The Use of Microbial Induced Calcite Precipitation to Reduce Trace Elements Leaching from Fly Ash.

North Carolina has over nineteen billion known gallons of coal ash, some of which the industry struggles to store safely.  The 2014 spill in Eden, NC released 39,000 tons of coal ash into the Dan River, jeopardizing wildlife and drinking water. With such an abundance of fly ash in the state, efforts have been made to reuse the material in a variety of ways, including construction, especially on highway embankments. In events such as large rainstorms, fly ash on construction sites could transport trace elements to water sources through percolation and surface runoff. The following research program focuses on reducing the leachability of trace elements found in coal ash using bio-mediated methods.  Microbial induced calcite precipitation (MICP) is used to immobilize trace elements within the fly ash. The MICP process is initiated within dry fly ash material set up in soil columns. Effluent is then collected from the treated fly ash material. The concentrations of the trace elements are measured using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The concentrations within the MICP-treated fly ash effluent are compared to baseline fly ash effluent. The MICP treatment is optimized to further reduce leachate concentrations. The MICP treatment process is also applied to ponded fly ash material to reduce leachate levels from storage ponds into groundwater. As the EPA has endorsed the use of fly ash material in construction materials, the use of fly ash continues to increase and therefore, there is a need to reduce the potential for trace elements leaching from fly ash. The MICP treatment process was allowed to take place, and then effluent samples were collected from percolating water. The MICP-treated leachate was compared to that of a baseline fly ash sample and the results from testing on ponded fly ash.