Articles & Case Studies


Posted: Tuesday 15th May 2012

A €175m milestone sanitation project in Belgium helping to achieve vital North European water quality targets has been completed following the installation of innovative vortex-powered stormwater treatment technology from Hydro International.

As part of the ambitious project, distributed at-source stormwater treatment is integral to the modernised combined sewer network at Namur in Belgium, with the installation of 33 Storm King® advanced hydrodynamic separators with self-cleansing screens.

More than 35 years after it was first conceived, the Namur project provides wastewater treatment for the city’s 125,000 inhabitants, meeting the requirements of the European Water Framework Directive.

Situated at the confluence of the Meuse and Sambre rivers, Namur is the historic capital of the Wallonia province of central Belgium. Its complex sewage and stormwater network, developed during two centuries, was previously discharging overflow wastewater through nearly 50 separate outfalls directly into the rivers.

Opened to great acclaim in February 2011 by European Environment Commissioner Janez Potocnik, a new state-of-the-art sewage treatment works 6km downstream at Brumagne will treat some 20,000 m3 of sewage a day.

To convey sewage to the treatment works, some 25km of new connecting pipeline have been retrofitted to the existing sewer network. In the central area of the city a combination of limited space, complex underground services and a level topography meant the pipes could not be buried deeply. Instead, the network is operated under pumped pressure, with a total of 54 pumping stations which inject wastewater from neighbourhood main sewers into the collection network.

The frequent risk of overflow of the pumping stations after rainfall could cause unwanted discharges into the river system via Combined Sewer Outfalls (CSOs). So, a total of 33 Storm King® units have been installed, spread between 37 of the pumping sites. The Storm King®s control onward flows preventing overloading of the downstream network, whilst providing pre-treatment of sediments, grits and floatables. In particular they prevent highly polluting sediments, resuspended as a result of ‘first flush’ flow from storm incidents, from entering the river system.

Several sites also used Hydro International’s Hydro-Brake® Flow Controls to control the pass forward effluent flow to the sewage treatment plant. The absence of power required by the Hydro-Brakes helped reduce the overall project running costs.

Pollutants collected from Storm Kings are re-introduced into the main sewers for eventual treatment at the wastewater plant, in just the same process as in dry weather and low flows. The treated stormwater overflow can safely be discharged via the CSO to the watercourse.

The Belgian utility INASEP is overseeing the project: “A major advantage of the Hydro units is that they operate as a decentralised system, located close to the sources of the wastewater,” said Marc Lemineur, Deputy Director General of INASEP.

“The solution avoided building a large, central stormwater treatment plant, saving cost and space. The Hydro stormwater treatment devices also greatly reduce the flow requirements of the network, saving both capital expenditure and reducing operating costs and pumping requirements.”

In the wastewater plant’s pre-treatment stage, a Hydro Grit-King® vortex separator provides central removal of grit and removal of grit down to 200 microns. Eventually, treated wastewater is discharged from the Brumagne plant back into the Meuse via a deep pipeline. A further two satellite treatment works upstream at Wepion and Floriffoux also form part of the system.

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