Impact of Wastewater use in Agriculture

Dr. Ali Muhammad Khushk

The reuse of wastewater in agriculture is a common practice in the world. However, evidences from literature show that the reuse of wastewater in agriculture has both positive and negative impacts. Wastewater is a reliable source of water supply to farmers for crop production; conserves nutrients thereby reducing the need for artificial fertilizers; increase crop yields and returns from farming; provides source of income through its use in other enterprises such as aquaculture and it is a low-cost method for sanitary disposal of municipal wastewater. Regarding the disadvantages of wastewater, it increases exposure of farmers, consumers and neighboring communities to infectious diseases; it lead to groundwater contamination; has negative impacts on socio-ecological systems and property values in the vicinity and it has a negative impact on soil resources by increasing soil acidity and salinity. The poor quality of ground water and lack of alternative water sources have resulted in the use of untreated wastewater for local irrigation in urban, peri-urban and even rural agriculture.

It has been estimated that 50 percent (100 million) of the population of Pakistan in 2025 will be residing in cities. The growing population and fresh water scarcity increase the scope of reuse of urban wastewater in agriculture. A recent nation wide assessment showed that total water supply is 4.6 x 10⁶ m³/day, and about 30 percent of wastewater is used for irrigating. An area of 32,500 ha. It has also been estimated that 64 percent of total wastewater of Pakistan disposed of either into rivers or into Arabian Sea. Similarly 400,000 m³/day wastewater is additionally added to canals. Therefore, it is the need of hour 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 the volume and source of wastewater, composition of wastewater, level of treatment before use and management of wastewater 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.

Impact of wastewater use

In case of its impact on public health, indicates that wastewater contains microorganisms such as bacteria, viruses and parasites that can pose high risk to health of consumers, users and neighboring community such as gastrointestinal disease. The health of individuals in all age groups can be affected though the effect varies across age groups living with in and outside the waste irrigation zone. 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 fertilizer cost and can increase/decrease yield depending on the plant nutrient content of the waste water, 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. At least four groups of impacts on soil resource have been identified from economic point of view. These include potential yield loss of soil productivity capacity depreciation in market value of land and cost of additional nutrients and soil reclamation measures. Similarly, the impact on property values can be seen in different ways, and one way is to see it through the impacts on the loss of soil productivity due to the induced salinity and sodicity.

This has, in turn, an impact on land value in that a 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. Secondly, 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. with regard to the ecological impact of wastewater use for irrigation it can be said that drainage of wastewater irrigation in to small confined lakes and water bodies can influence the presence of aquatic life such as plant communities of water bodies, water birds, fish and affect the biodiversity. Accordingly, the change in aquatic life (for e.g. death in fish.) 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 the society by creating odor, nuisance, poor environmental quality, etc, which deteriorates the life of the society. The society may develop risk perception on the impacts that may create business risks.

Karachi and Hyderabad are large cities of Sindh Province, where wastewater from these cities is used for irrigation in the peri-urban agriculture and disposed off downstream areas. Waste disposal service in the city is not only much below the required but it is also managed inefficiently. Industries in these cities, do not have functional waste treatment facilities or waste disposal systems connected with the city’s network. The wastes generated from these industries are categorized as toxic or hazardous to human and animal health. A number of reasons have been mentioned by different writers and researchers for the poor management of the waste generated in these cities. The rural areas around the city are highly integrated in to the economy of Karachi and Hyderabad since these cities 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. This untreated wastewater has both advantages and disadvantages to the society, and its use in irrigation shares the different impacts explained previously.

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. The government also did not consider the poor farmers who do not have other alternatives to sustain their livelihoods. Restricting crop production using wastewater may prevent human health problems but may have disadvantage of reducing economic benefits from the use of wastewater. Decisions made based on limited information usually do not meet Pareto optimal criteria since they usually benefit some group of people at the expense of others.

Therefore, to avoid such handicapped decisions, policy or decision makers should be provided reliable and full information based on scientific research findings that consider the different socioeconomic, health and environmental impacts of wastewater use in agriculture. The findings should also able to advise policy/decision makers to solve the biggest problem they have on how to best minimize the negative effects of wastewater use while at the same time obtain the maximum benefits of wastewater resources.

Conclusion

The existing situations the potential and actual impacts of wastewater, no systematic studies or researches have been undertaken on a holistic approach to understand advantages and disadvantages of municipal wastewater in agriculture in the area or country. There seems lack of awareness and information concerning the impacts of using untreated municipal wastewater for irrigation on the parts of the Karachi and Hyderabad cities 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 questions should be answered Given that there are no other options for farmers’ livelihood, it seems also very crucial to ascertain whether the current practice of wastewater use in the peri-urban villages should be discontinued so as to minimize the negative impact? Second, given that the high cost required and the budgetary problem it should also necessary to know whether treatment should be done, and if it is to be done, at what degree and at what cost? Third, should regulatory mechanisms be enforced or incentive based measures be adopted and what type? And fourth what should be the bases for policy decisions? In general, if meaningful results are to be achieved, both the cost and benefit of using wastewater in agriculture should be properly identified, and that policy interventions should be based on sound judgments.