Biological Source Treatment of Acid Mine Drainage Using Microbial and Substrate Amendments: Microcosm Studies

Microcosm studies in the laboratory demonstrate that sufficient dosages of wastewater effluent (microbial inoculum) and returned milk (substrate) can effectively raise the pH of pyrite-amended acid mine drainage water to circumneutral levels under aerobic conditions in as little as 7 days, and the pH remains at these levels for >19 months. Microbial analysis indicates that a complex biofilm (>70 species) forms over the pyrite. The biofilm dominantly consists of facultative anaerobes, which potentially interact with obligate anaerobes, such as sulfate-reducing Desulfosporosinus sp., to maintain an oxygen-free micro-environment surrounding the pyrite, even though the overlying water remains aerobic. The biofilm became established in water samples with an initial pH as low as 2, and subsequently caused the water pH to increase to circumneutral levels. Concurrently, concentrations of Al, As, Cu, Fe, Pb, Ni, and Zn all decreased substantially compared to baseline concentrations in the control microcosms.