RESUMO
To characterize the pollution characteristics of microbial aerosols emitted from municipal sewage treatment plants, microbial aerosols were sampled with an Andersen 6-stage impactor at different treatment units of a Xi'an sewage treatment plant between June 2011 and July 2011. The plate-culture and colony-counting methods were employed to determine the concentrations, particle size distributions and median diameters of the airborne bacteria, fungi and actinomycetes. The results showed that the highest concentrations of bacteria (7 866 CFU x m(-3) +/- 960 CFU x m(-3)) and actinomycetes (2 139 CFU x m(-3) +/- 227 CFU x m(-3)) were found in the sludge-dewatering house while the highest fungi concentration (2156 CFU x m(-3) +/- 119 CFU x m(-3)) in the oxidation ditch. The airborne bacteria, fungi and actinomycetes all showed a skewed distribution in particle size. The peaks of bacteria and fungi were in the size range of 2.1-3.3 microm, whereas the peak of airborne actinomycetes was between 1. 1-2.1 microm in size. In general, the order of the median diameters of different microbial aerosols generated from the sewage treatment plant was airborne bacteria > airborne fungi > airborne actinomycetes. In addition, the spatial variation characteristics of microbial aerosols showed that the larger the particle size of the microorganism, the faster the reducing rate of the aerosol concentration. The variations in the reducing rate of concentration with particle sizes can be ordered as airborne bacteria > airborne fungi > airborne actinomycetes.