The Water Occitanie – Water on Demand Project – Toward the Reuse of Raw Wastewaters in Urban Environments

The WOC-WOD project aims to assess the potential of direct filtration of raw wastewater for water reuse, with a particular focus on producing water in urban environments. This approach represents a major innovation compared to conventional treatment schemes, as it enables the direct treatment of raw effluents while limiting both the energy footprint and spatial requirements of treatment facilities. The first component of the project focused on the optimization of membrane systems to mitigate fouling. Initially, the effectiveness of various actuators (relaxation, backwash, aeration) was evaluated to reduce the fouling observed in this type of filtration. In parallel, the influence of the cut-off threshold (MF vs UF) and membrane material (PVDF vs PES) on fouling progression was analyzed. Next, optimal control algorithms able to deal with potential high water quality variations in load and the rapid fouling dynamics characteristic of raw effluents. These tools were applied to two different ultrafiltration processes at the Murviel-lès-Montpellier REUSE experimental site, with the objective of evaluating their ability to produce a stable water stream compatible with a number of non-potable urban uses. This integration of advanced modelling and experimental assessment formed the technological core of the project, Chaaben et al., 2025.A second component addressed micropollutants fate during filtration, a key issue for any water to be reused. Micropollutants were selected based on their occurrence in raw wastewater, their physicochemical properties influencing membrane retention (size, charge, hydrophobicity), and their regulatory relevance, including transformation products. Rather than conducting a broad screening, WOc-WoD built on previous monitoring campaigns at the experimental site, to target a representative set of about fifteen compounds and followed their behaviour within the two pilot membrane processes. Ongoing work will help determining the degree of additional treatment required to ensure the safety of the secondary water produced. Thirdly, the project incorporated a systemic impact analysis of greywater reuse, with particular attention to the level of centralisation of treatment systems and of the scale at which the reuse is to be dedicated, Besson et al., 2024. The findings show that the energy relevance of greywater recycling strongly depends on scale: highly decentralized systems (one per building) tend to require substantial energy inputs, whereas highly centralized systems (one per neighbourhood) involve significant infrastructure and network impacts. This analysis helped clarifying the conditions under which urban water reuse can be effectively combined with other complementary reuse sources, Manteaux et al., 2024. Crucially, WOc-WoD integrated an innovation in regulatory analysis, exploring the levers that could enable safe, practical deployment of treated raw wastewater reuse in urban contexts. This work maped existing legal frameworks and identified necessary adaptations (standards, monitoring requirements, acceptance pathways), Harmand et al., 2025 (in French). By combining technological innovation in the direct filtration of raw wastewater, targeted monitoring of micropollutants, multi-scale evaluation of reuse strategies and regulatory analysis, WOc-WoD proposes an integrated and operational framework for developing water reuse in urban environments.