Co-degradation detoxification of dichloromethane and n-hexane in a microbial electrolytic cell: Metagenomic insights into degradation pathways and functional genes

Volatile organic compounds (VOCs) are important precursors of ozone and secondary organic particulate matter, with an extensive range of sources and complex composition. Dichloromethane (DCM) and n -hexane, as common and typical VOCs, are extensively applied as solvents, extractants and cleaning agents in the pharmaceutical and chemical industries. The persistence, teratogenicity and carcinogenicity seriously harm the ecological environment and human health. In this study, combining the advantages of microbial electrolytic cell (MEC), the detoxification mechanism between low concentration n -hexane and DCM was analyzed. The results demonstrated that the n -hexane favored the enrichment of key functional genera, including degrading and electroactive microorganisms, which could be attributed to the mild toxicity of n -hexane at low concentrations and sufficient carbon sources. In contrast, DCM significantly inhibited the degradation of n -hexane. Metagenomic annotation results suggested that DCM was converted to formaldehyde via hydrolyzing haloalkane dehalogenase (DhlA) or DCM dehalogenase (DcmA). Formaldehyde was partly oxidized to carbon dioxide (CO 2 ) and partly assimilated into the ribulose monophosphate pathway or the serine pathway. And then converted to acetyl-CoA to enter the TCA cycle, which provided energy and material cycles for microbial metabolism. These results provided a new method for the detoxification of mixed VOCs and offer a new insight into the treatment and disposal of pollutants in practical engineering applications.