Courelas Wastewater Treatment Plant, Trancoso, Portugal

Courelas wastewater treatment plant is located in Trancoso, a municipality in the Guarda district of central Portugal. The facility serves a population of approximately 2,000 people, making it a small-scale municipal plant typical of rural inland communities in the region. The plant provides secondary treatment, which is the standard 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. The plant's designed capacity is 2,437 m³/day, and it currently discharges an average volume of 333.46 m³/day, indicating operational capacity well within design limits. The treated effluent is discharged into the local watershed, which ultimately drains into the Douro River basin. The Douro River flows westward through northern Portugal and Spain before reaching the Atlantic Ocean at Porto. The plant's inland location, over 50 km from the coast, reduces direct marine impact, but its discharge contributes to the overall water quality of the Douro basin, which supports agriculture, biodiversity, and downstream communities.

The plant discharges into the Douro River basin, one of the Iberian Peninsula's major watersheds. The Douro River flows approximately 897 km from its source in Spain to the Atlantic Ocean at Porto, supporting diverse aquatic ecosystems and irrigated agriculture along its course. The receiving waters are ecologically sensitive, hosting species such as the Iberian barbel and the Douro nase, and the basin includes areas of conservation importance. Proper treatment is essential to prevent nutrient loading and maintain water quality in this transboundary river system.