Characteristics Of Bioaerosol Emission In MBR Wastewater Treatment Process

The generation and control of bioaerosol in municipal wastewater treatment plants（WWTPs）has become one of the hot issues of public concern.In the wastewater treatment process,a host of microorganisms escape into the air under the action of mechanical agitation or aeration to form bioaerosols.Bioaerosols often contain pathogenic or potentially pathogenic bacteria.Through inhalation and frequent skin contact,it may cause allergic diseases,thereby threatening human health.At present,the MBR process has gradually become one of the mainstream processes for municipal wastewater treatment and reuse.The research of bioaerosols in WWTPs mainly focused on the conventional A²/O processes,oxidation ditch processes,and SBR processes.There were few studies on the characteristics and influencing factors of bioaerosols in MBR process,and the relevant emission mechanism was still unclear.In this paper,the concentration,particle size distribution,community structure and chemical composition of bioaerosols in typical MBR process wastewater treatment plant were analyzed.The exposure risk of bioaerosols was evaluated.The correlation of bioaerosol concentration and community structure with environmental factors and chemical components was determined.The source of bioaerosols in MBR process was revealed.The distribution of bioaerosols concentration,particle size and microbial structure in vertical space of MBR process were analyzed.The results can provide scientific basis for health risk assessment and pollution control of bioaerosol in MBR wastewater treatment process.There were significant differences in concentration,particle size distribution and community structure of bioaerosols in the full-scale of typical MBR process.Culturable bacterial aerosols and culturable fungal aerosols were detected in the full-scale of WWTPs,with concentrations of 1388±623-8687±103 CFU/m³、123±39-1000±555 CFU/m³。Among them,the concentration of culturable bacterial aerosols and culturable fungal aerosols in sludge dewatering room（SDR）were significantly higher than that in other sections.The particle size of bacterial aerosols was mainly distributed between 1.1-3.3μm,and 27.18-55.86%of bacterial aerosols were inhalable particles（with the particle size of 0.65-2.1μm）.The particle size of fungal aerosols was mainly distributed in the range of 1.1-4.7μm,and 0-75%of fungal aerosols were inhalable particles（with the particle size of 0.65-2.1μm）.The dominant phylum of bioaerosols in different sections were similar.However,there were obvious differences for the dominant genus of bacterial aerosols and the fungal aerosols in different sections.Bacterial aerosols and fungal aerosols also contained some genera that low-relatively abundance and pathogenic,such as Pseudomonas,Bacteroides,Micrococcus,Escherichia-Shigella,etc.,which would bring health risks to workers in the wastewater plants and surrounding residents.The risk of bioaerosols exposure in the full-scale of typical MBR process was evaluated,and the results show that the inhalation was the main route of bioaerosol exposure.Adult males were more susceptible to bioaerosol than adult females.Temperature and relative humidity had a significant impact on the community structure of bacterial aerosols and fungal aerosols in WWTPs.Appropriate temperature and relative humidity can promote the growth and reproduction of bacteria and fungi in bioaerosols.The water-soluble inorganic ions in the bioaerosols emitted from each section were mainly SO₄^2-,NO₃^-,Cl^-,Ca²⁺,Na⁺and NH₄⁺,with a concentration of 18.68～183.41μg/m³.The proportion of SO₄^2-in the water-soluble inorganic ions in the bioaerosols from the membrane tank was reduced.Cl^-and NO₃^-became the main anions,and NH₄⁺and Ca²⁺became the main cations.The existence of these water-soluble ions can not only provide nutrient environment for the growth of microorganisms in the bioaerosols,but also affect the community structure of the bioaerosols to a certain extent.Wastewater/sludge and ambient air had the same important contribution to the bioaerosols in the fine grid and sludge dewatering room,and ambient air was the main source of bioaerosols from membrane tank.The concentrations of cultivable bacteria aerosols and cultivable fungal aerosols at different heights in the vertical space of the MBR process both decreased at first and then increased.At 3 m from the water surface of the membrane tank,the concentration of cultivable bacterial aerosols and cultivable fungal aerosols were up to 6166±1095 CFU/m³ and 1696±71CFU/m³.The fine particles proportion of bacterial and fungal aerosol gradually increased with the distance from the water surface.The proportion of inhalable particles increased.With the increase of the height from the water surface,the diversity and richness of bioaerosols in the vertical space first decreased and then increased.At the height of 0.5 m from the water surface,the diversity and richness of bacterial aerosols were high,and the dominant bacterial genera were Romboutsia,Paracoccus,Rhodococcus,Kocuria,Bacillus,etc.Furthermore,the dominant microorganisms in the aerosol of different heights in the vertical space and membrane tank were different.Due to the different aerosolization potential and the ability to survive in the air of different bacteria,the dominant genera in water,such as Hypomicrobium,Densospora and Naumovozyma,had low abundance in aerosols.