Effect of introduced‐electrode on phenanthrene degradation in the soil microbial electrochemical remediation

Abstract

Soil microbial electrochemical remediation (MER) provides an inexhaustible electron acceptor (solid anode) to oxidize organic pollutants in soils where electron acceptors are generally limited. Simultaneously, bioelectricity recovery is directly implemented from the degradation of organic pollutants which is in turn accelerated by biocurrent stimulation. However, it has not been a concern in previous reports that the removal rates of open-circuit groups (OC) are significantly higher than non-electrode controls. Thus, the reasons for the enhanced degradation after the introduction of single or two electrodes were focused in this study. The removal rate of typical polycyclic aromatic hydrocarbon phenanthrene was higher in the closed-circuit soil MER than OC, with an electricity conversion efficiency of 12 ± 1 C∙mg−1 phenanthrene. The removal was 21-39% higher (P < 0.05) in soils near the cathodic position and adjacent to the water layer of upper surface, suggesting that the cathode even contributed more to phenanthrene degradation than the anode. The profile of power production showed two peaks with the maximum values of 84 ± 4 mA∙m−2 on days 0-26 and 70 ± 1 mA∙m−2 on days 27-100, respectively. Afterward, more phenanthrene (26-34 mg∙kg−1, P < 0.05) was removed in OC compared to closed-circuit systems (1-17 mg∙kg−1). However, in reactors with only a single electrode, a separate anode played a stronger enhanced effect on the degradation of phenanthrene than a separate cathode. These results were due to an increment of 128-425 OTUs on the surface of electrodes, for example, the relative abundance of Bacillus increased from 14.27% to 44.98%. Overall, the configuration with both electrodes contacting with the polluted matrix (eg, soils or sediments) is superior in terms of the remediation efficiency to that with one electrode (ie, anode), which provided a guidance of the MER application.