Environmental Engineering Reference
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order to predict the chemotactic sensitivity coefficient. The value obtained was
found to be approximately three times lower than previously reported values
from a relatively simpler model [48] that did not account for the bacterial
transport in the chamber. Another model that also incorporated substrate
consumption was able to predict chemotactic band formation, and replicated
capillary assay data well [45]. Hilpert [41] presents a numerical modeling
approach based on Lattice-Boltzmann methods for modeling bacterial chemo-
taxis and the fate and transport of a chemoattractant in bulk liquid. Chemo-
tactic traveling bacterial bands in a uniformly distributed substrate region were
simulated as a result of self-generated concentration gradients due to substrate
consumption. Based on simulation results, they suggest that only a fraction of a
bacterial slug injected into a chemoattractant domain forms a traveling band as
the slug length exceeds a critical value. These findings are consistent with the
capillary assay results from Adler [16].
7.6.2 Quantification of Chemotaxis in Saturated Porous Media
Pedit et al. [31] measured the chemotactic response of P. putida G7 toward
naphthalene in saturated porous media. To simulate saturated porous media, a
conventional capillary assay method was modified by packing glass beads in the
capillary tube and surrounding reservoir. A model was developed to estimate
transport parameters including naphthalene diffusion, random motility, and
chemotactic sensitivity. Simulations indicate that an order of magnitude higher
cell concentration of the non-chemotactic strain would be required to achieve
the same amount of naphthalene degradation as from a chemotactic strain.
Chemotaxis in porous media systems can be approximated by free-liquid sys-
tems by accounting for soil parameters including tortuosity and porosity [48].
Recently, an analytical solution for bacterial chemotaxis in homogeneous
porous media was presented by Long and Hilpert [47]. They derived analytical
solutions for chemotactic band velocities under different substrate input con-
ditions. This approach could be important in comparing the chemotactic band
velocity with groundwater velocity in order to assess the impact of chemotaxis
on an overall remediation scheme.
Olson et al. [21] have used immunomagnetic labeling and magnetic reso-
nance imaging (MRI) for non-invasive measurement of bacterial distributions
in a packed column. Simulation of experimental data required addition of a
non-zero chemotactic sensitivity term to account for the chemotactic response
of P. putida F1 toward TCE. In addition, Olson et al. [49] mathematically
demonstrated that bacteria traveling in a high-permeability region with advec-
tive flow can successfully migrate toward and accumulate around contaminant
diffusing from low-permeability regions. The effect of pore size on transport
parameters is also reported; a 50% reduction in both motility and chemotaxis is
reported for a similar reduction in pore size. These studies demonstrate that
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