| At present,various concentrations of antibiotic resistance genes(ARGs)have been detected in aquatic environments in China.The pollution of ARGs could not only cause irreparable damage to the environment,but also affect the healthy life of human beings.In terms of antibiotic concentration,the municipal wastewater treatment system can be divided into hospital wastewater treatment unit treating high concentration of antibiotics,municipal sewage treatment unit treating low concentration of antibiotics and advanced treatment unit treating trace concentration of antibiotics.It is very important for the sustainable protection of urban water environment to study the removal of ARGs by different urban sewage treatment units and the reduction of ARGs discharging into aquatic environment.In this research,the distribution and removal of ARGs in wastewater treatment plants(WWTPs)in cold region and the reduction efficiency of ARGs in different units in WWTP were explored firstly.The hospital wastewater should be treated on-site to control the spread of antibiotic resistance discharging into municipal WWTPs.Then,the removal efficiency and mechanism of ARGs in different advanced wastewater treatment processes were also investigated.The distribution and removal of ARGs in four WWTPs in Harbin were monitored by real-time fluorescent quantitative PCR.The biological treatment processes of the four WWTPs were A~2/O,A/O,CASS and CASS process,respectively.The results showed that int I1 and 6 ARGs except for bla TEM and bla SHV were detected in all samples.The removal efficiency of ARGs in the four WWTPs was 0.60±0.059-3.23±0.026 orders of magnitude.The removal efficiency of ARGs in biological treatment unit accounted for 52.63%-90.77% of the total removal efficiency of WWTPs.The ARGs removal efficiency in A WWTP with A2/O process was higher than that in other three WWTPs.The biological treatment unit played the most important role in ARGs removal(1-2 orders of magnitude),followed by UV disinfection(0.2-0.3 orders of magnitude).Physical treatment units can hardly remove ARGs.Hospital wastewater with high antibiotics concentration is the source of antibiotics and antibiotic resistance of wastewater discharging into river.So it is necessary to treat hospital wastewater on-site.We firstly analyzed the effect ofdifferent reactors and different concentrations of antibiotics on the bacterial community dynamics,the removal of organic substance and ARGs.Reactor configuration affected total nitrogen removal more,while antibiotics concentration affected total phosphorus removal more.Compared to the operational taxonomic unit(OTU)number before antibiotics addition,the OTU number decreased after the addition of high-concentration antibiotics.Reactor configuration contributed to higher dissimilarity of microbial community than antibiotics concentration.A/O-MBR system outperformed SBR in reducing sulfamethoxazole,norfloxacin and ARGs because of the retention effect of membrane module.Then the mechanism of A/O-MBR treating antibiotic-containing wastewater was analyzed.In A/O-MBR,overall chemical oxygen demand(COD)and NH3-N removal were not affected during the exposure to antibiotics(more than 90%).TP removal was significantly affected by antibiotics.The maximum removal efficiency of penicillin and chlorotetracycline reached 97.15% and 96.10% due to strong hydrolysis,and sulfamethoxazole reached 90.07% by biodegradation.However,only 63.87% of norfloxacin maximum removal efficiency was achieved mainly by sorption.The system had good ability to reduce ARGs,peaking to more than 4 orders of magnitude,which mainly depended on the biomass retaining of the membrane module.The diversity of microorganism decreased with the concentration of antibiotics increasing.Though antibiotics concentration influenced the evolution of ARGs and bacterial community in the reactor,there was no significant difference of ARGs distribution and microbial community structure between activated sludge and membrane module.The mechanism of sorption and biological degradation of sulfamethoxazole and norfloxacin were studied by batch experiments.The results showed that the increasing p H value could affect the existing form of antibiotics and the surface charge of activated sludge,leading to that the sorption removal rate of antibiotics decreased.The increasing temperature could result in the decreased sorption capacity.The results of biological removal experiment showed that aerobic condition played an important role in the removal of antibiotics.The addition of carbon and nitrogen sources had no effect on the removal of sulfamethoxazole,while promote the removal of norfloxacin.Under anoxic condition,sulfamethoxazole could be degraded a little,while norfloxacin could not be removed.Pseudomonas.putida KT2440 was the donor strain which contains RP4 plasmid carrying GFP,the mixed bacteria from A/O-MBR were recipient strain.The RP4 plasmid could transfer from donor strain to recipient strain.The results of plasmid transfer showed that with the initial bacteria concentration increasing,the conjugant number increased while conjugation transfer frequency(CTF)decreased.The CTF was higher at lower temperature than that at higher temperature.p H had no effect on CTF.Donor strain was inhibited by heavy metal and sulfamethoxazole,the higher concentration of heavy metal and sulfamethoxazole,the lower CTF.When the chlorotetracycline concentration was lower than 5 mg/L,the concentration of chlorotetracycline increased,the CTF increased.But when chlorotetracycline concentration was higher than 5 mg/L,inhibition was happened to donor strain,leading to the CTF decreased.The distribution and removal of antibiotic resistance in advanced treatment processes(ozonation and/or biofilters)in 5 WWTPs in Switzerland were investigated.There were 2 pilot-scale advanced treatment processes and 3 full-scale advanced treatment processes.The results showed that ozonation had good capacity to remove microbiota,live cell percent decreased from 77.17%-90.89% to8.20%-48.65% after the ozone treatment,the removal efficiency of cultivable bacteria was 0.14-1.21 orders of magnitude,however,the removal efficiency of ARGs by ozone was not obvious.The removal efficiency of microbiota by ozone in full-scale advanced treatment processes with higher dosage of ozone was better than that in pilot-scale advanced treatment processes with lower dosage of ozone.The microbiota and ARGs in the post-ozonation-biofilters were further removed at pilot-scale advanced treatment processes,but increased at full-scale advanced treatment processes.The percent of live cells increased from 8.20%-48.65% to 27.67%-77.87% after the treatment of biofilters.The advanced treatment processes in Switzerland could further reduce the clinical ESBL-producing bacteria. |
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