Treated wastewater reuse (TWWR) to irrigate crops is a relevant local solution for saving water and conserving its quality, maximizing nutrient levels for agricultural purposes, and conserving the environment. However, the practice is still not widely used in France. Irstea is carrying out field experiments and evaluating the feasibility and impact of using treated wastewater for irrigation.
Treated wastewater is taken from domestic, industrial and agricultural output and usually needs to be purified before it can be reused. Nevertheless, using it for irrigation would ease the pressure on water resources. Although TWWR is a promising solution, it also presents regulatory, health, environmental and technical challenges. As an expert in the field, Irstea is exploring solutions to encourage the development of safe and viable projects and to help develop legislation.
A full scale agricultural experiment
There isn’t enough research data yet to understand the mechanisms and impacts of TWWR practices. Can bacterial pathogens survive and become concentrated on plants? What is the long-term effect on soil quality? Can the longevity of irrigation systems be maintained despite contact with wastewater? Given these scientific obstacles, regulations are currently restrictive and can prevent projects from being adopted. “The Treated Wastewater Reuse for Irrigation Experimental Platform Project, funded by the RMC Water Agency,1 hopes to remove these obstacles, direct public policy and local decision-making processes,” explains Nassim Ait Mouheb, project coordinator and researcher at Irstea Montpellier. To achieve this, Irstea has been using a platform comprising an irrigated plot of 0.5 hectares in Murviel-lès-Montpellier (Hérault) since 2017, growing vines, alfalfa and fruit trees. Treated wastewater is sourced from the neighboring wastewater treatment plant and used to irrigate part of the plot. Lettuce and leeks grown in raised beds under glass are also being analyzed, using non-regulation wastewater. Through field experiments performed in partnership with farmers, the platform is also being used to evaluate the feasibility and farming, health and environmental impact of a TWWR sector.
Resolving identified technical problems
Coordinated by Irstea, the project at Murviel focuses on the various obstacles facing TWWR and aims to offer specific solutions to develop the sector. A key component of the project is to adapt treatment processes for wastewater, as requirements vary in relation to its use. “The idea is to use a membrane bioreactor during irrigation periods as this meets sanitary requirements while allowing nutrients to pass through for the plants,” describes Ait Mouheb. During non-irrigation periods, such as in winter, water is discharged directly to the environment and is subject to wastewater treatment plant regulations that are less restrictive in terms of presence of pathogens. The aim is to provide treatments ‘on demand’ depending on the season and uses.” Another part of the project is focusing on controlling health and environmental risks as well as agricultural yields. “We are monitoring soil salinity, an important issue that needs to be addressed in relation to treated wastewater as this contains greater amounts of salt. In partnership with regional research institutes, we are also measuring levels of pathogens and emerging pollutants, through the irrigation systems and onto the plants. We are looking to see if these contaminants are internalized at any point and how this affects soil and plants. Finally, we are also measuring the impact of this type of irrigation on farming yields,’” continues Ait Mouheb. Scientists are also working to optimize localized irrigation systems as wastewater is particularly rich in nutrients, which can cause blockages due to bacterial growth (biofilms).
A promising solution for farmers facing water shortages
Given the climate forecasts for the Mediterranean basin consisting of more intense and frequent droughts, increasing temperatures and changes in rainfall patterns,2 it is important to explore solutions to improve the resilience of these regions, including recovering wastewater. For the municipality of Murviel-lès-Montpellier, access to water will soon determine whether farming can continue in the area. Global warming means this situation could become more common. “Many farmers are aware that they will have to find new sources of water, as the resource becomes increasingly rare. For now, they are using groundwater or bringing in water from elsewhere. TWWR provides an alternative local solution,” explains Jean-Claude Mailhol, former research director at Irstea now working in the agricultural sector and managing the plots of the Murviel platform. “Additionally, the town of Murviel is rethinking the future of vine-growing in a context of global warming and fully supports the project.”
The Irstea platform is therefore an integral part of this thought process and could become a driver for innovation in the field: “The platform aims to become viable and could become a TWWR-based experimental farming center that brings together research organizations and is attractive to businesses,” concludes Ait Mouheb.
Find out more
- Feature. Treating and reusing wastewater
- Article. Different perspectives enhance research into reuse
- Article. Reuse and private sanitation: a winning combination
- Article. Use conflicts: using role-play to support public authorities
- Consult the web page of the Water Management, People and Uses (G-EAU) unit at the Irstea Montpellier Center