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 (O2) bio-enhanced granular activated carbon dynamic biofilm reactor (BhGAC-DBfR) was developed to treat greywater. Maximum removal efficiencies were achieved at saturated/unsaturated ratios (RSt/Ust) of 1:1.1 for chemical oxygen demand (97.6 +/- 1.5%), linear alkylbenzene sul-fonates (LAS) (99.2 +/- 0.5%), NH4+-N (99.3 +/- 0.7%) and total nitrogen (85.3 +/- 3.2%). Microbial communities were significantly different at various RSt/Ust and reactor positions (P < 0.05). The unsaturated zone with low RSt/Ust showed more abundant microorganisms than the saturated zone with high RSt/Ust. The reactor-top community was pre-dominant by aerobic nitrification (Nitrospira) and LAS biodegradation (Pseudomonas, Rhodobacter and Hydro-genophaga) 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.

Automated summary

A gravity flow self-supplying oxygen bio-enhanced granular activated carbon dynamic biofilm reactor (BhGAC-DBfR) was developed to treat greywater, achieving maximum removal efficiencies for various pollutants. Microbial communities varied significantly at different ratios and reactor positions. Most of the antibiotic resistance genes (ARGs) accumulated in the biofilm and were closely associated with microbial communities. The BhGAC-DBfR can effectively block the environmental dissemination of ARGs during greywater treatment.