A beady eye on our sewage
Covid-19’s implications for our wastewater service as a potential transmission pathway
ALTHOUGH infective, Sars-cov-2 has not been confirmed in raw sewage, so further transmission via a generation of virus-laden aerosols during flushing could be possible.
In this regard, the potential for a substantial viral load within the raw sewage plumbing system and main sewer system due to aerosolisation calls for plumbing systems to be considered a potential transmission pathway for Sars-cov-2.
The detection of the virus’s genetic material in raw sewage further raises concerns regarding raw sewage as a potential transmission route, particularly within the wastewater sector where raw sewage management challenges exist.
Generally, raw sewage treatment processes are designed to significantly reduce or inactivate pathogens such as bacteria, viruses and protozoa, which cause a variety of human diseases.
Inadequate treatment might mean the final effluent poses a health risk, particularly if used to irrigate agricultural fields or sports grounds, or the receiving waters are used for recreational activities or as a source of drinking water. However, to cause infection, viruses in raw sewage must retain their infectivity until they encounter the next host.
Once subjected to disinfection at a wastewater treatment works (WWTW), Sars-cov-2 and other viruses should be rendered inactive, as they are considered sensitive to disinfection methods.
In South Africa, chlorination is the widely used disinfection method. Tertiary treatment relies on chlorination followed by an optional polishing step in maturation ponds, with exposure to solar radiation further reducing pathogens in the ponds before discharge to the receiving environment.
Chlorination requires strict compliance with nutrients removal during secondary treatment to ensure the absence of chlorine-consuming components in the treated effluent.
Given that much of South Africa’s wastewater infrastructure is aged, overburdened, poorly maintained, operated and managed, resulting in inadequate treatment and disinfection at some WWTWS, there is concern regarding the potential for Sars-cov-2 transmission via raw sewage.
Even though there is no indication that WWTW workers are at risk, with existing protective protocols considered adequate, there is need to characterise the poorly understood exposure pathways for wastewater workers and the general public.
Sanitation staff, plumbers, healthcare workers and members of the public who come into contact with raw sewage or faecal matter should be aware of the potential risks.
However, despite concerns, current knowledge suggests that Sars-cov-2 is not an important waterborne pathogen, and is unlikely to be transmitted via raw sewage, as the following key aspects are considered scientific facts:
● Sars-cov-2 is sensitive to disinfectants and high temperatures.
● The new coronavirus is expected to be less abundant as an infectious virus in sewage compared to known viruses, and less stable in applied WWTW or a drinking water treatment plant.
● Drinking water systems are considered safe based on years of research and knowledge of other viruses that are more robust than Sars-cov-2.
With no epidemiological signals that sewage workers are at risk, the risk of Sars-cov-2 transmission via raw sewage is low and protective measures for the workers are adequate.
The conclusions should, however, be considered with an understanding of the wastewater sector challenges, particularly poorly maintained, offgrid sanitation systems and dysfunctional WWTW.
The monitoring of raw sewage for Sars-cov-2 fragments, as a measure of Covid-19 prevalence in communities, presents a great opportunity for the water sector to complement the health sector in fighting Covid-19.
Known as wastewater surveillance, it might provide an effective approach to predict the potential spread of the infection by testing for non-infective virus fragments in raw sewage and give information on the prevalence of Covid-19 in communities.
Monitoring the virus fragments in raw sewage presents an opportunity for an early warning system of virus circulation. The potential benefits:
● Measure the scope of the outbreak independent from patient testing or hospital reporting, including data on asymptomatic individuals.
● Provide decision support for officials determining the timing and severity of public health interventions to mitigate the overall spread.
● Better anticipate the likely impact on hospital capacity in order to inform hospital readiness and the necessity for public health interventions.
● Track the effectiveness of interventions and measure the wind-down of the outbreak; provide an early warning for re-emergence of Covid-19 if it does have a seasonal cycle.
With the Water Research Commission and its partners having launched a research programme in support of wastewater surveillance, there is a need to ensure successful surveillance is implemented. Such surveillance will ease the individual testing burden and bring the water and health sector to work together in fighting Covid-19.