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Contribution of Biosorption Processes to the Sustained Removal of Uranium from Groundwater in the Absence of Added Electron Donor


EMSL Project ID
25441

Abstract

An unexpected phenomenon occurred in the ongoing field studies at the Environmental Remediation Sciences Program study site in Rifle, CO. Long-term removal of uranium from the groundwater following active biostimulation with acetate amendments to the aquifer was observed for more that 18 months. Previous studies have demonstrated that addition of acetate to contaminated groundwater stimulates the growth of Geobacteraceae which are organisms able to reduce U(VI) to U(IV). After two years of three-month acetate additions to a contaminated aquifer resulting in successful and repeatable uranium removal from groundwater, reduced levels of the contaminant were sustained for a surprising extended period of time in the absence of the electron donor. Laboratory experiments demonstrated that this lost uranium was not transformed to U(IV) but instead was accumulated in the sediment in the form of U(VI). Further analysis of the sediment revealed that the presence of a live microbial population in the reduced sediment was essential for this phenomenon to occur. Microbial community analysis indicated that Mollicutes were predominant in the sediment exhibiting enhanced uranium sorption capacity. It is proposed that biosorption is an important mechanism responsible for the continued removal of uranium from groundwater following stimulation dissimilatory metal reduction. Therefore comparative sorption studies will be undertaken with bacteria found in the subsurface at different stages of biostimulation. Imaging of selected organisms with cryo-TEM will help in the localization of uranium sorption sites under various environmental conditions. Results will contribute to the development of both conceptual and mathematical models describing the unexpected field observation.

Project Details

Project type
Large-Scale EMSL Research
Start Date
2007-09-12
End Date
2008-11-16
Status
Closed

Team

Principal Investigator

Lucie N'guessan
Institution
University of Massachusetts Amherst

Team Members

Derek Lovley
Institution
University of Massachusetts Amherst