Managing Wastewater Use in Agriculture

Wastewater is increasingly seen as a source of water to supplement irrigation supplied in agriculture. Climate change, population growth and food insecurity are placing varying degrees of pressure on water resources throughout the world. Some regions are faced with acute physical water scarcity (Middle East/North Africa, parts of South Asia, China, Australia and Latin America) while other regions are challenged by economic water scarcity (much of Africa, parts of India). Given such scarcity, wastewater is seen as an attractive way to augment water supplies that are under pressure. Needless to say, wastewater use can pose health risks from a mix of microbiological and industrial pollutants and needs to be managed carefully.

Wastewater is used on an estimated 20 million ha – or 7% - of the total global irrigated area (WHO, 2006). Estimates of how much produce is irrigated with wastewater vary depending on how arid a region is and how diluted wastewater becomes before it is used. Research in Pakistan has suggested that 26% of all produce is irrigated with wastewater (Ensink et al, 2004), whereas in West African cities, the amount can vary from 50% to as high as 90% (Drechsel et al, 2006).

The challenge of managing wastewater is exacerbated by failures in sanitation systems. According to the joint monitoring program of UNICEF and WHO point to the fact that 2.6 billion people lack basic “improved” sanitation. Most are concentrated in sub-Saharan Africa and Asia (REF: http://www.who.int/water_sanitation_health/monitoring/jmp04.pdf). While cities generally have a higher rate of coverage, rapid urban growth on the fringes of cities has led to a higher concentration of wastewater being produced in low-income areas. Without collection, wastewater ends up in ditches, streams and rivers which further downstream are often used by farmers with little control. Such “indirect use” of wastewater is acknowledged as highly problematic from a health standpoint and also very difficult to control since there can be a very high number of downstream users.  Full treatment ofwastewater is obviously the preferred method to cope with wastewater use, however, in many contexts treatment is not possible. Some countries are faced with treatment plants that are failing and for which there is not enough technical expertise. Others simply have not been finance and construct adequate treatment facilities for wastewater.

Both treated and untreated wastewater is used. Treated wastewater use under controlled conditions is a popular method to increase available water resources in arid regions. Tunisia, Israel and Jordan are three countries that offer rich experience in the treated reuse of wastewater. According to the Israeli Ministry of Environmental Protection 70% of wastewater is reclaimed for use (Government of Israel, 2008). Most policy on wastewater, however, is highly restrictive when it comes to its reuse. A combination of the negative perception of wastewater use, high food quality standards and associated health problems have led to most laws banning wastewater use. A particular challenge relates to health standards. The WHO Guidelines on the Safe Use of Wastewater, Excreta and Greywater have recently been revised suggesting a much more pragmatic holistic management approach to reduce associated risks. The new guidelines also advocate for an approach that suggests wastewater quality standards be developed in line with the context in which they are being applied. Therefore, stringent standards applied in California of the EU should not be the same standards applied in some African countries that are faced with a more dire challenge (WHO, 2006). In practice, many ministries of health have done so.

Content Table

Characterizing Wastewater

Raw wastewater and treated wastewater

Wastewater has different characteristics that can determine how it is used. Raw wastewater use versus treated wastewater use clearly has different characteristics in terms of safety. Formal versus informal wastewater use is another important distinction. Where it is sanctioned and controlled, formal wastewater use is generally subject to close monitoring by authorities. This is easier when there are a few larger users as opposed to many small scale users. Informal wastewater use, which is much more common generally occurs in areas where policy is absent, or not enforced.

Industrial and domestic

Another important distinction is the difference between industrial wastewater and domestic wastewater. Domestic wastewater is easier to manage since most of the risk stems from micro-biological elements including bacteria (e.coli being prevalent) and viruses. Relatively simple treatment systems such as surface-aerated basins (or lagoons) can be applied that reduce biological risks. The main health impacts include diarrhoea, hookwork and cholera. Industrial pollutants can also be serious, however, specific research on industrial pollution in the heavily polluted Musi River (Hyderabad, India) has shown that the risks are not as serious as expected, with Lead and Zinc coming in at significantly lower levels of risk than expected (Amerasingh, et. al. 2009).  Irrigation infrastructure along the Musi has also been found to significantly improve water quality.

Greywater vs. blackwater

A further distinction is the difference between grey and black wastewater. Grey wastewater refers to all water that is generated from kitchens, bathrooms and laundry water, but excluding toilets  (Mcilwaine et al, 2010; Morel et al, 2008). Greywater use in agriculture is often done on-site, that is, home owners will reuse their wastewater to supplement irrigation waters for crops raised on their properties. This is considered “on-site disposal.” Naturally, health risks are relative to where disposal takes place and each option entails different management challenges. Despite the fact that greywater comprises 55-75% of all household wastewater, the contribution of greywater to alleviating water scarcity will be limited; it is best to see greywater as a strategy to alleviate poverty by providing a source of irrigation water to household or multi-household agricultural production (Redwood, 2008).

