Methods based on impaction and the polymerase chain reaction (PCR) were applied to monitor the concentrations, size distributions, and species diversity of bioaerosols at different treatment units in a Beijing municipal wastewater treatment plant (WWTP) that uses an Orbal oxidation ditch process. The concentrations of culturable bacteria and fungi recorded in the VVWTP varied from 459 +/- 88 to 5565 +/- 571 CFU m(-3) and 141 +/- 41 to 1590 +/- 152 CFU m(-3), respectively. The highest concentrations of culturable bacteria were obtained in the sludge-dewatering house, whereas the highest fungi concentrations were found in the fine grit chamber (FGC). The particle size distributions showed that 27.6% of culturable bacteria were detected in particles of 2.1-3.3 mu m in size, and 6.6% were in particles between 0.65 and 1.1 mu m in size. More than 67% of the fungi were detected in particles ranging from 1.1 to 3.3 in size, with only 5.0% found in particles less than 1.1 mu m in size. Both culturable and total airborne bacterial community in FGC samples demonstrated high microbial diversities. Airborne bacteria generated from adjacent treatment units showed a close genetic evolutionary relationship. Combination of pure-culture methods and PCR-based methods can provide additional information to verify the presence of bioaerosols. (c) 2011 Elsevier Ltd. All rights reserved.