Wastewater treatment commonly includes the production of air bubbles (aeration) at the bottom of activated sludge or during Dissolved Air Flocculation and Floatation. When the bubbles rise to the surface they burst, form droplets and ‘aerosolise’. This is how pathogenic microorganisms in the wastewater can become ‘airborne’.
The Experiment: Bioaerosol samples were collected from 0.1, 1.5 or 3m above the surface of six WWTP that use biochemical reaction tanks, or an aeration basin, or an aeration pool. Total Organic Carbon, insoluble, soluble, and total suspended particles were quantified. The particles in the samples were examined using Scanning Electron Microscopy, the composition was determined using Energy Dispersive X-Ray Spectroscopy (EDX), and bacteria and fungi were cultured.
Results: The highest numbers of large heavy particles were found near the water surface whereas 3m above the water surface there were fewer particles but 75% were small particles <2.5μm. There was a reduction in WW-derived chemicals to 5.36% at 3m, but still 76% of culturable bacteria and fungi. They did not examine virus.
The concentration of bioaerosols was highly influenced by wind speed, temperature and relative humidity.
Conclusion: The authors noted that ‘effective measures should be adopted to protect on-site workers’, not because of SARS-CoV-2 but because of general pathogen load. Surgical masks can prevent a worker breathing in approximately 66% of aerosolised pathogens (see Noti et al., 2012).
Yanjie Wang1,2, Huachun Lan3, Lin Li 1,2, Kaixiong Yang1,2, Jiuhui Qu3 & Junxin Liu1,2 (2018) Scientific Reports 8:9362 https://DOI:10.1038/s41598-018-27652-2