design in domestic wastewater irrigation

IRRIGATION AND DRAINAGE

Irrig. and Drain. 54: S113–S118 (2005)

Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/ird.191

DESIGN IN DOMESTIC WASTEWATER IRRIGATIONy

FRANS P. HUIBERS1* AND LIQA RASCHID-SALLY2

1 Irrigation and Water Engineering Group, Wageningen University, The Netherlands2 International Water Management Institute (IWMI), Accra, Ghana

ABSTRACT

When looking at the domestic wastewater streams, from freshwater source to destination in an agricultural field,

we are confronted with a complexity of issues that need careful attention. Social and economic realities arise, along

with technical, biological and institutional issues. Local realities are linked to the geophysical environment,

economic development and cultural context and may have an overriding impact on the necessity, enthusiasm and

willingness to adopt a policy to place wastewater irrigation on the agenda as an option to save water, to fight

environmental pollution and to support agricultural production.

It is, therefore, not realistic to propose a design for wastewater use in irrigation that is globally applicable. Yet,

considering the issues raised, it is increasingly feasible and informative to present a conceptual framework that

should help to structure information and design options. Such a framework guides the designer as well as the

researcher and acts as an instrument to keep an overview on alternative options, while local realities will be a

reason for different design decisions. Copyright # 2005 John Wiley & Sons, Ltd.

key words: design framework; wastewater; irrigation; environmental pollution; ICID

RESUME

Lorsque l’on observe les courants d’eaux residuaires domestiques, provenant des sources d’eaux potables a

destination d’un champ agricole, nous nous retrouvons face a un ensemble de questions qui necessitent une

attention toute particuliere. Des realites sociales et economiques apparaissent, liees a des problemes techniques,

biologiques et institutionnels. Les realites locales sont liees a l’environnement geophysique, au developpement

economique et au contexte culturel et peut avoir un impact primordial sur la necessite, l’enthousiasme et la volonte

d’adopter une politique ayant pour objectif de mettre l’irrigation des eaux residuaires a l’ordre du jour en tant

qu’alternative a la preservation de l’eau, afin de combattre la pollution environnementale et de soutenir la

production agricole.

C’est pour cette raison qu’il n’apparaıt pas comme realiste de proposer un programme pour l’utilisation des eaux

residuaires dans l’irrigation qui pourrait s’appliquer au niveau mondial. Neanmoins, au regard des problemes

abordes, il est de plus en plus realisable et instructif de presenter un cadre conceptuel qui devrait aider a structurer

l’information et a planifier les options. Un tel cadre permet d’orienter le programmeur ainsi que le chercheur et agit

comme un outil permettant de garder un vue d’ensemble sur les options alternatives, alors que les realites locales

presenteront une raison pour les decisions des differents concepts. Copyright # 2005 John Wiley & Sons, Ltd.

mots cles: cadre conceptuel; eaux usees; irrigation; pollution environnementale; CIID

Received 8 April 2005

Revised 25 April 2005

Copyright # 2005 John Wiley & Sons, Ltd. Accepted 25 April 2005

* Correspondence to: Frans P. Huibers, Irrigation and Water Engineering Group, Wageningen University, P.O. Box 47, 6700 AA Wageningen,The Netherlands. E-mail: [email protected] dessin pour l’utilisation des eaux usees domestiques dans l’irrigation.

INTRODUCTION

An overview of the contributions made by the different authors in this Special Issue, originating from very different

disciplines, leads us to conclude that all authors agree that the use and impacts of domestic wastewater in irrigation

should, first of all, be accepted as a reality. Unregulated and unplanned use of wastewater in agriculture certainly

carries the risks of pollution of soil profiles, surface waters and groundwater, not to mention health risks to farm

workers and possibly crop contamination. However, it has also been shown that wastewater use can contribute to

livelihoods at household level (Raschid-Sally et al., 2005, this volume) and to a recycling of water and nutrients

(Janssen et al., 2005, this volume). This agricultural use of domestic wastewater, if well designed and managed,

has the potential to address the problems of local water shortages and can also be viewed as part of a treatment

system to reduce environmental pollution (Jimenez, 2005, this volume).

