Ethanol Fed, Semi-Passive Bioreactors at the Leviathan Mine
Glenn C. Miller, Ph.D.
The use of sulfate-reducing bioreactors to treat acid mine drainage has advantages over current active treatment technologies due to the passive to semi-passive nature of the treatment as well as the lower volumes of sludge produced, which both contribute to lower operational costs. In 2002, a semi-passive bioreactor was constructed at the Leviathan Mine, Alpine County California. This remote site is located at approximately 7000 ft elevation on the eastern slope of the Sierra Nevada Mountains. Alcohols are utilized by sulfate-reducing bacteria to reduce sulfate to sulfide and precipitate metals as metal-sulfides. Because alcohols do not freeze under normal site conditions, this carbon and energy source can be gravity fed to supply the bacteria with specific concentrations of reducing equivalents throughout the year. A rock matrix with large pore spaces is utilized in conjunction with a flushing mechanism to reduce the chance of plugging and short circuiting within the bioreactor. In addition, the majority of the metals are removed outside of the bioreactor. Treated water, laden with sulfide is mixed with untreated water in a settling pond where the metals are removed. Water, essentially free of metals, is then passed through the bioreactor where sulfate-reduction and sulfide generation occurs. This system is less active than conventional lime treatment and can operate for longer periods of time without replacement of the matrix when compared to traditional passive bioreactors.
Key words. bioreactors, wetlands, acid mine drainage, acid rock drainage, sulfate reduction, sulfate reducing bacteria, water treatment, mining remediation, and passive treatment systems
BiographyGlenn C. Miller is a Professor of Natural Resources and Environmental Science at the University of Nevada, Reno. He is also the Director of the Graduate Program in Environmental Sciences and Health at UNR. He has a B.S. in Chemistry from the University of California, Santa Barbara and a Ph.D. in Agricultural and Environmental Chemistry (1977) from the University of California at Davis. Following graduate studies, he spent a year of postdoctoral study at the EPA's Environmental Research Laboratory in Athens, Georgia and has been at UNR since 1978. Current areas of research include acid mine remediation using anaerobic sulfate reducing systems, closure of precious metals heaps, and precious metals pit water quality. In the recent past he has examined emissions from marine engines into Lake Tahoe and the associated risks with those emissions. He teaches courses in Environmental Toxicology, Risk Assessment and Environmental Chemistry. He is a member of the American Chemical Society, SETAC, AAAS and Sigma Xi.