TREILLIERES Les Haies Wastewater Treatment Plant, La Ménardais, France

TREILLIERES Les Haies is an advanced wastewater treatment plant located in La Ménardais, Treillières, within the Loire-Atlantique department of Pays de la Loire, France. The plant serves a population of around 4,583, classifying it as a small to medium agglomeration under French and EU regulations. As an advanced treatment facility, it goes beyond secondary biological treatment to remove nutrients such as nitrogen and phosphorus, which is typical for plants discharging into sensitive areas. The plant has a designed capacity of 8,400 m³/day and a reported discharge volume of 817.60 m³/day, indicating it operates well below its maximum capacity. Under the EU Urban Waste Water Treatment Directive (91/271/EEC), such plants must meet stringent effluent quality standards. The treated wastewater is discharged into the local watershed, which ultimately drains into the Loire River and then into the Atlantic Ocean. The plant plays a crucial role in protecting the Loire estuary and downstream marine environment from nutrient pollution and organic loads.

The plant discharges into the Loire River basin, which flows through western France into the Bay of Biscay (Atlantic Ocean). The Loire estuary is a dynamic ecosystem supporting diverse aquatic life, including migratory fish species. Advanced treatment helps reduce eutrophication risks in the estuary and coastal waters, which are sensitive to nutrient enrichment from agricultural and urban runoff.