Route of SARS-CoV-2 in Sewerage and Wastewater Treatment Plants: Dilution, Decay, Removal, and Environmental Transmission

The detection of SARS-CoV-2 in the stool of COVID-19 positive persons raises the question of potential fecal-oral transmission. The virus is transported from feces to the sewer system where a dilution of about 103 times occurs, due to the discharge of drinking water, rainwater, or infiltrations. A progressive decay of SARS-CoV-2 occurs along the sewerage network and in wastewater treatment plants due to the presence of pollutants, solids, and detergents. The fragile envelope makes SARS-CoV-2 more rapidly inactivated than enteric viruses. In WWTPs, primary treatment and activated sludge process contribute partially to the virus reduction, while SARS-CoV-2 is more susceptible to disinfection such as chlorination, ozonation, or UV light. Potential sewage-associated transmission of COVID-19 may occur during flooding events in urban areas when untreated wastewater is spread or from the overload of untreated blackwater in the combined sewer systems.