In Vitro Evaluation of Microbial Effects on Bitumen Waste Form

Jacquot, F.; Libert, Marie; Romero, María Angustias; Besnainou, B.

doi:10.1007/978-94-011-5792-6_29

Cited by 3 publications

(3 citation statements)

References 3 publications

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“…Anthraquinone-2,6-disulfonate (AQDS), an extracellular electron shuttle and humic analogue, was also added to key bioreduction experiments to further explore the mechanisms of U(VI)-and Fe(III)-reduction in these high pH systems where metal solubility is expected to be low. Subsequent experiments examined reoxidation scenarios to assess the potential impact of reaction with oxidants such as nitrate in the waste forms, 22 and the potential for ingress of oxygenated groundwater. 23 ■ MATERIALS AND METHODS Sediment Collection and Storage.…”

Section: ■ Introductionmentioning

confidence: 99%

Microbial Reduction of U(VI) under Alkaline Conditions: Implications for Radioactive Waste Geodisposal

Williamson

Morris

Law

et al. 2014

Environ. Sci. Technol.

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Although there is consensus that microorganisms significantly influence uranium speciation and mobility in the subsurface under circumneutral conditions, microbiologically mediated U(VI) redox cycling under alkaline conditions relevant to the geological disposal of cementitious intermediate level radioactive waste, remains unexplored. Here, we describe microcosm experiments that investigate the biogeochemical fate of U(VI) at pH 10-10.5, using sediments from a legacy lime working site, stimulated with an added electron donor, and incubated in the presence and absence of added Fe(III) as ferrihydrite. In systems without added Fe(III), partial U(VI) reduction occurred, forming a U(IV)-bearing non-uraninite phase which underwent reoxidation in the presence of air (O2) and to some extent nitrate. By contrast, in the presence of added Fe(III), U(VI) was first removed from solution by sorption to the Fe(III) mineral, followed by bioreduction and (bio)magnetite formation coupled to formation of a complex U(IV)-bearing phase with uraninite present, which also underwent air (O2) and partial nitrate reoxidation. 16S rRNA gene pyrosequencing showed that Gram-positive bacteria affiliated with the Firmicutes and Bacteroidetes dominated in the post-reduction sediments. These data provide the first insights into uranium biogeochemistry at high pH and have significant implications for the long-term fate of uranium in geological disposal in both engineered barrier systems and the alkaline, chemically disturbed geosphere.

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Section: ■ Introductionmentioning

confidence: 99%

Microbial Reduction of U(VI) under Alkaline Conditions: Implications for Radioactive Waste Geodisposal

Williamson

Morris

Law

et al. 2014

Environ. Sci. Technol.

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“…To further understand the long-term fate of radionuclides under alkaline conditions, we considered reoxidation scenarios, for example, through ingress of oxygenated groundwaters or mediated by oxidants, such as nitrate, which may be present in some wasteforms. , To explore reoxidation processes, prereduced sediments that were reacted with TcO 4 – for 28 days to give significant solid-phase associated Tc(IV) were subsequently exposed to air or nitrate (3 × 10 –2 mol L –1 ).…”

Section: Resultsmentioning

confidence: 99%

Biogeochemical Cycling of ⁹⁹Tc in Alkaline Sediments

Williamson

Lloyd

Boothman

et al. 2021

Environ. Sci. Technol.

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99Tc will be present in significant quantities in radioactive wastes including intermediate-level waste (ILW). The internationally favored concept for disposing of higher activity radioactive wastes including ILW is via deep geological disposal in an underground engineered facility located ∼200–1000 m deep. Typically, in the deep geological disposal environment, the subsurface will be saturated, cement will be used extensively as an engineering material, and iron will be ubiquitous. This means that understanding Tc biogeochemistry in high pH, cementitious environments is important to underpin safety case development. Here, alkaline sediment microcosms (pH 10) were incubated under anoxic conditions under “no added Fe(III)” and “with added Fe(III)” conditions (added as ferrihydrite) at three Tc concentrations (10–11, 10–6, and 10–4 mol L–1). In the 10–6 mol L–1 Tc experiments with no added Fe(III), ∼35% Tc(VII) removal occurred during bioreduction. Solvent extraction of the residual solution phase indicated that ∼75% of Tc was present as Tc(IV), potentially as colloids. In both biologically active and sterile control experiments with added Fe(III), Fe(II) formed during bioreduction and >90% Tc was removed from the solution, most likely due to abiotic reduction mediated by Fe(II). X-ray absorption spectroscopy (XAS) showed that in bioreduced sediments, Tc was present as hydrous TcO2-like phases, with some evidence for an Fe association. When reduced sediments with added Fe(III) were air oxidized, there was a significant loss of Fe(II) over 1 month (∼50%), yet this was coupled to only modest Tc remobilization (∼25%). Here, XAS analysis suggested that with air oxidation, partial incorporation of Tc(IV) into newly forming Fe oxyhydr(oxide) minerals may be occurring. These data suggest that in Fe-rich, alkaline environments, biologically mediated processes may limit Tc mobility.

