Abstract
To characterize the emission of microbial aerosols from the widely used municipal sewage treatment plants (MSTP) in China, an Andersen six-stage impactor and the culture method were employed to determine the concentrations and size distributions of airborne viable bacteria, fungi and actinomycetes in a sewage treatment plant with an oxidation ditch process in Xi’an in summer. The results showed that the concentrations and size distributions of each of the airborne microorganisms varied greatly at different phases of sewage treatment process. The highest bacteria (7866 ± 970 CFU/m 3 ) and actinomycetes concentrations (2139 ± 229 CFU/m 3 ) were found in the sludge-dewatering house while the highest fungi concentration (2156 ± 119 CFU/m 3 ) at the oxidation ditch. The particle size distributions showed that similar singlepeak pattern for airborne actinomycetes, bacteria and fungi. Another important finding was that about 52% of airborne bacteria, 62% of airborne fungi and 65% of airborne actinomycetes were in respirable size range (less than 3.3 μm), indicating that most microbial aerosols from MSTP could easily penetrate into the human alveolus. Finally, the order of the count median diameters of different microbial aerosols was found to be similar at each phase, that is, airborne bacteria > airborne fungi > airborne actinomycetes. This implied that airborne actinomycetes emitted from MSTP might have a more significant effect on public health and urban air quality than bacteria and fungi.
Highlights
With the acceleration of urbanization recently, more and more municipal sewage treatment plants (MSTP) have been built and put into operation in China
Another important finding was that about 52% of airborne bacteria, 62% of airborne fungi and 65% of airborne actinomycetes were in respirable size range, indicating that most microbial aerosols from MSTP could penetrate into the human alveolus
The significantly higher numbers of airborne viable bacteria, fungi and actinomycetes were all detected at each phases of the sewage treatment process, indicating that the municipal sewage treatment plant was really an important source of microbial aerosols
Summary
With the acceleration of urbanization recently, more and more municipal sewage treatment plants (MSTP) have been built and put into operation in China. Many MSTPs and related sewage works become surrounded by new residential and shopping districts. In such situation the question of hygienic sustainability of MSTP site location arises in terms of frequent noxious odours, and of intermittent enteric illness and related syndrome of unknown origin among nearby residents (Stellacci et al, 2010). During handling sewage to protect water environment, sewage treatment plants have been proved to generate some hazardous air pollutants like microbial aerosols and have become growing concern in the public (Pascual et al, 2003; Fracchia et al, 2006; Heinonen-tanski et al, 2009).
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