Bacteria and fungi in aerosols generated by two different types of wastewater treatment plants

Raw wastewater is a potential carrier of pathogenic microorganisms and may pose a health risk when pathogenic microorganisms become aerosolized during aeration. Two different types of wastewater treatment plants were investigated, and the amounts of cultivable bacteria and fungi were measured in the emitted aerosols. Average concentrations of 17000 CFU m−3 of mesophilic, 2100 CFU m−3 of TSA-SB bacteria (bacteria associated with certain waterborne virulence factors), 1700 CFU m−3 of mesophilic and 45 CFU m−3 of thermotolerant fungi, were found in the aerosol emitted by the aeration tank of the activated sludge plant. In the aerosol of the fixed-film reactor 3000 CFU m−3 mesophilic and 730 CFU m−3 TSA-SB bacteria, and 180 CFU m−3 mesophilic and 14 CFU m−3 thermotolerant fungi were measured. The specific emissions per population equivalent between the two types of treatment plants differed by two orders of magnitude. The microbial flux based on the open water surface area of the two treatment plants was similar. The aerosolization ratios of cultivable bacteria (expressed as CFU m−3 aerosol/m−3 wastewater) ranged between 8.4×10−11 and 4.9×10−9. The aerosolization ratio of fungi was one to three orders of magnitude higher and a significant difference between the two types of treatment plants could be observed.