & Soil Improvement Crop Fertilisation & Soil

Improvement

Land Application Aquifer Recharge Land Reclamation

Aquaculture &

Silviculture

Fish Rearing Forest Fertilisation & Soil

Improvement Industrial Products;

Industry Industrial Processing;Cooling & Process Waters

Construction MaterialFertilisers & Fuels

Urban Usage Public garden irrigation; Street cleaning;Firefighting

Fertilisers

Recreational Golf Courses Fertilisers


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4.5.2 What are the key elements of a successful reuse strategy?

Transport to, and storage at, the reuse site can be an important cost element which may restrict takingadvantage of potential reuse opportunities. Indeed for wastewater reuse, the storage and distribution ofreclaimed water represents the principal cost. The location of the treatment works, bearing in mind possible

reuse sites such as farms, can therefore be a key factor in determining the scale of any reuse opportunity. Ifreuse is being considered at a green field site it may, for example, be appropriate to locate the proposed worksaway from the natural disposal location and closer to potential reuse sites. The requirements for conveyance,

storage and distribution storage may well be vital cost elements which will ultimately determine the economicviability of a reuse project.

Reuse needs to be considered as part of an overall strategy which covers an appropriate geographic region. Amarket survey to determine the potential demand and the economic benefits of reuse, is a vital first step. Field

contact, following a desk survey, is an important part of the market assessment, as it should provide an insightinto the desirability of reuse in a region, specific quality needs and individual practical constraints, including

the need for additional investment and the required pay back time.

It is probable that the potential users of wastewater effluents or sludges will need to be convinced that theseare a resource from which they can derive benefit, particularly where there is no previous experience in theregion. Reluctance to take effluent or sludge, even where benefit has been proven elsewhere, might be basedon prejudice, ignorance of the benefits, imagined or real risk to their own products and sales potential orpublicised poor or variable experiences in other locations. This area of public relations must be handled

carefully, possibly using local pilot trials to demonstrate the benefits, if adverse publicity and long termreaction are to be avoided.

Reuse opportunities require well trained managers to exploit them successfully. Generally, small communitieswith one or two plants, cannot afford such expertise alone. Reuse will therefore be more practical if smallmunicipalities in a given region join together, in some form of new institutional structure, to promote andmanage individual reuse projects.

4.5.3 What technology is sui table for reuse projects?

Opting for reuse will affect both the technology selection process and the potential locations of individualtreatment facilities. It will also necessitate the active control and possible restriction of industrial wastewaterdischarges into the sewer which could restrict reuse opportunities.

Secondary wastewater treatment and sludge stabilisation should be considered as the minimum requirementprior to reuse. The need for additional processing will depend on the reuse applications being considered andthe type of reuse site chosen. Two types of treatment are showing a great deal of promise in overcoming thequality constraints inherent in reuse applications; for wastewater, stabilisation ponds and for sludge, anaerobic

digestion.

4.6 Environmental Impacts

4.6.1 What are the potential environmental impacts of a sewerage and wastewater tr eatment project?

The siting of a wastewater treatment plant can be an emotive issue, particularly where it is being introducedfor the first time. The general public frequently perceives the construction of a plant in their immediatelocality as an intrusion and property owners may well fear that it will have a negative effect on properlyvalues. Although these fears may not necessarily be rational or based on fact, it is the preconception whichcounts and plans to build a treatment plant can generate stiff resistance, particularly from those whoseproperty will be in the immediate vicinity. On the other hand, there have also been instances when the publichave made known their resistance to wastewater schemes because they do not think that the plan proposedwill sufficiently protect or improve their local situation.


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Fig. 4.5 Protection of habitats can form part of a study of environmental impacts

The impact on the local and remote environment must be considered when planning the project. Theenvironment will be affected by a wastewater projec

urban wastewater projects - a layerperson's guide.docx

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