Anaerobic Bioremediation of Acid Mine Drainage using Emulsified Soybean Oil
Batch incubation and flow-through column experiments were conducted to evaluate the use of emulsified soybean oil for in situ treatment of acid mine drainage. Addition of soybean oil, soluble substrates, and a microbial inoculum to the batch incubations resulted in complete depletion of SO4, 50% reduction in Fe, and an increase in pH to >6. A one time injection of emulsified soybean oil, lactate, yeast extract, and a microbial inoculum stimulated SO4 and metal ion reduction for =300 days in laboratory columns packed with mine tailings receiving influent solutions with a pH =3 and =5. In all emulsion treated columns, SO4 and Fe were reduced, pH increased to >6, and Al, Cu and Zn removal efficiency was 99% or greater. Cu, Fe, Mn and Zn were removed as metal sulfides and/or carbonates with removal efficiency decreasing with increasing metal sulfide solubility. The low pH and high heavy metals concentrations did not significantly inhibit biological activity. However, SO4 removal with associated precipitation of metal sulfides may have been limited by the short hydraulic retention time (6-7 days) of the columns. There was a significant hydraulic conductivity loss in one of the four treated columns, indicating that hydraulic conductivity loss may be an issue under certain conditions.