Effect of vermicomposting on copper and zinc removal in activated sludge with special emphasis on temporal variation

Sewage sludge is reported to have a high nutrient content suitable for use as a fertilizer additive however the substantial metal loading poses major constraints for its practical use. Under this context, an effort was made to understand the effectiveness of vermicomposting in possibly solving the issue of metal leaching from sewage sludge to the water resources, if used as fertilizer supplements. For this purpose, sludge was collected from a wastewater treatment plant and vermicomposting was applied for selected duration of 15, 30, 45, 60 and 75 days. Various physicochemical parameters before and after different duration of vermiconversion were evaluated. A temporal variation in both total and water soluble fractions of copper and zinc were observed and correlated with a change in pH. In addition, a biosorption test was done by using monometallic solution and the results were interpreted to justify the objectives. The results showed that 1:1 (sludge + cowdung) was more effective at reducing the Zn concentration than 1:2 treatments while Cu reduction was not uniform. Biosorption tests revealed the importance of pH in an effective adsorption. Dependence of pH on water soluble fraction was not significant. Lower metal content of sewage sludge with respect to various guidelines, % metal removal due to vermicomposting, high nutrient content, 1:1 treatment showing better metal removal and stabilization duration of just 75 days of composting substantiate the possible use of sewage sludge amended cow manure as an agricultural additive.