Microbial Cycling of Iron in Acid Mine Drainage

Pennsylvania has more than 3800 miles of streams impacted by acid mine drainage (AMD) associated with past or current coal mining activities and AMD represents Pennsylvania’s single largest water quality problem. AMD is formed when coal bearing sediments that contain abundant pyrite – an iron containing mineral – are exposed to oxygen-containing waters via the mining process.

Neutralization and removal of dissolved iron represent the most pressing targets of AMD treatment. While passive treatment strategies may involve various levels of engineering, they all involve the neutralization of iron-containing waters using limestone. However, during the process, precipitates of iron oxide coat the limestone thereby reducing further neutralization capacity.

A possible solution to increase the effectiveness of passive treatment would be to remove the iron before neutralization with limestone. Bacteria communities in one AMD-impacted seep (Gum Boot seep in north-central Pennsylvania) appear to be removing iron prior to neutralization.

Penn State researchers Drs. John Senko, William Burgos with the Department of Civil and Environmental Engineering and Mary Ann Bruns with the Department of Crops and Soil Science are characterizing the microbial activities, community structure and oxygen requirements of bacteria in the Gum Boot system to identify the organisms that are catalyzing iron removal from AMD to potentially improve the design and efficiency of passive treatment systems.