LEACHING OF NUTRIENTS FROM DIGESTED SLUDGE

Abstract

In the developing countries like India, surface and ground water quality is deterioted to large extent by waste water. Apart from the direct disposal of waste to surface water, a large quantity of nutrients and metals are added during runoff from waste disposal sites and agricultural fields. The digested sludge from municipal sewage is widely used as manure both in liquid and dry forms for it's rich nutrient contents. Leaching from digested sludge is of major concern as it posess high concentration of nutrients and metals (toxic and nontoxic). Nutrient addition may create eutrophication of lakes and streams and high concentration of metal may impose toxicity to water. In fields and at waste disposal sites, flooding may occur due to rain, leading to leaching. The process of leaching is partly batch and partly continuous. Major part of leaching involves batch process. Batch reactors have been used to study the extent of release of nutrients and trace metals from digested sludge. Liquid sludges show fast leaching compared to dry sludge from the same source. Amongst the flu trient-n (N,P !I.rid K), N and K leaching is faster than P and amongst trace metals (Ni, Zn and Cu), Ni leaching was quick compared to Zn and Cu. It is observed that the solubilization, dispersion and dilution were the main mechanisms governing the leaching process.