ALPNACH SARNERAATAL Wastewater Treatment Plant, Alpnach, Obwalden, Switzerland

ALPNACH SARNERAATAL is a wastewater treatment plant located in Alpnach, in the canton of Obwalden, Switzerland. It serves a population of approximately 52,500, placing it in the medium-to-large agglomeration category. The plant is situated inland, away from the coast, and its operations are integrated into the local water management infrastructure. Under the EU Urban Waste Water Treatment Directive (91/271/EEC), which Switzerland aligns with through bilateral agreements, agglomerations of this size are required to provide at least secondary treatment, with tertiary treatment expected if discharging into sensitive areas. The plant's treatment processes are designed to meet these standards, ensuring effective removal of organic matter and nutrients. The treated effluent is discharged into local watercourses that feed into the Sarner Aa river, which flows into Lake Lucerne (Vierwaldstättersee). Lake Lucerne is a major water body in central Switzerland, supporting diverse aquatic life and recreational activities. The plant plays a crucial role in protecting the lake's water quality and the broader Rhine basin ecosystem.

The plant discharges into the Sarner Aa river, which flows into Lake Lucerne, a large alpine lake in central Switzerland. Lake Lucerne ultimately drains into the Reuss River, a tributary of the Rhine, which flows to the North Sea. The lake supports a diverse ecosystem, including fish species such as lake trout and whitefish, and is a vital resource for drinking water and recreation. The plant's treatment helps maintain the ecological balance of this sensitive alpine watershed.