NATURAL AND SYNTHETIC ZEOLITE AMENDMENTS TO MANGANESE PASSIVE BIOREMEDIATION SYSTEMS IMPACT MICROBIAL PROCESSES

Across much of Appalachia, coal mine drainage (CMD) remains an environmental issue, contributing to the acidification of streams and increasing metal loads in surface and groundwaters. Among the various pollutants associated with CMD, aqueous manganese (Mn) is persistent in the aqueous phase. Passive bioremediation systems mitigate Mn in CMD by promoting the oxidation of aqueous Mn(II) to solid Mn(IV/III) oxide minerals. The remediation systems are lined with limestone to increase pH, stabilizing Mn(IV/III) oxides. Mn oxidizing microbes additionally promote Mn oxidative precipitation and cost efficiency. We investigated the role of combining such passive bioremediation via the Mn oxidizing fungus Stagonospora sp. SRC1lsM3a with abiotic Mn adsorption to a naturally-occurring zeolite (clinoptilolite) and synthetic zeolite (13X). We find zeolites can greatly increase the rate of Mn removal from synthetic coal mine drainage, however, perturbations in solution chemistry readily releases the adsorbed Mn back into the solution, while microbial-limestone systems are more stable. We also find overall Mn oxidative precipitation is decreased with zeolite relative to limestone systems, but Raman spectroscopy reveals triclinic birnessites are produced in both zeolite and limestone systems. Of the 90% limestone-10% zeolite mixtures, 13X more rapidly removes Mn from solution than washed natural clinoptilolite, but washed clinoptilolite improves overall Mn remediation (reaching a similar Mn aqueous concentration as 100% limestone systems by experiment end). However, 10% zeolite amendments are not economically feasible, thus we explored 1%, 0.5%, and 0.1% zeolite amendments. Of these economically viable options, 1% clinoptilolite proved to be the most effective in terms of rate of Mn removal from solution and overall Mn remediation, while 13X did not improve Mn remediation, potentially due to its negative impact on fungal growth. These results indicate caution should be exercised prior to amending bioremediation systems with zeolites due to their potential negative impact on microbial communities, but that zeolites can help improve remediation under specific circumstances.