ARREAU Wastewater Treatment Plant, Ancizan, Occitanie, France

The ARREAU wastewater treatment plant is located in Ancizan, a commune in the Hautes-Pyrénées department of Occitanie, southern France. It serves a population of approximately 1,600 people and is designed to handle a capacity of 2,500 m³/day, with an average discharge volume of 285.44 m³/day. The plant employs advanced treatment processes, which go beyond the secondary treatment required by the EU Urban Waste Water Treatment Directive (91/271/EEC) for agglomerations of this size. This level of treatment is typically implemented in sensitive areas to reduce nutrient loads and protect receiving water bodies. The treated effluent is discharged into the local watershed, which ultimately drains into the Adour River basin and then to the Bay of Biscay. The plant plays a key role in maintaining water quality in the region, supporting aquatic ecosystems and downstream uses.

The plant discharges into the local stream network that feeds the Adour River, which flows through the Pyrenees foothills before reaching the Bay of Biscay. This watershed supports diverse aquatic life, including migratory fish species such as salmon and trout. Advanced treatment helps minimize nutrient pollution, protecting the ecological health of the river and its estuary.