Easy-to-biodegrade substrate could contribute to simultaneous elimination of amoxicillin and antibiotic resistance genes in an activated sludge reactor

Antibiotics are continuously released to and accumulated in the water environments and ecosystem, which caused risks from antibiotic resistance genes (ARGs). However, antibiotics are difficult to be completely treated by conventional biological methods, and especially ARGs spreading in the activated sludge should be concerned. Easy-to-biodegrade substrate has been known to improve toxic pollutants removal. Could the co-substrate eliminate ARGs abundance and transferring simultaneously? In this work, we investigated amoxicillin (AMO) degradation with 0-100 mg/L acetate sodium as the co-substrate in an SBR process. We found Proteobacteria, Bacteroidetes and Actinobacteria were the dominant phyla microbes for AMO removal and mineralization. Furthermore, the addition of acetate increased the abundances of adeF and mdsC as efflux resistance genes to improve the microbial resistance, coping with AMO toxicity and repairing the damage from AMO. As a result, acetate addition contributed almost 100% AMO removal and stable COD (~20 mg/L) in effluents. Besides, the total abundance of ARGs were declined approximately ~30 %, and the most dominant antibiotic resistance bacteria Proteobacteria proportion decreased by ~9 %. The total abundance of plasmids encoding ARGs decreased by as much as ~30 %, indicating ARGs spreading risks were alleviated. Taken together, easy-to-biodegrade substrate could contribute to simultaneous elimination of antibiotics and ARGs in the activated sludge reactor.