The potential health risks of airbe bacteria emission from a wastewater treatment process have been concemed.However,few studies have investigated the differences in community structure between indoor and outdoor bacteria.In this work,the characterization of airbe bacteria was studied in a municipal wastewater treatment plant in Beijing,China.Two indoor (i.e.,fine screen room and sludge dewatering house) and two outdoor (i.e.,aeration tank and control site) sampling sites were selected.An Andersen six-stage impactor was used for collecting culturable airbe bacteria in the air,and Illumina MiSeq sequencing was conducted to track the emission source of the culturable airbe bacteria.The results indicate that,compared with the outdoor aeration tank site,the concentrations of culturable airbe bacteria in the indoor fine screen room with poor ventilation were more than ten times higher and the particle size was about twice as large.The community structures of indoor and outdoor culturable airbe bacteria were obviously different.Enterobacteriaceae and opportunistic pathogens were detected in indoor culturable airbe bacteria,with wastewater and sludge dewatering machine identified as the primary sources.Conversely,Enterobacteriaceae and opportunistic pathogens were not detected in outdoor culturable airbe bacteria.Outdoor high wind speed might have resulted in rapid dilution and mixing of culturable airbe bacteria generated from the aeration tank with the ambient air.The results of the present research suggest that covering pollution sources,increasing ventilation rates,and using protective measures for personnel should be implemented to decrease the exposure risk to indoor culturable airbe bacteria.