Article

Resistance of Solid-Phase U(VI) to Microbial Reduction during In Situ Bioremediation of Uranium-Contaminated Groundwater

Department of Microbiology, University of Massachusetts, Morrill Science Center IVN, Amherst, MA 01003, USA.
Applied and Environmental Microbiology (Impact Factor: 3.67). 01/2005; 70(12):7558-60. DOI: 10.1128/AEM.70.12.7558-7560.2004
Source: PubMed

ABSTRACT

Speciation of solid-phase uranium in uranium-contaminated subsurface sediments undergoing uranium bioremediation demonstrated
that although microbial reduction of soluble U(VI) readily immobilized uranium as U(IV), a substantial portion of the U(VI)
in the aquifer was strongly associated with the sediments and was not microbially reducible. These results have important
implications for in situ uranium bioremediation strategies.

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    • "However, there are some disadvantages that contribute greatly to the overall effectiveness. For example, some studies have shown that acetate oxidizing sulfate reducing bacteria (SRB) are less efficient at mediating the redox reactions necessary for uranium immobilization (Yabusaki et al, 2010; Anderson et al, 2003; Ortiz-Bernad et al, 2004). Also, organic substrates will select for heterotrophic bacteria which have a high growth yield (Rittmann and McCarty, 2001), which could result in aquifer clogging, consequently, impeding further delivery into the aquifer. "
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    • "Here, bioremediation is used to refer specifically to the biomineralization phase of DMRB bioremediation strategies. Bioremediation has been successfully demonstrated in laboratory systems and in a general sense at the field-scale (e.g., Holmes et al., 2002; Senko et al., 2002; Anderson et al., 2003; Ortiz-Bernard et al., 2004). However, wider application of the technique would benefit from knowledge of its effectiveness in dual-porosity porous media. "
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    • "A key disconnect between the experimental data and the simulation results is that the simulation predicted complete reduction of U(VI) at the outset the Fe(III) reduction phase, whereas U(VI) reduction did not proceed to completion (Figure 4F). Other studies have documented incomplete reduction of solid-associated U(VI) in reduced subsurface sediments that contain excess electron donor and abundant Fe(II) as a potential chemical reductant for U(VI) (10, 42, 43). The persistence of substantial solid-associated U(VI) during active Fe(III) reduction provides an explanation for the increase in dissolved U(VI) that took place later on during the methanogenic phase of the experiment: complexation of residual U(VI) by DIC (>10 mM) produced during methanogenic oxidation of acetate could have easily shifted the balance between aqueous and surface-associated U(VI) (44). of the reduced slurries to assess possible metabolic (as opposed to geochemical) reasons for incomplete U(VI) reduction observed in the ethanol-amended slurries. "
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