Saint-Marcel Wastewater Treatment Plant, Saint-Marcel, Valle d'Aosta, Italy

The Saint-Marcel wastewater treatment plant is located in the municipality of Saint-Marcel, in the Valle d'Aosta region of northwestern Italy. This facility serves a population of approximately 4,800 residents, reflecting its role as a medium-sized agglomeration in a mountainous alpine setting. The plant is situated in the Dora Baltea river basin, which ultimately drains into the Po River and the Adriatic Sea. The plant provides secondary treatment, which is the standard biological treatment required under the EU Urban Waste Water Treatment Directive (91/271/EEC) for agglomerations of this size. With a designed capacity of 19,000 m³/day and an actual discharge volume of 950.23 m³/day, the plant operates well below its capacity, indicating potential for future growth or seasonal variations. The treated effluent is discharged into the local watercourse, which flows into the Dora Baltea River, a major tributary of the Po River. The Po River basin is ecologically significant, supporting diverse aquatic life and providing water for agriculture and industry in northern Italy. The plant's operation helps protect the sensitive alpine watershed and downstream environments from untreated wastewater pollution.

The plant discharges into a tributary of the Dora Baltea River, which flows through the Aosta Valley and joins the Po River near Turin. The Po River is Italy's longest river and its delta is a critical habitat for migratory birds and fish species. The alpine watershed is sensitive to nutrient loading, and secondary treatment helps reduce organic pollution and protect downstream ecosystems.