Emission level, particle size and exposure risks of airborne bacteria from the oxidation ditch for seven months observation

Özet

The emission of airborne bacteria and their human exposure risks were studied in a wastewater treatment plant(WWTP). Air samples were collected by an Andersen Cascade Impactor at different distances from the rotor discaerators (RDAs) equipped in the oxidation ditch in seven months. Spatial and seasonal variations in the concentrationsof airborne bacteria emissions were detected. The highest concentration was observed near the RDAs(835 ± 91 CFU/m3 to 8916 ± 155 CFU/m3) during each sampling process, with the concentration decreasingby 76.70% and 79.91% as sampling distance and height increased, respectively. Most of the airborne bacteriawere coarse particles that exceeded 4.7 μm in size. The dominant bacteria were Bacillus sp., Lysinibacillus sp., andSphingomonas sp. The spatial distribution of airborne bacteria visualized by contour maps indicated potentialhealth impact of wastewater treatment processes on biological pollution within the WWTP and surroundingareas. The deposition fraction of airborne bacteria that could penetrate the lung through inhalation were used toassess the human exposure risks. Hazard quotients ranged from 1.66×10−2 to 1.06. There were cumulativerisks to on-site workers and nearby residents posed by chronic exposure. The airborne microorganisms disseminatedby the RDAs should be reduced.