SAINTE PAZANNE Herpiniere Wastewater Treatment Plant, Saint-Mars-de-Coutais, France

The SAINTE PAZANNE Herpiniere wastewater treatment plant is located in Saint-Mars-de-Coutais, within the Pays de la Loire region of western France. This facility serves a population of approximately 3,883 residents, classifying it as a small agglomeration under the EU Urban Waste Water Treatment Directive (UWWTD). The plant is situated inland, more than 10 km from the coast, and treats wastewater from the local community. The plant employs advanced treatment processes, which go beyond the secondary treatment standard required by the EU UWWTD for agglomerations of this size. Advanced treatment typically includes nutrient removal (nitrogen and phosphorus) to protect sensitive receiving waters. The designed capacity is 7,000 m³/day, with a current discharge volume of 692.72 m³/day, indicating ample reserve capacity. As a French facility, it operates under national regulations transposing the EU UWWTD, 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 Loire River estuary and the Bay of Biscay. The Pays de la Loire region features a mix of agricultural and natural landscapes, and the plant's advanced treatment helps protect downstream water quality in the Loire basin, a major European river system supporting diverse aquatic life and migratory fish species.

The plant discharges into the local watershed that feeds the Loire River, one of France's longest rivers, which flows into the Bay of Biscay on the Atlantic coast. The Loire estuary is a dynamic ecosystem supporting diverse aquatic life, including migratory fish such as Atlantic salmon and European eel. The advanced treatment at this plant reduces nutrient loads, helping to mitigate eutrophication risks in the downstream river and coastal waters.