Wastewater use in agriculture

DAWN Economic & Business Review (June 15 to 21, 2009)

By Dr. Ali Muhammad Khushk

Today Dawn

THE growing population and fresh water scarcity increases the scope of reuse of urban wastewater in agriculture. Evidences show that it has both positive and negative impacts on crop productivity and yield, but certainly it heightens exposure of individuals or neighbouring communities to serious health hazards.

A recent nation-wide assessment showed that total water supply is 4.6 x 106 m3/day, and about 30 per cent of wastewater is used for irrigation. It has also been estimated that 64 per cent of total wastewater is disposed of either into rivers or into Arabian Sea. Similarly 400,000 m3/day wastewater is additionally added to canals.

There is a need to look into the prospects of sewerage irrigation to manage this nutrient-rich water resource. The magnitude of these potential benefits and costs of wastewater varies from region to region and from community to community depending on its volume, source, composition, level of treatment before use and management both at its disposal and its use at farm level. These potential impacts are reflected through the impacts on crop production, public health, soil resources, property value and ecosystem.

The wastewater contains microorganisms such as bacteria, viruses and parasites that can pose high risk to health of consumers, users and neighbouring community such as gastrointestinal disease.

Its economic impacts on crop production depend on the degree of treatment and composition of municipal wastewater, type and nature of crops grown and the overall farm level water management practices.

Given the agronomic and water management practice, it can be used as supplementary water for irrigation, reduce fertiliser cost and can increase/decrease yield depending on the plant nutrient content of the wastewater, which has implication for profitability of crop production.

The impact of wastewater on soil resources is mainly on its productivity, which, in turn, affects crop yields and farm household income. The impact depends on the presence of high nutrient content such as potassium and phosphorous, high total dissolved solids, heavy metals and others that pollute the soil resources, and result in soil salinity and water logging if used for longer time.

This may, in turn, result in lower crop yield though the impacts depend on soil property, plant characteristics, and source of wastewater.

Decline in soil productivity may have a negative influence on land price and lease revenue due to a decrease in crop yield or lack of demand for the crops produced in fear of the health impacts given other factors such as availability of information being constant. It may have positive impacts on property value depending on the attributes of the property such as proximity to waste irrigation site, to road, market and population center etc.The change in aquatic life due to the wastewater irrigation can have an economic impact to the communities who are using the aquatic life as means of livelihood. Wastewater has impacts on society by creating odor, nuisance, poor environmental quality, etc., which deteriorates the life. The society may develop risk perception on the impacts that may create business risks.

In Karachi and Hyderabad, the wastewater is used for irrigation in the peri-urban agriculture. Waste disposal service in these cities is not only highly poor, but it is also managed inefficiently.

Industries do not have functional waste treatment facilities or waste disposal systems connected with the city’s network. The wastes generated from these industries are categorised as toxic or hazardous to human and animal health.

The rural areas are highly integrated into the economy of these cities which are the main market place for their agricultural products. Farmers within these cities and the peri-urban areas are producing different types of crops both for market and home consumption using irrigated agriculture. The crops grown in the peri-urban areas of these cities possess high market value such as vegetables, and they are the main source of income for the villagers.

In the peri-urban areas, the main source of irrigation water for crop production is wastewater of these cities. No treatment is being done before the wastes are used.

However, government officials are condemning/denying the practice of using untreated wastewater in agriculture for public health reasoning based on the findings of few studies that focus on specific impacts such as the composition of waste and contribution of the different generators of the waste, or study on only the health impacts from epidemiological point of view, which is based on limited samples and focus on limited local negative health impacts, ignoring the different possible impacts on the down streams and other possible target groups.

No systematic studies or researches have been undertaken on a holistic approach to understand advantages and disadvantages of municipal wastewater in agriculture.There seems lack of awareness and information concerning the impacts of using untreated municipal wastewater for irrigation in rural areas adjoining to Karachi and Hyderabad and the farmers’ producing crops.

Therefore, regarding the socio-economic, health and environmental impacts of the reuse of wastewater in the peri-urban and urban area, certain basic issues should be addressed.


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