Are French consumers prepared to eat products irrigated with treated wastewater?

1.    Few projects reusing treated wastewater for agricultural irrigation are appearing in France. What are the obstacles?

B. M.: “Currently, the main obstacle is regulatory, linked to a lack of data relating to the effects of these practices on the environment and crops. Many questions surround the survival, dispersal and deposit of pathogenic bacteria on plants depending on the application methods. For spray irrigation, it is difficult to identify which pathogens contained in the water are capable of surviving in the air. This is the subject of a dissertation starting in 2018 and co-supervised by Irstea, Inra and Anses. Because of these scientific barriers, regulations err on the side of caution to impose distance constraints that seem particularly restrictive. To use sprayers with a 20m range, you would have to keep a 40m buffer between sprayed crops and any sensitive areas. This type of regulation can limit the adoption of projects.”

2.    Given the low water levels recorded in the Rhone Mediterranean basin (40% of the basin area) that have affected agricultural activities[2], and given the nitrogen and phosphorous pollution levels in aquatic environments, the RMC water agency has launched a call for projects entitled “Reusing treated wastewater“. What aims and approaches is Irstea using for the project in which it is participating?

 B. M.: “The point of this call for projects is to find answers to outstanding technical issues, in order to develop best practices for reusing water and, eventually, to offer suggestions to change the legislation. A whole series of experimental research and on-site demonstration approaches lie at the heart of the 6 complementary projects involving Irstea[3]. These are and will be implemented by teams in Montpellier and Lyon to study different aspects of this solution. One approach is looking at the sustainability of irrigation systems, which involves understanding how a system will withstand this type of water, which is particularly nutritious and may lead to bacterial biofilm blockages (Murviel-Les-Montpellier and Read'Apt projects). In terms of treatment, extensive methods based on new generation forced bed aeration reed filters are currently being evaluated (Murviel and Rur'Eaux). Initial experiments have shown that the pathogen rate, the main problem for planted filters, decreases due to the aeration. Other studies are focusing on the impact of reusing treated wastewater on crop output and the potential transfer of contaminants to the soil and plants (Murviel and Read'Apt). The demand for REUT, as well as the attitude of decision makers, users and consumers are also being assessed through modeling processes and consultation methods based on participatory tools, in a collaboration between sociology and economics (SoPoLo and Read'Apt). 

3.    Managing health and environmental risks is essential. Specifically, what types of experiments are ongoing to monitor micropollutants and pathogens?

 B. M.: “Irstea is coordinating the implementation and monitoring of an experimental platform for the reuse of treated wastewater through subsurface drip irrigation, in Murviel-Les-Montpellier. As part of this project, launched in July 2017, tests are being performed in the field as well as under controlled conditions in off-ground tanks to assess the transfer and storage of micropollutants[4], with the aim of evaluating the contamination risks. In order to analyze the dispersal of pathogens, we will use a characterization method developed during a previous project, in order to determine the proportion of surviving pathogenic bacteria in the atmosphere that originate directly from the EUT. At the same time, in partnership with students from the Dignes IUT and Narbonne Inra, we are carrying out experiments on plants sprayed with indicative pathogens to better understand their survival under various conditions.”

4.    Are French consumers prepared to eat products irrigated with treated wastewater?

P. G.: “There is a clear difference between the intention to consume these products and the reality. This was highlighted by an experiment carried out as part of the SoPoLo project, with two groups of people aware of REUT practices[5]. A survey of their intentions followed by a taste test showed that although both groups were predominantly accepting, depending on the product, between 5 and 30% of people refused to eat them. This is primarily linked to a lack of confidence in the management of treated wastewater, with greater reluctance in relation to products that come into direct contact with the water, such as salads. As part of the SoPoLo project, consumer opinions and expectations were evaluated alongside those of elected representatives and farmers in France to ensure these uncertainties were better represented in any analysis of opportunity for REUT projects.”

B. M.:“In addition, communication and media influence, as well as people's perceptions of any future REUT projects are being assessed as part of the Read'Apt project and of a CIFRE PhD led by Benjamin Noury in partnership with the Canal de Provence[6]. The aim is to improve our understanding of questions and potential obstacles using co-construction approaches to the subject, in order to provide specific answers to the discussions."  

Beyond irrigation for crops and green spaces, Irstea researchers are, in partnership with Ecofilae and the town of Cannes, looking at a wider REUT system. Why not reinject this water into a wetland to feed into a river, or use it in ship cleaning systems? These are ideas for future study, to encourage progress in the reuse of treated wastewater in urban areas.

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[2]Many agricultural parcels were abandoned in the region due to a lack of water

[3]Irstea is involved in 6 ongoing and future projects within the context of the RMC Agency call for projects: Murviel-Les-Montpellier, SoPoLo, Read'Apt (2017 - 2020), Rur'Eaux (2018-2021), Lama (2018-2019), and a project with the town of Cannes (2018-2021). These projects involve the G-eau unit at the Irstea Montpellier Center and the RiverLy unit at the Irstea Lyon Center

[4]From a list of 5 emerging contaminants, with various physical-chemical properties

[5]71 students on the M1 Masters in Water at Montpellier University and 20 members of the project pilot committee. Source: A. Gaillagot, 2017. What are consumers attitudes to products from crops irrigated with Treated Wastewater? Dissertation for a Masters in Water, specializing in “Water and Society”. Montpellier University, AgroParisTech, SupAgro Montpellier, co-supervised by Patrice Garin and Marielle Montginoul, researchers at Irstea

[6]Dissertation title «Social conditions surrounding the implementation of a REUT project