Pierrefontaine-les-Varans Wastewater Treatment Plant - Secondary Treatment, Doubs Basin

The Pierrefontaine-les-Varans wastewater treatment plant is located in the commune of Pierrefontaine-les-Varans, within the Doubs department of Bourgogne-Franche-Comté, France. This facility serves a population of approximately 1,800 residents, classifying it as a small agglomeration under French and EU regulations. As a secondary treatment plant, it provides biological treatment to reduce organic matter and suspended solids before discharge. The plant has a design capacity of 5,000 m³/day and currently treats an average daily flow of 321.12 m³, indicating significant spare capacity. Under the EU Urban Waste Water Treatment Directive (91/271/EEC), small agglomerations like this are generally required to provide secondary treatment, which this plant meets. The treated effluent is discharged into the local watershed, which ultimately drains into the Doubs River, a tributary of the Saône, then the Rhône, and finally the Mediterranean Sea. The plant plays a key role in protecting the water quality of the Doubs River and its downstream ecosystems, supporting aquatic life and recreational uses.

The plant discharges into the Doubs River basin, which flows through the Jura region before joining the Saône River. The Saône then meets the Rhône, which empties into the Mediterranean Sea. The Doubs River supports diverse aquatic life, including fish species such as brown trout and grayling, and its water quality is important for both ecological health and human uses like fishing and recreation. The plant's secondary treatment helps reduce nutrient and organic pollution, mitigating eutrophication risks in downstream waters.