Caldes de Montbui Wastewater Treatment Plant - Serving Caldes de Montbui, Catalonia

The Caldes de Montbui wastewater treatment plant is located in the Vallès Oriental comarca of Barcelona province, Catalonia, Spain. It serves the town of Caldes de Montbui, a historic spa town known for its thermal springs, with a population of around 14,252. The plant is part of the regional water infrastructure managed by the Catalan Water Agency (ACA). Under the EU Urban Waste Water Treatment Directive (91/271/EEC), agglomerations with a population equivalent (PE) between 10,000 and 150,000 are classified as medium agglomerations and are required to provide secondary treatment as a minimum. For plants serving populations over 10,000 in sensitive areas, more stringent treatment may be required. The regulatory framework ensures compliance with European standards. The treated effluent is discharged into the local water system, which ultimately drains into the Mediterranean Sea via the Besòs River basin. The plant plays a key role in protecting the water quality of the Besòs River and the coastal environment, supporting aquatic life and recreational uses downstream.

The plant discharges into the Besòs River basin, which flows through the Vallès Oriental region and into the Mediterranean Sea near Barcelona. The Besòs River is an ecologically important waterway that supports diverse aquatic habitats and is a key corridor for migratory fish species. The treatment plant helps reduce nutrient and pollutant loads, protecting downstream ecosystems and the coastal waters of the Catalan coast.