Collaborative Research: Enhanced Biogeochemical Flushing of Uranium in Groundwater

美国大约有1.15亿人使用地下水作为饮用水的来源。许多地下水含水层受到来自自然和人为来源的铀的污染。在将铀污染地下水用作饮用水水源之前，需要对其进行处理，以使其目标浓度低于美国环保局规定的最高浓度限值，即每升30微克(微克/L)。原位固定化是目前铀污染含水层的主要修复技术。这一方法依赖于操纵铀的氧化还原生物地球化学，以将可移动的铀酰[U(VI)]离子还原并转化为矿物铀矿(UO2)，后者通常被认为在被铀污染的含水层中是固定的。然而，铀矿极易被氧气等氧化剂再次氧化和再活化，从而限制了原位固定化作为修复技术的有效性。该项目的目标是研究加强生物地质化学动员和冲洗受污染含水层中的铀，以此作为替代补救技术。为了推进这一目标，首席调查员(PI)建议开展一项与野外、实验室和模型研究相结合的研究计划，以表征和揭示控制受污染含水层中铀动员的生物地球化学反应和微生物过程。这项研究的成功完成将使社会受益，因为它将产生新的基本知识、数据和经过验证的模型，以推动设计和实施更有效和更具成本效益的铀污染含水层补救技术。还将通过教育和外联活动实现对社会的其他好处，包括指导威斯康星大学密尔沃基分校的一名研究生和一名博士后学者以及威斯康星大学麦迪逊分校的一名研究生。受铀污染的含水层的修复主要集中在通过刺激非生物和生物过程和反应来固定铀，以控制可溶和可流动的铀酰[U(VI)]离子还原和转化为稳定和固定的铀矿矿物。然而，原位固定化的效果有限，估计将铀自然冲洗到环保局MCL以下的时间往往超过数百年。这项研究的首要目标是了解如何更好地调整和操纵控制受污染含水层中铀流动的生物地球化学过程和反应，目的是通过注入富含氧气和碳酸氢盐的地表水来加强铀的动员和从这些含水层中冲走铀。这项研究的具体目标是：1)利用地球化学模型和现有的热力学和动力学反应数据，表征和揭示铀迁移的生物地球化学机制；2)进行实验室实验，研究富氧和富碳酸盐条件下微生物活动对铀迁移的影响；3)利用有限差分数值模拟和来自单井示踪实验的现有铀迁移数据，确定流动和反应迁移参数，以支持铀迁移/迁移模型的实施和验证。这一项目的成功完成有可能产生变革性的影响，通过产生基本知识和建模工具，推动设计和实施现场强化动员和冲洗，作为铀污染含水层的替代补救技术。为了实现这一项目的教育和外展目标，首席调查员建议将这项研究的结果整合到威斯康星大学麦迪逊分校的现有课程中。此外，PIS计划利用各自机构的现有计划，设计和建造一个关于威斯康星州地下水和含水层中金属污染的展板，该展板将在2024年夏季之前在北部五大湖游客中心展出。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Approximately 115 million people in the United States use groundwater as source of drinking water. Many groundwater aquifers are contaminated with uranium from both natural and anthropogenic sources. Prior to its usage as source of drinking water, uranium contaminated groundwater needs to be treated to achieve a target concentration below the EPA MCL (Maximum Concentration Limit) of 30 micrograms per liter (µg/L). In-situ immobilization is currently the leading remediation technology for uranium-contaminated aquifers. This approach relies on the manipulation of the redox biogeochemistry of uranium to reduce and convert mobile uranyl [U(VI)] ions to the mineral uraninite (UO2) which is generally considered immobile in uranium-contaminated aquifers. However, uraninite is highly susceptible to re-oxidation and re-mobilization by oxidants such as oxygen, thus limiting the efficacy of in-situ immobilization as a remediation technology. The goal of this project is to investigate the enhanced biogeochemical mobilization and flushing of uranium from contaminated aquifers as an alternative remediation technology. To advance this goal, the Principal Investigators (PIs) propose to carry out an integrated research program with field, laboratory, and modeling studies to characterize and unravel the biogeochemical reactions and microbial processes that control uranium mobilization in contaminated aquifers. The successful completion of this research will benefit society through the generation of new fundamental knowledge, data and validated models to advance the design and implementation of more efficient and cost-effective remediation technologies for uranium contaminated aquifers. Additional benefits to society will be accomplished through education and outreach including the mentoring of one graduate student and one post-doctoral scholar at the University of Wisconsin-Milwaukee and one graduate student at the University of Wisconsin-Madison.The remediation of uranium-contaminated aquifers has been largely focused on immobilizing uranium by stimulating the abiotic and biotic processes and reactions that control the reduction and conversion of soluble and mobile uranyl [U(VI)] ions to stable and immobile uraninite minerals. However, in situ immobilization has limited effectiveness and the estimated times to naturally flush uranium to below the EPA MCL often exceed hundreds of years. The overarching goal of this research is to understand how to better tune and manipulate the biogeochemical processes and reactions that control the mobility of uranium in contaminated aquifers with the aim of enhancing uranium mobilization and flushing from these aquifers through the injection of oxygen and bicarbonate enriched surface water. The specific objectives of the research are to: 1) Characterize and unravel the biogeochemical mechanisms of uranium mobilization using geochemical modeling and available thermodynamic and kinetic reaction data, 2) Conduct laboratory experiments to investigate the effect of microbial activity on the mobility of uranium under oxygen- and carbonate-rich conditions, and 3) Determine flow and reactive transport parameters to support the implementation and validation of a uranium transport/mobilization model using finite difference numerical modeling and available uranium mobilization data from single-well tracer experiments. The successful completion of this project has the potential for transformative impact through the generation of fundamental knowledge and modeling tools to advance the design and implementation of in-situ enhanced mobilization and flushing as an alternative remediation technology for uranium contaminated aquifers. To implement the educational and outreach goals of this project, the Principal Investigators (PIs) propose to integrate the findings from this research into an existing course at the University of Wisconsin-Madison. In addition, the PIs plan to leverage existing programs at their respective institutions to design and build an exhibition panel on metal contamination in groundwater and aquifers in Wisconsin that will be displayed at the Northern Great Lakes Visitor Center for viewing by Summer 2024.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.