Date of Award

8-2017

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Engineering and Earth Sciences

Committee Member

Dr. Kevin Finneran, Committee Chair

Committee Member

Dr. Brian Powell

Committee Member

Dr. Christophe Darnault

Abstract

Microbial interactions with radionuclides in the environment are multi-faceted and play an important role on the fate and the extent of transport of these metals within the biosphere. Understanding how these biotic interactions affect radionuclides could prove useful in developing more suitable waste containment facilities and improve the overall risk management strategies at legacy waste sites around the world. This study investigates two microbial interactions with these metals: biosorption and bioreduction. To elucidate the impact of biosorption on uranium and cesium, active and inactive biomass were analyzed using batch sorption experiments in the presence of complexing ligands, EDTA and citrate, to determine whether whole cells or cell lysate increased sorption. Results demonstrated systems without soil showed a decrease in free aqueous uranium with biomass present in EDTA. Adding a second complexing ligand decreased the amount of biosorption to active biomass, but not inactive biomass. With soil present in the system, biomass increased the sorption of uranium to the soil regardless of the complexing ligand. In contrast, cesium was unaffected by the biomass and complexing ligands due to its affinity to sorption sites associated with the soil. Therefore, remedial strategies incorporating biomass as biosorbents increase the retention of uranium but have no effect on cesium. Further, the transformation of U(VI) to U(IV) via bioreduction was studied to quantify the rate and extent of U(VI) reduction using various electron donors. Re-oxidation of U(IV) experiments followed in the presence of nitrate or oxygen to determine the long-term viability of bioreduction as a remedial strategy for treating groundwater contaminated with uranyl carbonate. Results showed the various electron donors tested were sufficient to allow bioreduction of U(VI) to U(IV). However, re-oxidation occurred on the magnitude of days in the presence of oxygen or nitrate. Therefore, bioreduction of uranium as a remedial strategy does not offer long-term solutions for groundwater contaminated with uranyl carbonate.

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