Eisenia fetida mediated vermi-transformation of tannery waste sludge into value added eco-friendly product: An insight on microbial diversity, enzyme activation, and metal detoxification

Chromium contamination from tannery waste sludge (TWS) is a significant environmental concern. Vermicomposting is useful for conversion of toxic TWS into sanitized nutrient-enriched product for agricultural application. However, interactions among microbes and heavy metals are yet to be studied in Eisenia fetida incubated TWS-based vermireactors. The prime research hypotheses/objectives were to identify the most favorable feedstock combination for efficient vermiremediation; to generate novel information about the microbe-metal interaction during vermicomposting; and justify the functionality E. fetida by studying the TWS-induced shift in microbial community structure, nutrient dynamics, and metal removal. Earthworm population increased by 2.58-2.67 folds in TWS vermibeds. Water soluble and exchangeable fractions of potentially toxic metals (Cr, Pb, Ni, and Cu) considerably reduced by 48-69%. The alkalinity in TWS-dominated feedstocks [TWS + CD (3:1 and 2:1)] was also significantly neutralized with substantial reduction in organic C and increase in NPK availability. Microbial biomass C and different enzyme activities (fluorescein diacetate hydrolysis, urease, phosphatase, sulphatase, and glucosidase) substantially increased in the TWS-vermibeds. Interestingly, PLFA and species diversity analyses revealed that microbial community structure and fatty acid profiles greatly alter depending on the TWS proportion in the feedstocks and the metal-induced stress on microbial communities was substantially low in TWS + CD (1:1) feedstock. The correlation statistics explained that microbial activity and growth have strongly suppressed heavy metal bioavailability in TWS-vermibeds. Overall, the results indicate that TWS + CD (2:1 and 1:1) mixtures were favorable substrates for Eisenia fetida and microbial proliferation. The study revealed new information on microbial influence on metal remediation during vermicomposting and the results suggests that E. fetida could be utilized as a potential candidate for vermiremediation of toxic TWS.

Automated summary

This study provides new insights into the microbial influence on metal remediation during vermicomposting of tannery waste sludge (TWS). The results suggest that a mixture of TWS and organic waste can be an effective substrate for Eisenia fetida and microbial proliferation, leading to a reduction in the bioavailability of potentially toxic metals.