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Center for Biofilm Engineering
Subsurface
Biotechnology & Bioremediation
Project Summary
Title: Microbial biobarriers for the control of acid rock drainage from mine tailings
Period: September 1, 1998 – September 30, 2001
Goals: Acid rock drainage from hard rock mine lands is a major environmental problem that impacts both ground- and surface-water throughout the Western U.S. Waste rock and mine tailings often contain high concentrations of metal sulfides which, when contacted by oxygen-containing water, leach metals into solution and radically lower the pH of the receiving water. This research sought to further develop an inexpensive and potentially widely applicable treatment technology to utilize indigenous microorganisms within mine tailings to abate ARD at its source. An innovative method to prevent oxygen transport into tailings is the development and maintenance of a biologically active barrier within the near-surface zone of the tailings. This barrier is made up of naturally occurring aerobic and facultative bacteria which utilize dissolved oxygen in the infiltrating water, and therefore, maintain the reducing conditions which are necessary for pyrite to remain bound in mineral form. In addition, the generation of anoxic conditions stimulates the activity of sulfate-reducing bacteria (SRB) within the tailings. SRB produce hydrogen sulfide as a metabolic by-product, which may further react with dissolved metals, promoting their removal as metal-sulfide precipitates. This research included laboratory experimentation with columns filled with acid-producing mine tailings. Objectives for the research are to 1) determine the effectiveness of various carbon sources in stimulation of general heterotrophic bacteria and SRB, 2) determine the longevity of treatment effectiveness, and 3) determine the effects of carbon treatment on column effluent pH, oxidation-reduction potential (ORP) and dissolved metals.
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