Wastewater is a resource of increasing global importance, particularly in urban and peri-urban agriculture. Wastewater is used for crop production, which includes fodder grasses, vegetables, cereals, ornamental plants, trees and flowers, timber crops and fruit trees, as well as for aquaculture and is often the only source of irrigation available. Wastewater use for irrigation generates livelihoods for farmers, agricultural labourers, produce transporters, market brokers and produce vendors. Consumers also benefit by obtaining access to fresh and cheap produce due to low transportation costs. To prevent potential negative impacts on human health and the environment, the importance of wastewater reuse in urban and peri-urban agriculture has to be recognised and clear policy guidelines for reuse need to be established. Careful research and awareness raising needs to be stimulated. Women play a key role in this context both as producers and in food preparation. Wastewater use in urban, peri-urban agriculture is a cross-sectoral issue that requires a multi-sectoral and multi-actor approach to research and planning.

Wastewater Use for Urban and Peri-urban Agriculture

Stephanie Buechler
Gayathri Devi Mekala
Ben Keraita

Introduction

Agriculture is often associated with rural areas, even though it has been practiced in urban and peri-urban areas since ancient times in backyards, on roof tops and road sides, in vacant plots and un-constructed areas, on river and lake beds and in other such small land lots. Urban and peri-urban agriculture (UA) provides nutrition and income, improves the urban environment by using the organic solid and liquid wastes of the city, provides aesthetic value to these areas and helps to achieve optimum land utilisation. However, city planners often ignore this important economic activity and do not include it in their planning. Agricultural finance institutions do not provide loans to urban farmers due partly to the fact that most of them do not have land titles and because the activity itself is considered insignificant. In addition to these factors that can hinder the success of UA, urban and peri-urban farmers often do not have access to a safe and reliable water supply. Issues related to this essential resource for agriculture are discussed in this chapter.

Collecting water from a small pond

Increasing volumes of freshwater are being converted into domestic, hospital and industrial wastewater in rapidly growing towns and cities around the world. By 2015, the world will have one billion more people than it does now and 88 percent of this growth will be in cities, mainly in developing countries (UNDP 1998). This population growth will have a dual effect: 1) a substantial increase in the volume of urban wastewater produced, since greater volumes of surface and groundwater will be diverted to supply these burgeoning cities; and 2) an increase in urban demand for food. The increasing volume of wastewater will therefore be utilised by farmers on an even greater scale than at present. Particularly in the case of urban areas in semi-arid, drought-prone areas, the lucrative and large market for fresh produce and the urban water demand will make freshwater even more scarce. The use of wastewater for agriculture in and around cities across the world is a current and future reality that cannot be denied. In some countries, such as Mexico and China, it has been practised for centuries (Shuval et al., 1986). Since conventional treatment is very costly, most wastewater is allowed to be dumped, untreated, into water bodies or onto the land. Untreated wastewater use for urban and peri-urban agriculture is often either ignored or actively condemned by the public and by government officials.

There is a small but expanding set of literature on biophysical, social, public health, political and economic aspects of wastewater and its use for agriculture. These studies are being used to inform practitioners and policymakers of the reasons for the use of wastewater, the different types of wastewater (including raw, diluted, treated to primary/secondary/tertiary level), the likely increase in its use and possibilities for mitigating the multi-dimensional risks associated with wastewater and its use.

Freshwater Availability for Agriculture

As the world population increases, the competition for freshwater resources between domestic demands, industry, commerce, institutions such as hospitals, and agriculture is intensifying. Water demand has tripled since the 1950s (Brown, 2003). Figure 9.1 illustrates that increases in urban water supply coverage have been and will continue to be greatest in Asia followed by Africa, where absolute population figures as well as population growth are the highest (Scott et al., 2004). Imminent water shortages, however, are less likely to be visible than other natural resource disasters such as deforestation and soil erosion to both the public and policymakers. This is due to the fact that much of the water scarcity is induced by groundwater overdraft for agriculture, industry and domestic use made possible by increased electricity coverage, power subsidies for diesel and electricity, and the extension of cheap credit (Shah & Scott, 2004). A huge increase in the number of wells and over-pumping with increasingly powerful diesel and electrical pumps is leading to falling water tables. Particularly serious over-pumping is occurring in China, India, USA, Pakistan, Mexico, Iran, South Korea, Morocco, Saudi Arabia, Yemen, Syria, Tunisia, Israel and Jordan. Surface water from rivers is also tapped for freshwater and major rivers either completely dry up before reaching the sea or contain only a very small volume of water. Such over-exploited rivers include the Colorado river, the Yellow river, the Amu Darya, the Nile, the Indus and the Ganges. Currently, 70 percent of surface and groundwater is used for agriculture, however with increasing competition between agriculture, industry and domestic demand, agriculture is beginning to receive less water (Brown, 2003).

