Efects of earthworms on physiochemical properties and heavy metal content of sludge: a review

Vermicomposting has been reported as an alternative and ecofriendly way to recycle many organic wastes through a broad range of bioprocesses. This paper reviews the effects of different earthworms on the physical and chemical properties and heavy metal content. Vermicomposting process shiftes pH significantly towards neutral. The mutual reaction of earthworms and aerobic microbes accelerates the biodegradation of organic wastes. Earthworms strongly affect sludge organic carbon cycling. Endogeic earthworms may increase TOC content，while epigeic earthworms may decrease TOC content. Most earthworms can increase TN，TP and TK contents of sludge， but no significant differences among earthworm ecotypes were observed regarding these parameters. Epigeic and endogeic earthworms may decrease nutrient contents of sludge，while anecic earthworms increase available nitrogen and phosphorus content. The causes of inconsistent results may be attributed to the different ecotypes，and varying incubation time. Although slight differences were reported among mixtures and species，the effects of epigeic and anecic on reduction in final total metallic concentration showed basically similar.