COLMENAR DEL ARROYO Wastewater Treatment Plant, Colmenar del Arroyo, Spain

COLMENAR DEL ARROYO is a wastewater treatment plant located in the municipality of Colmenar del Arroyo, within the Comunidad de Madrid, Spain. The plant serves a population of approximately 2,017 residents, making it a small-scale facility in the region. Its location in the Molino del Cubo area along Calle San Roque places it within the local urban and agricultural landscape. The plant provides secondary treatment, which is the standard required by the EU Urban Waste Water Treatment Directive (91/271/EEC) for agglomerations with a population equivalent between 2,000 and 10,000. The designed capacity is 4,000 m³/day, and the current discharge volume is 586.61 m³/day, indicating operational capacity well below the design limit. As a Spanish facility, it operates under national regulations that transpose the EU directive, with oversight from the regional water authority in the Comunidad de Madrid. The treated effluent is discharged into a local watercourse that eventually drains into the Tagus River basin, one of the major river systems in the Iberian Peninsula. The Tagus River flows westward through Spain and Portugal before reaching the Atlantic Ocean near Lisbon. The plant's operations contribute to protecting the water quality of the local streams and the downstream Tagus ecosystem, which supports diverse aquatic life and is an important resource for agriculture and urban water supply.

The plant discharges into a local tributary of the Tagus River basin, which ultimately flows into the Atlantic Ocean. The Tagus River is the longest river in the Iberian Peninsula and supports a variety of fish species and riparian habitats. The region's Mediterranean climate, with seasonal droughts, makes the plant's role in maintaining water quality critical for downstream ecological health and agricultural use.