| The resistance gene has attracted wide attention due to the drug treatment failure caused by the increase of drug resistance of bacteria.There are a large number of antibiotic resistant genes（ARGs）and antibiotic resistant bacteria（ARB）in wastewater treatment plants（WWTPs）,whose transmission is influenced by many factors such as temperature,antibiotic concentration,sewage treatment process,etc.The distribution characteristics of ARGs in sludge samples from 22 provinces in China were studied.T he influence of environmental drugs including antibiotics and non-antibiotics on the spread of resistance genes in sludge was studied as well.Based on the high ARG abundance and concentration of antibiotics in sludge in winter from northern cities,Harbin was selected as the characteristic city to study the temproal variations,distribution and removal characteristics of ARGs and ARBs in sewage treatment process from northern cities in China.The distribution characteristics,environmental risks of ARGs and target PPCPs were analyzed in residual sludge samples from WWTPs in different cities in China.The total abundance of ARGs in the detected sludge samples ranged from 5.33×106to 3.74×1012 copies/g.Temperature is negatively correlated with the abundance of resistance genes.On the one hand,the bacterial abundance in winter was higher than that in summer,the host content of resistance genes increased,and the abundance of resistance genes increased.On the other hand,low temperature may affect the horizontal transfer of resistance genes through gene recombination or enhancement of transfer potential,so as to accumulate and enrich resistance genes in winter sludge.In addition,there was a significant positive correlation between non-antibiotic toxicity,ARGs and class I integrator int I1.Non-antibiotic drugs with high toxic increased the risk of horizontal transfer of ARGs.The importance of non-antibiotic environmental contaminants to the transmission of ARGs was emphasize in this study.Based on the high abundance of ARGs and antibiotic concentration in sewage sludge in northern China in winter,Harbin was further selected as a characteristic city to study the distribution and removal characteristics of ARGs in WWTP in northern China.The inflow of WWTP is not continuous.The ARG abundance in the influent fluctuated significantly,and the peak appeared between9:00-11:00 a.m.,which was related to human living habits.The fluctuation of ARG abundance in effluent was weaker due to the mixing effect of wastewater,and the peak time is related to the hydraulic retention time of the wastewater treatment plant.Compared with absolute abundance,the relative abundance of ARGs in WWTPs fluctuated slightly and tended to be stable.The seasonal variation of ARGs in influent and effluent was significant,which is high in spring,autumn and winter and low in summer.It is found that sul1 and int I1 are negatively removed in winter.Low temperature may induce horizontal gene transfer caused by cold stress response of bacteria and increase the risk of horizontal gene transfer in effluent.Studies on the distribution and abundance reduction of resistance genes and resistant bacteria in typical wastewater treatment processes A/O and BAF showed that the absolute abundance of resistance genes i n effluent decreased to only half of that in influent,and the relative abundance of resistance genes did not change significantly or even increased in effluent.The abundance of resistance genes increased in the biological treatment units of A/O process.However,after BAF process,the abundance of resistance genes decreased.The ratio of tetracycline resistant bacteria to total heterotrophic bacteria showed the same trend.The study of tetracycline resistant bacteria found that the resistance of some pathogenic bacteria increased in the secondary wastewater treatment process.The microbial removal capacity of BAF process is more effective than that of activated sludge system A/O process.In addition,the extracellular polymers in the BAF biofilm fouling la yer are conducive to the adhesion of suspended microorganisms or sludge floc,and can intercept some free resistance genes.Therefore,BAF the reduction of ARG abundance in BAF process is superior to A/O process.The occurrence characteristics of resistance genes in domestic wastewater and enterprise wastewater including hospital wastewater,pharmaceutical wastewater and aquaculture wastewater were further explored.Except for erm B and qnr S,the detection rate of the target resistance gene subtypes was 100%.Based on the cluster analysis and isomer composition analysis,it was found that the resistance gene compositions of urban sewage and wastewater were significantly different.The quinolone resistance gene qnr S accounted for the highest proportion in domestic sewage,while the abundance of sul2 resistance gene was dominant in aquaculture,hospital and pharmaceutical wastewater.Quinolones are the first class of antibiotics to be focused on as new pollutants.Based on the results of this study,it can be seen that the massive use of quinolone antibiotics may have affected the drug resistance characteristics of human intestinal flora.Therefore,high abundance levels of quinolone resistance genes were detected in the domestic sewage of urban resident s.This study provides scientific basis for exploring the environmental behavior of quinolone resistance genes. |