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“…Microbial nitrate reduction at near neutral or slightly alkaline pH is a well-known process (Libert et al, 1997;Bleyen et al, 2017Bleyen et al, , 2018aMijnendonckx et al, 2020). However, microbial nitrate reduction at highly alkaline conditions is less well studied (Albina et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

pH and microbial community determine the denitrifying activity in the presence of nitrate-containing radioactive waste

et al. 2022

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An important fraction of the currently stored volume of long-lived intermediate-level radioactive waste in Belgium contains large amounts of NaNO3 homogeneously dispersed in a hard bituminous matrix. Geological disposal of this waste form in a water-saturated sedimentary formation such as Boom Clay will result in the leaching of high concentrations of NaNO3, which could cause a geochemical perturbation of the surrounding clay, possibly affecting some of the favorable characteristics of the host formation. In addition, hyper-alkaline conditions are expected for thousands of years, imposed by the cementitious materials used as backfill material. Microbial nitrate reduction is a well-known process and can result in the accumulation of nitrite or nitrogenous gases. This could lead to the oxidation of redox-active Boom Clay components, which could (locally) decrease the reducing capacity of the clay formation. Here, we compared nitrate reduction processes between two microbial communities at different pH related to a geological repository environment and in the presence of a nitrate-containing waste simulate during 1 year in batch experiments. We showed that the microbial community from in Boom Clay borehole water was able to carry out nitrate reduction in the presence of acetate at pH 10.5, although the maximum rate of 1.3 ± 0.2 mM NO3−/day was much lower compared to that observed at pH 9 (2.9 mM NO3−/day). However, microbial activity at pH 10.5 was likely limited by a phosphate shortage. This study further confirmed that the Harpur Hill sediment harbors a microbial community adapted to high pH conditions. It reduced twice as much nitrate at pH 10.5 compared to pH 9 and the maximum nitrate reduction rate was higher at pH 10.5 compared to that at pH 9, i.e., 3.4 ± 0.8 mM NO3−/day versus 2.2 ± 0.4 mM NO3−/day. Both communities were able to form biofilms on non-radioactive Eurobitum. However, for both microbial communities, pH 12.5 seems to be a limiting condition for microbial activity as no nitrate reduction nor biofilm was observed. Nevertheless, pH alone is not sufficient to eliminate microbial presence, but it can induce a significant shift in the microbial community composition and reduce its nitrate reducing activity. Furthermore, at the interface between the cementitious disposal gallery and the clay host rock, the pH will not be sufficiently high to inhibit microbial nitrate reduction.

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In Vitro Evaluation of Microbial Effects on Bitumen Waste Form

Cited by 3 publications

References 3 publications

Microbial Reduction of U(VI) under Alkaline Conditions: Implications for Radioactive Waste Geodisposal

Microbial Reduction of U(VI) under Alkaline Conditions: Implications for Radioactive Waste Geodisposal

Biogeochemical Cycling of ⁹⁹Tc in Alkaline Sediments

pH and microbial community determine the denitrifying activity in the presence of nitrate-containing radioactive waste

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In Vitro Evaluation of Microbial Effects on Bitumen Waste Form

Cited by 3 publications

References 3 publications

Microbial Reduction of U(VI) under Alkaline Conditions: Implications for Radioactive Waste Geodisposal

Microbial Reduction of U(VI) under Alkaline Conditions: Implications for Radioactive Waste Geodisposal

Biogeochemical Cycling of 99Tc in Alkaline Sediments

pH and microbial community determine the denitrifying activity in the presence of nitrate-containing radioactive waste

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Biogeochemical Cycling of ⁹⁹Tc in Alkaline Sediments