Final Report DE-FG02-04ER63719 Page: 2 of 8
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environments and the application of these findings to the better design of strategies for in
situ bioremediation of uranium.
The research supported by this grant focused on field studies at the ERSP study
site in Rifle, CO. The field researchers supported under this grant were primarily
responsible for setting up the field experiments and sample collection during the field
experiments conducted in 2004-2006. This provided a substantial benefit to many
additional researchers in the ERSP/NABIR program that obtained samples and data from
those field experiments. For example, the following studies which were attributed to our
Community Dynamics ERSP/NABIR funding could not have been possible without the
establishment of the field experiments that were supported by this Biotransformations
Element grant: references (3-6, 9, 11).
Improving the Bioremediation Strategy at Rifle Site and
Documenting Aquifer Heterogeneity
The studies during this funding period built upon our first successful field trial of
in situ uranium bioremediation at the field study site in Rifle, CO (1), the description of
which was published during this funding period. That study demonstrated the potential
for effectively removing uranium from groundwater by stimulating the growth and
activity of Geobacter species in the subsurface. However, U(VI) reduction could not be
sustained because Geobacter species declined over time and there was an increase in
sulfate-reducing microorganisms, that were not effective in U(VI) reduction. This was
attributed to Geobacter species depleting Fe(III) oxides, their primary electron acceptor,
near the acetate injection wells. Without an Fe(III) oxide source the Geobacter species
were not able to compete with the sulfate reducers for the acetate being injected into the
Therefore, a new field study was designed with the goal of sustaining U(VI)
reduction for longer periods of time. The concentration of acetate injected into the
subsurface was increased. The concept was to provide more acetate than the sulfate
reducers could consume with the sulfate available to them in the groundwater. Thus, a
portion of the acetate would continue to move downgradient into zones in which Fe(III)
was still available. It was hypothesized that, in this manner, it would be possible to
continue to stimulate the growth of Geobacter species and promote sustained U(VI)
This approach was successful within some portions of the Rifle site (8, 12).
Detailed geochemical and microbiological analyses of both sediments and groundwater
provided insights into factors controlling the rate and extent of the U(VI) reduction (12).
Sediments close to the point of acetate injection were depleted in Fe(III) oxides and
sulfides accumulated. Sulfate-reducing microorganisms predominated within these
sediments and there was little, if any, U(VI) reduction within this zone. Further down-
gradient, where Fe(III) oxides were still available, Geobacter species were more
prevalent and U(VI) was reduced. These results were significant because they
demonstrated that from a knowledge of microbial physiology and ecology it was possible
to design a bioremediation strategy that could accommodate geochemical limitations to
sustain uranium removal.
However, the effectiveness of uranium bioremediation was not uniform
throughout the treatment plot (12). One reason for this was the method of acetate
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Lovley, Derek, R. Final Report DE-FG02-04ER63719, report, March 12, 2008; Amhearst, Massachusetts. (https://digital.library.unt.edu/ark:/67531/metadc898395/m1/2/: accessed April 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.