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Dynamics of Mn removal in an acid mine drainage treatment system over 13 years after installation

Crafton, Elizabeth, Pritchard, Casey, Guo, Lin, Senko, John M., Cutright, Teresa J.
Environmental earth sciences 2019 v.78 no.1 pp. 10
acid mine drainage, aluminum, bacteria, coal, environmental impact, iron, limestone, manganese, pH, watersheds, wetlands, Ohio
Acid mine drainage (AMD) from abandoned and active mines continues to pose a serious threat to the environment. Metal-rich fluids may emerge from abandoned mine works for hundreds of years, so the long-term performance of treatment systems must be evaluated to minimize the environmental impacts of AMD. A two-step process consisting of an aerobic wetland and a limestone bed is being used to treat coal mine-derived AMD in the Huff Run watershed of eastern Ohio, USA, and has been in operation for over 13 years. In 2002, the water was acidic (3.66 pH). From 2004 to 2014, water entering the treatment system had a pH of ~ 5.7 that increased to 7.25 by the time it exited the limestone bed. Since 2004, the effluent Al, Mn, and Fe concentrations have been between 0.05 and 0.12 mg/L, 0.04 and 0.25 mg/L, and 0.05 and 0.34 mg/L, respectively, with the majority of Fe and Al removal occurring in the wetland along with partial Mn removal. Subsequently, further Mn removal occurs as AMD flows through a limestone bed that was inoculated with a consortium of Mn(II)-oxidizing bacteria at the time of construction. An evaluation of historical system performance and current conditions indicate that effective metal removal has been sustained for over 13 years. While Mn(II)-oxidizing bacteria were most abundant in the limestone bed, they were detected throughout the system, indicating that indigenous Mn(II)-oxidizing microorganisms may be contributing to Mn removal well after the inoculation of the system.