Characteristics Of Antibiotic Resistance Genes Through Aerosols In Sewage Treatment Plants

As the join of human society and the ecological environment,sewage treatment plants(WWTPs)have been proved to be the reservoirs of antibiotic resistance genes(ARGs).Most of the large amount of antibiotics consumed by the medical and aquaculture industries will be collected in sewage in the form of excrement,which greatly aggravates the generation and transfer of ARGs.In the process of sewage treatment,factors such as turbulence,aeration and mechanical agitation will prompt the microorganisms carrying ARGs in sewage,and even pathogenic bacteria to escape into the air to form bioaerosols,so that ARGs can threaten human health through the respiratory system,and be transmitted over long distances.At the same time,the high dynamic characteristics of the atmospheric environment make ARGs through aerosols have a higher risk of transmission compared with media such as water and soil.However,there is still a lack of research on ARGs through aerosols in WWTPs,their occurrence characteristics are not clear,the relationship with bacterial communities is not clear,and there is no systematic understanding of their diffusion laws and cross-media escape behaviors.In this study,three typical sewage treatment plants with A~2O as the main process were selected as the targets.Except that the sewage received by sewage treatment plant A contained 20% industrial wastewater,the others were municipal sewage.Bioaerosol samples collected in each treatment unit were detected by metagenomic,real-time PCR,and high-throughput sequencing technologies to study the occurrence characteristics and interrelationships of bacteria in the whole process.Moreover,the characteristics of ARGs diffusion through aerosols,the influence of environmental factors and exposure dose were explored.At the same time,the cross-media migration behavior of ARGs in WWTPs and its influencing factors were deeply explored.This study will provide a scientific basis for the pollution control of resistant bacteria and ARGs in the sewage treatment process,which is of great significance to the health of the employees of the WWTPs and the surrounding residents and the safety of the ecological environment.For the process,the absolute abundance of ARGs through aerosol in the MBR tank was the highest,reaching 1.45×10~7 copies/m~3 in summer and 1.89×10~7 copies/m~3 in winter,followed by aerated grit chamber,while of that in the anoxic tank and UV disinfection tank was lowest.In terms of ARGs types,the relative abundance of multidrug ARGs was the highest,which reached about 40%,followed by MLS,tetracyclines and glycopeptides with relative abundances of about 12%,10% and 9%,respectively.Mac B,tet A(58),nov A,bcr A and ole C were the most abundant subtypes of ARGs,which showed a significant positive correlation with the total amount of ARGs and could be used as indicators of ARGs contamination.As for the season,the absolute abundance of ARGs through aerosol in winter was significantly higher than that in summer.The bacterial community had obvious seasonal differences at the phylum level,mainly Proteobacteria,Actinobacteria and Firmicutes,while the seasonal differences at the genus level were weak.The network analysis of the co-occurrence of ARGs subtype and bacterial genera showed that there was a strong symbiotic pattern between subtype ARGs,and the Ahniella,Sulfuritalea and Sphingomonas were the potential host bacteria of various subtypes of ARGs,and may had multiple drug resistance.The strong correlation between the biomarker ARGs and biomarker bacteria genera and the procrustes analysis showed that the bacterial community was the decisive factor for the ARGs through aerosol in the WWTP,and the spread of ARGs were mainly driven by the bacterial community.ARGs through aerosol attenuated with increasing distance in downwind.For ARGs type,the higher the escaped abundance,the faster the decay rate.For the ARGs subtype,the abundance first decreased rapidly within a short distance,and the decay rate reached a maximum of 42.54%within a range of 5 m,and then gradually entered the slow decay distance.The modified Gaussian plume model can describe the diffusion pattern of ARGs in the horizontal direction.Based on the model calculation,the ARGs escaped from the aeration tank can spread with the wind for distances of more than 1500 m.The diffusion of ARGs in the air was significantly affected by environmental factors such as temperature,relative humidity,wind speed,and total suspended particulate matter concentration,whose effects on ARGs through aerosol were discriminative in different WWTPs.In each treatment unit of the WWTPs,the exposure dose of ARGs through aerosol in adult males through respiratory route was higher than that of females,the exposure dose through skin contact route was lower than that of females,and the exposure dose through respiratory route was much higher than that of skin contact.The MBR tank,the aeration tank and the sludge dewatering room were the units with the highest exposure dose,while the UV disinfection tank and the ozone exposure tank had the lowest.In the downwind direction of the aeration tank,the exposure dose of ARGs through aerosol decreased with the increase of distance,and decreased by more than 43%in the downwind direction of 50 m.In sewage and sludge,the abundance of multidrug ARGs was the highest,with an average relative abundance of 42.01%,followed by MLS and tetracyclines,respectively.MacB,tetA(58),bcrA,evgS and novA were the most abundant ARGs subtypes in each sampling point.The main sources of ARGs through aerosol in WWTPs were sewage and sludge,and their aerosolization index vary among various ARGs.The ARGs types with the highest aerosolization index in sewage and liquid sludge were aminocoumarin,fluoroquinolone,and aminoglycoside,while that in the dewatering sludge wasβ-lactam.The occurrence and migration of ARGs in sewage and sludge were significantly affected by water quality indicators and heavy metals.