Aunay-sur-Odon Wastewater Treatment Plant, Les Monts d'Aunay, Normandy

The Aunay-sur-Odon wastewater treatment plant is located in Les Monts d'Aunay, within the Calvados department of Normandy, France. It serves a population of approximately 3,020 people, classifying it as a small agglomeration under French and EU regulations. The plant is situated inland, more than 10 km from the coast, and its operations are part of the regional water management infrastructure. The facility employs advanced treatment processes, which go beyond the secondary treatment standard required by the EU Urban Waste Water Treatment Directive (91/271/EEC) for agglomerations of this size. The plant has a designed capacity of 5,000 cubic meters per day and currently treats an average daily flow of 538.76 cubic meters, indicating significant spare capacity. As a French facility, it operates under national regulations that transpose EU directives, with permits issued by the local water agency (Agence de l'Eau). The treated effluent is discharged into the local watershed, which ultimately drains into the English Channel via the Odon River and the Orne River. The plant plays a key role in protecting the water quality of these rivers and the downstream coastal environment. Advanced treatment helps reduce nutrient loads, supporting aquatic life and preventing eutrophication in sensitive estuarine and marine areas.

The plant discharges into the Odon River, a tributary of the Orne River, which flows into the Baie de Seine and the English Channel. This watershed supports diverse aquatic habitats, including fish spawning grounds and migratory corridors for species such as Atlantic salmon. The advanced treatment level helps minimize nutrient and pollutant loads, protecting downstream ecosystems from eutrophication and maintaining water quality for recreational and ecological uses.