Figure 9.1 Growth in urban water supply coverage by world region

Source: Scott et al., 2004

Water reuse is not a new phenomenon; it has been a worldwide practice for centuries. Agricultural wastewater, sewage wastewater (including grey water and black water) and industrial wastewater have been used directly or after treatment and/or dilution in urban and peri-urban areas for agriculture, especially in drought years. With the dwindling supplies of fresh surface and groundwater, water reuse and recycling assumes a greater role than before to keep up with the increasing population growth and the demand for increased quality and additional quantities of food.

Wastewater Production by Growing Cities

The quantities of wastewater produced by cities are rising steadily with urban growth. As cities grow, the water supply to these cities also grows, resulting in ever-increasing quantities of wastewater produced by urban residents and industries. Municipalities, farmers, and irrigation and agriculture departments are ill-equipped, however, for the very sharp rise in urban-rural water transfers (Buechler and Scott, 2006). The sources of wastewater include sewage drains, storm drains used as sewage channels, surface water sources like rivers, lakes and natural streams polluted with wastewater from city sewage and drainage channels, ponds and tanks, shallow wells, house drainage spouts and channels, wastewater treatment plants etc. The composition of the wastewater varies according to its origin. There is storm water and other urban run-off, grey water (domestic water that is wastewater without urine and faeces) or black water (domestic wastewater with urine and faeces), industrial wastewater, wastewater generated by hospitals and other institutional/commercial establishments and combinations of all of these (each with varying concentrations of waste). The volumes of wastewater generated in Asia in the late 1990s are seen in Table 9.1. An example of urban growth far exceeding the capacity of sewage collection and treatment is Delhi, India. Only about 40 percent of the capital city of Delhi has sewerage at present, and of that less than half actually delivers sewage for treatment. Most is simply channelled through open drainage canals to the main river (the Yamuna) untreated. Despite investments in new treatment plants, the growth rate of the city is so rapid that progress in proportion to this growth has been very slow (Ganges River Partnership Project, 2002).

Domestic wastewater used for vegetable production in Accra

According to the United Nations Economic and Social Commission for Asia and the Pacific and the International Water Management Institute (IWMI), wastewater treated to primary or secondary levels is used for irrigation, in industry and cooling, whereas untreated wastewater is used mainly for agriculture. Wastewater treatment is costly, and even those cities that are currently able to procure funding to build treatment plants only treat a small percentage of the total volume of wastewater. The rest is left to flow into natural water bodies. Most of the water only receives primary treatment. The majority of developing countries treat less than 15 per cent of the wastewater they produce (Davis & McGinn, 2001). Many treatment plants in cities in the South go into disuse after a short period of time due to insufficient funds for operation and maintenance. This is the situation in cities like Vadodara, the third largest city in Gujarat state, India, where none of the three treatment plants is fully functional (Bhamoriya 2004); in Kathmandu, Nepal, where many of the valley's treatment plants are in poor condition (Rutkowski et al., n.d.) and in Cochabamba, Bolivia, where the one treatment plant that exists is overloaded and therefore not working properly, and most residential septic tanks and Imhoff tanks are not functioning (Huibers et al., 2004). The percentage of the population with full water-borne sewerage connections in sub-Saharan African is very low. Harare, Zimbabwe, is one of the cities in Sub-Saharan Africa with the highest coverage while Lagos, Nigeria, has one of the lowest. In Lagos (Nigeria), Africa's largest city, with a population of 10 million, only 5 percent of its population is connected to the sewage system and treatment of sewage is below recommended standards. Only 2 percent of the cities in sub-Saharan Africa have sewage treatment, and only 30 percent of these systems are operating satisfactorily. In Addis Ababa, with a population of 2.5 million, the sewage system serves only 35,000 people (www.unep.or.jp).

