Removal And Mechanisms Of Antibiotic Resistant Genes In The Secondary Effluent By The Combined Process Of Nano-iron/Ultrasonic Activated Persulfate And Ultrafiltration

Antibiotic resistance genes?ARGs?,as emerging environmental contaminants which have both physical and chemical properties that are not easy to perish or lasting long time in environment and biological properties that are reproducible or disseminated,can exist for a long time in the water environment and threaten human health and ecological security.As an important place for ARGs to gather,the secondary effluent of urban wastewater treatment plants still contain higher concentration of ARGs,and there are greater risks in their recycling process.In this study,advanced treatment processes are conducted to the secondary effluent of urban wastewater treatment plants.Specifically speaking,using iron nanoparticles?nFe?or ultrasound?US?to activate persulfate?PS?,then combined with ultrafiltration?UF?to compare the removal efficiency and influencing factors of the different process such as PS-UF,nFe/PS-UF and US/PS-UF on ARGs and organic pollutants in secondary effluent,and discuss their removal mechanisms.The research results showed that PS,nFe/PS,US/PS three pre-oxidation methods could effectively improve the removal efficiency of ARGs in the secondary effluent.The optimal dosage of PS was 4 mM,the optimal dosage of nFe was 2 mM and the optimal frequency of US was 40 KHz.The reduction of the four ARGs such as tetA,tetC,sul?,and sulII by the three combined processes were 0.66².06-log,2.51³.52-log,1.39³.11-log repectively under the optimal conditions.The ARGs removal efficiency by the process of nFe/PS-UF is the best.The decrease of pH value and the increase of temperature were beneficial to improve the removal efficiency of the three combined processes on ARGs.Compared with direct UF,the removal efficiency of dissolved organic matters?DOC?in the three combined processes was improved and the process of nFe/PS-UF had the best removal effect on DOC with removal rate was 30.0%.The three combined processes could effectively remove the tyrosine,tryptophan,fulvic acid,and humic acid organic matters in the fluorescent characteristic organic matters in the secondary effluent,but the content of microbial secretion organic matter in the membrane effluent increased.The three pre-oxidation methods of PS,nFe/PS,and US/PS could significantly enhance the removal efficiency of direct UF on organic compounds in different molecular weight ranges.Among them,the removal efficiency of organic matters with molecular weight range>100K Da had the most obvious improvement.In the oxidation process of the three combined processes,there were two free radicals such as SO₄^-·and OH·participating in the reaction.And nFe had a better activation effect on PS,and the concentration of SO₄^-·in the water was the highest.The concentration of free ARGs in the secondary effluent was higher than that of cellular ARGs.Direct UF has a better removal efficiency on cellular ARGs in water,and the three combined processes significantly improved the removal efficiency of direct UF on cellular and free ARGs in water.The combined process of nFe/PS-UF had the best removal effect on two forms of ARGs,and the reduction amount of cellular and free ARGs was 1.74³.14-log and 1.00².61-log respectively.The pollutants such as DOC,16S rRNA and int?1 in water were significantly correlated with the content of different types of ARGs.The purpose of improving the removal efficiency of ARGs by the combined process could be achieved by enhancing the removal of DOC,16S rRNA and intI1 in water.In summary,the pre-oxidation methods such as PS,nFe/PS,US/PS combined with UF could effectively improve the removal of ARGs and organic matters in the secondary effluent.The combined process could be used as an effective method for the advanced treatment of secondary effluent and reduce the safety risk of the reuse of reclaimed water.