SARS-CoV-2 in wastewater treatment plants

As for the SARS coronavirus in the 2003 epidemic, the presence of SARS-CoV-2 has been demonstrated in faeces and, in some cases, urine of infected people, as well as in wastewater. This paper proposes a critical review of the state of the art regarding studies on the presence of SARS-CoV-2 in wastewater and sewage sludge, the factors affecting its inactivation and the main proposed treatments, with the aim to provide useful information at operative level in order to better and safer manage wastewater and sewage sludge. Given the lack of literature on SARS-CoV-2, studies involving other HCoVs such as SARS-CoV and HCoV-229E have been also considered. In wastewater, the resistance of SARS-CoV has proven to be very limited, especially at temperatures above 20 °C, and the virus has been easily removed with the use of chlorine (> 0.5 mg L⁻¹ for 30 min). For sewage sludge, based on in vitro experiments, it is suggested to increase the retention times before a possible reuse in agriculture only for precautionary purposes, since SARS-CoV-2 is unlikely to occur in the sludge. SARS-CoV-2 in wastewater might track the epidemic trends: although being extremely promising, an effective and wide application of this approach requires a deeper knowledge of the amounts of viruses excreted through the faeces and the actual detectability of viral RNA in sewage.