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


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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    ABSTRACT: In situ recovery (ISR) of uranium alters the baseline groundwater geochemistry in order to mobilize and complex uranium to extract and concentrate it. ISR wellfield restoration is often challenging, and primarily relies on groundwater sweep, reinjection of treated permeate, and/or injection of reductants. Greater focus should be placed on injection-based approaches (using existing infrastructure) based on established engineering concepts used for in situ remediation of groundwater plumes. Such injection-based approaches could shorten restoration timeframes consequently reducing long-term operational costs. This paper addresses various types of injection-based approaches to wellfield restoration based on in-situ remediation success with other constituents that require similar treatment. This paper describes necessary design practices for injecting reactive chemicals (e.g., reductants or biostimulants), operations and maintenance (O&M) strategies to prevent fouling of the chemical delivery system and well network, and natural constraints to restoration. Best practices for successful biostimulation strategies that minimize residual uranium, radium, oxoanions, and other trace elements are as described. Advantages of such injection-based approaches could include significant reductions in restoration times, and consequently, lower restoration costs.
    Full-text · Conference Paper · Feb 2014
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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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    ABSTRACT: Uranium contamination is a serious environmental concern worldwide. Recent attention has focused on the in situ immobilization of uranium by stimulation of dissimilatory metal-reducing bacteria (DMRB). The objective of this work was to investigate the effectiveness of this approach in heterogeneous and structured porous media, since such media may significantly affect the geochemical and microbial processes taking place in contaminated sites, impacting remediation efficiency during biostimulation. A biogeochemical reactive transport model was developed for uranium remediation by immobile-region-resident DMRB in two-region porous media. Simulations were used to investigate the parameter sensitivities of the system over wide-ranging geochemical, microbial and groundwater transport conditions. The results suggest that optimal biomineralization is generally likely to occur when the regional mass transfer timescale is less than one-thirtieth the value of the volumetric flux timescale, and/or the organic carbon fermentation timescale is less than one-thirtieth the value of the advective timescale, and/or the mobile region porosity ranges between equal to and four times the immobile region porosity. Simulations including U(VI) surface complexation to Fe oxides additionally suggest that, while systems exhibiting U(VI) surface complexation may be successfully remediated, they are likely to display different degrees of remediation efficiency over varying microbial efficiency, mobile-immobile mass transfer, and porosity ratios. Such information may aid experimental and field designs, allowing for optimized remediation in dual-porosity (two-region) biostimulated DMRB U(VI) remediation schemes.
    Full-text · Article · May 2011 · Journal of Hydrology
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    • "A factorial experimental design was employed for the microcosm study, and three factors were considered, including bicarbonate (1 vs 40 mM), sulfate (1.1 vs 3.2 mM), and electron donors (ethanol, acetate, and control). The low concentration level of bicarbonate was to simulate the condition used in our field pilot-scale test (Wu et al. 2006; 2007), while the high level was to test if U(VI) reduction may be accelerated through the extraction or desorption of solid-phase U(VI) by bicarbonate (Phillips et al. 1995; Ortiz-Bernad et al. 2004; Zhou and Gu 2005). Two concentration levels of sulfate were used to test if an elevated sulfate concentration may inhibit the reduction of U(VI). "
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    ABSTRACT: A microcosm study was performed to investigate the effect of ethanol and acetate on uranium(VI) biological reduction and microbial community changes under various geochemical conditions. Each microcosm contained an uranium-contaminated sediment (up to 2.8 g U/kg) suspended in buffer with bicarbonate at concentrations of either 1 or 40 mM and sulfate at either 1.1 or 3.2 mM. Ethanol or acetate was used as an electron donor. Results indicate that ethanol yielded in significantly higher U(VI) reduction rates than acetate. A low bicarbonate concentration (1 mM) was favored for U(VI) bioreduction to occur in sediments, but high concentrations of bicarbonate (40 mM) and sulfate (3.2 mM) decreased the reduction rates of U(VI). Microbial communities were dominated by species from the Geothrix genus and Proteobacteria phylum in all microcosms. However, species in the Geobacteraceae family capable of reducing U(VI) were significantly enriched by ethanol and acetate in low-bicarbonate buffer. Ethanol increased the population of unclassified Desulfuromonales, while acetate increased the population of Desulfovibrio. Additionally, species in the Geobacteraceae family were not enriched in high-bicarbonate buffer, but the Geothrix and the unclassified Betaproteobacteria species were enriched. This study concludes that ethanol could be a better electron donor than acetate for reducing U(VI) under given experimental conditions, and electron donor and groundwater geochemistry alter microbial communities responsible for U(VI) reduction.
    Full-text · Article · Jan 2008 · Applied Microbiology and Biotechnology
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