Removal Of Antibiotic Resistance Genes In Drinking Water By Ozonation-biological Activated Carbon

Antibiotic resistance genes（ARGs）have been regarded as emerging environmental contaminants.The study on removal of ARGs in drinking water treatment is crucial to health risk control of antibiotic resistance.In this study,the removal,bacterial host,mobility,and host pathogenicity of ARGs in two full-scale drinking water treatment plants（DWTPs）were studied.The effects of pretreatment processes and operating parameters for ozonation-biological activated carbon（O₃-BAC）on removal of ARGs were investigated.This study aimed to provide a useful direction for decision-making concerning the treatment scheme and operating condition of drinking water treatment from the perspective of the risk control of antibiotic resistance.The combination of metagenomic analysis and flow cytometry was applied to investigate the relative abundance,absolute abundance,and composition of drinking water ARGs.Metagenomic assembly was applied to obtain the co-localization information of ARGs and mobile gene elements（MGEs）,identify potential ARG hosts and ARG-carrying pathogens（ARGPs）,and evaluate the mobility incidence and host pathogenicity incidence of resistomes.Metagenomic binning was adopted to recover metagenome-assembled genomes（MAGs）from water,identify ARG-carrying MAGs,and explore the host and host pathogenicity of ARGs based on MAGs.Multiple statistical analyses including network analysis were conducted to determine the co-occurrence patterns of ARGs-MGEs and ARGs-bacterial taxa,as well as key driver（s）for ARGs shifts in drinking water treatment.Main conclusions are as follows:1.The removal of ARGs in two full-scale DWTPs was investigated.Both the conventional and advanced DWTPs（applying O₃-BAC）were revealed to effectively reduce the concentration of total ARGs,with the average removal efficiency of 3.61-log₁₀ and 2.21-log₁₀,respectively.215 ARGs belonging to 20 types were detected in water samples of two DWTPs,with total concentration ranging from 6.30±1.83 to5.20±0.26×10⁴copies/m L.Two ARGs（mdt C and bpe F）were identified as indicators for resistome in DWTPs.Metagenomic assembly was applied to evaluate the mobility incidence（0.2%–8.2%）and host pathogenicity incidence（0.1%–14.0%）of ARGs in the two DWTPs.Proteobacteria phylum was identified as the major pool of ARGs in DWTPs.The major ARG-carrying pathogens were Enterococcus faecium and Ralstonia pickettii.Multiple statistical analyses indicated drinking water ARGs correlated tightly with MGEs and bacterial community,and bacterial community shift acted as the premier driver of ARGs alteration in DWTPs.2.The effects of pretreatment processes for O₃-BAC on ARGs removal were explored.Two O₃-BAC pilots,applying online coagulation-ultrafiltration and pre-ozonation-coagulation-sedimentation-sand filtration as pretreatment processes,respectively（called as UF-O₃-BAC pilot and conventional-O₃-BAC pilot,respectively）,were selected to investigate the ARGs removal.UF-O₃-BAC and conventional-O₃-BAC pilots were demonstrated to effectively reduce the concentration of total ARGs,with the average removal efficiency of 1.12-log₁₀ and 0.51-log₁₀,respectively.However,the relative abundance of total ARGs were elevated by both pilots,with the average enrichment efficiency of 0.28-log₁₀ and 0.22-log₁₀,respectively.The better removal capacity of ARGs by UF-O₃-BAC pilot than conventional-O₃-BAC pilot was attributed to the strong ability to intercept bacteria of UF.UF lead to the selective enrichment of ARGs because antibiotic resistance bacteria（ARB）might tend to pass through the UF membrane.The composition of ARGs changed greatly during UF-O₃-BAC pilot while remained stable during conventional-O₃-BAC pilot.The shift of relative abundance and composition of ARGs during two pilots was primarily driven by bacterial community change.3.The effects of operating parameters for O₃-BAC on ARGs removal were explored.The bench-scale O₃-BAC were built to investigate the ARGs removal with different O₃dosage and empty bed contact time（EBCT）of BAC columns.BAC filtration exhibited the best removal capacity for ARGs when EBCT was set as 18 min.O₃ treatment and O₃-BAC exhibited the best removal capacity for ARGs with O₃dosage of 1.0 mg/L.The BAC biofilm could serve as ARGs reservoir and export ARGs to the effluent.O₃ treatment contributed to selective enrichment of ARGs,with the highest enrichment at O₃dosage of 1.5 mg/L.When the O₃dosage was 1.0 mg/L and 1.5 mg/L,ARG-carrying and pathogenic MAGs were identified in ozonation effluent and O₃-BAC effluent,which might pose threat to human health.