[Comparative studies on vermicomposting of sewage sludge with two epigeic earthworms]

A comparative study was conducted two epigeic species earthworms (Bimastus parvus and Eisenia foetida) for the evaluation of their efficacy in vermicomposting of sewage sludge. The various changes studied during pot experiments were the physiochemical properties of the sewage sludge, sludge reduction and earthworm biomass. Vermicomposting resulted that both epigeic species earthworms showed same capability among sewage sludge mineralization and decomposition rate and reduction. By the end of experiment, the pH value declined to 6.27 with B. parvus and 7.07 with E. foetida, but both epigeic species earthworms showed same mineralization and decomposition rate. B. parvus produced 31.96%, 5.76% and 17.91% increases in nitrogen, phosphorus, and potassium as well as 44.14% and 30.69% decreases in C/N and C/P ratios as compared to initial after 30 days of inoculation. In contrast, E. foetida produced 35.48% and 11.58% increases in nitrogen and potassium as well as 10.12%, 46.73% and 20.50% decreases in phosphorus, C/N and C/P ratios as compared to initial after 30 days of earthworm activity. At the same time, both epigeic species earthworms resulted in significant reduction in heavy metal content. The reduction in heavy metal content for B. parvus and E. foetida was found in the order: Zn > Cu > Pb > Cr and Cu > Zn > Ph > Cr. At the end of experiment, the weight and cocoons of B. parvus and E. foetida showed significant increase, which the growth rate and the reproductive rate were 76%-86% and 156%-131% respectively.