Risk assessment of airborne coronavirus-2 in wastewater treatment plant: comparing two different wastewater aeration systems

Abstract

Numerous global studies have explored the fate of Coronavirus-2 within wastewater treatment plants. While research has confirmed virus transmission through aerosols generated in these facilities, the effect of different aeration methods on the potential transmission of this virus and other pathogens remains unclear. In this study, we aimed to examine the occurrence of Coronavirus-2 in air samples collected from two wastewater treatment plants employing diffused and surface aeration. Totally, 48 air samples (passive/active) were collected from 1.5, 10, and 50 m distances from both sequencing batch reactor and conventional activated sludge systems. Subsequently, a quantitative microbial risk assessment model was applied to evaluate the risk of Coronavirus-2 infection for staff. Results showed that all samples from the conventional activated sludge, and only 5 of samples from the sequencing batch reactor, were positive for Coronavirus-2 when tested at a 1.5-m distance from the aeration tanks. Quantification results revealed that the concentration of Coronavirus-2 in positive air samples from the CAS system, targeting the RdRp and N genes, varied from 15 to 239 and 15 to 119 genomic copies per liter, respectively. Quantitative microbial risk assessment revealed an annual infection risk of 3.6 x 10-1 (95 CI 1.8 x 10-7-1)/person/year for staff, which was 2-4 times higher than the suggested values by the United States Environmental Protection Agency (10-4/person/year). According to the results of this study, the diffused aeration system can be considered as a safer option due to the very low spread of pathogens.