Valenciennes Métropole has chosen Stradal's DDselect® solution to protect the Rhonelle river and improve the quality of its discharges.

Limiting water pollution during rainfall events

Until then, during heavy rains, the combined sewer system quickly became saturated, resulting in the discharge into the Rhonelle river of water loaded with heavy metals, microplastics or hydrocarbons.

To remedy this, the community has chosen to disconnect the networks: wastewater is now directed to the treatment plant, while rainwater is treated upstream to ensure compliant discharge into the natural environment.

Runoff water pollution is a major issue for the protection of aquatic environments and the preservation of water resources, particularly for communities facing urbanization and climate change.

Two DDselect® units to ensure efficient and continuous treatment

Two DDselect® devices with a diameter of 3 meters have thus been installed in Marly. Capable of treating up to 750 liters per second, they guarantee optimal efficiency, even in the event of heavy rainfall.

The technology relies on a combination of gravity and a centrifugal force generated by a vortex.

This liquid/solid separation process allows for the capture of:

• macro-waste (cigarette butts, paper, plastics...),
• suspended solids (SS) resulting from road wear,
• micropollutants.

Hydrodynamic decantation is distinguished by its ability to retain intermediate particles of 63 microns – the equivalent of a human hair – thus ensuring enhanced protection of the Rhonelle.

An exemplary project to reconcile development and the environment

Beyond the technical performance, this project illustrates Valenciennes Métropole's desire to reconcile urban development and the preservation of biodiversity.

As Jérôme Bourgoin, Head of Water and Sanitation at the Water Cycle Directorate, points out: “Climate change has intensified rainfall events in our region. The existing networks are no longer designed to absorb so much water in such a short time. It is now vital to reinject clean water into our rivers to sustainably preserve our resources.”

Low-carbon concrete equipment to reduce the environmental footprint

DDselect® are integrated into high-performance low-carbon concrete envelopes, allowing a reduction of approximately 30% in the ecological footprint compared to traditional concrete.

These structures guarantee perfect waterproofing, long-lasting resistance (estimated lifespan of over 50 years), and are fully recyclable. Furthermore, they are sourced from a local supply chain using locally sourced materials.

Compact and optimized, the DDselect® hydrodynamic decanter has an extremely small footprint, up to 10 times smaller than a lamellar decanter and 30 times smaller than a settling basin.

A major advantage for urban construction sites and constrained areas.