S Miguel de Lobrigos Wastewater Treatment Plant, Santa Marta de Penaguião, Portugal

S Miguel de Lobrigos is a wastewater treatment plant located in the parish of Lobrigos (São Miguel), within the municipality of Santa Marta de Penaguião, in the Vila Real district of northern Portugal. The plant serves a population of approximately 4,500 people, reflecting its role as a small-scale municipal facility in a rural, inland region of the Douro Valley. The plant provides secondary treatment, which is the standard biological treatment level required under the EU Urban Waste Water Treatment Directive (91/271/EEC) for agglomerations with a population equivalent between 2,000 and 10,000. With a designed capacity of 4,750 m³/day and an average daily discharge volume of 750.29 m³, the facility operates well within its capacity, indicating adequate infrastructure for current loads. The treated effluent is discharged into a local watercourse, likely a tributary of the Douro River, which flows westward through the Douro Valley and eventually reaches the Atlantic Ocean near Porto. The plant's operation helps protect the sensitive riverine ecosystem of the Douro basin, which supports diverse aquatic life and is important for regional agriculture and tourism.

The plant discharges into a local stream that feeds into the Douro River, one of the major rivers of the Iberian Peninsula. The Douro basin is ecologically significant, supporting diverse fish species and riparian habitats. Downstream, the river flows through the Douro Valley wine region and eventually reaches the Atlantic Ocean, where its estuary provides important nursery grounds for marine life. The plant's secondary treatment helps reduce organic pollution and nutrient loads, contributing to the overall health of this watershed.