Sobral de Monte Agraco Wastewater Treatment Plant, Sobral de Monte Agraço, Portugal

The Sobral de Monte Agraco wastewater treatment plant is located in the Lisbon District of Portugal, serving the town of Sobral de Monte Agraço. With a population equivalent of 3,100, it is classified as a small agglomeration under Portuguese and EU regulations. The plant is situated inland, approximately 50 km from the Atlantic coast. The plant provides secondary treatment, which is the standard required by the EU Urban Waste Water Treatment Directive (91/271/EEC) for freshwater discharges from agglomerations of this size. Its designed capacity is 3,607 cubic meters per day, with an average daily discharge of 516.87 cubic meters, indicating significant spare capacity. Secondary treatment typically involves biological processes to reduce organic matter and suspended solids. The treated effluent is discharged into a local watercourse that ultimately drains into the Atlantic Ocean via the Tagus River basin. The plant plays a key role in protecting local water quality and downstream ecosystems, including the Tagus estuary, which supports diverse aquatic life and is an important migratory corridor for birds.

The plant discharges into a small watercourse that flows into the Tagus River basin, which drains into the Atlantic Ocean near Lisbon. The Tagus estuary is a ecologically sensitive area supporting diverse aquatic life and serving as a critical stopover for migratory birds. Secondary treatment helps reduce nutrient and organic loads, protecting downstream water quality and the estuarine ecosystem.