Applying an electric field to stimulate the microbial reductive dechlorination of polychlorinated biphenyls (PCBs) represents a promising approach for bioremediation of PCB-contaminated sites. This study aimed to demonstrate the biocathodic film-facilitated reduction of PCB 61 in a sediment-based bioelectrochemical reactor (BER) and, more importantly, the characterizations of electrode-microbe interaction from microbial and electrochemical perspectives particularly in a time-dependent manner. The application of a cathodic potential (-0.45 V vs. SHE) significantly improved the rate and extent of PCB 61 dechlorination compared to the open-circuit scenario (without electrical stimulation), and the addition of an external surfactant further increased the dechlorination, with Tween 80 exerting more pronounced effects than rhamnolipid. The bacterial composition of the biofilms and the bioelectrochemical kinetics of the BERs were found to be time-dependent and to vary considerably with the incubation time and slightly with the coexistence of an external surfactant. Excellent correlations were observed between the dechlorination rate and the relative abundance of Dehalogenimonas, Dechloromonas, and Geobacter, the dechlorination rate and the cathodic current density recorded from the chronoamperometry tests, and the dechlorination rate and the charge transfer resistance derived from the electrochemical impedance tests, with respect to the 120 day-operation. After day 120, PCB 61 was resistant to further appreciable reduction, but substantial hydrogen production was detected, and the bacterial community and electrochemical parameters observed on day 180 were not distinctly different from those on day 120.
Keywords: Electrical stimulation; Electrochemical impedance spectra; High-throughput sequencing; PCB contamination; PCB dechlorination; Surfactant.
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