Drought and wastewater reuse: in France, new impetus 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 now, the subject had never been so prominent in public debate. As a reminder, this practice consists of reusing water directly from wastewater treatment plants, without returning it to the natural environment.

Julie Mendret, University of Montpellier

AdobeStock_219747651 ©kaliantye - stock.adobe.com

In France, it 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 companies apply the new rules.

According to Virginijus Sinkevičius, Commissioner for the Environment, Fisheries and Oceans, "it is our duty to stop wasting water and use this resource more efficiently 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 circulation throughout the European Union of food products grown with recycled water".

The benefits of WASTE water treatment are numerous: reduced pressure on resources that represent the main reservoir for drinking water production (groundwater, rivers, etc.), improved water quality for sensitive activities (swimming, shellfish farming) due to the elimination of wastewater treatment plant discharges, contribution 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 road cleaning, network cleaning (hydrocurage) or fire-fighting have now been added...

However, the decree excludes them from use for food purposes, personal hygiene, linen care, pleasure purposes (swimming pools, fountains, etc.), as well as indoor use in establishments open to the public (healthcare establishments, homes for the elderly, crèches, schools, etc.) and residential premises.

The use of treated wastewater will require a prefectoral authorization limited to a maximum of five years for use in the département where it is produced. It is to be feared, however, that the rather limited scope of application and cumbersome administrative procedures may discourage project developers.

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A local context to take into account

Despite its undeniable advantages, wastewater reuse is not the only solution to water scarcity. It is first and foremost a solution that depends on the local context, and therefore needs to be taken into account by local authorities when planning resource management.

It is particularly relevant in coastal areas, for example, where some wastewater treatment plants discharge their effluent into the sea, thereby wasting freshwater. In this way, a circular water economy is created, with the secondary benefits of reducing groundwater abstraction - which is more vulnerable when groundwater levels are low and subject to saltwater penetration, making it unfit for consumption - and improving water quality in bathing and shellfish-growing areas.

An emblematic example is the Jourdain project in Les Sables-d'Olonne, where treated wastewater will eventually be diluted directly into the water at a catchment point for potabilization.

In continental areas, on the other hand, wastewater treatment plant discharges sometimes play a significant role in supporting low-water levels - i.e., maintaining the minimum flow necessary for the proper functioning of aquatic ecosystems - and WASER is of less interest in this case, and could even have a negative environmental impact.

Fresh impetus after the drought

While there are currently around 80 WWTPs in France, the drought in the summer of 2022 may well encourage the development of this method, which is already widespread in some countries.

In a press release dated July 25, 2022, Veolia announced its intention to deploy LWR at around one hundred 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), via compact water recycling units.

The project is expected to save 3 millionm3 of drinking water, equivalent to the average annual consumption of a town with a population of 180,000. Initially, the recycled water will be used for plant maintenance, before other urban or agricultural uses are tested, subject to obtaining the necessary permits.

Acceptability, model, pathogens: concerns to be addressed

However, there are still many obstacles to overcome. One of them is the social acceptability of this practice, which is often misunderstood and subject to preconceived ideas on the part of the general public.

Another major obstacle is that WASW will have to find its own economic model, which will certainly require financial incentives to compete with river water, which farmers draw off at a price of around 10 to 30 centimes perm3.

After wastewater treatment, the presence of certain salts, mineral and organic pollutants and pathogenic micro-organisms is still possible. The extent of the associated negative impacts on ecosystems and human health is highly dependent on the characteristics of the soil, plants and the quality of the treated wastewater, as well as on agricultural practices.

It is therefore important to ensure that REUT remains a safe and sustainable practice. This will entail not only meeting set thresholds, but also implementing other processes, such as drip rather than sprinkler irrigation.

The need to work on pollutants

At a time when the sector is undergoing rapid change, there is a need for 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 all wastewater discharges, 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 would be advisable to improve treatment systems dedicated to LWR and to use them on soils rich in organic matter, which favors 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 revealed an absence of pathogen contamination.

Challenges for human health

Recently, in Murviel-les-Montpellier, a two-year experiment of 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 was carried out under greenhouse growing conditions.

The aim 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 in the range 1-30 ng/g and 1-660 ng/g respectively.

Overall, this study confirmed earlier reports of minimal risk to human health from the consumption of raw leafy green vegetables irrigated with treated domestic wastewater containing organic contaminant residues.

So, while REUT will have to overcome reluctance and overcome 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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