Microbial Degradation of Citric Acid in Low Level Radioactive Waste Disposal: Impact on Biomineralization Reactions.
Microbial Degradation of Citric Acid in Low Level Radioactive Waste Disposal: Impact on Biomineralization Reactions.
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DOI：
10.3389/fmicb.2021.565855
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发表时间：
2021
影响因子：
5.2
通讯作者：
Morris K
中科院分区：
文献类型：
--
作者：
Byrd N;Lloyd JR;Small JS;Taylor F;Bagshaw H;Boothman C;Morris K
有机络合物存在于一些放射性废物中，可能会对废物处理构成挑战，因为它们可以通过络合作用提高放射性核素和污染物物种的地下流动性。低放射性废物中有机络合剂的主要来源是化学去污活动。柠檬酸和草酸等多羧酸有机去污剂很有意义，因为目前关于它们在高pH值和处置条件下的生物降解的数据很少。这项工作探索了柠檬酸，一种模式去污剂，在高pH厌氧条件下的生物地球化学命运，与水泥处置环境中的低放废物处置相关。建立了厌氧微宇宙实验，使用一种高pH适应的微生物接种物，从一个良好的环境地点，以探索在典型的储存库条件下的柠檬酸盐的生物降解。实验在三种不同的pH值(10、11和12)下开始，柠檬酸盐作为电子供体和碳源，在发酵、硝酸盐、铁(III)和硫酸盐还原条件下进行。结果表明，在>；pH 11时，柠檬酸盐被硝酸盐或Fe(III)作为电子受体氧化；在pH 10和pH 11时，在硝酸盐还原体系中，柠檬酸盐被完全降解并从溶液中去除。在这里，微观世界pH降低，因为在柠檬酸盐氧化过程中产生了质子。在Fe(III)还原系统中，柠檬酸盐的去除速率慢于硝酸盐还原系统。这可能是因为对于相同摩尔浓度的电子受体，Fe(III)还原比硝酸盐还原消耗更少的柠檬酸摩尔。在Fe(III)还原体系中，pH变化不大。硫酸盐还原只发生在pH值为10的单一微观世界中。在这里，柠檬酸盐被完全从溶液中去除，同时醋酸盐和甲酸盐内生，很可能是发酵产物。在硫酸盐还原过程中，醋酸盐和乳酸盐随后被用作电子供体，溶液的pH值也随之降低。有趣的是，在Fe(III)还原实验中，在pH值高达11.7的情况下观察到Fe(II)的内生。在此，对生成的固体铁相的透射电子显微镜分析表明，在这些极端条件下，纳米晶磁铁矿是Fe(III)还原的最终产物。基于PCR的高通量16S rRNA基因测序显示，具有硝酸铁(III)和硫酸盐还原能力的细菌在相关的生物活性系统中变得丰富。此外，在Fe(III)-和硫酸盐还原体系中还发现了一些发酵菌。目前存在的微生物群落与基于地球化学数据的预期一致。这些结果对改善水泥垃圾处置的长期环境安全案例开发具有重要意义。
Organic complexants are present in some radioactive wastes and can challenge waste disposal as they may enhance subsurface mobility of radionuclides and contaminant species via chelation. The principal sources of organic complexing agents in low level radioactive wastes (LLW) originate from chemical decontamination activities. Polycarboxylic organic decontaminants such as citric and oxalic acid are of interest as currently there is a paucity of data on their biodegradation at high pH and under disposal conditions. This work explores the biogeochemical fate of citric acid, a model decontaminant, under high pH anaerobic conditions relevant to disposal of LLW in cementitious disposal environments. Anaerobic microcosm experiments were set up, using a high pH adapted microbial inoculum from a well characterized environmental site, to explore biodegradation of citrate under representative repository conditions. Experiments were initiated at three different pH values (10, 11, and 12) and citrate was supplied as the electron donor and carbon source, under fermentative, nitrate-, Fe(III)- and sulfate- reducing conditions. Results showed that citrate was oxidized using nitrate or Fe(III) as the electron acceptor at > pH 11. Citrate was fully degraded and removed from solution in the nitrate reducing system at pH 10 and pH 11. Here, the microcosm pH decreased as protons were generated during citrate oxidation. In the Fe(III)-reducing systems, the citrate removal rate was slower than in the nitrate reducing systems. This was presumably as Fe(III)-reduction consumes fewer moles of citrate than nitrate reduction for the same molar concentrations of electron acceptor. The pH did not change significantly in the Fe(III)-reducing systems. Sulfate reduction only occurred in a single microcosm at pH 10. Here, citrate was fully removed from solution, alongside ingrowth of acetate and formate, likely fermentation products. The acetate and lactate were subsequently used as electron donors during sulfate-reduction and there was an associated decrease in solution pH. Interestingly, in the Fe(III) reducing experiments, Fe(II) ingrowth was observed at pH values recorded up to 11.7. Here, TEM analysis of the resultant solid Fe-phase indicated that nanocrystalline magnetite formed as an end product of Fe(III)-reduction under these extreme conditions. PCR-based high-throughput 16S rRNA gene sequencing revealed that bacteria capable of nitrate Fe(III) and sulfate reduction became enriched in the relevant, biologically active systems. In addition, some fermentative organisms were identified in the Fe(III)- and sulfate-reducing systems. The microbial communities present were consistent with expectations based on the geochemical data. These results are important to improve long-term environmental safety case development for cementitious LLW waste disposal.
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DOI：
10.1038/ismej.2012.8
发表时间：
2012-08
期刊：
The ISME journal
影响因子：
--
作者：
通讯作者：
--
影响因子：
2.8
作者：
Blum, JS;Bindi, AB;Oremland, RS
通讯作者：
Oremland, RS
影响因子：
2.3
作者：
Burke, Ian T.;Mortimer, Robert J. G.;Stewart, Douglas I.
通讯作者：
Stewart, Douglas I.
影响因子：
11.4
作者：
Beyenal, H;Sani, RK;Lewandowski, Z
通讯作者：
Lewandowski, Z
影响因子：
3.3
作者：
Dyksma, Stefan;Gallert, Claudia
通讯作者：
Gallert, Claudia