THOIRY 78 Wastewater Treatment Plant, Thoiry, Île-de-France

THOIRY 78 is a wastewater treatment facility located in Thoiry, a commune in the Yvelines department of Île-de-France, France. The plant serves a population of approximately 2,363 residents and has a designed capacity of 5,100 cubic meters per day, with an average discharge volume of 421.56 cubic meters per day. The plant employs advanced treatment processes, which go beyond the secondary treatment required by the EU Urban Waste Water Treatment Directive (91/271/EEC) for agglomerations of this size. Advanced treatment typically includes nutrient removal (nitrogen and phosphorus) to protect sensitive receiving waters. As a French facility, it operates under national regulations transposing the EU directive, with oversight from the local water agency (Agence de l'Eau Seine-Normandie). The treated effluent is discharged into the local watershed, which ultimately drains into the Seine River basin. The Seine flows through Paris and into the English Channel, supporting diverse aquatic ecosystems and providing drinking water for millions. The plant's advanced treatment helps reduce nutrient loading and protect downstream water quality.

THOIRY 78 discharges into the Seine River basin, which flows through Île-de-France and eventually reaches the English Channel. The Seine supports a variety of fish species and is an important ecological corridor. The plant's advanced treatment helps minimize nutrient pollution, which can cause eutrophication in downstream waters, including the Seine estuary and coastal marine environment.