Optimum utilization of municipal wastewaters as a source of fertilizer

Abstract

Municipal wastewaters carry appreciable concentrations of nutrients which have a nuisance value if disposed of in surface waters. In contrast, conservation and proper utilization of these nutrients through wastewater recycling in a soil-plant system will not only augment manurial potential, but also will provide a mechanism for control of water pollution. The value of the nutrients in the wastewater in India is around Rs. 1752 million (US $140 million) per annum.

The application of wastewater to the land is a common practice in India. Relative concentrations of major plant nutrients, N, P and K in the wastewater are not properly balanced for crop requirements. Long-term field experiments at the National Environmental Engineering Research Institute (NEERI), Nagpur, India, have shown that the nitrogen contribution from wastewater irrigation is usually in excess of crop requirements, while phosphate is deficient. Dilution of sewage to reduce the contribution of nitrogen and the application of supplemental NPK through fertilizers provide balanced nutrition and improve crop yields. Appropriate dilution of sewage this way has been shown to increase nutrient utilization efficiency (yield of crop per kg of nutrient) and reduce the organic, inorganic and microbial load on the soil. This approach also makes it possible to extend the benefit of the fertilizing potential of wastewater to a larger area.