Spontaneous Detachment and Retardation of Bacteria: Physical and Chemical Controls on these Processes and Their Impact on Bacterial Transport in Groundwater

细菌的自发脱离和阻滞：对这些过程的物理和化学控制及其对地下水中细菌迁移的影响

• 批准号: 0087522
• 负责人: William Johnson
• 金额: $ 29.96万
• 依托单位: University of Utah
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-04-01 至 2006-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0087522&HistoricalAwards=false
• 关键词: Spontaneous; Detachment; Retardation; Bacteria; Physical

0087522W. JohnsonThe long-term transport of low concentrations of bacteria in groundwater is important to understand the purpose of protecting groundwater resources, and for interpreting the wide-ranging distribution of bacteria that is observed in the subsurface. In contrast, the bulk of the existing body of bacterial transport knowledge focuses upon the short-term transport of high concentrations of bacteria, and correspondingly on the rate of bacterial attachment to sediment. However, for long-term transport behavior, other aspects of bacterial transport become important, such as the observed slow rate of detachment from sediment that occurs in the absence of any physical or chemical perturbations (spontaneous detachment), and the observed retardation of low concentrations of bacteria in sediment. The impact of spontaneous detachment and retardation on the distance over which bacteria may be transported in groundwater is unknown. The work proposed herein will serve to determine the mechanisms governing spontaneous detachment and retardation of bacteria during transport, and will determine their potential impact on the long-term transport of low concentrations of bacteria in groundwater.Laboratory experiments will be performed using repacked sediment columns to examine changes in kinetic constants that describe bacterial breakthrough, retardation, and extended tailing (spontaneous detachment) with variations in the potential energy profile describing interaction forces between the bacteria and the sediment grain. It is expected that variation in the kinetic constants will illuminate differences in the mechanisms of attachment that control retardation, as opposed to the mechanisms of attachment that control steady state breakthrough.Column experiments and direct visual analyses in parallel plate chambers will examine the hypothesis that spontaneous detachment of bacteria and other colloids from sediment that is observed during elution may be caused by hydrodynamic shear operating at the surface of the sediment grains. The variation in kinetic constants with pore water velocity for equivalent experiments performed with different colloid sizes will indicate whether hydrodynamic shear is important in spontaneous detachment (as indicated by preferential detachment of larger-sized colloids relative to smaller-sized colloids). Experiments will also examine whether spontaneous detachment in response to hydrodynamic shear at the grain surface involves an "erosion" effect that is corollary to the shadow effect. Experiments will also examine the hypothesis that the observed decrease in probability of detachment with increased bacterial residence time on a grain surface is not necessarily related to bacterial metabolic activity.Concentration of bacteria on the sediment following long and short elution times will be examined in order to observe potential differences in the centers of mass of the attached populations, and to further constrain numerical models. Potential impacts of spontaneous detachment and retardation to bacterial transport over long time periods under different physical and chemical conditions will be simulated with a one-dimensional model using experimentally determined kinetic constants.

0087522 w。低浓度细菌在地下水中的长期迁移对于理解保护地下水资源的目的，以及解释在地下观察到的细菌的广泛分布是很重要的。相比之下，现有的大部分细菌转运知识集中在高浓度细菌的短期转运上，并相应地关注细菌附着在沉积物上的速度。然而，对于长期运输行为，细菌运输的其他方面变得重要，例如在没有任何物理或化学扰动（自发脱离）的情况下，从沉积物中观察到缓慢的脱离速率，以及观察到的沉积物中低浓度细菌的延迟。自发脱离和延迟对细菌在地下水中可能传播的距离的影响尚不清楚。本文提出的工作将有助于确定细菌在运输过程中自发脱离和延迟的机制，并将确定它们对地下水中低浓度细菌长期运输的潜在影响。实验室实验将使用重新包装的沉积物柱来检查描述细菌突破，延迟和延伸尾（自发脱离）的动力学常数的变化，以及描述细菌与沉积物颗粒之间相互作用力的势能分布的变化。预计动力学常数的变化将阐明控制延迟的附着机制的差异，而不是控制稳态突破的附着机制。柱实验和平行板室的直接视觉分析将检验这样一种假设，即在洗脱过程中观察到的细菌和其他胶体从沉积物中自发分离可能是由沉积物颗粒表面的水动力剪切作用引起的。在不同胶体尺寸下进行的等效实验中，动力学常数随孔隙水速度的变化将表明水动力剪切在自发脱离中是否重要（正如大尺寸胶体相对于小尺寸胶体优先脱离所表明的那样）。实验还将检验响应于颗粒表面流体动力剪切的自发剥离是否涉及影子效应必然导致的“侵蚀”效应。实验还将检验这样一个假设，即随着细菌在谷物表面停留时间的增加，观察到的脱离概率的降低不一定与细菌的代谢活动有关。在长时间和短时间洗脱后，沉积物上的细菌浓度将被检查，以观察附着种群的质量中心的潜在差异，并进一步约束数值模型。在不同的物理和化学条件下，自发脱离和延迟对细菌长时间运输的潜在影响将通过实验确定的动力学常数用一维模型模拟。