Electrostimulated bio-dechlorination of a PCB mixture (Aroclor 1260) in a marine-originated dechlorinating culture

Highlights: • Bio-dechlorination of PCB mixture (Aroclor 1260) was enhanced by electric potential. • PCB dechlorination activity was well maintained solely by the cathodic biofilm. • Dominant PCB dechlorination pathways in various culturing systems were inferred. • Dehalococcoides abundance in cathodic biofilm was higher than in suspension culture. • Dehalococcoides in cathodic biofilm showed a high PCB dechlorination activity. Aroclor 1260, a commercial polychlorinated biphenyl (PCB) mixture, is highly recalcitrant to biotransformation. A negatively polarized cathode (−0.35 V vs. standard hydrogen electrode) was applied for the first time to a marine-origin PCB dechlorinating culture that substantially increased the microbial dechlorination rate of Aroclor 1260 (from 8.6 to 11.6 μM Cl⁻ d⁻¹); meta-chlorine removal was stimulated and higher proportions of tetra-CBs (43.2–46.6%), the predominant dechlorination products, were observed compared to the open circuit conditions (23.7–25.1%). The dechlorination rate was further enhanced (14.1 μM Cl⁻ d⁻¹) by amendment with humin as a solid-phase redox mediator. After the suspension culture was renewed using an anaerobic medium, dechlorination activity was effectively maintained solely by cathodic biofilms, where cyclic voltammetry results indicated their redox activity. Electric potential had a significant effect on microbial community structure in the cathodic biofilm, where a greater abundance of Dehalococcoides (2.59–3.02%), as potential dechlorinators, was observed compared to that in the suspension culture (0.41–0.55%). Moreover, Dehalococcoides adhering to the cathode showed a higher chlorine removal rate than in the suspension culture. These findings provide insights into the dechlorination mechanism of cathodic biofilms involving Dehalococcoides for PCB mixtures and extend the application prospects of bioremediation to PCB contamination in the natural environment.