In fact, agricultural use of wastewater provides an option to safely handle and discharge the increasing

volumes of wastewater under present economic conditions as encountered in many countries of the world.

However, it should be stressed that there cannot exist a single design solution, as there are wide differences

between locations, not only in climate and physical environment, but also in social acceptance, economic and

technical opportunities and perceptions related to the use of (treated) wastewater. A pricing framework, adapted to

local situations, would be very helpful to decide on design choices and cost allocations (Hatton MacDonald et al.,

2005, this volume).

In reviewing the facts surrounding the present pollution of surface water, the main cause is seen to be sanitation

which is posing a problem around the world in developing countries (Raschid-Sally et al., 2005, this volume). The

Millennium Development Goals for sanitation, as applied in many countries, focus on the provision of latrines or

toilet facilities and much less on what happens afterwards. This in itself is not an issue in low-density rural areas

where each household deals with its own wastewater through onsite sanitation as land is not a problem. In more

densely populated areas, however, this is not always an option and some form of water-borne sewerage is being

applied–whether it is conventional sewerage or small bore sewers, giving rise to questions of safe disposal and

management of wastewater.

The problem is compounded by the fact that cities usually receive all the water they need, with much less

attention paid to the fact that up to 70% of this water returns as waste. Growth of cities along with improved water

supplies could easily double the wastewater flows in few years’ time (van Rooijen et al., 2005, this volume).

Present data from cities highlight the inability of municipalities and other local authorities to fully address the

issue. This is a limitation arising from the fact that there are insurmountable costs involved, when conventional

thinking about wastewater management and disposal is applied.

Two approaches commonly cited to study water management issues are the water cycle approach (closing the

water loop) and the integrated water resource management as a basin approach (balancing multiple needs). When

addressing wastewater flows and their management for use in agriculture, a systems approach is suggested, which

combines the assumptions underlying the two approaches cited, with those of a water chain approach (Huibers and

van Lier, 2005, this volume) which introduces the concept of interlinked elements.

Following a systems approach, a design framework for wastewater irrigation can be developed for which four

elements are needed:

� Understanding of the existing wastewater agricultural practices, typologies of use and the local sanitation and

wastewater management situation.

� The institutional and economic constraints faced by authorities dealing with them.

� The potential for environmental pollution control through recycling of nutrients in a given socio-cultural and

institutional context.

� Knowledge of physical and biological processes.

Upstream: significance of sanitation and wastewater management

Various upstream issues will directly affect the downstream water management, such as the choice of

appropriate sanitation and wastewater collection (van Lier and Huibers, 2004). When new sanitary systems are

S114 F. P. HUIBERS AND L. RASCHID-SALLY

Copyright # 2005 John Wiley & Sons, Ltd. Irrig. and Drain. 54: S113–S118 (2005)

considered, choices like decentralisation and the separate collection of black and grey water can be steered by the

eventual reuse schemes as well. Applying ECOSAN principles would produce less wastewater.

Decentralisation of sewage collection provides opportunities to better check and control actual water quality

through addressing smaller planning and management units and addressing decision making at the level of the

people who are the source of wastewater generation. Source separation, waste minimisation and primary treatment

at factory level will minimise the contribution of industrial wastewater to the municipal sewage, reducing the

concentration of hazardous compounds in the reclaimed water (Maclaren et al., 2002). Choice of treatment

technology has an enormous influence on size of flows, composition of the effluents and costs of water.

Downstream: significance of location and typology

For an individual farmer, permanent or temporary lack of access to other water sources could be a driver to use

wastewater, making wastewater irrigation a reality, not only in arid and semi-arid regions, but also in more humid

areas where seasonal water shortage occurs. Wastewater may be used directly but is in fact also used where sewage

is discharged into the natural drainage system, from where the polluted water is used by farmers (indirect use).

Such practices usually occur as part of informal farming typically, but occasionally even in a more formal context

in urban and peri-urban agriculture. Recycling of treated wastewater under planned and controlled conditions

occurs with the approval of the relevant authorities (Van der Hoek, 2004; Cornish and Kielen, 2004), though

planned use may also take place where inadequately treated wastewater is the source for irrigation in formal

irrigation schemes.

