The water of France’s water targets 10 % of reuse of wastewater treated by 2030. How to achieve it without increasing the amount of water consumed in total-that is to say, without risking a rebound effect? Panorama of good practices identified by scientific research.
In France, the water plan announced by the President of the Republic in 2023 displayed an objective of development of 1,000 projects to reuse “unconventional waters (ENC)” in 2027. This is an intermediate objective before targeting 10 % reuse of treated wastewater (reut) by 2030.
If he is pursued without sufficient discernment, this national quantitative objective could lead to inadequate misappropriation and projects. For example, projects that would have the consequence of increasing the overall quantity of water consumed thanks to the “rebound effect”. The risk would be to present the reut as a new resource, even though this remobilized water is likely to miss natural environments.
However, the state of scientific art and the analysis of international experiences confirm the interest of reusing water to respond to situations of strong tensions. These same experiences also demonstrate that projects are strongly conditioned by local constraints.
In other words, their success will depend on the involvement of actors, the adequacy between the required water quality and the level of technology of treatments, the economic viability of projects, etc.
Wastewater, a resource rather than waste
To help our companies to adapt to climate change and preserve our environment, controlled and responsible management is essential, both from a quantitative and qualitative point of view. This is a strategic issue to ensure supporting living conditions for everyone.
This involves in particular sobriety and optimization of uses and the sharing of the resource. Above all, we must not forget to take into account the state of aquatic environments. For example, considering the environmental role of wastewater treated in maintaining low water flows during periods of drought.
In this context, wastewater should no longer be considered as waste to be treated and evacuated, but as a resource. These waters can for example be rich in fertilizers useful for agricultural crops. In a logic of circular economy, we can consider them as value flows, depending on the territorial specificities (adequacy between the needs of cultures and available water, proximity to uses, etc.).
Domestic wastewater is the main resource that can be mobilized. However, it is necessary to widen the concept of circular water economy to all unconventional waters. For example, rainwater, swimming pool waters or water evacuated from the basement to allow the exploitation of buried works such as metros, tunnels or parking lots … This makes it possible to best balance the uses and levies on the scale of a territory.
Close the “small” and the “big” water cycle
To deal with tensions on the resource, we must therefore invent new approaches. The challenge is to rethink its use throughout the value chains. For this, one can imagine uses in loops (reusing after a previous use), where they were so far linear (mobilization, use, rejection).
This involves designing more integrated water management on the scale of a territory, which will force resources and needs. The objective is that the use cycle disrupts the “large” cycle (or natural cycle) of water as little as possible, both quantitatively and qualitatively.
The agricultural, urban or industrial context is also important. It requires examining environmental and health risks. Indeed, it is a question of modifying the water cycle. The implementation of solutions promoting short cycles can impact circles and populations on various degrees. This is particularly true in periods of severe drought.
For example, the microbiological quality of water can ask questions in indirect reuse situations. In this case, the water is not taken directly at the resort of the station (where it would then be subject to quality standards in order to be reused), but downstream, in the watercourse in which the station exit was poured. This type of withdrawal is only regulated only on quantitative, and no longer qualitative constraints.
What are the projects that lead?
The state of scientific art and the analysis of feedback from international experiences are useful for identifying the success factors of these projects.
They first take advantage of a favorable geographical context. For example, when the distance between deposits and potential uses is reasonable or hydraulic arrangements already exist.
They also organize the consultation of the various stakeholders concerned (managers, farmers, consumers, funders, etc.). The challenge is to involve them in governance to better align their respective interests.
They also set up a health and environmental risk control plan, for example by adopting a multibarric approach.
These projects would benefit from being part of a clear and harmonized regulatory and normative framework, on a scale exceeding the national framework in order to take advantage of the feedback from international experiences. With the exception of reuse for agricultural use, wastewater regulations could be improved to be better calibrated, more coherent, less complex and more listed.
