Electrostimulated bio-dechlorination of trichloroethene by potential regulation: Kinetics, microbial community structure and function

Bioelectrochemical system with biocatalyzed cathode is regarded as a promising approach for the enhanced bio-dechlorination of chlorinated aliphatic hydrocarbons (CAHs). However, the microbial community structure variation law and the corresponding function in the cathodic biofilm in response to the different cathode potentials remain poorly understood. In this study, biocathode systems were established for trichloroethene dechlorination under four cathode potentials (- 0.06, -0.26, -0.46 and -0.66 V vs standard hydrogen electrode). About 2.6-4.3 times higher dechlorination rates were obtained in biocathodes than opened circuit, verifying the efficient electrostimulated bio-dechlorination. The highest trichloroethene dechlorination rate (1.01 mmol/L.d) was observed at -0.26 V, while higher ( -0.06 V) or lower potentials ( -0.46/ - 0.66 V) resulted in the 7.2-48.9% lower dechlorination rates. Under the different cathode potentials, the similar TCE dechlorination pathway was observed with cis-1,2-dichloroethene and ethene as the major and minor dechlorination products, respectively. The correlation and sharing network analysis of bacterial community illustrated that the negative potentials facilitated the enrichment of cathode-utilizing and dechlorination populations. The highest abundance of electroactive and dechlorinating bacteria (Lactococcus, Bacillus and Pseudomonas) and the highest expression of reductive dehalogenase (pceA and tceA) were observed at - 0.26 V. The expression of extracellular electron transfer related gene omcX was promoted as the potential decreased. The decreased dechlorination capacity at potentials of -0.46 and -0.66 V could possibly be attributed to the lack of H-2-utilizing dechlorinators and the low expressed pceA. This study offers insights into the molecular mechanism involved in the electrostimulated bio-dechlorination of CAHs by potential regulation.