Rennes Métropole protects the Vilaine River with smart pumping

Challenge

Rennes Métropole serves 450,000 residents across 43 municipalities in Brittany, France. Its Wastewater Department manages 25 wastewater treatment plants and 1,460 kilometers of gravity sewer networks — the invisible infrastructure that protects public health and local waterways every day. The people who run this network keep water flowing safely for nearly half a million people.

The Constant Véron station sits at the heart of this system. It acts as a buffer storage basin upstream of the Beaurade wastewater treatment plant — the largest treatment plant in Brittany, serving more than 360,000 inhabitants. When the station works well, it protects the plant from surge flows and keeps wastewater moving where it should. But the station's aging pumps were no longer up to the task.

During storms, the old equipment could not handle incoming flows. The result was repeated discharges into the Vilaine River — 17 overflow events in 2018 alone. Each discharge carried environmental consequences for the river and the communities that depend on it. The wastewater department faced a decision: expand the buffer basin through major civil works, or replace the pumps with more powerful technology that could do the same job in a smaller footprint.

Expanding the basin would mean significant construction, cost and disruption for users in central Rennes. Rennes Métropole chose a different path — one that its 30-year partnership with Xylem made possible.

Solution

Together with Rennes Métropole, we installed two Flygt Concertor pumps at the Constant Véron station in September 2020. The pumps were dry-installed in a pit, making them fully accessible to operators for inspection and maintenance.
Each pump was coupled with a Xylem XPC module, an automated electrical control cabinet that manages flow rates and pump power based on real-time conditions. A radar probe positioned in the wet well continuously monitors water levels, allowing the system to adjust performance automatically. When storm flows surge, the pumps respond. When flows recede, they scale back. No manual intervention required.
The decision to replace pumps rather than expand the basin saved Rennes Métropole from months of disruptive civil construction. It also reflected the trust built over more than 30 years of partnership — a relationship in which the wastewater department knew from experience that Xylem technology could meet the challenge.

Results

Since the Flygt Concertor pumps were commissioned in September 2020, the results have been measurable across three dimensions.

Environmental: Overflow discharges into the Vilaine River dropped from 17 events in 2018 to seven in 2021 — and to zero to date in 2022. The river that runs through Rennes is cleaner because of it. Rennes Métropole plans to install a third Flygt Concertor pump at the station in the coming months, which should eliminate all remaining risk of discharges entirely.

Economic: Electricity consumption has remained stable since 2020, even as the station conveys a much higher volume of water than before. The pumps' adaptive power management — driven by the Xylem XPC module and radar probe — ensures that energy use scales with actual need, not with maximum capacity.

Operational: Dry-pit installation makes the equipment accessible to operators, simplifying maintenance and reducing the time and effort required to keep the station running. Automatic flow and power management means the system adapts to conditions without manual adjustment, freeing operators to focus on other priorities across the network.

The Constant Véron station will now serve as a model for similar modernization projects across the Rennes metropolitan area, with plans underway to replicate the approach in other zones.