Ferrihydrite enhanced the electrogenic hydrocarbon degradation in soil microbial electrochemical remediation

• Effect of iron minerals on the efficiency and functions of soil MES was assessed. • More electricity generation in insulative ferrihydrite treatment than magnetite. • More than 13000 mg·kg −1 of petroleum hydrocarbons were removed in soil MES. • Addition of iron minerals obviously reinforced the synergistic effect of microbes. • Relations between functional gene richness and eleven iron states were revealed. Iron transformation determines the exoelectrogen activity and electron transfer and thus the bioelectricity generation and the contaminant degradation in soil microbial electrochemical remediation. Herein the addition of soil microbe with (semi)conductive, insulative iron minerals and ferric iron degrades the petroleum hydrocarbons under the biocurrent stimulation. The hydrocarbon removal increased by 74% in ferrihydrite treatment compared to the control. Next to magnetite treatment that was superior to hematite and ferric treatments. The accumulated charge was ferrihydrite (1964C) > control (1698C) > magnetite (1587C) > hematite (1405C) > ferric (1108C) after 148 days. The efficiencies of hydrocarbon degradation and electricity production were ascribed to the soil functions determined by substance transformation genes. Based on the correlation analysis between eleven iron states and functional genes richness, organotrophic dissimilatory iron reduction and short-distance conduit were the main enhancement ways on the system performance. Meanwhile, conversions of nitrogen, sulfur and manganese exhibited a synergetic coupling relationship with the carbon metabolism. This work comprehensively revealed the transformation of iron states and their effects on ecological functions of soil microbial electrochemical system.