Unveiling the role of aeration systems in the bioaerosol emission rate, particle size and microbial composition from wastewater treatment plants

Wastewater treatment plants (WWTPs) are important sources of bioaerosols; however, the influence of aeration on emission characteristics, particle size distribution, and microbial composition remains poorly studied. This study investigates how surface aeration (SA) and diffused aeration (DA) systems affect bioaerosol emission rates, particle size distribution, and microbial diversity using an 8-stage Andersen cascade impactor and shotgun metagenomics. Bioaerosol emission rates were estimated by combining measured particle concentrations with system-specific airflow rates. Abiotic factors were analysed through redundancy analysis to determine their influence on community structure. SA consistently generated higher emission rates, particularly in respirable particles (0.43-2.1 µm), which are capable of deep respiratory deposition. Dominant taxa included Rhodococcus, Pseudomonas, Bacillus, Meyerozyma, and Siphoviridae, with SA showing higher relative abundance of opportunistic pathogens even in smaller particle sizes. In contrast, DA systems exhibited a lower emission rate but broader microbial diversity, reflecting more stable aeration conditions. The study indicated that activated sludge was the main source of microbial populations, with a larger bioaerosol -activated sludge overlap in SA than DA. Redundancy analysis revealed that wind speed (WS) and relative humidity (RH) significantly influenced bacterial and viral populations, while WS and air temperature (AT) affected eukaryotes. Notably, SA emissions decreased with distance (100 m), while DA emissions increased. By quantifying emission rates rather than concentrations and integrating high-throughput metagenomics, this study provides a comprehensive framework for characterising bioaerosol hazards in WWTPs. These findings highlight the need for mitigation strategies in WWTPs, especially near SA systems.