Table 9.1 Estimated volumes of wastewater (million m³/year) in Asia

Policymakers' current focus is on wastewater regulation and treatment. However, to make realistic policies, information must be gathered on where wastewater irrigation takes place, the reasons for and extents of its use, the socio-economic characteristics of the main actors deriving direct and indirect livelihood benefits from this use, the risks to livelihoods and human and animal health of this use and the different types of wastewater use. A common typology of wastewater use that addresses aspects such as direct use (i.e. 'end-of-pipe' sewage irrigation), dilution of wastewater with natural surface water before use, and the relative contributions of domestic wastewater, industrial effluent, and storm water to urban wastewater is required. Van der Hoek (2004) has developed a typology (See Figure 9.2) that categorises wastewater use into three types: direct use of untreated wastewater where wastewater is directly applied to land from a sewage system; direct use of treated wastewater where treated wastewater is channelled to a particular area for irrigation; and indirect use of wastewater where wastewater is taken from another receiving water body such as a pond, lake, canal, tank or river.

Wastewater Use in Urban and Peri-urban Agriculture and its Contribution to Livelihoods and Food Security

Urban and peri-urban farmers from different caste and class groups in developing countries in Asia and Africa derive their livelihoods by using wastewater for various activities such as horticulture, fodder production for dairy activities, agroforestry, orchard keeping, floriculture, aquaculture and cereal production. There are also many areas in which the government runs sewage farms near treatment plants which are hired out to farmers for cultivation such as those around Madurai, South India (documented by Chandran et al., 2003) and around Hyderabad, India (Buechler & Devi, field observations).

Figure 9.2 Basic types of wastewater use

Source: Wastewater Typology developed by Wim van der Hoek, IWMI (2004)

To date, assessments of the extent of wastewater irrigated areas have been carried out in Pakistan, India, Vietnam, China, Mexico and Jordan. In Pakistan an IWMI study estimated that there were 32,500 hectares irrigated directly with wastewater (Ensink et al., 2004). Strauss and Blumenthal (1990) estimated that 73,000 hectares were irrigated with wastewater in India. However, Buechler and Devi (2002) estimated that just only along the Musi river that runs through Hyderabad city in Andhra Pradesh state and the canals and tanks off this river approximately 16,000 hectares of land is irrigated with urban and industrial wastewater (2003). An estimated Rs 1 million per day at least (personal communication by IRDAS, the NGO) is generated due to wastewater irrigated urban agriculture in Hyderabad. In the down stream of Vadodara, third largest city in Gujarat, India, alone, wastewater supports annual agricultural production of Rs 266 million (US $ 5.5 million) (Bhamoriya 2004). In Ghana, it was estimated that if just 10 percent of the 280 million m³ of wastewater from urban Ghana could be (treated and) used for irrigation, the total area irrigated with wastewater alone could reach 4600 ha. At an average dry season farm size of 0.5 ha, this could provide livelihood support for about 9,200 farmers in the peri-urban areas of Ghana (Agodzo et al., 2003). In Vietnam, at least 9,000 hectares of land were found to be irrigated with wastewater mostly to grow paddy, and in and around 93 percent of the cities wastewater is used in agriculture or aquaculture (Rachid-Sally et al., 2004). Mara and Cairncross (1989) estimated that 1.3 million hectares were irrigated with wastewater in China. For Mexico, estimates of the number of hectares irrigated with wastewater vary greatly between studies. Castelán has estimated the number irrigated with domestic wastewater at 344,000 ha, but states that in 1997, 403,000 ha of restricted crops (i.e. crops that are illegal to grow with wastewater as the produce is eaten raw) were cultivated (2000:25). Scott et al., 2000) has put the number at closer to 500,000 ha.

