Abstract An important fraction of the currently stored volume of long-lived intermediate level radioactive waste in Belgium is immobilized as Eurobitum. This type of waste typically contains large amounts of NaNO3 homogeneously dispersed in a hard bituminous matrix. Geological disposal of Eurobitum in a water-saturated sedimentary formation such as Boom Clay will result in the leaching of high concentrations of NaNO3 in the Boom Clay formation. This could cause a geochemical perturbation of the surrounding clay, possibly affecting some of the favorable characteristics of the host formation such as its hydraulic conductivity, sorption potential or the redox conditions. The latter might result in a decrease of its reducing capacity and an increase in the mobility of redox-sensitive radionuclides. Microbial nitrate reduction is a well-known process, which could be stimulated by the chemical and radiolytical water-soluble organic bitumen degradation products. The present study carried out different series of long-term anoxic batch experiments to investigate the ability of the microbial community of Boom Clay borehole water to reduce nitrate, leaching from thermally aged non-radioactive Eurobitum in the presence or absence of acetate, formate and oxalate, being part of the most important organic bitumen degradation products. Obtained results indicate that all three organic bitumen degradation products can be used as electron donor to fuel microbial nitrate reduction, albeit with a different efficiency. The highest nitrate reduction rate was observed in the presence of acetate, while oxalate was the least efficient electron donor for nitrate reduction. Moreover, organic compounds that leached from the Eurobitum during the course of the experiment were used as electron donor for microbial nitrate reduction in all conditions. Furthermore, calcium oxalate crystals were observed, indicating that if oxalate is present, it will probably be less bioavailable compared to other organic compounds.

中文翻译：

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水溶性沥青降解产物可以促进非放射性沥青化废物的硝酸盐还原

摘要 目前比利时储存的长寿命中放废物的重要部分被固定为 Eurobitum。这种类型的废物通常包含大量均匀分散在硬质沥青基质中的 NaNO3。对水饱和沉积地层（如 Boom Clay）中的 Eurobitum 进行地质处置将导致 Boom Clay 地层中高浓度的 NaNO3 浸出。这可能导致周围粘土的地球化学扰动，可能影响主体地层的一些有利特征，例如其水力传导率、吸附势或氧化还原条件。后者可能导致其还原能力降低和氧化还原敏感放射性核素迁移率增加。微生物硝酸盐还原是一个众所周知的过程，这可能会受到化学和放射性水溶性有机沥青降解产物的刺激。本研究进行了不同系列的长期缺氧批次实验，以研究 Boom Clay 钻孔水中的微生物群落减少硝酸盐的能力，在存在或不存在醋酸盐、甲酸盐和草酸盐的情况下，从热老化的非放射性 Eurobitum 中浸出，是最重要的有机沥青降解产物的一部分。获得的结果表明，所有三种有机沥青降解产物都可以用作电子供体，以促进微生物硝酸盐的还原，尽管效率不同。在乙酸盐存在下观察到最高的硝酸盐还原率，而草酸盐是最不有效的硝酸盐还原电子供体。而且，在实验过程中从 Eurobitum 浸出的有机化合物被用作电子供体，用于在所有条件下还原微生物硝酸盐。此外，还观察到草酸钙晶体，表明如果存在草酸盐，与其他有机化合物相比，它的生物利用度可能较低。