Effects of different cathodic potentials on performance, microbial community structure and function for bioelectrochemical-stimulated dechlorination of 2,4,6-trichlorophenol in sediments

Bioelectrochemical systems with biocathodes constitute a promising means to enhance the biological dechlorination of 2,4,6-trichlorophenol (2,4,6-TCP) in constructed wetland (CW) sediments. However, the effect of different cathodic potentials on the structure and function of 2,4,6-TCP-reducing biocathode communities in CW sediments is largely unknown. Here, we evaluated the performance and microbial community structure of 2,4,6-TCP-reducing biocathode systems at different cathodic potentials (− 0.5, − 0.7, − 0.9, and − 1.1 V vs. saturated calomel electrode). The dechlorination efficiency of 2,4,6-TCP with the biocathode relatively increased by 16.02%–33.17% compared to that in the open circuit. The highest 2,4,6-TCP dechlorination efficiency (92.34 ± 0.86%) was observed at − 0.7 V in sediment, which may be due to the highest abundance of functional genera (e.g., Pseudomonas , Spirochaeta ) at − 0.7 V. Metagenomic analysis provided new insights into the metabolic potential of microorganisms in CW sediments and suggested possible 2,4,6-TCP conversion pathways in sediments. 2,4,6-TCP was gradually dechlorinated to form 4-chlorophenol, followed by a ring-opening step via the activities of chlorophenol reductive dehalogenase and oxygenase (e.g., cprA , tfdB ). Interestingly, micro-electrical stimulation enhanced the expression of chlorophenol reductive dehalogenase ( cprA ). Therefore, our findings at the molecular and gene expression levels provide insights into the effects of different cathodic potentials on the performance and community structure of 2,4,6-TCP-reducing biocathode systems in CW sediments.