Removal And Horizontal Transfer Mechanisms Of Antibiotic Resistant Genes In The Reclaimed Water Treatment By The Process Of BPAC-UF

In view of the unconventional pollutants such as antibiotic resistance genes(ARGs)in the treatment of reclaimed water,the combined process of biological powdered activated carbon-ultrafiltration(BPAC-UF)was adopted to treat the secondary effluent from the wastewater treatment plant in this study.The molecular weight distribution,main morphology and removal effect of ARGs were studied.In addition,the effects of BPAC on the concentration of ARGs and the horizontal transfer of resistance plasmids were discussed.The results showed that the molecular weight of the ARGs in the secondary effluent was mainly distributed in the interval of more than 100 KDa,there were great differences and no obvious regularity in the molecular weight distribution of ARGs in the direct UF membrane effluent,the ARGs in the effluent of the combined process were mainly distributed in the interval of more than 30 KDa.Exploring the presence of the ARGs in the secondary effluent and the treatment process was showed that the ARGs were mainly cell-free genes,and the cell-free gene was more difficult to remove than the cell-associated gene.The removal effect of the BPAC-UF combination process on the pollutants was found that the BPAC-UF combination process was better than direct UF on the removal of ARGs.The DOC removal rate was 36.5% by the combined process,which is better than direct UF and BPAC adsorption.And the the combined process had better removal of the fulvic acid and humic acid matters,and the fluorescence intensity could be effectively reduced by the combined process.The results of BPAC on the concentration of ARGs and microbial community structure in water showed that ARGs were degraded and adsorbed by microorganisms on the surface of BPAC,but at the same time,microorganisms on the surface of BPAC also promoted the transfer and amplification of ARGs.From the analysis of microbial community structure,it was found that BPAC increased the microbial abundance and population diversity,and among the dominant strains,such as Proteus,Planctomycetes,Bacillus,Firmicutes,Pseudomonas,Hydrogen bacterium Pseudoxanthomonas etc that most of them were gram-negative bacteria and have flagella which was conducived to the conjugative transfer of ARGs.By constructing the fluorescent resistant plasmid pHS-AVC-LW1144 and observing the process of plasmid conjugation and transfer by laser scanning confocal microscopy,it was found that the plasmid could transferred between the same or cross-species bacteria through the contact of the donor and recipient bacteria.The concentration of conjugates of resistant plasmids could be increased and the conjugation and transfer of resistant plasmids could be promoted by adding BPAC.And the optimal dosage of BPAC was 20 mg/L.Under the action of microorganisms on BPAC surface,the concentration of plasmid was increased in the period of 0~24 hours,and the concentration of plasmid was decreased gradually in the period of24~48 hours.The concentration of conjugates at low temperature(4℃)was higher than that at normal temperature(25℃)and high temperature(50℃).The concentration of conjugates at alkaline(pH=9)was higher than that at acidic(pH=5)and neutral(pH=7)condition.