Saint Martin du Tertre Wastewater Treatment Plant, Presles, Val-d'Oise, France

The Saint Martin du Tertre wastewater treatment plant is located in Presles, a commune in the Val-d'Oise department of northern France, within the Île-de-France region. The plant serves a population of approximately 2,666 residents and 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 biological process that removes organic matter and suspended solids. With a designed capacity of 5,000 m³/day and an average daily discharge of 475.61 m³/day, the facility operates well below its capacity, indicating room for future growth. As a small agglomeration (under 10,000 population equivalent), the EU directive requires appropriate collection and treatment systems, which this plant fulfills. The treated effluent is discharged into local waterways that eventually drain into the Seine River basin, which flows through Paris and into the English Channel. The plant plays a key role in protecting the Oise River and downstream aquatic ecosystems from nutrient pollution and pathogens, supporting water quality in a densely populated region.

The plant discharges into the Oise River watershed, a major tributary of the Seine River. The Seine flows through Paris and into the English Channel, supporting diverse aquatic life and providing drinking water for millions. The plant's secondary treatment reduces organic load and suspended solids, helping to prevent eutrophication in downstream waters. The region's temperate climate and urban-agricultural landscape require consistent treatment to maintain ecological balance.