In past years, microbial reduction has been explored as a remediation method for uranium-contaminated groundwater at U.S. Department of Energy sites with promising results. Although transport models have been improved to include variations in geochemical concentrations, reductive microbial processes, and adsorption of uranium to minerals, they do not incorporate the presence of microorganisms as sorption sites that may influence the overall transport of uranium. The main objective of this research was to determine the effects of uranium biosorption on the overall transport of uranium by understanding the solution chemical equilibrium and its effects on modeling sorption. This was done by first evaluating the uncertainty associated with uranium equilibrium speciation and its effect on the prediction of uranium sorption to minerals. Then, the partition coefficient between U(VI) and the microbial species Geobacter uraniireducens and Acholeplasma palmae were experimentally determined. The experimentally obtained partition coefficients were used to incorporate biosorption into a thermodynamic model that describes the distribution of uranium in a system with microorganisms available as sorption sites. When considering mineral adsorption equilibrium, modeling predictions were robust with respect to adsorbed U(VI) concentration, as indicated by the resulting normal Gaussian distributions. Modeling predictions also indicated the amplification of uncertainty with background levels of total U(VI) and higher estimates of input uncertainty (spatial and temporal variability), as indicated by the resulting bi-modal Gaussian distributions. Experimental results indicate that U(VI) sorbs more strongly, approximately 300 times, to G. uraniireducens under low-dissolved inorganic carbon (DIC) conditions and decreases as DIC increases. Under low-DIC conditions, the KD obtained for uranium sorption to G. uraniireducens is 7985 ± 1024 L kg-1, which is larger than the KD of 1850 ± 1.8 L kg-1 determined for uranium sorption to the surface of A. palmae. Beamline analysis on sorption tests with G. uraniireducens detected reduction had occurred in these experiments without the addition of an external electron source, indicating that the obtained KD values are overestimated for G. uraniireducens. While the partition coefficients of the bacteria in high-DIC waters are comparable to reported U(VI)- mineral sorption, when combined with the bacterial concentration during and after remediation, the amount of uranium sorbed to the microorganisms is not large enough to produce a noticeable effect on the transport of uranium in a bioremediated aquifer. Finally, the reactions that describe sorption as captured by the experimentally obtained partition coefficients were best described by the sorptive site reacting with uranium and one or two carbonate groups.
Uranium--Absorption and adsorption, Uranium--Migration, Radioactive wastes--Biodegradation, Groundwater--Purification--Uranium removal.
This work was funded by DOE Environmental Remediation Science Program DE-FG02-08ER64585 Novel Sensor for the In Situ Measurement of Uranium Fluxes.' Various sources of intellectual and/or analytical support were made by the following: Steve Cabaniss, Kerry Howe, Yamane Asmerom, Victor Polyak, Bruce Thomsone, and Andrew Schuler (University of New Mexico); Kirk Hatfield and Mark Newman (University of Florida); Jim Ranville and Valerie Stucker (Colorado School of Mines); Lucie N'Guessan (Exon); Aaron Peacock (Haley Aldrich); Steve Yabusaki and Philip Long (Pacific Northwestern National Laboratory); Ken Williams, Luis Comolli, Birgit Luef, and Roseann Csencsits (Lawrence Berkeley National Laboratory); Melissa Barlett, Roberto Ornella, and Derek Lovley (University of Massachusetts); John Bargar, Don Pham, and NoÃ©mie Janot (Stanford Linear Accelerator Center National Accelerator Laboratory); and Paul Reimus (Los Alamos National Laboratory).'
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Leavitt, Jeanette. "Biosorption of uranium and its effect on uranium transport in groundewater." (2012). https://digitalrepository.unm.edu/ce_etds/3