Castrojeriz Wastewater Treatment Plant - Secondary Treatment in Castilla y León, Spain

The Castrojeriz wastewater treatment plant is located in the municipality of Castrojeriz, in the province of Burgos, Castilla y León, Spain. It serves a population of approximately 2,500 residents, making it a small-scale facility typical of rural towns in the region. The plant is situated along the BU-405 road, reflecting its integration into the local infrastructure. The plant provides secondary treatment, which is the standard level required under the EU Urban Waste Water Treatment Directive (91/271/EEC) for agglomerations with a population equivalent between 2,000 and 10,000. Secondary treatment involves biological processes to reduce organic matter and suspended solids. The designed capacity of 2,500 m³/day matches the population served, indicating adequate sizing for current demand. The plant discharges a daily volume of approximately 137 m³ of treated wastewater. The treated effluent is discharged into a local watercourse, likely a tributary of the Arlanzón River, which flows into the Duero River basin. The Duero River ultimately reaches the Atlantic Ocean near Porto, Portugal. The plant plays a key role in protecting the local aquatic environment and downstream water quality in the Duero basin, which supports diverse ecosystems and agricultural activities.

The plant discharges into a local stream that feeds into the Arlanzón River, a tributary of the Duero River. The Duero basin is one of the largest in the Iberian Peninsula, supporting irrigated agriculture and diverse freshwater habitats. Downstream, the Duero flows into the Atlantic Ocean, where nutrient inputs can affect coastal ecosystems. The secondary treatment provided helps reduce organic pollution and protect the ecological health of the receiving waters.