MERVILLE_31 Wastewater Treatment Plant, Merville, Occitanie, France

MERVILLE_31 is a municipal wastewater treatment plant located in Merville, a commune in the Haute-Garonne department of the Occitanie region in southern France. The plant serves a population of around 2,831 residents and is situated near the city of Toulouse. It operates under the regulatory framework of the European Union's Urban Waste Water Treatment Directive (91/271/EEC), which sets standards for collection and treatment of wastewater in agglomerations. The plant provides secondary treatment, a standard level required for agglomerations of this size under the EU directive. With a designed capacity of 7,000 m³/day and an actual discharge volume of 505.05 m³/day, the facility operates well below its capacity, indicating room for future growth or seasonal variations. Secondary treatment typically involves biological processes to reduce organic matter and suspended solids. The treated effluent is discharged into the local watershed, which ultimately drains into the Garonne River via smaller tributaries. The Garonne flows through Toulouse and continues to the Gironde estuary on the Atlantic coast. The plant plays a key role in protecting the water quality of the Garonne basin, supporting aquatic life and downstream uses such as agriculture and recreation.

The plant discharges into the Garonne River basin, which flows through the Occitanie region and empties into the Gironde estuary on the Atlantic coast. The Garonne supports diverse aquatic ecosystems, including migratory fish species such as salmon and eels. Secondary treatment helps reduce nutrient loads that could otherwise contribute to eutrophication in the estuary and coastal waters.