Opportunistic bacterial pathogens in bioaerosols emitted at municipal wastewater treatment plants, South Africa

Aeration tanks at wastewater treatment plants (WWTPs) emit significant amounts of bioaerosols containing potentially hazardous infectious material. Occupational exposure to airborne pathogens can pose health risks to WWTP workers. Bioaerosol samples collected at aeration tanks of two typical municipal WWTPs that use different aeration modes were analysed to investigate the composition and diversity of airborne bacteria in wastewater environments, using the Illumina MiSeq platform. Thirty-six potential airborne bacterial pathogens were identified in the air samples, and these were dominated by Bacillus, Enterococcus, Clostridium, Streptococcus, Acinetobacter, Enterobacter, Pseudomonas, Bacteroides fragilis, Acinetobacter baumannii, and Escherichia/Shigella. Bioaerosols from mechanical aeration tanks (72%, 26/36) had a relatively higher richness and diversity of airborne bacterial pathogens than diffused aeration tanks (17%, 6/36). Furthermore, most of the identified airborne bacterial pathogens (78%, 28/36) were classified as Risk Group 2 according to the revised South African Regulation for Hazardous Biological Agents, 2022, and up to 70% of these were gram-negative bacteria. The presence of potentially pathogenic bacteria in the ambient air at WWTPs suggests an elevated risk of bioaerosol exposure for workers. Therefore, further research and site-specific risk assessments are recommended to guide the implementation of effective bioaerosol strategies to protect workers' health, with special attention paid to WWTPs that use mechanical aerators.