Use of cement and quicklime to accelerate ripening and immobilize contaminated dredging sludge.

In this study cement and quicklime are examined as binders to enhance the ripening process and immobilize contaminants in dredging sludge. Ripening comprises the drying in the open air till a dry matter content of 50-55% is reached. For this study, a dredging sludge of the highest contamination category was used. The binders speed up the ripening process substantially since the binders as such increase the dry matter content upon mixing, but they also modify the structure so that evaporation is facilitated. Furthermore, the reaction of cement and quicklime with water generates heat that also stimulates evaporation, and both binders, in combination with dredging sludge, bind water chemically (twice as much as expected). The total time for ripening could be reduced by 70%, which means that existing treatment depots can be used more effectively. The emission of contaminants was determined by a standard leaching test. The cement and quicklime had opposite effects on the leaching of constituents. The addition of cement had negative effects on sulphate, fluoride, and zinc, which were compensated by the addition of quicklime. On the other hand, cement reduced the emission of chloride, copper, and nickel, while quicklime seemed to increase the emission of these constituents. The concentration and emission of contaminants of the treated dredging sludge meet the requirements of the current legislation. It is therefore concluded that the presented method is able to produce, in a much shorter time, an applicable building material from contaminated dredging sludge.