Aviam Orli, Bar-Nes Gabi, Zeiri Yehuda, Sivan Alex
Department of Biotechnology Engineering, Ben Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84100, Israel.
Appl Environ Microbiol. 2004 Oct;70(10):6031-6. doi: 10.1128/AEM.70.10.6031-6036.2004.
Disposal of low-level radioactive waste by immobilization in cement is being evaluated worldwide. The stability of cement in the environment may be impaired by sulfur-oxidizing bacteria that corrode the cement by producing sulfuric acid. Since this process is so slow that it is not possible to perform studies of the degradation kinetics and to test cement mixtures with increased durability, procedures that accelerate the biodegradation are required. Semicontinuous cultures of Halothiobacillus neapolitanus and Thiomonas intermedia containing thiosulfate as the sole energy source were employed to accelerate the biodegradation of cement samples. This resulted in a weight loss of up to 16% after 39 days, compared with a weight loss of 0.8% in noninoculated controls. Scanning electron microscopy of the degraded cement samples revealed deep cracks, which could be associated with the formation of low-density corrosion products in the interior of the cement. Accelerated biodegradation was also evident from the leaching rates of Ca(2+) and Si(2+), the major constituents of the cement matrix, and Ca exhibited the highest rate (up to 20 times greater than the control rate) due to the reaction between free lime and the biogenic sulfuric acid. Leaching of Sr(2+) and Cs(+), which were added to the cement to simulate immobilization of the corresponding radioisotopes, was also monitored. In contrast to the linear leaching kinetics of calcium, silicon, and strontium, the leaching pattern of cesium produced a saturation curve similar to the control curve. Presumably, the leaching of cesium is governed by the diffusion process, whereas the leaching kinetics of the other three ions seems to governed by dissolution of the cement.
全球范围内正在评估通过水泥固化来处置低水平放射性废物的方法。环境中水泥的稳定性可能会受到硫氧化细菌的损害，这些细菌通过产生硫酸来腐蚀水泥。由于这个过程非常缓慢，无法进行降解动力学研究以及测试具有更高耐久性的水泥混合物，因此需要加速生物降解的程序。采用以硫代硫酸盐作为唯一能源的那不勒斯嗜盐硫杆菌和中间硫单胞菌的半连续培养物来加速水泥样品的生物降解。39天后，这导致重量损失高达16%，相比之下，未接种的对照样品重量损失为0.8%。对降解后的水泥样品进行扫描电子显微镜观察发现了深裂缝，这可能与水泥内部低密度腐蚀产物的形成有关。从水泥基质的主要成分Ca(2+)和Si(2+)的浸出率也能明显看出加速生物降解，由于游离石灰与生物源硫酸之间的反应，Ca的浸出率最高（比对照率高20倍）。还监测了添加到水泥中以模拟相应放射性同位素固定化的Sr(2+)和Cs(+)的浸出情况。与钙、硅和锶的线性浸出动力学不同，铯的浸出模式产生了一条与对照曲线相似的饱和曲线。据推测，铯的浸出受扩散过程控制，而其他三种离子的浸出动力学似乎受水泥溶解控制。