Agricultural practices as described above may occur in different geographic settings within and close to cities

generating wastewater. Two typical situations are the ‘‘urban’’ setting and the ‘‘peri-urban extending-to-rural’’

setting. In the urban situation, farmers, some of them city dwellers, move towards the wastewater sources, which

are often open drains. They search for water in the first place, being happy that the water contains nutrients as well,

since many cannot afford the purchase of (sufficient) chemical fertiliser. Most commonly, year-round vegetable

production is practised, for which they have a good market. In many places in the world this form of production has

great importance as a source of income and livelihood for many. Farmers usually have no land rights and make use

of available urban land belonging to property owners or the state, until they are thrown out. As a consequence,

there is no irrigation infrastructure and no means of regulation and control. Watering of the plants is done by simple

means, like buckets or watering cans. This practice leads both to health risks, for the irrigators who are in close

contact with the polluted water, and risk of crop contamination. However, interestingly crop contamination may

also occur in the crop handling after harvest (Amoah et al., 2005, this volume). Risk of groundwater pollution is

much less, as there is no overirrigation.

Peri-urban wastewater irrigation is described as the agricultural production in the areas outside of cities where

wastewater or heavily polluted surface water arrives from urban areas. In this definition, the peri-urban area could

extend to places quite far away from the cities, which is the case of mega-cities with high wastewater outflow (Van

Rooijen et al., 2005 this volume). This typifies the movement of wastewater beyond the urban limits,

simultaneously taking the benefits and risks of wastewater use further and further downstream. The farmers did

not move to the wastewater source in a search for water, instead the wastewater stream increasingly moved to their

fields. In cases cited in this volume, farmers were cultivating under rainfed conditions or under irrigation, well

before the wastewater flows reached their area. Yet, these flows do increase the water availability, particularly in

the dry season, allowing farmers to expand cultivation areas or cultivate more intensively. Depending on the

distance from the city, vegetables may be grown, but fodder crops and grain crops start becoming more important.

When these sources extend beyond the peri-urban areas as is the case with ‘‘rivers of wastewater’’ that carry large

flows with almost no dilution in the dry season, rural farmers too are obliged to make use of this source. Health

risks for farm labourers remain important through direct water contacts. Poor irrigation infrastructure, poor

irrigation water management and unidentified composition of the water are causes for further pollution of surface

water and groundwater.

Wastewater irrigation schemes represent an example of planned and institutionalised use of wastewater in the

downstream rural areas of big cities. This wastewater is generally treated at secondary level, although in many

cases the quality of the effluent is below standard because of poor performance of the treatment system. Under

DESIGN IN DOMESTIC WASTEWATER IRRIGATION S115


these schemes an effort is made for an optimal recycling of both water and nutrients. As these schemes are formal,

government rules on crop choice and management are strict and much more controlled than in the other situations

described above. This restricts farmers from growing the crops of their choice suitable to the market, or forces them

to apply expensive management systems. Theoretically, farmers could compensate income loss due to crop

restrictions by the lower water price they would normally pay and by saving on fertilisers. However, in practice

farmers have insufficient insight into the nutrient value of the water they use and keep applying chemical fertiliser

as well. This brings unnecessary costs to the farmer, while the resulting over-fertilisation is a source of further

pollution.

A systems approach to design for wastewater agriculture and sanitation

The complexity of issues shows that a one size fits all design will not work. Each wastewater system will have to

be designed within the local socio-cultural requirements and institutional and economic constraints (Carr, 2005,

this volume). At best a framework for analysis and decision making can be proposed (Hussein et al., 2001) which

follows a systems approach.

The requirements of such framework are that it should be complete but comprehensive to the user, and should

provide decision support to help address existing situations of wastewater irrigation, as well as to respond to new

needs and situations. Such a framework can also be useful in defining knowledge gaps, which is the starting point

for further fundamental and applied research.

A design framework is a plan or systematic approach that helps the designer or the policy maker to

systematically address relevant design and management elements and to understand their possible linkages.

