Microbial community acclimation via polarity reversal supports extensive dechlorination and anaerobic mineralization of 2,4,6-trichlorophenol in biocathode

In the anaerobic biocathode, reductive dechlorination of 2,4,6-trichlorophenol (2,4,6-TCP) mainly proceeded to produce 4-monochlorophenol (4-MCP) and phenol, while anaerobic mineralization was challenging. In this study, biocathodes microbial communities were first acclimated via potentials repeatedly adjusted between-0.278 V and +0.200 V (T-200),-0.278 V and +0.400 V (T-400), and-0.278 V and +0.600 V (T-600). Subsequently, all biocathode potentials were stabilized at-0.278 V for the degradation of 2,4,6-TCP. The results revealed that the T-600 achieved the highest degradation rate of 2,4,6-TCP (0.43 d-1), outperforming T-200 (0.051 d- 1 ), T-400 (0.020 d- 1 ), and open-circuit bioreactor (OC, 0.038 d- 1 ) groups. In T-600, pare-dechlori- nation was facilitated, allowing for the conversion of 2,4,6-TCP to 2-monochlorophenol (2-MCP). Additionally, the detection of 4-hydroxybenzoic acid, an anaerobic mineralization intermediate of 2,4,6-TCP, indicated that anaerobic mineralization was also occurring. Polarity reversal occurred only in T-600 during the acclimation period, resulting in alterations to the electrical properties of the biocathode and microbial community. The cyclic voltammetry (CV) and differential pulse voltammetry (DPV) results indicated that there were more electroactive sites in biocathode of T-600, and the bidirectional extracellular electron transfer (EET) might be related to cytochrome. Mycobacterium (24.33% in slurry and 19.92% in biofilm), Thiobacillus (2.47% in slurry and 17.85% in biofilm), and Arenimonas (4.23% in slurry and 4.32% in cathode biofilm) were identified as the dominant electroactive bacteria in T-600, with Mycobacterium also playing an important role in the degradation of chlorophenols. These findings suggested that polarity reversal may represent a viable strategy for constructing microbial communities capable of achieving simultaneous dechlorination and mineralization of 2,4,6-TCP.