Castellar de Santiago Wastewater Treatment Plant, Castilla-La Mancha

The Castellar de Santiago wastewater treatment plant is located in the town of Castellar de Santiago, within the province of Ciudad Real in the autonomous community of Castilla-La Mancha, Spain. The facility serves a population of around 4,466 residents, classifying it as a small agglomeration under European Union classification. The plant operates with secondary treatment, which is the standard required by the EU Urban Waste Water Treatment Directive (91/271/EEC) for freshwater discharges from agglomerations of this size. Secondary treatment typically involves biological processes to reduce organic matter and suspended solids, ensuring compliance with EU effluent quality standards. The treated effluent is discharged into the local watershed, which ultimately drains into the Guadiana River basin. The Guadiana River flows westward through Spain and Portugal before reaching the Gulf of Cádiz in the Atlantic Ocean. The plant plays a key role in protecting the ecological health of the Guadiana basin, supporting aquatic life and water quality in the region.

The plant discharges into the Guadiana River basin, one of the major river systems in the Iberian Peninsula. The Guadiana River flows through semi-arid landscapes and supports diverse aquatic habitats, including wetlands and riparian zones. Downstream, the river reaches the Gulf of Cádiz, an ecologically productive area of the Atlantic Ocean. The treatment plant helps reduce nutrient and organic pollution, safeguarding water quality for both local ecosystems and downstream coastal environments.