Sanfins do Douro Wastewater Treatment Plant, Alijó, Portugal

Sanfins do Douro wastewater treatment plant is located in the parish of Sanfins do Douro, within the municipality of Alijó in the Vila Real district of northern Portugal. The plant serves a population of approximately 4,000 residents, making it a small-scale municipal facility in the Douro Valley region. As a secondary treatment plant, it employs biological processes to reduce organic matter and suspended solids. The plant has a designed capacity of 4,200 m³/day and currently treats an average daily flow of 666.92 m³/day, indicating significant spare capacity. Under Portuguese and EU regulations, secondary treatment is the standard requirement for inland freshwater discharges, in line with the EU Urban Waste Water Treatment Directive (91/271/EEC). The treated effluent is discharged into a local watercourse that eventually drains into the Douro River, one of the Iberian Peninsula's major rivers. The Douro River flows west through Portugal's wine-growing region and empties into the Atlantic Ocean near Porto. The plant plays a key role in protecting the Douro River basin from untreated sewage, supporting water quality for agriculture, tourism, and aquatic ecosystems.

The plant discharges into a tributary of the Douro River, which flows through the UNESCO-recognized Douro Valley wine region before reaching the Atlantic Ocean. The Douro basin supports diverse aquatic life, including migratory fish species such as lamprey and shad. The plant's secondary treatment helps reduce nutrient and organic pollution, safeguarding downstream water quality for irrigation, recreation, and ecological health.