Drought and wastewater reuse: in France, new momentum and obstacles to overcome
The summer of 2022, with its drought conditions, marked a turning point for the reuse of treated wastewater (REUT) in France. Until then, the subject had never been so prominent in public debate. As a reminder, this practice consists of directly reusing water from wastewater treatment plants without returning it to the natural environment.
Julie Mendret, University of Montpellier
In France, it has been regulated since 2010 for watering green spaces and agricultural irrigation, which must comply with the thresholds set by the European Union in 2020 by 2023. On August 3, 2022, the European Commission published guidelines to help national authorities and affected companies apply these new rules.
According to Virginijus Sinkevičius, Commissioner for Environment, Fisheries, and Oceans, "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 advantages: reduced pressure on resources that represent the main reservoir for drinking water production (aquifers, waterways, etc.), improved water quality for sensitive activities (swimming, shellfish farming) due to the elimination of wastewater treatment plant discharges, provision of nutrients for agricultural irrigation, etc.
A still very restrictive framework
In March 2022, a new decree on the uses and conditions for reusing treated wastewater was published in France: in addition to agricultural irrigation and green spaces, urban uses such as street cleaning, network cleaning (hydrocleaning), and firefighting have been added.
However, this decree excludes its use for food, personal hygiene, laundry, recreational purposes (swimming pools, fountains, etc.), as well as indoor use in establishments open to the public (health facilities, nursing homes, daycare centers, schools, etc.) and residential premises.
The use of treated wastewater will require a prefectural authorization limited to a maximum of five years for use in the department where it is produced. However, there is concern that the rather limited scope of application and administrative burdens may discourage project developers.
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Local context to consider
Despite its undeniable advantages mentioned above, wastewater reuse is not the only solution to overcome water shortages. Above all, it is a solution that depends on the local context and must therefore be taken into account when local authorities plan their resource management.
It is particularly relevant in coastal areas where some wastewater treatment plants discharge their effluent into the sea, resulting in a loss of fresh water. By practicing REUT, a circular water economy is created, with secondary benefits including a reduction in groundwater extraction—which is more vulnerable when levels are low and subject to saltwater intrusion, which can render it unfit for consumption – and improved water quality in bathing areas and shellfish farming areas.
A prime example of this is now the Jourdain project in Les Sables-d'Olonne, where treated wastewater will eventually be diluted directly into water from a collection point for purification.
In continental areas, however, wastewater treatment plant discharges sometimes play a significant role in supporting low water levels—i.e., maintaining the minimum flow necessary for aquatic ecosystems to function properly—and REUT is less beneficial in this case and could even have a negative environmental impact.
New momentum after the drought
While around 80 stations currently practice REUT in France, the drought experienced during the summer of 2022 could encourage the development of this method, which is already widely used in certain countries.
In a press release dated July 25, 2022, Veolia announced its intention to deploy REUT in around 100 wastewater treatment plants where consumption volumes justify it (consumption of more than 2,000m³ of drinking water and/or 5,000m³ taken directly from the resource), using compact water recycling units.
This operation should save 3 millioncubic meters of drinking water, equivalent to the average annual consumption of a city with 180,000 inhabitants. Initially, the recycled water will be used for station maintenance before being tested for other urban or agricultural uses, subject to obtaining the necessary authorizations.
Acceptability, model, pathogens: concerns to be addressed
However, there are still many obstacles to overcome. One of these is the social acceptability of this practice, which is often misunderstood and subject to preconceptions on the part of the general public.
Another significant obstacle is that REUT will have to find its economic model, which will certainly require financial incentives in order to compete with river water, which farmers draw at a price of around 10 to 30 euro cents percubic meter.
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, plants, the quality of the treated wastewater, and agricultural practices.
It is therefore important that REUT remains well regulated in order to ensure it is a safe and sustainable practice. This will involve meeting the thresholds set, but also implementing other processes, such as drip irrigation rather than sprinkler irrigation.
The need to address pollutants
As the sector is undergoing rapid change, it appears necessary to conduct scientific studies on the fate of pollutants, viruses, and parasites during agricultural irrigation with treated wastewater.
In Israel, where REUT has been practiced since the 1980s and now accounts for around 80% of wastewater treatment, a study has shown that pharmaceutical molecules are mainly found in the soil, leaves, and roots of plants irrigated with treated wastewater, with fruits and tubers being less contaminated.
This study concludes that it is beneficial to improve treatment processes dedicated to REUT and to use them on soils rich in organic matter that promote the degradation of pollutants.
In France, the successful example of Limagne Noire, where cereal crops have been irrigated with treated wastewater from the city of Clermont-Ferrand for several decades, has revealed no contamination linked to pathogens.
Issues for human health
Recently, in Murviel-les-Montpellier, a two-year experiment was conducted on drip irrigation of lettuce and leek crops with municipal wastewater treated without and with the addition of fourteen contaminants at a concentration level of 10 μg/L under greenhouse growing conditions.
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 1-30 ng/g and 1-660 ng/g, respectively.
Overall, this study confirmed previous reports on the minimal risk to human health associated with the consumption of raw leafy greens irrigated with treated domestic wastewater containing residual organic contaminants.
Thus, while REUT will have to overcome reluctance and dispel certain fears, it nevertheless appears to be a solution for the future in the face of current challenges, and its usefulness is exacerbated by the effects of climate change.
Julie Mendret, Senior Lecturer, HDR, University of Montpellier
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