Quantification of Bacterial Transport Processes in Subsurface Environments

地下环境中细菌传输过程的量化

• 批准号: 9524544
• 负责人: Roseanne Ford
• 金额: $ 12万
• 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: 1996
• 资助国家: 美国
• 起止时间: 1996-04-15 至 1999-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9524544&HistoricalAwards=false
• 关键词: Quantification; Bacterial; Transport; Processes; Subsurface

9524544 Ford In situ bioremediation relies on the ability of bacterial populations to biologically transform chemical contaminants such as chlorinated hydrocarbons into less toxic substances. A critical factor in successfully implementing this technology is assuring sufficient contact between the bacteria and contaminant to allow degradation to proceed. Therefore, mathematical models capable of predicting the dynamic distribution of bacterial populations within contaminated aquifers are necessary for determining the changing contaminant levels due to bacterial degradation. Many soil-inhabiting bacteria which degrade chemical contaminants are motile and capable of directing their migration in response to chemical concentration gradients (chemotaxis) The goal of this work is to evaluate bacterial transport coefficients in terms of fundamental properties which can be measured in simple laboratory experiments. Reliable values for these coefficients are required as input for advection-dispersion models which describe bacterial migration in subsurface environments. Current methods for evaluating these coefficients are highly empirical and typically not generalizable to a variety of subsurface conditions. Progress toward achieving this goal will be guided by the following specific objectives: 1. To develop and experimentally confirm a theoretical expression for calculating the effective random motility coefficient for bacteria in the absence of advective flow. 2. To develop and experimentally confirm a theoretical expression for the bacterial dispersion coefficient based on a microscopic-level characterization of the swimming behavior of bacteria, the porous matrix and the fluid flow. 3. To quantitatively assess the impact of motility on irreversible attachments to the porous matrix and its relationship to collector efficiency as defined by colloid filtration theory. 4. To unify theoretical relationships from solute transport, chromatography and colloid filtration currently u sed to describe bacterial transport into one consistent theory based on microscopic-level characterization. A combination of mathematical modeling, laboratory-scale experiments and computer simulation will be used to study the behavior of E. coli, P. putida, and soil isolates (A0500 from the Savannah River Deep Subsurface Collection, P. fluorescens Pf0-15 adhesion mutant and E1B2 from a field site in Oyster, VA). The swimming behavior of individual bacteria will be analyzed in terms of speed, run length and turn angle distribution with a tracking microscope. Random motility coefficients for the bacterial population will be measured in the stopped-flow diffusion chamber (SFDC) and compared to theoretical predictions determined from the single cell properties. More complex experimental systems with advection and porous media will be studied in sand columns and micromodels with well-defined porous patterns to obtain effective random motility, dispersion and irreversible adsorption coefficients. Theoretical relationships for these coefficients based on analogies to solute diffusion and transport, colloid filtration theory, and cellular dynamics computer simulations will be evaluated in terms of bacterial properties, flow characteristics and porous media geometry in an effort to unify the various approaches. Values for these macroscopic transport coefficients are required in advection-dispersion models to describe bacterial distributions in subsurface environments. The tracking microscope, SFDC assay and cellular dynamics algorithms, capabilities unique to the PI's state-of-the-art experimental and computational laboratories, provide an ideal environment for the proposed development of mechanistic-based models for predicting large-scale migration. Future studies will apply the same combination of mathematical modeling, laboratory experiments, and computer simulation to determine apparent velocities and reversible adsorption/desorption coefficients used in models for bacterial transport.

9524544福特 原地生物补救依靠细菌种群将氯化烃等化学污染物生物转化为毒性较低的物质的能力。 成功实施该技术的一个关键因素是确保细菌和污染物之间的充分接触，以允许降解进行。 因此，有必要建立能够预测受污染含水层内细菌种群动态分布的数学模型，以确定细菌降解引起的污染物水平变化。 许多降解化学污染物的土壤细菌是能动的，能够响应化学浓度梯度（趋化性） 这项工作的目的是评估细菌的传输系数的基本属性，可以在简单的实验室实验中测量。 这些系数的可靠值需要作为对流扩散模型，描述细菌在地下环境中迁移的输入。 目前用于评估这些系数的方法是高度经验性的，并且通常不能推广到各种地下条件。 实现这一目标的进展将以下列具体目标为指导： 1.建立并实验验证了在无平流情况下计算细菌有效随机运动系数的理论表达式。 2.基于细菌、多孔基质和流体流动的游动行为的显微水平表征，开发并实验确认细菌分散系数的理论表达式。 3.定量评估运动性对多孔基质不可逆附着的影响及其与胶体过滤理论定义的收集器效率的关系。 4. 将目前用于描述细菌转运的溶质转运、色谱法和胶体过滤的理论关系统一为一个基于显微镜水平表征的一致理论。 本研究采用数学模型、实验室模拟和计算机模拟相结合的方法，对E.大肠杆菌、恶臭假单胞菌和土壤分离物（来自萨凡纳河深地下收集中心的A0500、荧光假单胞菌Pf 0 -15粘附突变体和来自Oyster，VA的田间点的E1 B2）。 用跟踪显微镜分析单个细菌的游泳行为的速度、运行长度和转向角分布。 将在停流扩散室（SFDC）中测量细菌群体的随机运动系数，并与根据单细胞特性确定的理论预测值进行比较。 更复杂的实验系统与平流和多孔介质将在砂柱和微观模型与明确定义的多孔模式，以获得有效的随机运动，分散和不可逆的吸附系数进行研究。 这些系数的理论关系的基础上类比溶质扩散和运输，胶体过滤理论，细胞动力学计算机模拟将在细菌的特性，流动特性和多孔介质的几何形状，努力统一的各种方法进行评估。 这些宏观输运系数的值需要在对流扩散模型来描述细菌分布在地下环境。 跟踪显微镜、SFDC分析和细胞动力学算法是PI最先进的实验和计算实验室所独有的功能，为拟议的基于机制的模型开发提供了理想的环境，用于预测大规模迁移。 未来的研究将采用相同的数学建模，实验室实验和计算机模拟相结合，以确定表观速度和可逆的吸附/解吸系数用于细菌运输模型。