SULFATE REDUCTION IN THREE INDIANA WETLANDS RECEIVING ACID MINE DRAINAGE

Constructed wetlands have been shown to be effective in treating various types of wastewater. One type, Acid Mine Drainage (AMD), is characterized by high acidity, iron and sulfate. Three Constructed Wetlands, Friar Tuck, Tecumseh, and Midwestern in southwestern Indiana were studied to determine their treatment efficiencies for sulfate removal. Sulfate Reduction by microorganisms in constructed wetlands can remove sulfate and dissolved metals, and can generate alkalinity. Approximately 100 water samples and 50 soil samples were taken during the winter and summer seasons at the three wetlands and analyzed for sulfate/sulfide concentrations, sulfur isotope values, and pH, Eh and conductivity. Resulting data indicates that sulfate reduction is active at all three wetlands, but varies in degrees of effectiveness. The Friar Tuck wetland shows little evidence of sulfate reduction, with dilution being the main remediation mechanism. A small volume of AMD is being overwhelmed by numerous freshwater inputs resulting in a significant improvement in water chemistry. The Tecumseh wetland shows little change in influent/effluent sulfate and sulfide values suggesting that treatment of the influent wastewater by sulfate reduction was inactive for both sampling seasons. The Midwestern wetland for the summer season shows a significant increase in the 34S/32S isotope ratio, from -5.03 per mil to +0.27 per mil with a corresponding drop in sulfate concentrations from 1740 ppm to 831 ppm, demonstrating successful sulfate reduction and wastewater treatment. However, the winter season sampling showed no change in the 34S/32S isotope ratio, indicating only minor sulfate reduction, but sulfate concentrations still fell from 1740 ppm to 831 ppm, indicating that an additional SO4 precipitation process is occurring.