Vidais Wastewater Treatment Plant, Caldas da Rainha, Portugal

Vidais is a secondary wastewater treatment plant located near Caldas da Rainha in the Leiria district of Portugal. It serves a population of approximately 2,200 people, classifying it as a small agglomeration under Portuguese and EU regulations. The plant is situated in a rural area near the village of Alvorninha. As a secondary treatment facility, Vidais provides biological treatment to remove organic matter and suspended solids. The plant has a designed capacity of 2,250 m³/day and currently treats an average daily flow of 366.81 m³/day, indicating significant spare capacity. Under the EU Urban Waste Water Treatment Directive (91/271/EEC), secondary treatment is the minimum requirement for freshwater discharges from agglomerations of this size. The treated effluent is discharged into local watercourses that ultimately drain to the Atlantic Ocean. The plant's proximity to the coast (within 10 km) means its discharge can influence coastal water quality. The region's watershed supports agricultural activities and local ecosystems, making proper treatment essential for environmental protection.

The Vidais plant discharges into small streams that flow toward the Atlantic Ocean near the Óbidos Lagoon, a coastal lagoon system of ecological importance. The lagoon supports diverse aquatic life and migratory birds. The plant's secondary treatment helps reduce nutrient and organic loads, protecting downstream water quality in this sensitive coastal environment.