(428d) Invited Speaker: Transport Phenomena of Microbes in Groundwater and Porous Media

Nonaqueous phase liquid (NAPL) contaminants are difficult to eliminate from natural aquifers due, in part, to the heterogeneous structure of the soil matrix. Residual NAPL ganglia remain trapped in regions where the hydraulic conductivity is relatively low. Bioremediation processes depend on adequate mixing of microbial populations and the groundwater contaminants that they degrade. The ability of microbes to sense a chemical gradient and swim preferentially toward locations of higher concentration, known as chemotaxis, can enhance the mixing of microbes with contaminant sources that may not be readily accessible by advection and dispersion alone. Accumulation of microbes at the oil-water interface enhances the rate at which contaminants are degraded.

Apparent diffusion and dispersion coefficients determined from the experimental observations are used in mathematical models to predict macroscopic-scale transport of bacterial populations. A dimensionless chemotaxis number is proposed to ascertain a priori the conditions under which a chemotactic response will impact bacterial transport relative to other processes such as advection and dispersion. This presentation will focus on observations of microbial chemotaxis in a microfluidic device and sand-packed column designed to mimic features associated with residual NAPL contamination in groundwater.