Study Of Longitudinal Distribution Of Typical Antibiotic Resistance Genes In Wastewater Treatment System

The widely use and misuse of antibiotics in medical treatment,and livestock and poultry industry has resulted in serious pollution in environment which has become a hot issue recently.Antibiotic resistance genes(ARGs),as a new type of contaminant were widely detected in varied environmental medium including rivers,lakes,underground water and soil environment.ARGs could transfer to human body through drinking water and food chain,and the pathogenic bacteria in human body would acquire antibiotic resistance and pose a threat to people’s health.Wastewater treatment plants(WWTPs)are supposed to be an important channel for ARGs to spread to the natural environment,and the environmental behavior and feature have already get extensive attention from researchers.But domestic relevant research mainly focused on status survey in WWTPs(especially domestic wastewater),lacking detailed research on the distribution,migration and transformation of ARGs in WWTPs.Method of Polymerase chain reaction(PCR),quantitative PCR and denaturing gradient gel electrophoresis(DGGE)were used to systematically study the distribution and transformation of typical ARGs in WWTPs,in order to reveal the distribution,migration and reduction of ARGs and provide theoretical basis for the controlling of ARGs in WWTPs.Main conclusions obtained are as follows:1.The distribution of typical ARGs in different WWTPs.In all the samples,the detection frequency of tetracycline resistance genes tetB,tetE and tetQ were obviously lower(15%-19%),while the frequency of tetracycline resistance genes tetC and tetG,and sulfonamides resistance genes sulland sul2,and class 1 integron gene intll were higher than other target ARGs(92%-100%);Generally,the number of ARGs in effluent was fewer than that in influent water;The concentrations of sull and intll were overwhelmingly higher than other genes in five plants with concentration range of 104.94-107.20 copies/mL,and the concentration of tetracycline resistance genes was 101.77-106.29 copies/mL;The concentrations of ARGs in effluent water of plant A(domestic wastewater,A/O),plant B(domestic +industry wastewater,MBR)and plant E(petrochemical wastewater,A/O)were all decreased in some extent compared to influent;While in plant C(VC wastewater,A/O),concentrations of ARGs were increased along the treatment process(except tetW);In plant D(cephalosporin wastewater,A/O),concentration of ARGs decreased in anaerobic effluent but increased in the aerobic effluent(except tetW);Differences exist among WWTPs in different location,and the concentrations of ARGs in domestic wastewater in this study were generally 0.18-2.35 log lower than previous studies;Concentrations of ARGs in industrial wastewater(VC,cephalosporin,petrochemical wastewater,)were 1-3 order of magnitudes lower than domestic wastewater,and the petrochemical wastewater had the highest level of ARGs of all the three kinds of industrial wastewater.2.Seasonal variation and longitudinal distribution of typical ARGs in WWTPIn influent and effluent water samples of all the 11 months,the concentration trend of five ARGs(median)was:sull>intll>tetX>tetG>tetW,and the concentration of sull was significantly higher than other three tetracycline resistance genes(p<0.05);Concentration of ARGs in influent water exhibited certain seasonal variation:it reached to the highest in spring(105.81-107.32 copies/mL)and reached to the lowest in autumn(104.61-106.81 copies/mL)(except intll and tetG);ARGs in MBR effluent were all decreased in some extent compared to the influent,and the reduction of ARGs were significantly correlated with the reduction of 16S rDNA and the reduction of COD;The concentration of ARGs in water samples along the treatment plant decreased in anaerobic and anoxic effluent water and then increased in aerobic effluent,finally dropped sharply in the MBR effluent.The abundance of ARGs(normalized to 16S rDNA)in sludge samples differed among different months.The least abundance of ARGs appeared in August and September(10-5.41-10-2.89)and the most abundance of ARGs appeared in April,June and July(10-3.74-10-1.07);Concentration of ARGs in water samples along processes decreased in anaerobic and anoxic effluent,and increased in aerobic effluent,then decreased sharply in MBR effluent;The decrease of the ARGs in MBR effluent was accompanied by the increase of ARGs in membrane sludge,indicating that a portion of ARGs in water samples transferred to the sludge samples.