Drought and wastewater reuse: In France, a new push and obstacles to overcome
The summer of 2022, against the backdrop of a drought, marked a turning point for the reuse of treated wastewater (REUT) in France. Until then, the issue had never been so prominent in public debate. As a reminder, this practice involves directly reusing water as it exits the wastewater treatment plant without first returning it to the natural environment.
Julie Mendret, University of Montpellier
In France, water use has been regulated since 2010 for the watering of green spaces and agricultural irrigation, which must comply by 2023 with the thresholds set by the European Union in 2020. On August 3, 2022, the European Commission published guidelines to help national authorities and affected businesses implement these new rules.
According to Virginijus Sinkevičius, Commissioner for the Environment, Fisheries, and the Ocean, “It is our duty to stop wasting water and use this resource more efficiently in order to adapt to climate change and ensure the security and sustainability of our agricultural supply. “The guidelines adopted today can help us achieve this and ensure the safe movement of food products grown with recycled water throughout the European Union.”
REUT offers numerous benefits: reduced pressure on resources that serve as the primary source for drinking water production (groundwater, waterways, etc.), improved water quality for sensitive activities (swimming, shellfish farming) due to the elimination of wastewater treatment plant discharges, and the provision of nutrients for agricultural irrigation…
A framework that remains highly restrictive
In March 2022, a new decree regarding the uses and conditions for the reuse of treated wastewater was issued in France: in addition to agricultural irrigation and the watering of green spaces, the decree now includes urban uses such as street cleaning, pipeline cleaning (hydrocleaning), and firefighting…
However, this decree prohibits their use for food-related purposes, personal hygiene and laundry, recreational purposes (swimming pools, fountains, etc.), as well as indoor use in public facilities (healthcare facilities, senior care facilities, daycare centers, schools, etc.) and residential premises.
The use of treated wastewater will require a prefectural permit valid for a maximum of five years for use within the department where it is produced. However, there is concern that the rather limited scope of application and the administrative burdens may discourage project proponents.
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Local context to consider
Despite the undeniable advantages mentioned above, wastewater reuse is not the only solution to water shortages; it is, above all, a solution that depends on local conditions and must therefore be taken into account when local authorities plan their water management strategies.
For example, it is particularly relevant in coastal areas where some wastewater treatment plants discharge their effluent into the sea, which constitutes a loss of freshwater. By implementing REUT, a circular water economy is established, with secondary benefits including a reduction in groundwater withdrawals—which are more vulnerable when water levels are low and the aquifers are subject to saltwater intrusion that can render them unfit for consumption – and improved water quality in bathing areas or shellfish farming sites.
A prime example is now the Jourdain project in Les Sables-d’Olonne, where treated wastewater will eventually be directly diluted into the water at a intake point for purification.
In inland areas, however, effluent from wastewater treatment plants sometimes plays a significant role in maintaining low-flow conditions—that is, in sustaining the minimum flow necessary for the proper functioning of aquatic ecosystems—and in such cases, reusing treated wastewater is less beneficial and may even have a negative environmental impact.
A New Start After the Drought
While there are currently around 80 stations using REUT in France, the drought experienced during the summer of 2022 could encourage the further adoption of this method, which is already widely used in some countries.
In a press release dated July 25, 2022, Veolia announced its intention to deploy REUT at approximately 100 wastewater treatment plants where consumption volumes warrant it (consumption of more than 2,000m³ of drinking water and/or 5,000m³ drawn directly from the water source), using compact water recycling units.
This initiative is expected to save 3 millioncubic meters of drinking water—equivalent to the average annual consumption of a city with 180,000 residents. Initially, the recycled water will be used for plant maintenance, with plans to explore other urban or agricultural uses once the necessary permits are obtained.
Acceptability, model, pathogens: concerns that need to be addressed
However, there are still many obstacles to overcome. One of these is the social acceptance of this practice, which is often misunderstood and subject to prejudice on the part of the general public.
Another major obstacle is that REUT will need to establish a viable business model, which will likely require financial incentives to compete with river water, which farmers obtain at a price of around 10 to 30 euro cents percubic meter.
Even after wastewater treatment, certain salts, mineral and organic pollutants, and pathogenic microorganisms may still be present. The extent of the associated negative impacts on ecosystems and human health depends heavily on soil characteristics, vegetation, the quality of the treated wastewater, and agricultural practices.
It is therefore important that REUT remains well regulated to ensure it remains a safe and sustainable practice. This will require not only meeting the established thresholds but also implementing other processes, such as drip irrigation rather than sprinkler irrigation.
The need to address pollutants
As the sector undergoes rapid change, there is a clear need for scientific studies on the fate of pollutants, viruses, and parasites during agricultural irrigation using treated wastewater.
In Israel, where REUT has been practiced since the 1980s and is now used in about 80% of cases, a study has shown that pharmaceutical compounds are found primarily in the soil, leaves, and roots of plants irrigated with treated wastewater, while fruits and tubers are less contaminated.
This study concludes that it is beneficial to improve treatment processes designed for REUT and to apply them to soils rich in organic matter, which promotes the degradation of pollutants.
In France, the successful example of the Limagne Noire region—where cereal crops have been irrigated with treated wastewater from the city of Clermont-Ferrand for several decades—has shown that there is no contamination from pathogens.
Issues related to human health
Recently, in Murviel-les-Montpellier, a two-year experiment was conducted under greenhouse conditions to test the drip irrigation of lettuce and leek crops using treated municipal wastewater, both with and without the addition of fourteen contaminants at a concentration of 10 μg/L.
The objective was to study their accumulation in soil and leaves in order to assess potential health risks. The results revealed limited accumulation of contaminants in soil and plant leaves, with concentration levels ranging from 1 to 30 ng/g and 1 to 660 ng/g, respectively.
Overall, this study confirmed previous reports that the risk to human health from consuming raw leafy green vegetables irrigated with treated domestic wastewater containing residues of organic contaminants is minimal.
Thus, while REUT will need to overcome resistance and address certain concerns, it nonetheless appears to be a forward-looking solution to current challenges, and its importance is further underscored by the effects of climate change.
Julie Mendret, Associate Professor, HDR, University of Montpellier
This article is republished from The Conversation under a Creative Commons license. Readthe original article.