Emission Characteristics And Control Techniques Of Microbial Aerosols In Typical Municipal Wastewater Treatment Plants

With the acceleration of urbanization,more and more sewage treatment plants have been built and operated.The sewage treatment plant is an important infrastructure to control water pollution,protect water environment and realize sustainable urban development.A large number of microorganisms from sewage/sludge could escape into the air in the process of sewage flow and drop,mixing,aeration and dewatering.These microbes could spread to the surrounding with the help of wind and its own diffusion.It could not only cause air pollution,but also caused serious impact on human health through breathing and skin contact.In this study,the laboratory scale SBR reactor was used as the research object to investigate the effects of different operation parameters of biochemical treatment unit on the escape of microbial aerosol.At the same time,the concentration,particle size,community structure and diversity of microbial aerosol in different areas were measured in a typical municipal wastewater treatment plant.The distribution features and sources of microbial aerosols were analyzed.The effects of ultraviolet radiation and adding iron-rich carrier filler on the dissipation of microbial aerosol were investigated.The main results are as follows:（1）With the increase of COD concentration and water temperature,the concentrations of bacteria,fungi,actinomyces and total microbial aerosols increased.The aerosols concentrations of bacteria,actinomyces and total microbial were significantly higher with the aeration of sand head than that of the other two aeration modes（p<0.05）,but the effect of aeration mode on fungal aerosols was not significant（p>0.05）.With the increase of aeration intensity,the aerosols concentrations of bacteria,fungi and total microbial aerosols increased.However,the change of aeration intensity had no significant effect on the aerosol concentration of actinomyces（p>0.05）.There was a negative correlation between sludge concentration and the emission of microbial aerosol,when MLSS was 2550 mg/L,the aerosols concentrations of bacteria,fungi and total microbial were significantly higher than the other two sludge concentrations（p<0.05）.The experimental results showed that the optimization of the operation parameters of the biochemical treatment unit could reduce the escape of microbial aerosol under the premise of ensuring the effluent quality to meet the discharge standard.（2）The aerosols concentrations of bacteria,fungi,actinomyces and total microbial were3543±42 CFU/m³,1116±59 CFU/m³,313±20 CFU/m³and 4972±391 CFU/m³,respectively.Bacteria,fungi and actinomyces accounted for 71.26%,22.44%and 6.30%,respectively.The aerosols concentration of bacteria was significantly higher than fungi and actinomyces（p<0.05）.（3）There are obvious seasonal and regional differences in the distribution of microbial aerosol concentration in sewage treatment plants.In the same season,the concentration of microbial aerosol in sludge dewatering room was significantly higher than that in other areas（p<0.05）.The concentration of bacterial aerosol were the highest in sludge dewatering room and control group during winter,while the concentration of bacterial aerosol in fine grid room and aeration tank was the highest during summer.The concentration of fungi aerosol was the highest in summer.The concentration of actinomyces aerosol was higher in winter.In the same sampling period,the concentration of microbial aerosol in sludge dewatering room was higher than that in other areas（p<0.05）.The concentrations of bacteria,fungi,actinomyces and total microbial aerosols between fine grid room and aeration tank were the highest at8:00～9:00.Environmental factors such as ambient temperature,PM_2.5and PM₁₀have great influence on the distribution of microbial aerosols in wastewater treatment plant.（4）There are seasonal and regional differences in particle size distribution of microbial aerosols in wastewater treatment plants.The aerosol particles of bacteria,fungi and actinomyces were mainly distributed in the first four levels（>2.1μm）in the air environment of control point,fine grid room and aeration tank during spring,summer and Autumn.The aerosol particles of bacteria and actinomyces were mainly located in the last four grades（<4.7μm）,while the aerosol particles of fungi were chiefly distributed in the first four grades（>2.1μm）in sludge dewatering room.The median diameter of aerosol particles of bacteria,fungi and actinomyces were 2.99～4.15μm、3.60～4.01μm and 3.28～3.98μm.The median diameter of microbial aerosol particles in fine grid room and aeration tank was larger than that in the control group,which was closely related to the forms and sources of microorganisms in the air environment.（5）Richness and diversity index of community structure on bacterial and fungi in different areas of sewage treatment plant were different.Proteobacteria,Firmicutes,Actinobacteria,Deinococcus-Thermus,Bacteroidetes,Ascomycota,Basidiomycota and Olpidiomycota were the dominant microorganism in the air environment of wastewater treatment plant.Enterococcus,Staphylococcus,Pseudomonas,Acinetobacter,Fusobacterium,Arcobacter,Penicillium,Aspergillus,Malassezia,Candida and Cryptococcus are potential pathogenic pathogens in the air environment of sewage treatment plants.（6）The community structure and source of bacteria and fungi in sewage treatment plant were different.Proteobacteria,Deinococcus-Thermos,Basidiomycota and Olpidiomycota mainly came from the external environment.Firmicutes,Bacteroidetes,Actinobacteria,Chloroflexi,Patescibacteria,Epsilonbacteraeota,Nitrospirae and Ascomycota were mainly from sewage/sludge.Source tracker analysis showed that the possible sources of microbial aerosols were sewage/sludge,external environment and unknown sources,and the sources of microbial aerosols were different in different regions.（7）Ultraviolet radiation and adding iron-rich carrier filler could reduce the dissipation of microbial aerosols.Ultraviolet radiation had an appreciable effect on the reduction of microbial aerosols for SBR-1.Adding iron-rich carrier filler could not only reduce the escape of microbial aerosol,but also affect the composition and diversity of microbial community in the air environment.The relative abundance of Firmicutes,Deinococcus-Thermus,Ascomycota and Mucoromycota increased,while the relative abundance of Proteobacteria,Bacteroides,Acidobacteria,Basidiomycota and Mortierellomycota decreased.In this paper,the effects of different operation parameters,ultraviolet radiation and iron-rich carrier filler on the escape of microbial aerosols in the process of wastewater biological treatment were studied.The concentration,particle size,composition and source of microbial aerosols were systematically analyzed in typical municipal wastewater treatment plants.The results provide basic data for the reduction and control of microbial aerosols in wastewater treatment plants.It also provides a scientific basis for the sustainable development of urban atmospheric ecological environment and the protection of human health.