Fe2O3 micron particles are critical for electron transfer and the distribution of electrochemically active bacteria in soil MFCs

Abstract

Fe₂O₃ plays a complex role in soil electron transfer. A microbial fuel cell (MFC) was constructed to drive the directional transfer of electrons in soil, and the results revealed that Fe₂O₃ acts first as a capacitor, intercepting and reserving the electrons produced by electrochemically active bacteria (EAB) in the soil, which leads to a decrease in hexachlorobenzene (HCB) removal efficiency with increasing proportions of Fe₂O₃ dosing (R² = 0.85). The Fe₂O₃ then exerted its semiconductor properties in synergy with dissolved Fe²⁺ as an electron mediator to promote the flow of electrons in the soil. Power generation by the MFC was significantly and positively correlated with the concentration of dissolved Fe²⁺ (r = 0.51) and the Fe₂O₃ dosing proportion (r = 0.97). The higher HCB removal efficiency, spatial distribution of intercepted electrons, and abundance of electron transfer metabolic pathways confirmed that Fe₂O₃ promoted electron-flow fluxes in soil. Additionally, Geobacter sp., (direct electron transfer) and Pseudomonas sp., (indirect electron transfer) were the dominant electrochemically active bacteria in the anode and soil of MFC, respectively. In this study, both dissolved (Fe²⁺) and solid state (Fe₂O₃) electron mediators functioned as electron transporters in soil, we propose an internal "electron internet" of soil consisting of points and lines.

Keywords: Electrochemically active bacteria; Fe(2)O(3); Hexachlorobenzene; Soil MFC; electron transfer.