Biochar-enhanced remediation of Cr(Ⅵ)-contaminated soil by Penicillium oxalicum SL2: Enhanced reduction based on extracellular electron transfer

Hexavalent chromium has gained significant attention due to its high mobility and toxicity. Efficaciously reducing the bioavailability of Cr(VI) to maintain its stability in soil poses a substantial challenge for soil remediation efforts. In this study, a stable and efficient remediation approach is proposed, utilizing biochar-enhanced Penicillium oxalicum SL2 to reduce and stabilize heavily Cr(VI)-contaminated soil. The research investigates the impact of this method on the effectiveness of Cr(VI) reduction and its biochemical characteristics. The findings reveal that the combined application of SL2 and biochar resulted in a substantial decrease in soil Cr(VI) concentration from 751.3 to 3.9 mg/kg and the bioavailable Cr (F1, Exchangeable + F2, Bound to carbonates) from 25.9 % to 4.5 %, thus ensuring a sustained level of stability. Post-remediation, alterations in soil pH, Eh, and CEC were noted, successfully alleviating the detrimental effects of Cr(VI) on soil microorganisms. Biochar aids SL2 in reducing Cr(VI) via electron transfer mechanisms. Key environmental factors like Cr(VI), Cr(F1+F2), Eh, and sDHA significantly influence the structure of microbial communities in soil. The integration of SL2 and biochar is anticipated to offer an environmentally friendly, effective, and cost-efficient strategy for the stabilization and reduction of Cr(VI).