19 Aug 2021
Science for Environment Policy: Wastewater should be considered a potential pathway for COVID-19 transmission
In the past century, many infections evolved into pandemics, and 2 of them were Coronaviruses: SARS-Cov-1 in 2003 and MERS-CoV in 2012. Previous studies show that SARS-Cov-1 could be transmitted through wastewater, suggesting that this could be an indirect infection pathway for SARS-CoVs. Wastewater must be explored as a possible transmission pathway of COVID-19, say the researchers of a review study, to support the early detection and containment of future viral outbreaks.
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The study of Bogler, A. et al. (2020), titled “Rethinking wastewater risks and monitoring in light of the COVID-19 pandemic”, found that, in two-thirds of confirmed COVID-19 cases, SARS-CoV-2 genetic material is found in stool samples, and often remains even after respiratory infection resolves and patients test negative. It is unclear if this genetic material originates from swallowed sputum or active replication within the gastrointestinal tract. SARS-CoV-2 enters wastewater systems via human stools and urine, with greywater (e.g. from showers and sinks) unlikely to be a major source.
The study also discovered that SARS-CoV virus particles can remain infectious for several days in raw (untreated) wastewater, with infectivity affected by organic content, pH and temperature (with colder temperatures prolonging infectivity). Without adequate treatment (e.g. chlorine disinfection) these particles can be further disseminated to water bodies and enter aquatic ecosystems. While infectious SARS-CoV has not been directly found in aquatic environments, similar viruses are able to survive and travel long distances in such conditions, highlighting a potential risk.
The scientists conclude that there is a need for innovative tools for environmental monitoring, risk assessment and risk management to provide necessary scientific evidence for policymakers on the possible transmission of SARS-CoV-2 via wastewater.
WWTP processes that involve long treatment times and maximise the retention and removal of solids (for example, membrane bioreactors) may be especially effective at removing viral loads from wastewater. For resulting sludge, treatment by biodigestion, addition of lime, drying and composting is the most promising route for SARS-CoVs inactivation given the viruses’ properties. The researchers highlight low-pressure membrane filtration technology as a possible way to halt SARS-CoV-2 dissemination and remove virus particles of ~100 nm in size.
Wastewater treatment plants are seen also as a major potential source of microplastics pollution in aquatic systems, so their degradation into harmless elements is crucial. Researchers of the CLAIM project therefore propose a new methodology that uses nanocoating and light energy for microplastics degradation. Actual remediation methods include filtration, incineration and advanced oxidation processes such as ozonation, but those methods require high energy or generate unwanted by-products.