Study Reveals Survival Time of SARS-CoV-2 in Wastewater: Public Health Impact

The rapid global spread of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has caused a pandemic commonly known as coronavirus disease 2019 (COVID-19). To date, the pandemic has affected approximately 686 million people worldwide and claimed more than 6.8 million lives.Although the virus is primarily transmitted through respiratory droplets or direct contact with an infected person, SARS-CoV-2 is also detected in fecesTherefore, SARS-CoV-2 can be excreted in human faeces and body secretions such as saliva and urine, and then transported to wastewater treatment plants.

study: Survival of SARS-CoV-2 in wastewaterImage Credit: Avigator Fortuner/Shutterstock

Background

The recent identification of SARS-CoV-2 in faeces has raised concerns that it may be an additional route of viral transmission. Similar events were recorded during the first SARS pandemic in 2003. During this period, there was an increase in SARS cases due to aerosolized faeces resulting from a faulty sewage pipeline in an apartment building in Hong Kong.

Data on viable isolation of SARS-CoV-2 from wastewater are lacking. The majority of developing countries with low vaccination coverage still struggle to provide clean drinking water and safe disinfection, so understanding how this virus persists in wastewater is essential.

Previous studies assessing SARS survival found that enveloped viruses survived for a shorter period of time compared to non-enveloped viruses. Unfortunately, due to the risks associated with culturing viable virus and the need for biosafety level 3 laboratories, few studies have determined live SARS-CoV-2 in wastewater and other environmental water matrices. Not done. However, a previous study revealed that infectious SARS-CoV-2 survived 2.3 days in a river environment at 20°C and 1.1 days in seawater.

Another study noted that SARS-CoV-2 survived in wastewater at room temperature for 1.7 days. Survival of SARS-CoV-2 was found to be greater in filtered river and wastewater compared to unfiltered river and wastewater samples.

About research

Recent research in journal Comprehensive Environmental Science We investigated SARS-CoV-2 survival in filtered and unfiltered raw wastewater at 20 °C (room temperature). This study also evaluated the viability of SARS-CoV-2 in secondary effluents at the same temperature.

Wastewater samples were collected on December 13, 2021 from a wastewater treatment facility in Arizona, USA. The facility has an inflow of approximately 22 million gallons per day. The physicochemical properties of the samples were evaluated. Raw filtered wastewater samples were prepared by passing crude samples through 0.2 μm filter membranes.

Investigation result

A gradual decline in SARS-CoV-2 infectivity was observed in three wastewater matrices. Consistent with previous studies, this study revealed a rapid decrease in infectivity in unfiltered unfiltered and filtered raw wastewater compared to secondary wastewater. This finding demonstrates rapid inactivation of SARS-CoV-2 in complex matrices compared to simple matrices.

Similar inactivation rates of SARS-CoV-2 were observed in filtered and unfiltered raw wastewater during the first 4 hours. This inactivation may be caused by enzymes present in the wastewater. SARS-CoV-2 is an enveloped virus containing a lipid bilayer membrane and is susceptible to enzymes (such as lipases and proteases) that lead to its inactivation.

Inactivation rates were higher in unfiltered raw wastewater than in filtered wastewater after 24 hours. This may be due to competition for survival between unique microbial populations such as bacteria, metazoans, protozoans and SARS-CoV-2. Some indigenous microorganisms produce proteolytic enzymes in unfiltered wastewater that affect survival of SARS-CoV-2.

Previous studies have shown that viruses attach to organic matter and suspended solids present in wastewater, protecting them from predation, photodegradation, disinfection, and other processes that affect their viability. . Time required to inactivate 90% of SARS-CoV-2 (T₉₀) was estimated to be 10.4, 10.8, and 18.3 h for unfiltered raw, filtered raw, and secondary effluent, respectively.

Isolation of viable SARS-CoV-2 from raw wastewater using standard filtration elution procedures is usually difficult due to the high decay rate of the virus in this matrix.

Conclusion

The authors claim that this study is the first to assess survival of SARS-CoV-2 in secondary treatment wastewater. This study revealed survival of SARS-CoV-2 in unfiltered/filtered raw sewage and secondary wastewater at room temperature. Since the residence time of wastewater in sewage systems is typically less than 24 hours, it is unlikely that aerosols from wastewater treatment plants will contain high concentrations of SARS-CoV-2 at room temperature. In the future, viability of SARS-CoV-2 in wastewater should also be evaluated at other temperatures.