Policy Options

Requirements for wastewater treatment are highly dependent on the end-use of the effluent. The serious problem of perception related to wastewater translates into policy limitations. For example, some countries are unwilling to accept that wastewater is used as frequently as it is thus limiting a proactive policy response. For reference, most countries have referred to the 1989 WHO Guidelines on the Safe Use of Wastewater, however, the sophisticated approach to the guidelines has not been very effective in resource constrained countries where enforcement is limited. The new 2006 Guidelines offer considerably more data and research on safe wastewater use, as well as options for management. The Guidelines are complemented by a series of information kits published by the WHO and partners (WHO, 2010).

Health ministries, and to a lesser degree ministries of environment and water, are usually those most engaged with the management of wastewater. Given the broad importance of wastewater use in all of the above sectors, coordination between such different authorities is important but unfortunately rare. Municipal governments also play a role in local health promotion and often can have a positive impact when working directly with farmers who use wastewater, in markets and amongst food sellers and consumers. The “farm to fork” health approach is an approach that sees wastewater management as a system. To manage risks, barriers can be established along this system reducing the potential impact of wastewater use. For example, hand and produce washing, clean water being made available in markets, education on the risks associated with wastewater use and irrigation techniques that minimize direct contact between wastewater and farmers are all effective at reducing health risks.  

Despite advances, most countries still have a restrictive policy prohibiting the practice. In countries where wastewater is an important part of the national water budget, policies are more comprehensive. Notable examples are Jordan, Tunisia and Mexico. Saudi Arabia`s 1978 fatwa allowing wastewater reuse is notable given the religious conservatism in the country (Faruqui et al, 2002).

Resources

This article was was adapted from 'WASTEWATER GOVERNANCE AND ADOPTION OF RISK-REDUCTION OPTIONS: Challenging Conventional Approaches to Managing Wastewater Use in Agriculture' in WASTEWATER IRRIGATION AND HEALTH: Assessing and Mitigating Risk in Low-income Countries Edited by Pay Drechsel, Christopher A. Scott, Liqa Raschid-Sally, Mark Redwood, and Akiça Bahri.

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Potable Water Solutions - Stewart Burn, Stephen Gray and Don Begbie

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Publication Date: Nov 2012 - ISBN - 9781780404004

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References

Amerasinghe, P., P. Weckenbrock, R. Simmons, S. Acharya, and A. Drescher. 2009. An atlas of water quality, health and agronomic risks and benefits associated with wastewater irrigated agriculture: A study from the banks of the Musi river, India.

Drechsel, P., Graefe, S., Sonou, M. and Cofie, O. 2006 ‘Informal irrigation in urban West Africa: An overview’, Research Report 102, International Water Management Institute, Colombo, Sri Lanka

Drechsel, P., C. A. Scott, L. Raschid-Sally, M. Redwood, and A. Bahri. 2010. Wastewater irrigation and health: Challenges and outlook for mitigating risks in low-income countries. Wastewater Irrigation and Health: Assessing and Mitigating Risk in Low-Income Countries: 381pp.

Ensink, J., Mahmood, T., van der Hoek, W., Raschid-Sally, L. and Amerasinghe, F. 2004 “A nation-wide assessment of wastewater use in Pakistan: An obscure activity or a vitally important one?”, Water Policy, vol 6, pp197–206

Faruqui, N. I., A. K. Biswas, and M. J. Bino. 2001. Water management in Islam United Nations University Press and IDRC.

Government of Israel, Ministry of Environmental Protection, 2010. (Cited, August 15th, 2010). http://www.sviva.gov.il/bin/en.jsp?enPage=e_BlankPage&enDisplay=view&enDispWhat=Zone&enDispWho=Wastewater_sub&enZone=Wastewater_sub

McIlwaine, S., and M. Redwood. 2010. The use of greywater for irrigation of home gardens in the middle east: Technical, social and policy issues. Waterlines 29 (2): 90-107.

Morel, A., and S. Diener. 2007. Greywater management in low and middle-income countries. EAWAG.

Redwood, M. 2008. The application of pilot research on greywater in the middle east north africa region (MENA). International Journal of Environmental Studies 65 (1): 109-17.

WHO, 1989. Guidelines for the Safe Use of Wastewater in Agriculture, World Health Organization, Geneva.

WHO, 2006 Guidelines for the Safe Use of Wastewater, Excreta and Greywater, Volume 1-4, World Health Organization, Geneva.

WHO, FAO and IDRC, 2010. Information Kit on the 2006 Guidelines for the Safe use of Wastewater, Excreta and Greywater. http://www.who.int/water_sanitation_health/wastewater/en/

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