IMPROVING COAL MINE DRAINAGE MANGANESE BIOREMEDIATION: THE IMPACTS OF DIFFERENT LINER ROCKS AND OF COMPETITIVE COPPER ADSORPTION

Coal mine drainage (CMD) remains a persistent issue across the Appalachian region of the United States, resulting in metal contamination of ecosystems and water distribution. With manganese (Mn) remediation from CMD primarily relying on the oxidative precipitation of aqueous Mn(II) to form Mn(III/IV) oxide minerals, Mn contamination often persists in CMD due to the particularly slow kinetics of abiotic Mn oxidation. CMD passive bioremediation sites typically introduce carbonate rocks (e.g., limestone or dolostone) to increase the water pH and promote Mn bioremediation by microbial Mn-oxidizers, primarily Mn-oxidizing fungi.

This current work focuses on the effect of potential liner rocks on Mn oxidation from a synthetic CMD by Ascomycete Mn-oxidizing fungi (in this study, Stagonospora sp. SRC1lsM3a and Paraconiothyrium sporulosum AP3s5-JAC2a). Aqueous Mn concentrations and pH were tracked throughout the experiments. The resulting solids were analyzed using scanning electron microscopy paired with energy dispersive X-Ray spectroscopy (SEM-EDS) and Mn K-edge X-ray absorption near edge structure (XANES) spectroscopy to determine average Mn oxidation state. The myco-limestone solids contain discrete, nearly spherical Mn mineral precipitates with relatively high fractions of Mn(II) overlying the limestone. Meanwhile, the myco-zeolite system contains coatings of high weight percent Mn(III/IV) oxides nearly covering the zeolite surface. In zeolite systems (both abiotic and with fungi), 95-99% aqueous Mn is removed from synthetic CMD within just 24 hours. Meanwhile, limestone systems do not achieve a similar threshold until day 12 but ultimately remove more Mn(II) from solution. Select samples were additionally reacted with varying concentrations of copper (Cu) chloride to assess the stability of Mn removal, as zeolites preferentially bind Cu over Mn. The results show that Cu initially desorbs Mn and causes a slight reduction in the average Mn oxidation state of the resulting solids, but has no long term effect on macroscopic removal of Mn. This research demonstrates that liner rocks play an important role in both the rate and overall extent of Mn bioremediation from CMD.