The effect of extracellular electron transfer on arsenic speciation transformation in a soil bioelectrochemical system

The control and characterization of microbial extracellular electron transfer (EET) reaction-mediated soil arsenic mobilization is still not well understood, which has limited the application of biotechnologies for the remediation of contaminated wastes. In this study, we developed an improved soil bioelectrochemical system (BES) that can decrease the dissolution of As-bearing Fe/Al oxides from anoxic submerged soil by more than 80 % under the application of a 0.9 V external voltage. Combining the results of chemical property and microbial characteristic analyses indicated that an applied voltage was accompanied by a dramatic increase in acetate oxidization and soil substrate bioavailability, facilitating electron transfer reactions for methanogenesis, whereas the applied voltage exhibited a negative effect on microbial EET activities for As/Fe reduction. Subsequently, an additional dual-chamber configuration was employed for comparison and to study the effect of bacteria-electrode interactions on arsenic mobilization; we found that the bioanode and biocathode had reverse effects on the release of As/Fe, suggesting a correlation between the disparate microbial communities and EET-mediated reaction mechanisms on the electrodes. Overall, this study is vital to expand the knowledge of the intimate links between arsenic speciation transformation and microbial electron transport system activity, improve our understanding of BES operation and move towards its application.