Freezing Out Sludge

by C. James Martel, (M.ASCE), Environmental Engr.; U.S. Army Cold Regions Research and Engineering Laboratory, 72 Lyme Rd., Hanover, NH 03755,

Serial Information: Civil Engineering—ASCE, 1991, Vol. 61, Issue 11, Pg. 64-65

Document Type: Feature article


Sludge dewatering is one of the most difficult problems in water and wastewater treatment. This has been especially true for treatment plants in cold regions. Drying beds, the most common dewatering method, need lots of land because of the short warm season. Mechanical techniques such as centrifuges and filter presses are hard to maintain because skilled operators are few and plants are generally remote from replacement and repair facilities. But now there is a dewatering method specifically suited for cold regions—the sludge freezing bed. This new technology works on the principle that ice crystals grow by incorporating water molecules only. All other impurities—such as the solid particles in sludge—are forced to the boundaries of the ice crystal, where they become compressed or dehydrated. During thaw, the meltwater drains away between the consolidated particles, leaving a dewatered sludge. The process seems to work on all types of aqueous sludges. This article is the first full-scale demonstration of a freezing-bed concept developed by the U.S. Army Cold Regions Research and Engineering Laboratory at army bases in Wisconsin and Alaska in the winter of 1990-91.

Subject Headings: Dewatering | Freezing | Sludge | Ice | Particles | Wastewater treatment | Filters | Rehabilitation

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