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Process and Apparatus to Accelerate Restoration of Acidified Water by Pretreatment with Carbon Dioxide


Industrial, chemical, and mining processes resulting in acid deposition in streams and lakes have had a significant negative effect on aquatic resources in North America, including the loss of important commercial and recreational fisheries. Direct effects of acidification on fish include acute mortality, reproductive failure, altered growth rates, and chronic impairment to body organs and tissues. Negative indirect effects of acidification include fish habitat degradation, increase in concentrations of soluble toxic metals, such as aluminum, and changes in predator-prey relationships.

Within the coal deposit regions of Appalachia and the Ohio River Basin, acid mine drainage contributes significantly to acid deposition in surface waters. Given the severity of the problem and associated environmental/economic ramifications, the Biological Resources Division of the

U.S. Geological Survey (USGS), signed the statement of Mutual Intent for "Restoration and Protection of Streams and Watersheds Polluted by Acid Mine Drainage from Abandoned Coal Mines," put forth by the Office of Surface Mining and the Environmental Protection Agency. Work has been done to increase the understanding and application of the best technologies available for remediating and preventing mine drainage and to support the development of new technologies.

About the Process

A variety of processes and apparatus designs using calcium carbonate have been developed in an attempt to treat effluent acidity. In addition, a variety of apparatus designs have been used to dose acid mine drainage with calcium carbonate. Researchers at the USGS have invented an improved process and apparatus using carbon dioxide pretreatment of the effluent to accelerate limestone (calcium carbonate) dissolution with subsequent recycling of the carbon dioxide gas stripped or recovered from water exiting the apparatus. This invention is a method of using an intermittently fluidized (pulsed) limestone bed system incorporating carbon dioxide pretreatment to enhance restoration of acidified water from acid mine drainage and chemical industrial processes.


The main advantages of this method are acceleration of limestone dissolution rates by increasing dissolved carbon dioxide concentrations and reduction of treatment system sensitivity to limestone armoring by intermittent fluidization of limestone beds. Other advantages include the ability to:

  • allow for sidestream treatment. Side streaming eliminates the need to dam the entire flow and reduces significantly the size of the reactor and plumbing required for treatment, thus reducing capital and site preparation costs,
  • enhance rates of biological productivity in acidified impaired waters,
  • improve the efficiency and reduce the cost of limestone beds for the treatment of acid drainages,
  • to increase the hardness and alkalinity of very soft waters,
  • make acid drainage suitable for development of aquaculture production, and
  • obtain the release of calcium ions from calcium carbonate to reduce the toxicity of certain dissolved metals.

For More Information

For more information about licensing of this and other patents and for cooperative research opportunities with the USGS, please contact:

U.S. Geological Survey
Branch of Business Development
12201 Sunrise Valley Drive, MS 500
Reston, VA 20192
Tel: (703) 648-4344
FAX: (703) 648-4706
Email: Branch of Business Development

For information about the technical details of this invention please contact the inventor:

Barnaby J. Watten
U.S. Geological Survey
Leetown Science Center
1700 Leetown Road
Kearneysville, WV 25430
Tel: 304-724-4425
FAX: 304-724-4435

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