ST MAXIMIN Wastewater Treatment Plant, Saint-Leu-d'Esserent, Hauts-de-France

ST MAXIMIN is a wastewater treatment plant located in Saint-Leu-d'Esserent, within the Oise department of Hauts-de-France, France. The facility serves a population of approximately 3,000 residents and has a designed capacity of 5,000 m³ per day, with a current discharge volume of 535.19 m³/day. The plant employs advanced treatment processes, which go beyond the secondary treatment requirements of the EU Urban Waste Water Treatment Directive (91/271/EEC). For small agglomerations under 10,000 population equivalent, the directive mandates appropriate treatment, and France's national regulations often require advanced treatment in sensitive areas to protect water quality. The treated effluent is discharged into the Oise River, a major tributary of the Seine, which flows through the Paris Basin and eventually reaches the English Channel. The plant plays a key role in protecting the Oise River ecosystem, which supports diverse aquatic life and is used for recreation and drinking water abstraction downstream.

The plant discharges into the Oise River, which flows into the Seine River and ultimately the English Channel. The Oise River basin supports a variety of fish species and is an important ecological corridor. The advanced treatment helps reduce nutrient loading, protecting the river from eutrophication and maintaining water quality for downstream communities and habitats.