At the Mont Terri rock laboratory (Switzerland), an in situ experiment is being carried out to examine the fate of nitrate leaching from nitrate-containing bituminized radioactive waste, in a clay host rock for geological disposal. Such a release of nitrate may cause a geochemical perturbation of the clay, possibly affecting some of the favorable characteristics of the host rock. In this in situ experiment, combined transport and reactivity of nitrate is studied inside anoxic and water-saturated chambers in a borehole in the Opalinus Clay. Continuous circulation of the solution from the borehole to the surface equipment allows a regular sampling and online monitoring of its chemical composition. In this paper, in situ microbial nitrate reduction in the Opalinus Clay is discussed, in the presence or absence of additional electron donors relevant for the disposal concept and likely to be released from nitrate-containing bituminized radioactive waste: acetate (simulating bitumen degradation products) and H2 (originating from radiolysis and corrosion in the repository). The results of these tests indicate that—in case microorganisms would be active in the repository or the surrounding clay—microbial nitrate reduction can occur using electron donors naturally present in the clay (e.g. pyrite, dissolved organic matter). Nevertheless, non-reactive transport of nitrate in the clay is expected to be the main process. In contrast, when easily oxidizable electron donors would be available (e.g. acetate and H2), the microbial activity will be strongly stimulated. Both in the presence of H2 and acetate, nitrite and nitrogenous gases are predominantly produced, although some ammonium can also be formed when H2 is present. The reduction of nitrate in the clay could have an impact on the redox conditions in the pore-water and might also lead to a gas-related perturbation of the host rock, depending on the electron donor used during denitrification.

中文翻译：

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电子供体对 Opalinus 粘土中原位微生物硝酸盐还原的影响：来自 Mont Terri 岩石实验室（瑞士）的结果


Mont Terri 岩石实验室（瑞士）正在进行一项原位实验，以研究在用于地质处置的粘土主岩中从含硝酸盐的沥青放射性废物中浸出硝酸盐的命运。硝酸盐的这种释放可能会引起粘土的地球化学扰动，可能影响母岩的一些有利特征。在这个原位实验中，在 Opalinus 粘土钻孔的缺氧和水饱和室内研究了硝酸盐的联合传输和反应性。溶液从钻孔到地面设备的连续循环可以定期取样并在线监测其化学成分。本文讨论了 Opalinus 粘土中微生物硝酸盐的原位还原，无论存在或不存在与处置概念相关的额外电子供体，并且可能从含硝酸盐的沥青化放射性废物中释放：乙酸盐（模拟沥青降解产物）和 H2（源自储存库中的辐射分解和腐蚀）。这些测试的结果表明，如果微生物在储存库或周围粘土中活跃，则可以使用粘土中天然存在的电子供体（例如黄铁矿、溶解的有机物）来发生微生物硝酸盐还原。然而，粘土中硝酸盐的非反应性传输预计将是主要过程。相反，当存在易氧化的电子供体（例如乙酸盐和H2）时，微生物活性将受到强烈刺激。在氢气和乙酸存在的情况下，主要产生亚硝酸盐和含氮气体，尽管当存在氢气时也可以形成一些铵。 粘土中硝酸盐的减少可能会对孔隙水中的氧化还原条件产生影响，并且还可能导致主岩与气体相关的扰动，具体取决于反硝化过程中使用的电子供体。