Collaborative Research: Chemotaxis in Porous Media--Experimental Observations and Upscaling for Development of a Descriptive Theory

合作研究：多孔介质中的趋化性——实验观察和描述性理论发展的升级

• 批准号: 0711377
• 负责人: Roseanne Ford
• 金额: $ 24.01万
• 依托单位: University of Virginia Main Campus
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-09-15 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0711377&HistoricalAwards=false
• 关键词: Collaborative; Research; Chemotaxis; Porous; Media

Chemotaxis is the ability of bacteria to sense chemical concentration gradients in their local surroundings and swim toward higher concentrations of chemicals, which they perceive to be beneficial to their survival. In this work, we propose to examine how the pore-scale process of chemotaxis influences the Darcy-scale observation of bacterial transport in porous media. In the subsurface, bioremediation is often hindered by the inability to achieve good mixing between injected substances and the resident contaminants. In such situations, chemotaxis might be exploited to enhance the mixing of bacterial populations within contaminated zones. This would be a multiscale phenomenon in which bacteria migrate in response to pore-scale variations in pollutant concentration that results in greater mixing at the field-scale. There are two closely related open questions for this scheme: (1) how does one relate the pore-scale description of chemotaxis to the effective dispersion tensor that is used to predict bacterial spreading in Darcy-scale applications, and (2) can one also predict the spatial variance of the bacterial concentration to predict the microscale mixing that has occurred within the porous medium. Objective and Approach: The overall goal of this project is to quantify the impact of pore-scale chemotaxis on bacterial transport at the Darcy-scale. We will accomplish this through a combination of theory development and laboratory experimentation in the following steps. 1. Derive a Darcy-scale transport equation for bacteria that accounts for chemotactic responses to local chemical gradients via volume averaging. This will be used to predict (i) the effective dispersion tensor, and (ii) the Darcy-scale spatial variance of the concentration of bacteria.2. Compare theory and experiment for several simplified test cases in which the velocity field and chemical gradients are well-defined. Represent these results as engineering correlations that relate dispersion to dimensionless groups such as the Peclet number and chemotactic driving force.3. Test these correlations experimentally for more complex porous media systems by using microfluidic devices, which allow for direct visualization of fluid flow patterns and bacterial distributions at the pore- and Darcy-scales. Intellectual Merit: To understand the impact of chemotaxis on the biological degradation of chemical contaminants in groundwater systems requires a quantitative analysis that relates the chemotactic response to local chemical gradients over length scales of millimeters to bacterial dispersion over length scales of meters. In our approach we build on current work of hydrologists to model transport of chemical contaminants in groundwater and extend it to motile colloids that are transported due to chemical gradients in addition to hydraulic gradients. The potential for exploiting chemical gradients as a driving force to control the migration of bacterial populations is intellectually appealing. State-of-the-art approaches both in mathematical modeling (upscaling by volume-averaging) and experimental design (microfluidic devices) will be employed in the project.Broader Impact: A new partnership between researchers at the University of Virginia and Oregon State University brings together expertise in the design of experimental systems to quantify bacterial migration and mathematical modeling to relate pore-scale phenomena to field-scale observations. We will encourage students to broaden their experiences through international student exchange and collaboration. Investigators with a proven commitment to recruiting underrepresented groups in engineering will broadly educate one graduate student and one post-doctoral associate in an interdisciplinary context to meet critical needs for environmental engineers in our national workforce. Outreach to local high schools will provide hands-on laboratory experience in genetic engineering for Honors Biology students and their teachers to engage the next generation in the wonder of science. Results from this study will yield engineering correlations to better inform decision-makers about the feasibility of monitored natural attenuation as a treatment option at polluted sites where biological degradation has been documented.

趋化性是细菌在其当地环境中感知化学浓度梯度并朝着更高浓度的化学物质游泳的能力，它们认为这对它们的生存有益。 在这项工作中，我们建议研究趋化性的孔隙尺度过程如何影响多孔培养基中细菌转运的达西尺度观察。 在地下，通常无法在注射物质和居民污染物之间实现良好的混合而妨碍生物修复。 在这种情况下，可能会利用趋化性来增强受污染区域中细菌种群的混合。 这将是一种多尺度现象，其中细菌会响应污染物浓度的孔隙尺度变化而迁移，从而导致野外尺度上的混合更大。 该方案有两个密切相关的开放问题：（1）如何将趋化性的孔隙尺度描述与有效的分散张量相关联，用于预测在Darcy尺度应用中细菌扩散的孔隙张量，并且（2）也可以预测细菌浓度的空间方差，以预测Microscale混合物中发生的MIDER MIDER中会发生的。目的和方法：该项目的总体目标是量化孔隙趋化性对达西级细菌运输的影响。 我们将在以下步骤中通过理论发展和实验室实验的结合来实现这一目标。 1。用于细菌的达西尺度传输方程，该方程通过体积平均来解释对局部化学梯度的趋化反应。 这将用于预测（i）有效分散张量，以及（ii）细菌浓度的达西级空间方差2。比较几个简化的测试用例的理论和实验，其中速度场和化学梯度定义明确。 将这些结果表示为工程相关性，将分散体与无量纲组（例如小子数和趋化驱动力）相关联。3。通过使用微流体设备，通过实验测试这些相关性的多孔培养基系统，从而可以直接可视化流体流动模式和孔隙和达西尺度的细菌分布。智力优点：要了解趋化性对地下水系统中化学污染物生物学降解的影响，需要进行定量分析，将趋化性反应与局部化学梯度相关联，而毫米的长度尺度上的局部化学梯度与细菌分散量相对于仪表的细菌分散体。 在我们的方法中，我们以水文学家的当前工作为基础，以建模地下水中化学污染物的运输，并将其扩展到除液压梯度外，由于化学梯度而运输的机动胶体。 利用化学梯度作为控制细菌种群迁移的驱动力的潜力在智力上吸引人。 在项目中，将采用数学建模（通过数量平均进行扫描）和实验设计（微流体设备）中的最先进方法。项目的影响：弗吉尼亚大学研究人员与俄勒冈州立大学的研究人员的新合作伙伴关系，在实验系统中汇总了现场迁移和数学模型的设计专业知识，从观察。 我们将鼓励学生通过国际学生交流和合作来扩大自己的经验。 具有良好承诺在工程领域招募代表性不足的团体的调查人员将在跨学科的环境中广泛教育一名研究生和一名博士后助理，以满足我们国家劳动力中环境工程师的关键需求。 向当地中学的宣传将为荣誉生物学学生及其老师提供基因工程实验室实验室经验，以使下一代参与科学奇观。 这项研究的结果将产生工程相关性，以更好地为决策​​者提供监测的自然衰减作为治疗选择的可行性，以记录生物降解的污染部位。