Anaerobic biodegradation of BTEX mixtures with humin as electron acceptor: Substrate interactions and microbial community/humin evolutions.

Solid-phase humin (HM), a ubiquitous natural electron mediator, shows promise for anaerobic biodegradation of contaminants. However, its capacity to support coexisting pollutants exhibiting complex interactions, and the co-evolutionary dynamics between which and microbial communities throughout anaerobic biodegradation processes remain unknown. In this study, benzene, toluene, ethylbenzene and xylene (BTEX)-the primary hazardous pollutants in gasoline-contaminated groundwater, were selected as target contaminants. Results demonstrated that individual B, T, E, and X achieved effective anaerobic biodegradation in defined medium assay with HM supplementation, displaying a degradation rate sequence of T > E > X > B. Although B inhibited T biodegradation in BT dual mixture assay, BTEX achieved complete anaerobic biodegradation in quaternary mixtures without substrate inhibition. Similar degradation results were observed in real groundwater, where 96 % of electrons derived from BTEX oxidation to CO2 were recovered via HM reduction. Microbial communities and HM's redox moieties both changed during incubation. Genera Azoarcus and Geothrix exerted dominant roles, and the relative abundance of Azoarcus exhibited significant correlation with HM's redox moieties, suggesting its potential involvement in HM reduction. Significant correlations between abundances of extracellular electron transfer-related enzymes and CO, Fe(III) moieties indicated that CO and Fe(III) moieties of HM may interact with microorganisms.