This study was conducted to investigate the feasibility of vermicomposting by using vermicast as the substrate for the stabilization of municipal activated sludge, called hereafter as direct vermistabilization, in which the pre-treatment and bulking materials required in previous practices were all omitted. For this purpose, two epigeic earthworm species, namely Eisenia foetida and Bimastus parvus, were inoculated into substrate for composting fresh dewatered activated sludge. Direct vermistabilization resulted in significant reductions in pH, TOC, C/N ratio and the content of heavy metals, as well as increases in EC, total N, total P and total K in the final vermicast. Moreover, both Eisenia foetida and Bimastus parvus showed faster growth rate and higher cocoon production. The results of this study suggest that the direct vermistabilization has the advantages of being simple, cost-effective and efficient, and can thus be used as a feasible vermicomposting approach to convert fresh dewatered activated sludge into a valuable product for agricultural use. The results also suggest that Bimastus parvus can be used as a new potential candidate for vermicomposting of municipal activated sludge.
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