Freeze dewatering and drying is a method where large volumes of contaminated sediment, from land or seabed, are frozen in place in large specially designed freezer drawers that can hold 5 tons of contaminated material.
- The big gain with this technology is that we remove the water from the sediments. The dry powder that remains is significantly less expensive to keep in landfills than contaminated sediment containing water, says researcher Susanne Rostmark. When dredging in the lake Alalombolo, we froze 50 000 tonnes of mercury contaminated sediments. After dewatering and drying we got left 5,000 tons. By first freeze the contaminated areas and then thaw them, the pollution is left in the powder that remains after the water has melted away. The melt water is free of contaminants.
The method works on all types of pollution, and now we are about developing real large scale freeze dewatering.
The technique commonly used when dredging stirs up lots of contaminated sediment unlike freezer dredging technology that is not disrupting the material and where sediment is transported away in frozen five-ton blocks. Freeze dewatering and drying has also been used to collect aircraft parts and remnants after a large plane crash. The technology is already used by the Sellafield reprocessing plant in the UK and a collaboration with Swedish reprocessing plant Studsvik is discussed.