Exploration of Natural and Induced Biological Activity in Weathered and Unweathered Fly Ash

Coal fly ash, a residual material generated during combustion of fuel for energy production, is often land disposed, and subjected to long-term physical and chemical weathering. In the present study, in situ biological activity of fly ash that weathered in a disposal pond in the southeastern US was investigated through laboratory experimentation and analysis of samples under scanning electron microscopy. Induced biological activity was studied using microbially induced calcite precipitation with biostimulation. In both cases, biological activity was observed in the ash samples, including diatoms found in weathered fly ash, and bacterial cells that were grown in bio-stimulated fly ash columns. The results demonstrate that despite harsh geochemistry and pore size limitations, biological activity in microorganisms spanning two orders of magnitude in size is possible in fly ash. This diverse biological activity can impact ash pond management through hydraulic conductivity and dewatering issues, as well as beneficial use in concrete through pozzolanic activity.