SESMA Wastewater Treatment Plant, Sesma, Navarra, Spain

SESMA is a wastewater treatment plant located in Sesma, a town in the autonomous community of Navarra, northern Spain. The facility serves a population of approximately 1,264 residents, classifying it as a small agglomeration under Spanish and EU regulations. The plant is situated inland, away from coastal areas, and its treated effluent ultimately flows into the Ebro River system, which drains into the Mediterranean Sea. The plant provides 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. The designed capacity of 2,883 cubic meters per day indicates the facility is sized to handle peak flows, while the current discharge volume of 246 cubic meters per day suggests operational levels well within capacity. As a Spanish facility, it operates under national transposition of EU directives, with oversight from regional authorities in Navarra. The treated wastewater from SESMA is discharged into the local watercourse, which feeds into the Ebro River basin. The Ebro is one of Spain's major rivers, supporting diverse aquatic ecosystems and agricultural irrigation downstream. The plant's secondary treatment helps protect water quality in the Ebro system, reducing organic load and nutrients before discharge. This contributes to the ecological health of the river and its eventual delta, a biologically rich area on the Mediterranean coast.

SESMA's treated effluent enters the Ebro River basin, a major hydrological system in northeastern Spain that flows into the Mediterranean Sea. The Ebro River supports diverse aquatic life, including fish species such as the European eel and various cyprinids, and its delta is an important wetland for migratory birds. The plant's secondary treatment helps mitigate nutrient loading and organic pollution, safeguarding the river's ecological balance and downstream water quality.