Addition of iron oxides in sediments enhances 2,3,4,5-tetrachlorobiphenyl (PCB 61) dechlorination by low-voltage electric fields

Abstract

Despite the growing interest in exploiting low-voltage electric fields for bioremediation of chlorinated contaminants, little information is known about whether iron-rich minerals, naturally abundant components in environments, affect bioelectrochemical dechlorination. Here, we made the first attempt to investigate the role of iron oxides on the dechlorination of polychlorinated biphenyls in a sediment-based bioelectrochemical reactor (BER) poised with a potential of −0.50 V vs. SCE (saturated calomel electrode). We found that the addition of iron oxides significantly enhanced the rate and extent of 2,3,4,5-tetrachlorobiphenyl (PCB 61) transformation. Analysis of the bacterial structures suggested that the key species detected in the BERs were genera Geobacter and Desulfovibrio, well-known dissimilatory iron-reducing bacteria (DIRB) that were more dominant when iron oxides (e.g., α-Fe₂O₃) were added. A positive correlation between the rate constant of PCB 61 reduction and the biogenic adsorbed Fe(II) concentration suggests that DIRB-induced Fe(II) should be critical for enhancing PCB dechlorination in the system.