Envisan treats the dredged sediments

In 2015, Envisan opened a soil and sediment treatment centre in La Seyne-sur-Mer, near Toulon (France). Here, polluted sediments from Monaco are remediated ready for reuse.

Hannes Van den Berghe coordinated the activities between Envisan and the teams that were working in Monaco: “Overall we handled about 100,000 tonnes of sediments that were removed from the site and were treated here. In a first step, the sediment is pumped in a big lagoon where we let the material drain, a process called lagooning.

"It's really a challenge to process large quantities of sediments."

Then we subdivide the material in different partial fractions: sand on the one hand and very fine clay on the other. The sediment is passed through hydrocylones so that the sand can be filtered out and re-used. Pollution (PCBs, heavy metals, oil) tends to adhere to the finer fraction only. After having separated the fine clay, we continue dewatering it through chamber filter presses. After this process, we are left with a fraction of dry substance that cannot be purified any further and is sent to a land fill. The main part, i.e. the remaining sand, is purified and re-used, for instance for road construction works. The water is treated in our own plant and discharged back into the sea, for which we obviously have a permit. Envisan does not only treat the main part of the influx of polluted material but also remediates it, ready to be used again, and contributing to the circular economy.”

According to Hannes, the challenge in this project was that we immediately had to process large quantities of sediments to create new capacity in the centre. “Our lagoon isn’t big enough to simultaneously store 100,000 tonnes, and as we didn’t want to slow down the dredging works, as soon as sediments arrived, we immediately dewatered part of the load to create new capacity.”

Given the potential for further treatment with hydrocylones and chamber filter presses, Jan De Nul itself plans to invest in a brand new plant for Envisan. “As such, we will become the first centre in southern France giving soils and sediments a second life.” 

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