Savings in dribs and drabs
Irrigate crops with wastewater? Installing connected water meters for farmers? These are just some of the avenues that researchers are exploring to preserve water resources, of which the agricultural sector is a major consumer.
Turn off the tap when brushing your teeth. Limit the time spent in the shower. So many everyday gestures to reduce our water consumption. Good, but clearly insufficient on a global scale, especially when you consider that 50% of the water consumed in France is used by the agricultural sector. This figure rises to 70% worldwide.
"It's a major challenge, because irrigation needs are increasing with global warming, particularly as we move northwards, where we now have to irrigate certain crops that until now could do without it," explains Nassim Ait-Mouheb*. Everywhere, the need to irrigate is being felt earlier in the year, and is affecting more and more crops. " This is particularly true of vines, for which irrigation is now authorized in France", explains the researcher, a specialist in fluid mechanics and process engineering applied to irrigation techniques.
And it's precisely this ingenious process that he's implementing to help reduce pressure on the blue gold resource: the reuse of treated wastewater. The idea is simple: to use non-potable wastewater from treatment plants to irrigate crops, thereby reserving good-quality water for consumption. "It's a way of avoiding conflicts of use in a context where resources are likely to be limited.
While the alternative is an interesting one, its implementation represents a real challenge, and one that the researcher from the G-EAU laboratory has tackled. Technological challenge, agronomic aspect, health issues, social acceptance... the reuse of wastewater for agriculture raises many questions.
To answer this question, Nassim Ait-Mouheb has a full-scale laboratory at his disposal. A small plot of vines, olive trees and fruit trees nestled in Murviel-Lès-Montpellier, which hosts an experimental platform for the reuse of treated wastewater in drip irrigation. " A system of pipes that run along the ground with drippers is an increasingly popular technique that can save water, provided it is properly implemented and its efficiency and durability are ensured, in particular by avoiding the risk of biofilm clogging". In other words, the risk that all these devices will become clogged with clumps of bacteria or other micro-organisms that populate wastewater...
Thanks to this unique platform in France, set up in 2017, researchers can test the effects of this type of irrigation in real-life conditions: "We have an agricultural plot and an experimental field with above-ground tanks where we can irrigate crops either with wastewater that has not passed through the treatment plant, or with clear water," explains Nassim Ait-Mouheb. The aim is to observe the effects of water quality on crops, from both an agronomic and a sanitary point of view.
From an agronomic point of view, the surprise is rather pleasant: "We obtain good yields thanks to nutrients such as nitrogen, phosphorus and potassium, which are naturally found in wastewater", explains the specialist. From a health standpoint, researchers scrutinize salads and leeks for antibiotic residues, Escherichia Coli and enterococci. " Pathogen indicators are a key point in our studies", explains Nassim Ait-Mouheb. Another parameter to be taken into account: the effects of irrigation with wastewater on soils, "which can be problematic due to its salinity, which ultimately risks altering soil quality". "The reuse of wastewater represents an interesting lever for reducing water consumption in the agricultural sector, but a number of drawbacks need to be taken into account before we can move from theory to practice. At Murviel-les-Montpellier, these drawbacks are being tackled head-on, to make reuse a solution for the future. Currently in France, less than 5% of treated wastewater is reused, and for very limited purposes.
To reduce their water consumption, some farmers have adopted a smart meter. What makes it special? It gives them real-time information on their withdrawals, so they can better manage their watering and facilitate water sharing on a common network. Another advantage: these meters provide water managers with frequent, precise measurements of consumption. This data is invaluable for regulating hydraulic structures and optimizing water releases from reservoirs. To be effective, a sufficient number of farmers need to opt for this system," explains Raphaële Préget. But today, only a minority of farmers are equipped.
How can they be encouraged to adopt a smart meter? This was the question posed by a researcher at CEE-M**(Montpellier Centre for Environmental Economics) as part of the C4EAU project. " We interviewed 1,272 farmers to test different incentive mechanisms". Among the instruments tested and approved was a conditional subsidy "which would be paid to farmers if, and only if, a certain number of them adopted the smart meter. It' s a way of launching a collective dynamic of change by playing on social norms", explains Raphaële Préget.
As part of these behavioral economics approaches, the researchers also tested various "nudges", or "non-monetary incentives that aim to guide choices without constraining them", explains the researcher. An example of a nudge ? We shared with them a testimonial from a farmer who has been fitted out with smart meters, extolling their benefits." Effective incentive tools, to move towards greater cooperation, essential to the management of a common resource.
* G-EAU (CIRAD - AgroParisTech - IRD - INRAE - Institut Agro)
** CEE-M ((UM - CNRS - INRAE - Institut Agro)
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