Santo Estevao Chaves Wastewater Treatment Plant, Chaves, Portugal

Santo Estevao Chaves is a municipal wastewater treatment plant located in Santo Estêvão, Chaves, in the Vila Real district of northern Portugal. The plant serves a population of approximately 2,600 residents, reflecting its role as a small-scale facility for the local community. Its location near the Tâmega River places it within the Douro River basin, a region known for its agricultural and ecological significance. The plant provides secondary treatment, which is the standard biological treatment required under the EU Urban Waste Water Treatment Directive (91/271/EEC) for agglomerations with a population equivalent between 2,000 and 10,000. Secondary treatment typically involves biological oxidation and sedimentation, effectively reducing organic matter and suspended solids before discharge. The plant's designed capacity is 3,593 cubic meters per day, with a current discharge volume of 433.5 cubic meters per day, indicating operational headroom. Treated effluent from the plant is discharged into the local watercourse, which flows into the Tâmega River, a tributary of the Douro River. The Douro River ultimately reaches the Atlantic Ocean at Porto. The plant plays a key role in protecting water quality in this transboundary river system, supporting aquatic life and downstream uses such as irrigation and recreation.

The plant discharges into a small watercourse that feeds the Tâmega River, a major tributary of the Douro River. The Douro basin is ecologically important, supporting diverse fish species including the Iberian barbel and trout. The river flows through Portugal and Spain before reaching the Atlantic Ocean, making water quality management critical for both countries. The plant's secondary treatment helps reduce nutrient loads that could otherwise contribute to eutrophication in downstream reservoirs and coastal waters.