Wastewater users, who come from a wide range of socio-economic backgrounds, have a variety of motives for using wastewater for irrigation. In semi-arid and arid areas it is often the only source of water available in sufficient quantities for irrigation; it is also available year-round unlike freshwater from rainfall which is concentrated in the often short and sporadic rainy season. It is also an inexpensive source, not only of water but also of nutrients. In fact, farmers often need few or no additional fertilisers. Crop yields are often higher with wastewater than with freshwater. For example, in Haroonabad, Pakistan, it was found that wastewater farmers earn $US 300–600 more per year than non-wastewater farmers and that the majority of wastewater farmers were landless and leased in land for agricultural production (van der Hoek et al., 2002). In Kumasi, Ghana, Danso et al (2002) found that urban market farmers can earn 2-4 times more than farmers who grow maize and cassava. Wastewater farmers in and around Kumasi earn an average of US$ 340/ha per season (Cornish and Kielen, 2004). Wastewater can easily be channelled to the fields from city drains, from a river, or from broken sewer lines or carried to the fields in watering cans. Using this water is also attractive as UA fields are often conveniently located near city markets where the produce is sold, or are near urban-based buyers who purchase the produce directly from the (peri-)urban plots. As urban populations and incomes of the urban residents increase, so too does the demand for fresh vegetables and dairy products (Brown, 2005). Often, nearly all of the perishable produce for urban consumption is grown in and around urban areas due to the lack of refrigerated transportation in cities. For example, 90 percent of the lettuce and spring onions consumed in Kumasi, Ghana, are produced in the city itself (Danso et al., 2002).

Wastewater used for vegetables without prevention

Despite the widespread use of wastewater, municipalities and water boards underestimate its value, and for policymakers it is a non-issue. The lack of information and awareness both among producers and consumers about the inherent risks of wastewater use further compounds the problem. The difficulties faced in wastewater use for aquaculture relate to the non-availability of guidelines for selection of species and stocking density (Kaul et al., 2002:3). The compatibility of the reclaimed water with its intended usage is an important consideration in developing a wastewater reuse system. Higher level uses such as for irrigating public access lands (eg. Parks) and the cultivation of vegetables requires higher levels of treatment compared to lower level usage such as pasture maintenance, floriculture and agroforestry irrigation.

Impact of Wastewater Irrigated Urban and Peri-urban Agriculture on Health

Fifty percent of all children in developing countries (10.4 million children) under the age of five die per year due to malnutrition (Rice et al., 2000, WHO, 2000). Healthy individuals make healthy communities and wastewater, if well-managed, can help alleviate malnutrition especially for children of poor households. According to the draft WHO report 2005, "Guidelines for Wastewater Use in Agriculture" wastewater use in agriculture may have important economic benefits for households and communities that can improve the health of families through better access to healthcare, education, nutritious food and improved access to both water and sanitation in the household. In Hyderabad, a wastewater reuse case study showed that vegetable producers in the urban and peri-urban areas save about 20 percent of their household expenditure which they would otherwise have spent on the purchase of vegetables. Most of the households with livestock in the urban and peri-urban areas of Hyderabad, India, use wastewater irrigated para grass as fodder and generate an income through the sale of the milk. Typically, 25 percent of the milk produced (assuming a household of 6 members owns one buffalo) is retained for household consumption and 75 percent is sold (Buechler et al., 2003c). The Hyderabad and Kumasi case studies further elaborate on these topics.

On the one hand, wastewater can contribute to improved health of poor communities through income generation and increased access to food. On the other hand it can be associated with a number of health risks since most wastewater is untreated or contaminated with industrial and other wastes.

Negative impacts on farming families and local communities

The people who face potential risks from the use of wastewater for agriculture are agricultural field workers and their families, crop-handlers, consumers and those living near irrigated fields. Wastewater can have direct and indirect health impacts. Direct contact with untreated wastewater through flood or furrow irrigation can lead to increased helminth infection (mainly Ascaris lumbricoides -roundworm, Trichuris trichiura -whipworm, Ancylostoma duodenale and Nector americanus - hookworm). Two case studies that examined the impact of untreated wastewater on health, environment and income in Pakistan indicated higher hookworm infections in farmers and farm workers who use wastewater for irrigation than those who do not (Ensink et al., 2004). The main risk for the public arises when vegetable or salad crops grown with untreated wastewater are consumed raw. This can be linked to cholera and typhoid as well as to faecal bacterial diseases, bacterial diarrhoea and dysentery among consumers of wastewater-irrigated produce. Municipal and industrial wastewater is a major source of chemical pollutants that could affect human health. Chemical contaminants that pose potential health concerns and identified in untreated wastewater are shown in Box 9.1.

