Cr(VI) reduction, electricity production, and microbial resistance variation in paddy soil under microbial fuel cell operation

Abstract. Microbial fuel cell (MFC) is an efficient in-situ approach to combat pollutants and generate electricity. This study constructed a soil MFC (SMFC) to reduce Cr(VI) in paddy soil and investigate its influence on microbial community and microbial resistance characteristics. Fe₃O₄ nanoparticle as the cathodic catalyst effectively boosted power generation (0.97 V, 102.0 mW/m²), whose porous structure and reducibility also contributed to Cr reduction and immobilization. After 30 days, 93.67 % of Cr(VI) was eliminated. The bioavailable Cr decreased by 97.44 % while the residual form increased by 88.89 %. SMFC operation greatly changed soil enzymatic activity and microbial structure, with exoelectrogens like Desulfotomaculum (3.32 % in anode) and Cr(VI)-reducing bacteria like Hydrogenophaga (2.07 % in cathode) more than 1000 folds of soil. In particular, SMFC operation significantly enhanced the abundance of heavy metal resistance genes (HRGs). Among them, chrA, chrB, and chrR increased by 99.54~3314.34 % in SMFC anode than control, probably attributed to the enrichment of potential tolerators like Acinetobacter, Limnohabitans, and Desulfotomaculum. These key taxa were positively correlated with HRGs but negatively correlated with pH, EC, and Cr(VI), which could have driven Cr(VI) reduction. This study provided novel evidence for bioelectrochemical system application in contaminated paddy soil, which could be a potential approach for environmental remediation and detoxification.