With present insights, the design framework proposed by Huibers et al. (2002) could be further developed, as

depicted in Figure 1.

The framework has two dimensions. The first is the physical path traced by the wastewater flow from the source

to the sink and what happens to it. The second brings out the issues that need to be addressed at any stage, leading

to a sustainable layout and management. The latter could be defined as secondary decision tools.

Design and management choices depend on the overall construction and management of a system. Measures to

improve could be taken at different places in the system (Martijn and Redwood, 2005, this volume), showing the

dependency between environmental engineering, and irrigation design parameters (Capra and Scicolone, 2005 this

volume) and the operational choices of managers and farmers.

Crop choice

Water pricing policyCost allocation

Up-streamissues

(Partial)treatment

Agriculture

Other usesand disposal

Surface waterGroundwater

Technological Societal Environmental Economic

Other water

sources

Legislation

AcceptanceHealth matters

Irrigation technique

Supply-DemandWater management

Pollution prevention

Resource conservationLand treatment

Sustainability

Treatment capacity

Sewage collectionTreatment technology

Costs and cost sharing

Water availability, incl. water rights

Figure 1. Conceptual design framework in wastewater irrigation



CONCLUSIONS

From the ICID Special Session on the Use of Wastewater a number of key messages emerged in support of

sustainable use of what is otherwise considered as a source of environmental pollution.

Increasing wastewater flows are the result of increasing water supplies to urban areas and should not be viewed

in isolation as a problem to be resolved, as is the case to date. It has to be integrated firstly into an urban context and

secondly into a basin context. The urban context refers to the water chain linking the upstream producers to the

downstream users, who are the urban and peri-urban farmers. The basin context relates to resource allocation and

how transfers to the urban sector and the resulting wastewater flows will affect other users. The magnitude and

significance of such reallocation are basin specific.

Environmental consequences of the use of treated or untreated wastewater, including soil and (ground) water

pollution, have to be taken seriously, although its use in irrigation would probably be an advantage over

indiscriminate discharge, as irrigated agriculture with wastewater could be considered as a land treatment system.

Related health risks undoubtedly need attention, both at field level as well as with respect to food contamination.

The question was raised whether the highest risk is from the use of the wastewater in the field as such or if

contamination also occurs in the crop-handling stages. However, with proper measures taken, such risks are not

insurmountable.

Guidelines should be country, location and resource friendly. They should not be viewed just as numbers but

they also represent best available technologies and practices.

Nutrients in wastewater can and should substitute for fertiliser but a clear understanding of the conditions under

which they can best be used is still lacking. Applied at the wrong time the nutrients in wastewater can be more of a

hindrance than a help. More defined and targeted work is needed in this area.

In applying economic research to wastewater issues, many levels and types of economic studies are spoken of.

The objectives of these are not always clear. Which are the most relevant to a given situation? These must be

identified before studies are undertaken. Some advice to developing countries is to know where the irreversibilities

are, as charging for externalities in poor country contexts may not be a good solution. If pricing of wastewater is the

issue then there is a need to develop a long-term strategy which adopts a stepwise approach, and cost is an essential

factor in setting the right standards.

Modifying a technology for use in a different situation may not be the best answer when seeking appropriate

technologies. A visit to the root of the design is necessary where the objectives of the original design are

understood. Adapting a technology that was designed with a different objective in mind may not always be

effective. The use of drip irrigation as a safe method of irrigating comes to mind. The drip system was defined for

efficient use of water where nozzle size is related to water availability, pressure and other factors. In situations

where wastewater is the source, availability is not always a limitation. Where the need of the day is minimising

exposure of plants and users to pathogens, the design of the system could be modified accordingly.

It is important to have a clear understanding of what wastewater is, with respect to its source, density and

treatment. There is certainly a need for knowledge packaging and sharing, and involving stakeholders. Such a

process can change the solutions to the problem or even change the nature of the problem.

However, looking at the partial solutions proposed in the different contributions, it seems very possible to find an

agreed way to deal with wastewater as a source of agricultural water if the proper conditions are met at the different

stages. It was agreed that a conceptual framework could act as a structuring device to better understand

interdependencies.

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design in domestic wastewater irrigation

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