Hazard remediation and recycling of tea industry and paper mill bottom ash through vermiconversion

•Bioconversion of tea factory and paper mill coal ash is a novel effort.•Solubility of Cr and Ni in coal ashes is reduced due to vermiconversion.•Vermicomposted coal ashes improve soil health.•Vermicomposted tea factory coal ash enhances crop yield.

Considerable amount of bottom ash (BA) is produced by tea and paper factories in Northeast India. This significantly deteriorates soil and surface water quality through rapid acidification, releasing sulfur compounds and heavy metals. The present investigation endeavoured to convert this waste to organic manure through vermicomposting by Eisenia fetida. Substantial increment in bioavailability of N, P, K, Fe, Mn and Zn along with remarkable decline in toxic metal like Cr due to vermicomposting was noteworthy. Furthermore, vermicomposted mixtures of Tea Factory BA (TFBA) or Paper Mill BA (PMBA) with organic matter (OM) attributed profuse pod yield of French Bean (Phaseolus vulgaris L.). Hence, bioconversion of TFBA and PMBA is highly feasible through vermicomposting and the converted materials can be utilized as potential organic fertilizer.