Middelburg: Boskalis and Promeco

Dredging company Boskalis opts for sludge processing by Promeco.

At the end of January 2015, by order of the Department of Waterways and Public Works (‘Rijkswaterstaat’), work was commenced on the clean-up of the Canal through Walcheren, at the entrance to the harbour in Middelburg. At this location, Boskalis removed sludge contaminated with copper (originating from the former Vitrite factory). This work got even more complex when, in 2014, unexploded ordnance from the Second World War was found at the site. For this, Boskalis constructed a special unit with which the sludge is excavated under water and also deposited in an underwater container. This container moved under a pontoon and then lifted upwards in an armoured space. The sludge was then sifted and transported to a location outside built-up areas. The sifted material was checked with cameras for the presence of unexploded ordnance. Any ordnance found was handed over to the Explosive Ordnance Disposal Unit.

Settling with the help of flocculant
The sludge was transported with the addition of a great deal of water. Ton Broeders from Promeco: “This water must then be removed. This takes partly place as a result of natural settling in large barges and partly due to settling using flocculant in the polishing stage before discharge into the surface water. Boskalis selected Promeco for the sludge processing.”

New installation developed by Promeco
For the polishing, Promeco used optimised flocculant dosing including the use of in-line dry solids measurements, based on ultrasonic sound. The measuring instrument for this project was imported from Canada because the microwave technique that is usually used is less suitable for salt water. The installation and software from Promeco can detect a rapid change in dosage requirement. Unique in the world! Naturally, the discharged water meets the requirements of the competent authorities.

Remote measuring
As always, we can control the installation remotely with the help of telemetry. The operators can monitor all of the relevant parameters on their smart phones, at any time of the day.

The water quality will eventually be improved, and the eco-system in the entire Canal will benefit from this.

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