Structural Characteristics and Functional Genes of Biofilms in Microbial Electrolysis Cells for Chlorobenzene Abatement

Chlorobenzene (CB) is typically emitted during industry and waste incineration, posing hazards to the safety of humans and the ecosystem. Successful CB elimination has been achieved in microbial electrolysis cells (MECs), whereas little is known about elimination effectiveness in response to the structural and functional characteristics of biofilms. Herein, the bacterial viability and functional gene abundance of biofilms in MECs with carbon cloth (CC), reticulated vitreous carbon (RVC), and nickel foam (NF) as cathodes are emphasized. Experimental results reveal that bacterial viability on RVC is 62 and 92% higher than that of CC and NF, respectively, achieving 30 and 65% superior CB removal efficiency. Notably, the MEC with RVC outperforms that with the highly conductive NF due to low electron loss, causing a twice as much increase in coulombic efficiency. Metagenomic analysis indicates that the CB degrader (i.e., Pandoraea), electrochemically active bacteria (i.e., Chryseobacterium), and genes responsible for CB metabolism (i.e., todD and clcB) in RVC biofilms increase by over 30%, fourfold, and 10%, respectively, compared to CC and NF. Moreover, CB degradation is found to occur via two possible pathways: (1) thorough elimination by dechlorination, hydrolysis, and oxidation after conversion to 3chlorocatechol, and (2) conversion into phenol and benzoate for complete degradation.