During the onsite construction of one of our projects I got in contact with the Van Doorn Group from Nieuwerbrug. This company consists of three specialized subsidiary and right now we are working with one of them (Bunnik BV) on the project Graafse Waard, Bodegraven.
I was invited to come and look at one of the dredging which Bunnik BV is currently undertaking. Of course I accepted this invitation because I was curious to see the modern method of dredging in combination with polymer. This way of working is completely new to me but after the site visit, I am convinced that this type of dredging can save a lot of time and costs.
The dredged material is released during various maintenance dredging of waterways (which are an important part of the Dutch polder landscape).
The standard procedure for processing the sludge is to storage the material on grassland where is can be drained and dewatered. After the mud has dried, a process which takes about two years, it is used for terrain modeling in the near surrounding.
An innovative storage solution are Geotubes (very large porous big bags of approximately 500-1000 m3) in which the dredged material can be drained in no time. It is necessary to add polymer to this process in order to succeed.
Polymer is an additive component. This polymer uses the electrical characteristics of both, the water and the sludge particles. Both, water and silt, has a positive and a negative charge. The polymer ensures that the sludge particles have the same charge so they attract each other. This causes large flakes. The polymer also generates a repulsive force between the flakes and water. This chemical reaction precipitates the formed flakes directly into the Geotube and the water flows through the porous walls of the Geotube off. After several weeks the sludge is dried enough inside the Geotube and can be processed.