| Bioaugmentation is an attractive alternative of traditional pump-and-treat methods to cleanup underground contamination. This innovative biotechnology requires efficient delivery of pollutant degrading bacteria to the contaminated region. The goal of this dissertation is to evaluate bacterial transport and chemotaxis within porous media over different length and time scales.;First of all, a micro-scale bacterial random walk computer simulation algorithm was developed to simulate the swimming trajectories of E. coli NR50 and P. putida F1, within a static porous medium. These simulations successfully illustrated bacteria highly impeded diffusion profiles observed from previous static column experiments, highlighting the significance of bacterial idling time (tI).;Then, a meso-scale homogeneous sand-packed column was utilized to investigate the impact of bacterial idling time (tI) on their breakthrough curves (BTCs) Under a typical groundwater flow velocity, the smooth-swimming mutant E. coli HCB437, which has the largest tI, exhibited the most retarded and longitudinally dispersed BTCs. The degree of this retardation and dispersion was reduced for bacteria with smaller tI.;Moreover, a series of micro-scale static capillary assays revealed that, compared with the nonchemotactic conditions, the presence of chemoattractants (e.g sodium acetate) within the pore space of the porous medium led to more chemotactic bacteria (e.g. P. putida F1) transferring from their original positions within free solution into the porous medium region. Referring to a corresponding 3-D Monte Carlo computer simulation, such an attractant gradient facilitated chemotactic bacterial migration by reducing tI spent on associating with the solid surfaces.;Finally, a bench-scale 2-D microcosm was applied to explore bacterial chemotactic response to a transverse chemoattractant gradient under typical groundwater flow condition. Upon establishing a relatively steady sodium acetate transverse gradient at a certain vertical level, the pulse injected chemotactic bacteria P. putida F1 responded to this gradient by migrating upward during their horizontal transit across the entire 2-D microcosm length. In comparison, the nonchemotactic bacteria P. putida F1 CheA did not show such an upward movement. A 2-D convection and dispersion mathematical model with the input transport parameters evaluated from aforementioned micro-scale and meso-scale studies provided a good match to the experimental observations. |
