LOCO ONSERNONE Wastewater Treatment Plant, Onsernone, Ticino, Switzerland

LOCO ONSERNONE is a municipal wastewater treatment plant located in the village of Loco, part of the Onsernone municipality in the Ticino canton of Switzerland. Serving a small population of 214 residents, this facility is situated in the Swiss Alps at an elevation of approximately 800 meters, reflecting the rural and mountainous character of the region. The plant provides secondary treatment, which is the standard biological treatment required under Swiss water protection legislation. With a designed capacity of 500 m³/day and a current discharge volume of 97.14 m³/day, the facility operates well below its capacity, indicating room for future growth or seasonal variations. Swiss regulations, aligned with the EU Urban Waste Water Treatment Directive, mandate secondary treatment for agglomerations of this size to protect sensitive alpine water bodies. The treated effluent is discharged into the local stream network, which feeds into the Isorno River and eventually the Melezza River, a tributary of the Maggia River. The Maggia flows into Lake Maggiore, a large subalpine lake shared with Italy. This watershed supports diverse aquatic life and is ecologically sensitive due to its alpine character and the importance of Lake Maggiore for biodiversity and tourism.

The plant discharges into the Isorno River, a tributary of the Melezza River, which flows into the Maggia River and ultimately Lake Maggiore. This alpine watershed is ecologically sensitive, supporting species such as the marble trout and providing critical habitat for migratory birds. Lake Maggiore is a major freshwater resource for the region, and its water quality is protected under international agreements between Switzerland and Italy.