Assessing the arsenic-saturated biochar recycling potential of vermitechnology: Insights on nutrient recovery, metal benignity, and microbial activity

Abstract

Biochar mediated pollutant removal is gaining attention because of high efficiency of the process. However, effective recycling avenues of the pollutant-saturated biochars are scarce in the knowledge base; while such materials can be a new source of long-range contamination. Therefore, potential of vermitechnology for eco-friendly recycling of pollutant-loaded biochar was assessed by using arsenic-saturated native (NBC) and exfoliated (EBC) biochars as feedstocks for the first time. Interestingly, the bioavailable arsenic fractions (water soluble and exchangeable) considerably reduced by 22–44 % with concurrent increment (~8–15 %) of the recalcitrant (residual and organic bound) fractions in the biochar-based feedstocks. Consequently, ~2–3 folds removal of the total arsenic was achieved through vermicomposting. The earthworm population growth (2.5–3 folds) was also highly satisfactory in the biochar-based feedstocks. The results clearly imply that Eisenia fetida could compensate the arsenic-induced stress to microbial population and greatly augmented microbial biomass, respiration and enzyme activity by 3–12 folds. Moreover, biochar-induced alkalinity was significantly neutralized in the vermibeds, which remarkably balanced the TOC level and nutrient (N, P, and K) availability particularly in EBC + CD vermibeds. Overall, the nutrient recovery potential and arsenic removal efficiency of vermitechnology was clearly exhibited in NBC/EBC + CD (12.5:87.5) feedstocks. Hence, it is abundantly clear that vermitechnology can be a suitable option for eco-friendly recycling of pollutant-saturated sorbing agents, like biochars.