Protect and Enhance the Nations Natural Resource Base and Environment

Improving Bioreactors at Super Fund Waste Sites

Issue (Who cares and why?)
     Industry, labor, government, and environmentalists agree on one issue: that acid mine drainage is the number one environmental problem facing the mining industry. Acid mine drainage occurs when sulphide-bearing minerals in rock are exposed to air and water, changing the sulphide sulphur to sulphuric acid. This acid can dissolve heavy metals found in waste rock and tailings such as lead, zinc, copper, arsenic, selenium, mercury, and cadmium, into ground and surface water. Acid mine drainage and heavy metals pollution can poison ground and drinking water. It can also destroy aquatic life and habitat.
      Sulfate-reducing systems have the potential to remediate acid drainage at abandoned mine sites by reversing the oxidation processes which are responsible for creation of the acidic water and the release of the metals. In this process, a carbon source is used to biologically reduce sulphuric acid to hydrogen sulfide, followed by precipitation of metals (and others) as metal sulfides. This process raises the pH of the water and effectively removes most metals, and also reduces sulfate concentrations.

What has been done?
     For the completed project, University of Nevada scientists have developed a metals and sulfate reducing bioreactor for use as treatment systems for acid mine drainage, utilizing inexpensive alcohols (methanol, ethanol and ethylene glycol) as carbon sources that can be dripped into bioreactors. To date, investigators have demonstrated that each of these alcohols can serve as a carbon source for sulfate reduction and metal precipitation. This year, scientists installed a recirculation system that has proven to remove 99 percent of all metals found in the mine’s waste water.

Impact
      The University of Nevada alcohol driven bioreactor demonstrates one of the most cost-effective method of treating acid mine drainage, and has wide applicability to other sites. At a cost of about $2.00 per day to treat roughly 8000 gallons of water (the maximum flow from Leviathan Mine, CA), remediation efforts could effectively treat this facility for the next thousand years and still not have spent as much as some lime treated facilities — the previously least expensive method. The combination of passive treatment and low sludge generation render this process appropriate for a wide variety of acid mine drainage sites. Four new bioreactors were installed at Silver Equity Pit Lake to treat high levels of zinc. These bioreactors are proving highly successful for treatment of zinc contaminated fluids that may not have high acidity, reducing toxic zinc levels to below 0.1mg per liter.

Contact
Glenn Miller
Natural Resources and Environmental Science/186
University of Nevada
Reno, Nevada 89557
gcmiller@unr.nevada.edu