The Bioaugmentation And Influence Factors Of Steroid Estrogen In An A/O-MBR Process

As typical endocrine disruptors,steroid estrogens(SEs)pose a serious threat to human health at a very low concentration(ng/L).The existing municipal sewage treatment process has limited removal capacity for these SEs,which becomes an important source of SEs enterring the environmental water.Researchers have isolated a number of functional strains with high degradation SEs abilities.However,their efficiency were affected by many abiotic/biotic factors in the full-scale biolocial wastewater treatment systems,and it was hard for them to obtain ideal quantity and activity,and gradually reduced with the contant operation of the process.Therefore,it is necessary to carry out technical innovation on biolocial wastewater treatment to improve the removal of toxic and harmful trace pollutants such as SEs.In this study,typical SEs,estrone(E1),estradiol(E2)and ethinyl estradiol(EE2)were selected as the target pollutants,and bioaugmentation with the genera of Enterobacter and Brevibacillus was used as the main technical means to investigate the removal patterns of SEs in an anoxic-aerobic membrane bioreactor(A/O-MBR)process.The effects of sludge retention time(SRT),hydraulic retention time(HRT)and dissolved oxygen(DO)concentration on the performance of biodaugmented process were investigated.The results showed that the average removal efficiencies of El,E2 and EE2 in bioaugmentation A/O-MBR process increased by 9.13%,9.75%and 6.21%,as compared to those in the non-bioaugmentation process.The longer SRT was helpful to the removal of SEs in A/O-MBR process.When the SRTs were 10 d,30 d and 60 d,the removal efficiencies of El were 83.26%,85.88%and 86.39%,that of E2 were 81.02%,89.43%and 90.17%,that of EE2 were 62.5%,73.64%and 75.63%.In addition,under different SRT,the time required for stable SEs removal was also different.When the SRT was 60 d,E2 removal rate stablized at 91%within 14 days,while 20 days when the SRT was 30 d.The removal efficiency of SEs was affected by HRT.When the HRT increased from 6 h to 12 h,the removal efficiencies of E1,E2 and EE2 increased from 83.45%,82.64%and 67.52%to 88.39%,85.96%and 70.31%.But when the HRT extended to 24 h,the removal rate of E1 and E2 decreased,while the removal rate of EE2 continued to increase,indicating that the removal of EE2 may require longer contact time than E1 and E2.Increasing DO concentration could promote the removal of SEs.When DO concentrations were 2 mg/L,4 mg/L and 6 mg/L,the removal rates of E1 and EE2 increased.Compared with EE2,the increase of DO concentration had slight effect on the removal of E2.The results of 16S rDNA high-throughput sequencing showed that the diversity of bacterial community decreased with SEs,which revealed the negative effect of SEs on the microbial community.After bioaugmentation,Shannon values of A and O pools changed from 4.47 and 4.39 to 4.63 and 4.57,SEs removal efficiencies enhanced.The Simpson value decreased with the increase of SRT,while the Chaol and Shannon value increased with the increase of SRT.Proteobacteria,Actinobacteria,and Chloroflexi were the main bacterial phylum in the non-bioaugmentation process.The addition of SEs and bioaugmentation led to the change of bacterial community structure.The relative abundance of Bacteroidetes was higher in the presence of SEs,but decreased after bioaugmentation,which may have a competitive relationship with the bioaugmentation stains.The relative abundances of Enterobacter and Brevibacillius decreased with the operation of the bioaugmentation process,from 2.57%and 3.15%to 1.03%and 1.61%.However,Bacillus,Conexibacter and Hyphomicrobium increased,the growth of these genera might be promoted by the bioaugmentation stains,which might contribute to the improvement of SEs biodegradation.Under different SRTs,the microbial community structure showed different degrees of variation.With the extention of SRT,the relative abundance of Chlorofloxi,Patescibacteria and Nitrospira increased,and the highest SEs removal was observed at SRT of 60 d.Therefore,the efficient removal of SEs may be related to these bacterial phylum.Through network analysis,there was no bacteria closely related to the biodegradation of E1 and EE2,but most of them were negatively related to the removal efficiency of E2.There were also negative correlations among some genera,indicating that the addition of bioaugmentation stains had certain impacts on the microbial community structure,and there might be competition while the overall role of the but the overall role of bioaugmentation stains in total microbial community was promotion.