463394 Transport of Chemotactic Bacteria in Granular Media Containing a Distribution of Non-Aqueous Phase Liquid Contaminants
This experimental study employed a laboratory-scale continuous flow sand column to better understand chemotactic transport in response to a uniform distribution of entrapped NAPL. The presence of NAPL within the column created localized concentration gradients. 2,2,4,4,6,8,8-heptamethylnonane (HMN) containing dissolved naphthalene was used as a model NAPL. An equal concentration of Pseudomonas putida G7, which is chemotactic to naphthalene, and Pseudomonas putida G7 Y1, a non-chemotactic mutant strain, was introduced simultaneously into the sand column and effluent bacterial concentrations were measured with time. To aid differentiation between bacterial strains, each cell type was stained with a fluorescent label prior to injection into the column. Experiments with sand only and sand/HMN-NAPL with no dissolved naphthalene were also conducted to serve as controls. We tested the hypothesis that due to chemotaxis, an increase in the retention of P. putida G7 will be observed within the sand column containing the HMN-naphthalene-NAPL (as compared to the control cases). This increase in chemotactic bacterial retention within the polluted porous media is expected to lead to an increase in contaminant biodegradation. Moment analysis parameters, such as percent recovery and mean travel time, were obtained from species breakthrough curves. Additionally, a one-dimensional advection-dispersion equation was fitted to species breakthrough curves and the influence of chemotaxis on apparent model parameters was analyzed. Initial experiments in which solid naphthalene crystals were evenly distributed throughout the sand column resulted in a 43% decrease in percent recovery of P. putida G7 from the column, compared to the control case with no naphthalene present, thus supporting our hypothesis. In contrast, transport of the non-chemotactic mutant strain was not influenced by the presence of naphthalene. The results of this experimental study are important for understanding how bacterial chemotaxis may influence the accessibility of contaminants present within NAPL contaminated aquifers.