Mordelles Wastewater Treatment Plant, Bretagne, France

The Mordelles wastewater treatment plant is located in the commune of Mordelles, part of the Rennes metropolitan area in the Bretagne region of France. The facility serves a population of approximately 5,400 residents and operates with advanced treatment processes, ensuring high-quality effluent before discharge. As an advanced treatment plant, Mordelles goes beyond the secondary treatment requirements of the EU Urban Waste Water Treatment Directive (91/271/EEC). For agglomerations of this size (5,400 population equivalent), the directive mandates secondary treatment, but the plant's advanced level indicates additional nutrient removal or polishing steps, likely to protect sensitive receiving waters in the region. The plant discharges treated wastewater into local watercourses that ultimately drain into the Vilaine River basin and then into the Atlantic Ocean. The advanced treatment helps protect downstream aquatic ecosystems, including the Vilaine River and its associated wetlands, which support diverse fish and bird populations.

The plant discharges into the Meu River, a tributary of the Vilaine River, which flows into the Atlantic Ocean via the Vilaine estuary. The Vilaine basin supports diverse aquatic life, including migratory fish species such as Atlantic salmon and European eel. Advanced treatment at Mordelles helps reduce nutrient loading, protecting downstream water quality and the ecological balance of the estuary.