Wastewater can be valuable because of the bad quality of groundwater

Strategies for Managing Health Risks

There is no single solution to the problems mentioned above. Combinations of different strategies that can reduce the health risk to humans need to be adopted. Pathogens and other inorganic contaminants in the fields do not necessarily represent a health risk if other suitable health protection measures are taken. The different health protection strategies as per the draft WHO report 2005 (currently being tested), "Guidelines for Wastewater Use in Agriculture" are:

Wastewater treatment: Most conventional domestic wastewater treatment plants focus on the removal of environmental pollutants (eg. suspended solids, BOD - Biochemical Oxygen Demand-, COD - Chemical Oxygen Demand -, etc.) but not on pathogens, as the latter is more difficult and more costly and therefore not easy to undertake in developing countries. For the quality of treated water to meet the WHO standards, secondary treated water needs to be supplemented by tertiary treatment (disinfection) or retained in a maturation pond for five more days. Some research has been done to develop decentralised and cheaper treatment solutions. One example is the pilot project, "Ecology and Development with Sustainable Sanitation" (ECODESS) of the Urban Development Institute in the district of San Juan de Lurigancho near Lima, Peru. In this arid urban area on the Peruvian coast, where freshwater availability per person per year is projected to be five times less than the global average by 2025, and only 4 percent of the sewage is currently treated, this project has set up a household and a community system to collect, treat and recycle wastewater. The treated wastewater is channelled into an underground irrigation network for use in green areas and urban agriculture (Calizaya, 2002). Another economical model in Kolkata, India, for improving the quality of wastewater used in peri-urban aquaculture is the cultivation of dense plantations of crops or trees on the sides of wastewater canals, which controls soil erosion, absorbs some amount of the pollutants and provides nutrient-rich water for aquaculture (Mukherjee, 2003).

* The toxicity of a chemical depends on its concentration, the route of exposure to the chemical and the duration of exposure to the chemical. The health effects above include both acute toxicities (high chemical concentration and short exposure duration) and chronic toxicities (relatively low chemical concentration and long exposure duration) with all routes of exposure. Some of the toxicities may not be applicable to wastewater.

Sources: Chang, Page & Asano, 1995; National Research Council, 1998; WHO, 1999; WHO, 1992; WHO, 1991; WHO, 1989; ATSDR, 2000.

Choice of irrigation techniques: Farmers use different irrigation techniques depending on convenience and knowledge. However, farmers using wastewater for irrigation need to take some precautions during irrigation. Sprinkler/spray irrigation has the highest potential to spread bacterial and viral diseases and hence a buffer zone of 50–100 meters from houses or roads should be maintained to prevent health risks to local communities. Workers in the fields and their families should wear protective clothing in case of furrow or flood irrigation to prevent direct contact with wastewater. Localised irrigation techniques like bubbler/drip/trickle offer the best health protection but are expensive to implement. Still for all, drip irrigation is being taken up by some farmers as seen in Cape Verde and India (FAO 2001; Kay 2001). Vaz da Costas Vargas et al., (1996) show that cessation of irrigation for 1-2 weeks prior to harvest, wherever possible, can be effective in reducing crop contamination.

Simple techniques can be used to prevent pollution

Crop Selection: Water of poorer quality can be used to irrigate non-edible crops such as cotton or flowers, or crops that are cooked before consumption. Plants (eg. zucchini) with rough, textured surfaces, deep crevices or hairy surfaces that grow close to the ground may harbour bacteria or contaminated soil and should be avoided. But crop restriction cannot be a stand-alone solution. In Chile, the use of crop restriction, when implemented together with a general hygiene education programme, reduced the transmission of cholera related to the consumption of raw vegetables by 90 percent (Monreal, 1993).

Human exposure control: Field workers are the most exposed to wastewater. The health risks faced by these individuals can be reduced by using appropriate irrigation techniques such as bed and furrow cultivation and protective clothing in the form of boots and gloves (van der Hoek et al 2002; Ensink et al., 2004). Field workers should also be provided with sanitation facilities and drinking water. Provision of safe water in vegetable markets to wash produce is important to prevent further contamination of wastewater irrigated agricultural products. Consumers should wash fresh produce thoroughly and cook it before use. Governments should invest in employing additional health inspectors who do periodic checks on milk and meat products in the city. Finally, awareness campaigns on these issues would be of great help in minimising the health hazards of wastewater irrigation.

Treatment with chemicals and Vaccination: Immunisation against typhoid and hepatitis A for highly exposed groups is recommended (Carr et al., 2004). This therapy for adults and children in particular at regular intervals can reduce helminth infections (Ensink et al., 2004).

Developing alternatives: Improvement of sanitation, or use of innovations in the existing sanitation systems. One such innovation is Eco-Sanitation (see Box 9.2).