Vermicomposting of Anaerobically Digested Sewage Sludge with Hazelnut Husk and Cow Manure by Earthworm Eisenia foetida

Abstract

Vermicomposting of organic waste has an important part to play in an integrated waste management strategy. The aim of the present study was to investigate the ability of an epigeic earthworm Eisenia foetida to transform anaerobically digested sewage sludge (SS) amended with hazelnut husk (HH) and cow manure (CM) in different proportions under laboratory conditions (in darkness at 25 degrees C +/- 0.5 degrees C). Three approaches investigated in the study were: (1) to find the best medium for growth and reproduction of E. foetida in different feed mixtures, (2) to analyze the heavy metal concentrations in different feed mixtures of SS & sbnd;HH & sbnd;CM before and after vermicomposting, and (3) to explore heavy metals accumulation of earthworms in sewage sludge with different feed mixtures. Number and biomass of earthworms and heavy metal contents in feed mixtures and earthworms were periodically monitored. The results indicated that maximum earthworm biomass was attained in a feed mixture of 20% SS + 40% CM + 40% HH, while the earthworm number was highest in a feed mixture of 30% SS + 35% CM + 35% HH during the vermicomposting period. Heavy metals concentration (Zn, Cu, Cd, Pb, Ni, and Cr) in all feed mixtures decreased associated with the increasing vermicomposting time. The heavy metals' content in the feed mixtures was lower than that of initial mixtures. Metal analysis of earthworms revealed considerable bioaccumulation of heavy metals in their bodies' tissue. Heavy metal analysis of earthworm body showed that increasing proportion of SS in the feed mixtures promoted the heavy metal content of earthworm body.