ONA Wastewater Treatment Plant, Oña, Castilla y León, Spain

ONA is a wastewater treatment plant located in Oña, a municipality in the province of Burgos, within the autonomous community of Castilla y León, Spain. The plant serves a population of approximately 2,000 residents, reflecting its role in managing domestic wastewater for this small inland community. The facility operates with advanced treatment processes, which go beyond the secondary treatment standards required by the EU Urban Waste Water Treatment Directive (91/271/EEC) for agglomerations of this size. With a designed capacity of 2,650 m³/day and an average discharge volume of 684.93 m³/day, the plant has sufficient capacity to handle current loads. As a Spanish plant, it is subject to national regulations transposing EU directives, ensuring compliance with discharge standards. The treated effluent is discharged into the local watershed, which ultimately drains into the Ebro River basin via tributaries in the region. The Ebro River flows into the Mediterranean Sea, making the plant's advanced treatment important for protecting downstream aquatic ecosystems and the sensitive coastal environment of the Ebro Delta.

The plant discharges into the Ebro River basin, which flows through northeastern Spain before reaching the Mediterranean Sea. The Ebro Delta is an ecologically significant area that supports diverse aquatic life and migratory birds. Advanced treatment at ONA helps reduce nutrient loads and pollutants, protecting downstream water quality and the sensitive marine environment.