Effects Of Different Treatments On The Removal Of Antibiotic Resistance Genes And Bacteria From Wastewater Treatment Plants

The abuse of antibiotics has led to the widespread existence of antibiotic resistance genes(ARGs)and bacteria(ARB)in the environment,which poses a great threat to human health.Abundant nutrients and microbial species in wastewater treatment plants(WWTPs)provide conditions for ARGs and ARB proliferation and transfer.Thus,there was a high abundance of ARGs and a large number of ARB in wastewater.Currently,the effects of wastewater treatment processes on ARGs and ARB were insufficiently studied to fully assess the risk of antibiotic resistance spread in wastewater.This study explored the effects of different mainstream wastewater treatment processes(including Oxidation ditch,Circulating activated sludge system,Anaerobic-anoxic-aerobic,and Membrane bioreactoron)on ARGs and ARB,in order to provide theoretical basis for controlling the spread of antibiotic resistance in WWTPs.In addition,the effects of ultraviolet disinfection,chlorination,and Fenton oxidation on ARGs in wastewater were compared to provide a theoretical basis for controlling the spread of antibiotic resistance in aquatic environment.The spread of ARGs in an aquatic environment was simulated by co-culturing the algae with the above disinfection wastewater.The main conclusions of this study were as follows:(1)High levels of diversity(187-207 species)and absolute abundance(about 6.59-7.56 logs units)of ARGs were found in the influent of WWTPs in this study,and similar ARG diversity and abundance were found in wastewater from different treatment processes.High levels of mobile genetic element(MGE)diversity(23-44 species)and absolute abundance(about 4.40-7.97 logs units)suggest that ARGs may disseminate among host bacteria through horizontal gene transfer(HGT).However,the main processes could effectively decrease the diversity(57-90 species)and the absolute abundance(about 2.14-3.47 logs units)of ARGs though removing nutrients and MGEs.The combined process of anaerobic-anoxic-aerobic and membrane bioreactor could reduce ARGs and MGEs more effectively.In addition,many pathogenic bacteria(such as Arcobacter and Aeromonas)that may carry ARGs could also be effectively removed.However,ultraviolet disinfection and chlorination even increased the relative abundance of ARGs and activated the regeneration of ARB.(2)Under laboratory conditions,the removal of target ARGs and int I1 by chlorination(15 mg/L)was about 1.84-4.22 logs units;the removal of target genes by ultraviolet(15 min)was about 1.29-3.87 logs units.However,increasing chlorine concentration or ultraviolet exposure time did not significantly enhance the removal efficiency.In this study,Fenton oxidation was more effective way than ultraviolet disinfection and chlorination in removing most of the target genes(about 0.15-1.56 logs units higher).(3)Chlorination and Fenton oxidation could reduce ARG diversity in the Chlorella coculture system(37 and 4 species,respectively).Chlorination,ultraviolet disinfection,and Fenton oxidation inhibited the absolute abundance of ARGs(about 0.20-2.75 logs units)and MGEs(about 0.17-1.83 logs units).Chlorination had the most obvious inhibitory effect on ARGs.In addition,the disinfection process could significantly change the bacterial community structure and effectively reduce the abundance of ARG host and pathogenic bacteria(such as Arcobacter and Aeromonas)in wastewater.In this study,mainstream wastewater treatment processes greatly reduce ARGs and ARB in wastewater.However,due to the limited cost and dose of the disinfection process in practical application,there are still residual ARGs and activated ARB in WWTPs effluent.Under laboratory conditions,Fenton oxidation could remove ARGs and ARB more effectively than ultraviolet disinfection and chlorination,which has certain application potential.Chlorination could inhibit the activation and regeneration of ARGs more effectively.It is recommended to maintain an effective chlorine concentration of 15 mg/L in WWTPs.This study will provide a basis for the comprehensive assessment and control of antibiotic resistance in wastewater.