(181a) Influence of Bacterial Chemotaxis On Biodegradation of Distributed Sources of Toluene within a Pore Network In A Microfluidic Device

Title: Influence of Bacterial Chemotaxis
on Biodegradation of Distributed Sources of Toluene within a Pore Network in A
Microfluidic Device

Authors: Xiaopu Wang, Larry Lanning and Roseanne
M. Ford

Abstract

Organic solvents such as toluene are the
most widely distributed pollutants in groundwater. Subsurface bioremediation is
often limited by the poor contact between injected microorganisms and residual pollutants,
which may be dispersed as pore-size organic-phase droplets within the saturated
soil matrix. Chemotaxis toward chemical pollutants provides a mechanism for
bacteria to migrate to locations of high contamination, which may not normally
be accessible to bacteria carried along by groundwater flow, and thus it may
improve the efficiency of bioremediation. A porous microfluidic device (µ-chip)
was used to mimic the dissolution of an organic-phase contaminant from a pore network
into a larger macropore representing a preferred pathway for microorganisms
that are carried along by groundwater flow. The µ-chip was designed to trap the
organic pollutant in a regular and reproducible pattern within the porous
network as shown in Figure 1, and its glass windows allowed direct image
analysis of bacterial distributions within the vicinity of the organic
contaminant at different points along the flow pathway. Enhanced accumulation
of P. putida F1 near the pollutant sources
was observed relative to that of the control experiments. Velocities in the macropore
pathway were varied over a range from 0.5 to 10 m/d.  Bacterial chemotaxis
was observed at the lower flow rates, which are comparable to natural
groundwater flow rates. At the higher velocities, accumulation of chemotactic
bacteria was similar to the control experiments. Biodegradation rates were
measured for both chemotactic bacteria and its nonchemotactic mutant based on
the toluene concentration at the outlet. Computer-based simulation using finite
element analysis software  (COMSOL) was also performed to understand the
effects of various model parameters on bacterial chemotaxis to NAPL. Results
from computer simulations (generated using reasonable values of the model
parameters) were compared to the experimental data for chemotactic and
nonchemotactic bacterial strains.

Figure 1.
Residual toluene trapped within the microfluidic device. The toluene droplets
have been dyed red and are trapped within the circular pore bodies of the
micromodel network.