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Demonstration of the Natural Freeze-Thaw Process for the Desalination of Water from the Devils Lake Chain to Provide Water for the City of Devils Lake

B.C. Technologies, Inc.; Laramie, WY.
University of North Dakota; Energy & Environmental Research Center; Grand Forks, ND.
August 2002

Report #71 - Executive Summary -

The purpose of this project, conducted by the Energy & Environmental Research Center (EERC) and B.C. Technologies, Ltd. (BCT), was to demonstrate the potential of using the natural freeze-thaw (FT) process for the treatment of saline surface water from the Devils Lake chain to provide a new water supply for beneficial use applications by the city of Devils Lake, ND. This project took saline feedwater for treatment directly from Devils Lake and desalinized the water using the natural FT process. Samples of feed, treated water (TW), and concentrated brine were collected and analyzed during operations to allow sufficient data to be collected to determine the approximate performance and cost of a full-scale FT plant and to validate the demonstration of the FT process.

Successful demonstration of the FT process under North Dakota climatic conditions could facilitate application of the FT process throughout the region. The successful demonstration of the FT process for the desalination of Devils Lake water also provided data for planning a permanent facility in the Devils Lake chain. Furthermore, demonstration of the FT process in this application provided information allowing assessment of the potential of the process to contribute to future disaster mitigation efforts related to the overflow of Devils Lake water into the surrounding area.

The demonstration project included the following deliverables:

  • Task 1 - FT demonstration site selection
  • Task 2 - FT simulation testing with Devils Lake water
  • Task 3 - FT demonstration plant design
  • Task 4 - Acquisition of required site permits
  • Task 5 - FT demonstration plant construction
  • Task 6 - Demonstration plant startup and shakedown
  • Task 7 - Operation of the FT demonstration plant
  • Task 8 - Site reclamation
  • Task 9 - Plant performance assessment, economic evaluation, and integration into flood migration plans

    Site selection, FT simulation testing, and FT plant design and construction were performed during the summer and fall of 1998. FT plant startup and shakedown were performed from December 28, 1998, through January 1, 1999. From January 1, through March 15, 1999, the FT plant was operated in a freezing mode, applying and freezing approximately 4,400,000 gallons of Devils Lake water to two freezing pads. From March 15, through June 2, 1999, the ice piles were allowed to melt, and 3,684,290 gallons of TW were recovered, having an electrical conductivity (EC) of approximately 450 parts per million (ppm), representing a freshwater yield of 84-percent, by volume. In addition, 123,701 gallons of brine having an EC of approximately 11,500 ppm, 253,507 gallons of nondischargeable intermediate water, and 182,583 gallons of discharable intermediate water were recovered. Approximately 7,700 pounds of precipitate (primarily calcium carbonate) were formed and left behind on the freezing pads.

    On the basis of technical data, the FT demonstration plant operated at Devils Lake was successful at reducing salt concentration of Devils Lake water to acceptable levels, compared to other raw water sources.


    For more information about the DWPR program, contact Kevin Price at: Bureau of Reclamation, 86-69000, PO Box 25007, Denver CO 80225; phone (303) 445-2260; or e-mail a message to MPrice@usbr.gov.