Study On The Removal Of Antibiotic-resistant Bacteria In Carbon-oxygen Regulated Rainwater Bioretention Pond

In recent years,the abuse of antibiotics has led to the increasingly serious pollution of antibiotic resistance in the environment.In particular,the presence of antibiotic resistant bacteria（ARB）was found in stormwater runoff.As one of the main stormwater best management practices（BMPs）,bioretention has been widely used to treat conventional pollutants in stormwater runoff.Biochar and aeration are common means to improve its performance.However,there is still no available literature about the application of carbon and oxygen regulation（CO）to enhance ARB reduction in stormwater bioretention cells.In this study,batch experiments were conducted to investigate target ARB（E.coli K-12 carrying bla TEM,tet R and aph A）reductions in bioretention cells with different biochar application（S/C）,ratios of air to water（A/W）and aeration time（AT）.Through analyzing the removal mechanism of CO,including the adsorption capacity of biochar,the content and contribution of ROS,changes in microbial communities and extracellular polymeric polysaccharides（EPS）,and potential risks of CO application were explored,including the antibiotic resistance（AR）transmission and transmission response mechanisms,in order to provide a new insight for blocking AR risks from stormwater runoff.Through the determination of ARB and the detection of conventional pollutants,the removal characteristics of ARB in the bioretention cells with CO were studied.The results showed that the application of reasonable biochar and aeration to the traditional bioretention cells could effectively improve the removal of ARB.When modified by biochar only,the volume of biochar accounted for 10%of the total volume of the filler,and the ARB effluent concentration was the lowest.When modified by aeration only,the AT was 4 h,the A/W ratio was 20:1,and the ARB effluent concentration was the lowest.When modified by biochar and aeration simultaneously,the biochar accounts for 20%of the total volume of the filler,the AT was 4 h,and the A/W ratio was 25:1.The ARB effluent concentration was the lowest and the conventional pollutants removal effect was the best.There was no strong correlation between conventional pollutant removal and ARB removal.Through material characterization,adsorption test,high-throughput sequencing and other methods,the removal mechanism of ARB in bioretention cells with CO was studied.The results showed that biochar had good adsorption performance for ARB and tended to multi-layer physical adsorption;a certain level of H₂O₂ was detected in the bioretention cells modified by biochar,and the concentration range was 0.012-0.044mmol/L.The level was low,but it could still assist the bioretention cell to remove ARB.Before and after the operation of the bioretention cell,the structure and diversity of the microbial community at the phylum and genus levels in each type of bioretention cell changed,and showed different responses to carbon and oxygen regulation.The development of some functional bacteria enhanced the removal of conventional pollutants.The combined regulation of carbon and oxygen promoted the production and recruitment of EPS.There was a strong negative correlation between the protein（PN）level in the EPS and the concentration of ARB.In cells with lower PN levels,more ARB tend to flow out relatively.Through the establishment of conjugation and transformation system,flow cytometry and other methods,the risk of the transmission of ARB in the bioretention cells with CO was studied.The results showed that the excessive application of biochar in the bioretention system was not conducive to the control of ARB.The transmission capacity of ARB in anaerobic and anoxic environments was weak,and the risk in the cells was low when modified by biochar and aeration simultaneously,which was an ideal scheme for ARB transmission control.The study on the mechanism of ARB transmission response found that the accumulation of intracellular ROS had a resistance and defense effect on ARB transmission,while the increase of cell membrane permeability（CMP）had a promoting effect on ARB transmission.