Bioremediation of High-Concentration Heavy Metal-Contaminated Soil by Combined Use of Acidithiobacillus ferrooxidans and Fe3O4–GO Anodes

Soils heavily contaminated with potentially toxic elements (PTEs) pose substantial risks to the environment and human health. However, conventional remediation methods are often plagued by high energy consumption and the potential for secondary pollution. To address this challenge, this study developed a synergistic system combining acidophilic bacteria with a Fe-modified anode, aiming to enhance the remediation of PTEs in such contaminated soils. This system integrates the following three core components: the catalytic function of Fe₃O₄-graphene-oxide (Fe₃O₄-GO) nanocomposites, the acclimation of microbial communities, and the optimization of process parameters-specifically, applied electric current, pH, and oxidation-reduction potential (ORP). Experimental treatments were designed to assess the individual and combined effects of three key factors: bacterial inoculation, the Fe-modified anode, and the addition of Fe₃O₄-GO. The results revealed that the integrated synergistic system effectively reduced the soil pH from 2.9 to 2.0 and maintained the ORP at approximately 600 mV. For PTE removal, the system achieved efficiencies of 89% for Zn, 85.89% for Cu, 66.3% for Pb, 77.89% for Cd, and 40.63% for Cr, respectively. In contrast, control groups lacking bacteria, applied current, or Fe₃O₄-GO exhibited significantly lower metal removal efficiencies. Notably, the bacteria-free treatment led to a more than 50% reduction in Cr removal. Additionally, the group with an unmodified anode only achieved 1/3 to 1/2 of the removal efficiencies observed in the full synergistic system; this discrepancy is likely attributed to reduced electron transfer efficiency and compromised microbial adhesion on the anode surface. These findings demonstrate that the coupling of electrochemical enhancement, acidophilic microbial activity, and Fe₃O₄-GO catalysis constitutes an effective and energy-efficient approach for remediating soils contaminated with high concentrations of PTEs while simultaneously minimizing the risk of secondary pollution.