Local authorities: how can you implement a permanent system of continual diagnostic analysis?
At the end of 2021, some local authorities will have to implement a permanent system of continual diagnostic analysis for their wastewater treatment...
There are well-defined protocols for detecting viruses in wastewater. But for the specific case of the SARS-CoV-2 coronavirus responsible for the Covid-19 pandemic, the member laboratories of the Obépine French national epidemiological monitoring network in many ways set the gold standard for the quality and consistency of results.
Like the gastroenteritis virus, traces of the SARS-CoV-2 coronavirus responsible for the Covid-19 pandemic can be found in the wastewater managed by your local authority and in its treatment facilities. This has been confirmed by experts on the basis of measurements taken initially from a small number of representative sites, and then from a wider population of locations.
Obépine... the wastewater analysis experts
An epidemiological observatory for wastewater was set up very soon after the health crisis broke. The Obépine working group brings researchers from public and university laboratories together with representatives of local authorities and public/private sector wastewater treatment operators.
Their remit includes monitoring 150 wastewater treatment plants selected on the basis of their geographic spread and surrounding environment to track the dynamic circulation of viruses through local authority wastewater drainage and treatment networks to detect any signs of a possible resurgence.
Those laboratories that have joined the Obépine network, which include that of the Eau de Paris water authority that serves the French capital, have developed a detailed, safe and specific methodology for detecting traces of the SARS-CoV-2 coronavirus in wastewater. This work has been carried out with the support of professional wastewater system operators, which have the most detailed knowledge of how wastewater treatments work, and the precautions to be put in place to ensure that the samples taken give meaningful results.
The SARS-CoV-2 detection methodology
How does SARS-CoV-2 detection actually work in local authority wastewater systems?
The samples are taken at the point at which inflows enter the treatment plant. This is the most efficient way of gaining an overview of the general status of the system, but only when great care is taken to sample water over a 24-hour period at a frequency proportional to the inflow rate to ensure that the sampling process is representative of the pollutant load entering the plant.
The samples must also be put into context by the plant operator. The daily flow rate and the physicochemical parameter data for water quality - such as Chemical Oxygen Demand (COD) or the presence of ammonia - are all essential information inputs that will enable the most accurate interpretation of analytical results. Samples taken on a rainy day may create the misleading impression of extremely low traces of SARS-CoV-2, whereas a discharge rich in nitrogen may also indicate abnormal pollution levels at the plant inflow point.
The samples are then loaded into refrigerated containers for transport to an appropriate laboratory. As an operator of wastewater treatment facilities for local authorities, Saur Group has made the conscious decision to work with Obépine network member laboratories to guarantee high-quality results and contribute to the volume of national data centralized by the network.
Rapid quantification of coronavirus in wastewater
After concentration by centrifuging, the expert virologists at the EAU DE PARIS laboratory extract the RNA from any viral cells present in the sample, and then amplify certain specific sequences. To be more precise, sequences of just two genes: one is common to all coronaviruses, and the other specific to SARS-CoV-2. The result is then expressed in genome units per liter. The detection limit is around 1,000 genome units per liter.
This method is fast, and the laboratory is able to return results within two working days, which are sufficiently accurate to determine whether or not the wastewater analyzed contains traces of SARS-CoV-2.
However, they cannot tell us anything about how infectious these traces may be. This requires a longer analysis using a specific protocol now under development by the experts at Obépine. The other purpose of the Obépine network is to assess the risks of wastewater contamination in local authority areas.
Although the scientific literature has yet to confirm the findings, initial results suggest that the risk of infection through this route is negligible.
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