This research investigated the effectiveness of biofiltration systems for the attenuation of antibiotics and antibiotic resistance genes (ARGs) from drinking water. Five antibiotics, including amoxicillin, clarithromycin, oxytetracycline, sulfamethoxazole, and trimethoprim, and the relevant resistance genes (blaCTX-M, blaOXA-1, blaTEM, ermB, tetA, tetG, tetQ, tetW, tetX, sul 1, sul 2, dfrA1 and dfrA12) as well as integrase genes (intI 1 and intI 2) were targeted. In addition, the role the biofilm plays as a gene transfer site was also investigated. Both chemical (LC-MS/MS) and molecular biology (real-time qPCR, high-throughput qPCR and 16S rRNA amplicon sequencing) methodologies were used. A total of three biofiltration experiments using sand, granular activated carbon (GAC) and anthracite as filter media were set-up at bench-scale. Results showed that the target antibiotics were substantially removed (> 90%) by GAC-associated biofilters and partially removed (< 20%) by sand and anthracite-sand dual media biofilters. The position of GAC layer within the sand filter bed showed no effect on antibiotic removal. The absolute abundance of ARGs decreased (1.0-log reduction on average) after biofiltration, while ARGs’ normalised copy number remained unchanged or showed an increasing trend in the filtered water, especially when exposed to the target antibiotics, indicating that the biofilters did not contribute greatly to the elimination of ARG pollution from the feedwater despite the effective removal of antibiotics. Exposure to the target antibiotics affected the bacterial community in biofilm samples and the differences in bacterial community structure were correlated with the changes in the resistome. Plasmid conjugative transfer experiment based on biofiltration showed that the GAC media is more conducive to the horizontal transfer of ARGs in biofilms and the transfer occurred more frequently in biofilms than in the influents and effluents. Overall, the results of this study could enhance our understanding of the prevalence of ARGs during drinking water treatment
