Kinetics of bacterial transport, attachment and toluene biodegradation in saturated porous media

The aim of this dissertation was to study bacterial transport, attachment and dissolved organic biodegradation in water-saturated porous media and its applications for subsurface bioremediation. This study reports the effects of salt type and concentration on the change in attachment kinetics when bacteria are pumped through a column of water-saturated clean sand over relatively long periods of time (up to 35 pore volumes). The species Pseudomonas fluorescens UPER-1 was found to exhibit three different kinds of attachment kinetics: first-order, second-order and an intermediate-order. The attachment kinetics of bacteria was modeled by using the advection-dispersion equation coupled with a set of equations for each kind of attachment kinetics while using colloid filtration theory to predict collector efficiencies. At low or zero salt concentrations (≤10-4M), a second-order kinetic model (blocking), a first-order kinetic model and an intermediate-order kinetic model (ripening), were all found to fit the data equally well. At intermediate and high salt concentrations (≥10-3M), the ripening model was found to fit the data best. We report values for collision efficiencies of bacteria in the range 0.01--0.2, depending upon the salt type and concentration. This study points out the importance of long-term experiments to study the effect of ionic strength on bacteria attachment kinetics in saturated porous media; and the phenomenon of cell-to-cell attachment at high ionic strength. This study further points out the range of kinetics to expect when bacteria attach to natural porous media and suggests a modeling framework.;This study also reports an improved spectrophotometric method for studying bacterial (Pseudomonas fluorescens UPER-1) transport and attachment in saturated porous media (silica sand). While studying the effect of ionic strength, an artifact might be encountered in the traditional packed-column spectrophotometric method. The absorbance of well-stiffed bacterial suspension was found to decrease with time in the presence of high concentrations of sodium and potassium phosphate salts (≥10-2M), as the cells continue to age in a resting stage. Our results show that collision efficiency (alpha) and a bed 'ripening' index (n) will be in error by as much as 20% if breakthrough is measured using the traditional spectrophotometric technique. An improved experimental technique is presented which will minimize the artifact and lead to more accurate breakthrough data.;Two methods have been presented to study toluene biodegradation using Pseudomonas putida 1A at different initial toluene concentrations. Flask studies for toluene biodegradation at 100 ppm initial toluene concentration were conducted using a gas chromatograph. Flask studies at 1 ppm initial toluene concentration were conducted using a UV-spectrophotometer to monitor toluene depletion. A new dilute Bushnell-Haas media was developed which can be used with a UV-spectrophotometer and in which the Pseudomonas putida 1A cells can grow reproducibly.;Biodegradation data from the flask studies was analyzed using Monod kinetics equations coupled with mass balance equations, while considering the half-saturation constant as negligible as compared to the substrate concentration. The maximum specific growth rate for the 100 ppm study was found to be 0.29 +/- 0.04 hr-1. For the 1 ppm study, the value was 0.21 +/- 0.02 hr-1.;Column biodegradation experiments were designed to achieve a cell density in the sand column of equal to or more than 5 x 106 cells/(cm 3 of sand bed). Cells were attached to the sand column using the techniques developed in this research and toluene biodegradation experiments were conducted in which the column served as a lab-scale biobarrier, reducing the inlet concentration of toluene to a fairly steady outlet concentration.;Analysis of the attached cells revealed that most of the cells had attached to the initial part of the column. If the toluene residence time is modified to take this into account, the values of the specific growth rate constants obtained from the column study are closer to those obtained from the flask study. This shows that it is crucial to know the distribution of the attached cells inside the porous media while designing subsurface biobarriers.