Redox mediator-regulated microbial electrolysis cell to boost coulombic efficiency and degradation activity during gaseous chlorobenzene abatement

Microbial electrolysis cell (MEC), a promising technology, is being developed for volatile organic compounds (VOCs) abatement. One of the critical issues to limit its industrial application is the poor electron transfer. In this work, anthraquinone-2,6-disulfonate (AQDS) and flavin mononucleotide (FMN) are dosed to MECs for the chlorobenzene (CB) removal, which are denoted as MEC-AQDS and MEC-FMN, respectively. The MEC performance is significantly promoted due to that RMs lower down the internal resistance. The CB removal efficiency in MEC-AQDS and MEC-FMN are increased by 40% and 20%, respectively, compared with neat MEC. Moreover, ECmax and Ks of MEC-AQDS are 26% and 75% higher than that of neat MEC, respectively. AQDS is a more suitable RM with 66% and 50% higher in dechlorination efficiency and coulombic efficiency, respectively, compared with FMN. The enhancement of dechlorination process in MEC-AQDS is ascribed to two reasons. The lower resistance accelerates the electron transfer rate during dechlorination; and the enhancing growth of dechlorinating bacterium leads to an abundant excretion of dechlorination enzymes. Additionally, electrochemical analysis and intermediate detection imply that RMs affect the electron transfer pathways but not the degradation mechanism, that is, CB converts into 2-chlorophenol and 3-chlorocatechol successively, then ring-opens and dechlorinates for mineralization.