Distribution characterization of microbial aerosols emitted from a wastewater treatment plant using the Orbal oxidation ditch process

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 WWTP 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 μm in size, and 6.6% were in particles between 0.65 and 1.1 μm in size. More than 67% of the fungi were detected in particles ranging from 1.1 to 3.3 μm in size, with only 5.0% found in particles less than 1.1 μm 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.