Finally, these projects must mobilize balanced economic models between the stakeholders producing and beneficiaries. They should be based on an analysis on a case -by -case basis of the profitability of infrastructure, whose financing and exploitation often meet private and public actors.
Good practices to adopt
To promote the success of reut projects, it is first necessary to make responsible management of water a priority in each country of the world. This implies registering in the law of regulatory instruments of environmental policy allowing it, without weighing down and complicating current executives.
This also involves promoting preliminary measures. In particular the sobriety, optimization and in situ recycling of waters during the design and then the exploitation of infrastructure news. To minimize the anthropogenic impacts of man on the natural water cycle, it is better to reuse a cubic meter of wastewater rather than drawing it from the natural environment.
It is necessary to integrate into the analysis of profitability of the project, its impacts and health, social and environmental benefits on the whole of its life cycle, as well as the cost of global renunciation.
We could also integrate the recycling of the water taken from all the guidelines for the development and management of water. The reut can thus be integrated into territory projects for water management (PTGE) and water development and management diagrams (SAGE).
It is on this condition that we can design and plan a multi -rifle and multiusage reuse (when possible and relevant) of wastewater. This makes it possible to replace the reut for other samples from the environment or for the use of drinking water. To do this, you must systematically take into account the challenges of restoration and preservation of resources and ecosystems
This also requires rethinking calls for tenders and public service delegation contracts. It would be necessary to take into account the raison d’être and the various functions of the wastewater treatment stations, and to expand their role of “purification stations” to that of real valuation factories, when it is relevant.
Beyond the recovery of water, we can take nutrients there, such as nitrogen or phosphorus, or even produce heat. But, for this possible, it is necessary to adapt the tax instruments, the pricing methods and more broadly the economic models.
Emmanuel Dunand / AFP
Strengthening financial support for research on this issue is crucial. At various scales, we can for example cite the Water Occitanie key challenge (WOC), the Reutosud project, the Water4all financing program or the European Water4reux research network.
This also involves the creation and animation of awareness -raising, exchange of knowledge and consultation structures. These must involve national, regional and local authorities alongside other stakeholders. These interdisciplinary action research systems, called ” Living Labs », Are anchored in the territories and at the Science-Politique-Société interface. Like the Living Labsset up within the framework of the WOC already mentioned, they must facilitate the design of new tools, services or uses around water recycling.
Finally, the acculturation of the whole technical and administrative chain should be promoted. This involves the initial and continuous training of professionals, design offices, elected officials and central and territorial officials. This will allow a easier implementation of these new water management approaches, serving a circular water economy.
The following persons collaborated on this article, in alphabetical order:
Nassim Ait-Mouheb (Inrae; Water, Agriculture and Territories), Claire Albasi (University of Toulouse, Water Occitanie key challenge), Christophe Audouin (Suez), Gilles Belaud (Eacc chair; Water, Agriculture and Territories), Sami Bouarfa (Inrae; Water, Agriculture and Territories), Frédéric Bouin (University of Perpignan via Domitia, UPVD) Pierre Compère (Explicit Consulting), Ehssan El Meknassi (Costea), Jérôme Harmand (Inrae; Eau, Agriculture and Territories), Marc Heran (European Membranes Institute, Simev Chair), Barbara Howes (SCP), Marie-Christine Huau (Veolia, Department of Water Development), Vincent Kulesza (SCP; Water, Agriculture and Territories) Lombard-Latune (Inrae; Epnac; National Working Group Unconventional Water), Alain Meyssonnier (Mediterranean Institute of Water), Bruno Molle (EIA/INRAE), Simon Olivier (Aqua-Valley competitiveness center), Carmela Orea (Water, Agriculture and Territories), Céline Papin (Water, Agriculture and Territories), Nicolas Roche ( University/University Mohammed VI Polytechnic, Water, Agriculture and Territories), Stéphane Ruy (Inrae, Institut Carnot), Pierre Savey (BRL; Water, Agriculture and Territories) and Salomé Schneider (Chair EACC).
