Site-related and seasonal variation of bioaerosol emission in an indoor wastewater treatment station: level, characteristics of particle size, and microbial structure

The emission of the airborne bacteria and fungi from an indoor wastewater treatment station adopting an integrated oxidation ditch with a vertical circle was investigated. Microbial samples were collected by the six-stage viable Andersen cascade impactor, and the samples were collected in triplicate in each sampling site per season. Culture-based method was applied to determine the concentrations of the airborne bacteria and fungi, while the cloning/sequencing method was used to characterize the genetic structure and community diversity of airborne bacteria. The highest concentrations of airborne bacteria (4155 +/- A 550 CFU/m(3)) and fungi (883 +/- A 150 CFU/m(3)) were obtained in June (summer). The lowest concentration of bacteria (1458 +/- A 434 CFU/m(3)) was determined in January (winter), and the lowest concentration of fungi (169 +/- A 40 CFU/m(3)) was found in March (spring), respectively. The particle size distribution analysis showed that most culturable bacteria obtained in all the sampling sites were in the particle size range of 1.1-4.7 A mu m. Most culturable fungi had particle sizes in the range 1.1-3.3 A mu m. Microbial population analysis showed that Bacillus sp., Acinetobacter sp., and Lysinibacillus were the main groups obtained in S1. Enterobacter was the dominant group in sampling site S2. Both the concentrations and particle size distribution of the bioaerosols in the enclosed space presented a seasonal and site-related variation. Concentration and richness of microorganisms in bioaerosols in June were higher than in September and January. The particle size distribution varied between the sampling sites, and proportion of large particles was higher in S2 than in S1 because of the settlement of large particles. Pathogenic species, such as Acinetobacter lwoffii, Staphylococcus saprophyticus, and Enterobacter sp., were isolated from the bioaerosols, which could pose serious latent danger to sewage workers' health.