VIONNAZ Wastewater Treatment Plant, Vionnaz, Valais, Switzerland

VIONNAZ is a municipal wastewater treatment plant located in Vionnaz, a municipality in the Valais/Wallis canton of Switzerland. The plant serves a population of approximately 1,870 and has a designed capacity of 3,125 m³/day, with an average daily discharge of 848.83 m³/day. It is situated near the Rhône River basin, close to the eastern shore of Lake Geneva. The plant provides secondary treatment, which is the standard biological treatment required under Swiss water protection legislation. Switzerland's Waters Protection Act (GSchG) and its ordinances mandate that wastewater from agglomerations of this size receive appropriate treatment to protect water bodies. Secondary treatment typically involves biological processes to reduce organic matter and suspended solids. The treated effluent from VIONNAZ is discharged into the local hydrological network, which ultimately drains into the Rhône River and then into Lake Geneva (Lac Léman). Lake Geneva is a large, deep alpine lake that supports diverse aquatic life and serves as a critical freshwater resource for the region. The plant's proximity to the lake underscores the importance of effective wastewater treatment to prevent nutrient enrichment and maintain water quality.

The plant's discharge enters the Rhône River system, which flows into Lake Geneva, one of the largest freshwater lakes in Western Europe. Lake Geneva is ecologically sensitive, supporting a variety of fish species and providing habitat for migratory birds. Effective secondary treatment helps control nutrient loads that could otherwise contribute to eutrophication in the lake, preserving its water quality and biodiversity.