Agricultural use of untreated wastewater in low income countries (E-conference - 24 June - 5 July 2002)
Use of urban wastewater in agriculture
Globally on an average 47% of the population live in urban areas. Even at the lower consumption figures of 100 -150 litres per capita per day the water consumption in Africa would be 45 mill m3 and in Asia 200 mill (Water and sanitation assessment report prepared for the 2nd World Water Forum). Most of this water returns as waste.
On the other hand agriculture consumes more than 70 percent of exploited water resources globally and cities are increasingly competing for water with agriculture.
With increasing water scarcity, it is mandatory to find alternative sources of water for irrigation. One such means is to enhance the use of urban wastewater transforming wastes into a resource to yield products needed by the population.
The use of the urban wastewater in agriculture is a widely established practice, particularly so in urban and peri-urban areas of arid and seasonally arid zones. Wastewater is used as a source of irrigation water as well as a source of plant nutrients (such as nitrogen, phosphorus and potassium) and trace elements (K, Na, etc) allowing farmers to reduce or even eliminate the purchase of chemical fertilizer and of organic matter that serves as a soil conditioner and humus replenisher Lunven (1992) estimated that one tenth or more of the world's population currently eats food produced on wastewater (but not always in a safe way).
In the developed world planned use (of treated wastewater) is more common, as is evident in Israel, Australia, Germany, and the USA. A literature review (Haruvy,1997) indicated that Israel is at the forefront of planned wastewater use with fully 70 % of the total agricultural demand for water in 2040 to be met by treated effluent.
For developing countries like India, Pakistan, China and Mexico, to quote a few examples, wastewater for irrigation originated as an unplanned often spontaneous activity and has been practiced for decades and even centuries by poor farmers in urban and peri-urban areas. Studies have concluded that an estimated 80% of wastewater may be used for irrigation, with China and South Asia making significant use of untreated waste for irrigation (Mara and Cairncross, 1989). In Latin America alone at least 500,000 ha of land is being irrigated with untreated wastewater, over half of which is in Mexico (Rodriguez et al, 1994). The same is the case in Africa where case studies (Bakker et al, 2000) in major cities in Africa (Accra, Dakar, Nairobi,) indicate the extensive use of wastewater.
Current wastewater use practices in developing countries includes official distribution of primary or secondary treated wastewater (i.e. after mechanical and biological treatment), the use of diluted wastewater from urban waterways and farmers accessing raw wastewater from open drains or buried trunk sewers.
The informal use of untreated wastewater by intra-urban and peri-urban farmers and gardeners is the most common situation. For large groups of poor citizens (as well as for some better off) access to wastewater is the main factor that determines their food security and income generating capacity. Without the wastewater their production would be limited to the rainy period and productivity would be minimal.
Health and environmental risks
However, irrigating with untreated wastewater poses serious public health risks, as sewage is a major source of excreted pathogens - the bacteria, viruses, protozoa- and the helminths (worms) that cause gastro-intestinal infections in human beings. Wastewater may also contain highly poisonous chemical toxins from industrial sources. Relevant groups of chemical contaminants are heavy metals, hormone active substances (HAS) and antibiotics. The risks associated with these substances may, in the long run, turn out to constitute a greater threat to public health and be more difficult to deal with than the risks from excreted pathogens.
Unregulated and continuous irrigation with sewage water may lead to problems such as soil structure deterioration (soil clogging), salinisation and phytotoxicity. . The abovementioned risks are not limited to official wastewater but often also apply to rivers and other open water sources, as indicated by figures gathered by Westcott: 45% of 110 rivers tested carried faecal coliforms levels higher than the WHO standard for unrestricted irrigation (FAO, unpublished, cited in Birley and Lock, 1999).
Treatment of wastewater
In order to prevent health risks treatment, is normally recommended as the main solution. There exists a large array of technological and process options for wastewater treatment. Centralised, technologically complex and capital-intensive treatment systems have received the most attention to date. Decentralised, low-cost options, eco-technologies and eco-sanitation approaches have only recently received more attention.
However, in practice most cities in low income countries are not able to treat more than a modest percentage of the wastewater produced in the city, due to low financial, technical and/or managerial capacity, the quick and unplanned growth of the city and the multiple and dispersed outlets of the wastewater. In many cities a large part of the wastewater is disposed of untreated to rivers and seas, with all related environmental consequences and health risks. The perspectives regarding the increase in wastewater treatment capacity in these cities are bleak. It may safely be assumed that urban farmers and gardeners increasingly will use urban wastewater for irrigation, irrespective of the municipal regulations and quality standards for irrigation water.
Alternative and complementary measures
Against this background the organisers have chosen to focus this electronic conference on the strategies that may be applied to reduce the health risks associated with the use of untreated, partially treated or diluted wastewater in agriculture whilst maintaining or enhancing the social and economic benefits for the poor urban citizens involved in irrigated production. Rather than focusing on (end of pipe) treatment of wastewater, we want to discuss:
Planning for the improved management of wastewater for reuse in urban agriculture encompasses a wide range of aspects and activities. These comprise, among others, stakeholders involvement (concepts and operational patterns), strategic water resources planning, treatment at the source of pollution and separation of wastewater flows (especially between household water and industrial wastewater), farmers education on risk management strategies (e.g. appropriate choice of crops and appropriate selection and timing, of irrigation techniques), improved institutional coordination (especially between agriculture, health, sanitation sectors); revision of municipal regulations and standards and enforcement of regulations at farmers level and vis-à-vis polluting industries, monitoring of the quality of wastewater and agricultural products, and training of professionals on sound alternatives for sanitation and recycling, among others.
To exchange, analyse and discuss strategies - as alternatives or complementary to wastewater treatment - to reduce the associated health and environmental risks of using "untreated" urban wastewater in agriculture, while maintaining or enhancing the socio-economic benefits
The conference is a platform to facilitate exchange of experiences and debate between:
The moderators will produce a summary of the discussions in each group at the end of the first and second week. At the end of the second week also the conclusions and recommendations emerging from the discussions will be drafted by the moderators and send to all participants. The results of the E-conference, together with the results of regional workshops on these topics in West Africa and South East Asia, will be used to prepare a policy paper on the use of untreated wastewater for the World Water Forum in March 2003.
A selection of the most interesting contributions to the E-conference will be included in the special issue of the Urban Agriculture Magazine on this topic.