Although the countless lakes and woods in Sweden are its most important environmental asset, 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 were found in two lakes near the city of Hultsfred in Sweden.
What we do
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Challenge
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Solution
DEME designed and dimensioned an environmental dredging method to clear the mercury sediments and other pollutants from the two lakes, even building a special new vessel called the ‘Pixie’ that is able to dredge mechanically and transport the sediments hydraulically. In the summer of 2006, we eventually dredged 280,000 m³ of contaminated sediment using the new vessel. Then after dredging the sediment was pumped to a disposal site.
This pioneering project also made large-scale use of geotubes for dewatering the sediments. By deploying a system of geotubes, the sludge is encapsulated and protected from the surrounding soil. The geotubes had a diameter of a few metres and were 50 to 100 m long. Water that came from the dewatering process was purified before discharge. A custom-built water treatment plant, with a capacity of 200 m³ per hour, treated the water over a 1.5 year period.