Characteristics Of Microbial Community Structure And Distribution Of Antibiotic Resistance Genes(ARGs)in Wastewater Treatment Plants(WWTPs)at High Altitude Cold And Drought Area

Due to the climatic characteristics of low temperature,low oxygen content in the air,low air pressure and drought in high-altitude cold and drought areas,it is difficult for wastewater treatment plants(WWTPs)in this area to maintain a good pollutant removal performance.Aiming at this hot issue of poor performance of WWTPs in high-altitude cold and drought areas,this paper uses three conventional WWTPs(A²/O,CASS and oxidation ditch)in Lanzhou as the high-altitude group,and a WWTP in Yantai(A²/O)and two WWTPs in Qingdao(CASS and oxidation ditch)served as a plain group.On the basis of comparing the pollutant removal performance of WWTPs in high altitude area and plain area,the microbial community in activated sludge and the distribution of antibiotic resistance genes(ARGs)are further compared.It aims to explain the poor performance of WWTPs in high-altitude cold and drought areas,and guide the development of appropriate strategies to effectively operate WWTPs in high-altitude cold and drought area.The research of compairing the treatment performance of WWTPs in high-altitude cold and drought area and plain area shows that the WWTPs in high-altitude group and plain group both have good nitrogen and phosphorus removal performance.However,compared with the control group,the removal rate of ammonia nitrogen and total phosphorus(90.2%-95.5%,95.1%-98.5%)of the WWTPs in the high-altitude group is slightly lower than that of the plain group(98.5%-99.8%,97.6%-99.8%);the removal rate of total nitrogen(average 69.0%)of the WWTPs in the high-altitude group is significantly lower than that of the plain group(average 84.5%),indicating that the conditions of high-altitude,cold and drought are slightly reduced the nitrogen and phosphorus removal performance of WWTPs.Moreover,it will also reduce the organic removal performance of WWTPs.The removal rate of COD in WWTPs of the high-altitude group(66.4%on average)is lower than that of the plain group(78.8%on average).We compare the difference of the microbial community structure in the activated sludge of WWTPs at high-altitude cold and drought area and plain area based on 16S r RNA high-throughput sequencing technology.The results show that the community richness and diversity in the high-altitude group are lower than those in the plain group.Combined with the removal performance of pollutants,it shows that the low microbial diversity and richness in the activated sludge may cause the lower removal efficiency of organic matter and nutrients in the high-altitude cold and drought WWTPs.Proteobacteria,Bacteroidetes,Planctomycetes and Chloroflexi are the dominant phyla in the activated sludge of the WWTPs in both high-altitude group and plain group.At the same time,the relative abundance of Bacteroidetes,Chloroflexi,Firmicutes and Cyanobacteria in the high-altitude group is higher than that of the control group,indicating that the phenotype of some microorganisms in the WWTPs in high-altitude group may have been mutated,making it could resistant to harsh environmental conditions.Under class-level,Gammaproteobacteria is the most dominant class among the six sludge samples;the clustering heat map analysis of the genus-level species shows that the communities between high-altitude and plain WWTPs are different,and the communities in the same group are most relevant.The correlation network of dominant spiecies(Spearman'?>0.75,?<0.05)shows that environmental variables such as NH₄⁺-N,COD,temperature,TP and TN have a synergistic effect on most spiecies.In contrast,altitude has a negative impact on most microbial communities and other environmental variables.In addition,lower wastewater concentration and higher altitude will reduce the complexity of the microbial community in WWTPs.LEf Se analysis shows that most bacteria are significantly enriched in the control samples.Analyzing the functional microorganisms in the activated sludge,the relative abundance of aerobic heterotrophic bacteria(HET),nitrifying bacteria(AOB and NOB),denitrifying bacteria(NAR and NIR)and glycogen accumulating organisms(GAO)in high-altitude group is lower than that in plain group.However,for phosphorus accumulating organisms(PAO),the conditions of high-altitude cold and drought are more conducive to the growth of PAO.Based on the KEGG pathway database,amino acid metabolism,carbohydrate metabolism,energy metabolism and membrane transport in the high-altitude group are lower than those in the plain group.Based on the high-throughput q PCR technology and the absolute quantitative technology of 16S r RNA gene,the difference of ARGs in the influent,activated sludge and effluent of the WWTPs between high-altitude cold and drought area and plain area are explored.The results have shown that the high-altitude group and the plain group have similarities in the composition of ARGs.However,the number of ARGs in the high-altitude group was obviously lower than that in the plain group,indicating that the pollution degree of ARGs in the WWTPs in the high-altitude cold and drought area is relatively low.The main resistance mechanism of ARGs detected in the six WWTPs is antibiotic inactivation.PCA principal component analysis shows that the same process and the same area have similar distribution characteristics of ARGs.The sewage treatment process significantly reduces the diversity of ARGs.For the absolute abundance of ARGs,the plain group can remove more ARGs;for the relative abundance of ARGs,the six WWTPs can significantly reduce the relative abundance of ARGs.At the same time,the results show that there is a synergistic relationship between MGE and ARGs.The activated sludge and effluent of the control group are enriched in more ARGs and the enrichment ratio is higher.The correlation network analysis at phylum level shows that Dncccs.Thr,Euryarchat and Thaumarcht may be the hosts of ARGs;the correlation network analysis at genus level shows that Actnbctr.Ct,Dncccs.TD,Actnbctr.Mc and Dncccs.Thrms.Th may be host of ARGs.