Microbial niches and dynamics of antibiotic resistance genes in a bio-enhanced granular-activated carbon biofilm treating greywater.

Accumulation and transmission of antibiotic resistance genes (ARGs) in greywater treatment systems present risks for its reuse. In this study, a gravity flow self-supplying oxygen (O) bio-enhanced granular activated carbon dynamic biofilm reactor (BhGAC-DBfR) was developed to treat greywater. Maximum removal efficiencies were achieved at saturated/unsaturated ratios (R) of 1:1.1 for chemical oxygen demand (97.6 ± 1.5%), linear alkylbenzene sulfonates (LAS) (99.2 ± 0.5%), NH+ 4-N (99.3 ± 0.7%) and total nitrogen (85.3 ± 3.2%). Microbial communities were significantly different at various R and reactor positions (P < 0.05). The unsaturated zone with low R showed more abundant microorganisms than the saturated zone with high R. The reactor-top community was predominant by aerobic nitrification (Nitrospira) and LAS biodegradation (Pseudomonas, Rhodobacter and Hydrogenophaga) related genera; but reactor-bottom community was predominant by anaerobic denitrification and organics removal related genera (Dechloromonas and Desulfovibrio). Most of the ARGs (e.g., intI-1, sul1, sul2 and korB) were accumulated in the biofilm, which were closely associated with microbial communities at reactor top and stratification. The saturated zone can achieve over 80% removal of the tested ARGs at all operation Phases. Results suggested that BhGAC-DBfR can provide assistance in blocking the environment dissemination of ARGs during greywater treatment.