Rennes Métropole cuts wastewater overflows into the Vilaine River with smart pumping

Rennes Métropole provides public services for 450,000 residents across the Rennes metropolitan area in Brittany, France, including wastewater management, transportation, waste collection and public infrastructure. Its Wastewater Department manages 25 treatment plants and a 1,460-kilometer gravity sewer network.

Within this network, the Constant Véron pumping station in central Rennes provides buffer storage upstream of the Beaurade wastewater treatment plant. The largest treatment plant in Brittany, Beaurade treats wastewater from more than 360,000 residents.

Aging pumps at Constant Véron could no longer reliably handle incoming flows, particularly during storms. When flows exceeded pumping capacity, wastewater overflowed into the Vilaine River.

Rennes Métropole worked with Xylem, a technology partner for more than 30 years, to modernize the station. By replacing the aging pumps with Xylem’s Flygt Concertor® intelligent wastewater pumping systems, the authority increased pumping capability without expanding the existing buffer basin. Since installation, the station has reduced wastewater overflows while keeping electricity consumption stable despite significantly higher throughput.

Challenge

Rennes Métropole faced a choice: expand the Constant Véron buffer basin or increase the station’s pumping capacity.

Expanding the basin would have required major construction work in central Rennes and caused significant disruption in the surrounding area. Rennes Métropole therefore looked for a pumping solution that could handle higher and more variable flows within the existing station footprint.

The challenge was particularly acute during storms, when incoming wastewater flows could rise sharply. The existing pumps were no longer able to handle these peaks reliably, contributing to overflows into the Vilaine River.

Rennes Métropole also wanted to improve maintenance access and operate the station more efficiently as flow conditions changed.

Solution

Rennes Métropole installed two Flygt Concertor pumps at Constant Véron, paired with Xylem Nexicon pump station control. The new system entered service in September 2020.

Flygt Concertor XPC combines intelligent wastewater pumping with automated station control. Key capabilities include:

• Automatic adjustment of pump operation as station conditions change
• Real-time control of pump flow and power based on basin level data
• Automated clog detection and pump-cleaning functions
• Built-in sump and discharge pipe cleaning
• Energy optimization across multiple pumps

At the Constant Véron pumping station, a radar level sensor in the basin provides real-time input to the control system. The system automatically adjusts pump flow and power as conditions change, helping the station respond more effectively to peaks in incoming wastewater.

The two Concertor pumps were also installed in a dry pit, making them easier for maintenance teams to access. Staff can reach the equipment directly for inspection and maintenance rather than working with submerged pumps.

Results

Since the new system entered service, Rennes Métropole has reported significant environmental and operational improvements at Constant Véron:

• Wastewater overflows into the Vilaine River fell from 17 in 2018 to seven in 2021 and zero in 2022
• Electricity consumption remained stable despite significantly higher wastewater throughput
• Dry-pit installation improved access for inspection and maintenance

Together, the improvements have strengthened environmental performance while making the station easier to operate and maintain.

A model for future modernization

Rennes Métropole sees Constant Véron as a model for similar wastewater pumping station modernization projects across the metropolitan area.

By increasing pumping capability within the existing station footprint, the project avoided the disruption and construction work associated with expanding the buffer basin. The combination of intelligent pumping, automated control and improved maintenance access provides a model for upgrading other sites facing similar capacity and operational challenges.