FUENTES DE ONORO Wastewater Treatment Plant, Fuentes de Oñoro, Castilla y León, Spain

The FUENTES DE ONORO wastewater treatment plant is located in the municipality of Fuentes de Oñoro, in the province of Salamanca, Castilla y León, Spain. It serves a population of approximately 3,500 residents, reflecting the scale of a small agglomeration in a rural inland setting. The plant operates with secondary treatment, which is the standard required under the EU Urban Waste Water Treatment Directive (91/271/EEC) for freshwater discharges from agglomerations of this size. With a designed capacity of 3,500 m³/day and a reported discharge volume of 875 m³/day, the facility is operating well below its capacity, indicating potential for future growth or seasonal variability. The treated effluent is discharged into the local watershed, which ultimately drains into the Duero River basin. This river system flows westward through Spain and Portugal, reaching the Atlantic Ocean near Porto. The plant's operation helps protect downstream water quality and supports the ecological health of the Duero basin.

The plant discharges into the Duero River basin, one of the largest watersheds in the Iberian Peninsula. The Duero River flows through Spain and Portugal, supporting diverse aquatic life and providing water for agriculture and human consumption. Downstream, the river forms the border between the two countries before emptying into the Atlantic Ocean. The treatment plant's secondary treatment helps reduce organic pollution and nutrient loads, contributing to the ecological balance of this important transboundary river system.