LE MESNIL SAINT DENIS Wastewater Treatment Plant, Élancourt, France

LE MESNIL SAINT DENIS is a wastewater treatment plant located in Élancourt, within the Île-de-France region of France. The facility serves a population of approximately 13,826, placing it in the medium agglomeration category under European Union regulations. The plant is situated in a suburban area near the Rambouillet forest, contributing to the region's water management infrastructure. As a French treatment plant, it operates under the EU Urban Waste Water Treatment Directive (91/271/EEC), which mandates secondary treatment for agglomerations of this size. The directive also requires appropriate treatment to protect sensitive areas, which may include nutrient removal if the receiving waters are designated as sensitive. Compliance with national and EU standards is expected. The treated effluent from the plant is discharged into local watercourses that eventually flow into the Seine River basin. The Seine River drains into the English Channel, supporting diverse aquatic ecosystems and providing water for agriculture, industry, and recreation. The plant plays a key role in protecting downstream water quality and the ecological health of the Seine watershed.

The plant discharges into local streams that are part of the Seine River basin, which flows through Paris and into the English Channel. The Seine watershed supports a variety of aquatic life and is an important ecological corridor in northern France. Downstream areas include sensitive estuarine and coastal habitats that benefit from effective wastewater treatment to reduce nutrient and pollutant loads.