Sediment and Sludge Treatment

Environmental dredging of two lakes contaminated with mercury (Hultsfred, Sweden)

The sediment is located in two lakes near the city of Hultsfred in Sweden. Countless lakes and woods are Sweden’s most important environmental asset. Nevertheless, the wood and timber industry – and the paper industry in particular – have severely contaminated the lake beds with unmonitored discharges and dumping. Unacceptable levels of mercury in particular have been found.

In the summer of 2006, DEC, in a joint venture with affiliate Dredging International, dredged 265,000 m³ of contaminated sediment according to the “environmental dredging technique”, which prevents contaminated sediment from polluting surrounding waters during dredging.

After dredging the sediment is pumped to a disposal site. A system of geotubes is used for dewatering the sediment.

Geotubes can be compared with a type of stocking made of geotextile. The sludge is encapsulated and protected from the surrounding soil. The geotubes have a diameter of a few metres and are 50 to 100 m long.

The water that comes from the dewatering process is purified before discharge.

The project lasts three years and it is expected that the disposal site can be covered over in the summer of 2007. The harsh winters limit the operational period to eight months a year.