ARROYO DE LA VEGA Wastewater Treatment Plant, San Sebastián de los Reyes, Spain

ARROYO DE LA VEGA is a wastewater treatment plant located in San Sebastián de los Reyes, within the Comunidad de Madrid, Spain. The plant serves a population equivalent of 173,624, classifying it as a large agglomeration under EU regulations. As a large agglomeration, the plant is subject to the EU Urban Waste Water Treatment Directive 91/271/EEC, which requires secondary treatment as a minimum, and tertiary treatment if discharging into sensitive areas. The regulatory framework ensures compliance with European standards for wastewater treatment. The plant discharges treated water into the local watershed, which ultimately drains into the Jarama River, a tributary of the Tagus River. The Tagus River flows through central Spain and into Portugal, reaching the Atlantic Ocean near Lisbon. The plant plays a key role in protecting the Jarama-Tagus river system from pollution, supporting aquatic life and downstream water quality.

The plant's treated effluent enters the local drainage network, which flows into the Jarama River, a major tributary of the Tagus River. The Tagus is the longest river in the Iberian Peninsula, supporting diverse aquatic ecosystems and providing water for agriculture and urban use. The plant helps maintain water quality in this ecologically sensitive basin, reducing nutrient loads and organic pollution that could impact downstream habitats and the Atlantic coastal zone.