A Micofluidic Device for Studying Contaminant Mixing inPorous Media

摘要

Understanding bacterial transport through subsurface porous media is critical both for characterizing contamination of drinking-water bodies and designing successful bioremediation strategies for contaminated sites. There has been much effort devoted to studying bacterial and colloidal transport in porous media, where the black box approach has been used to predict transport phenomena based on input and output parameters. Recently, flow cells and micro-models have been used to visualize colloidal transport in porous media to simulate bacterial transport. However, additional factors such as bacterial random motility, chemotaxis (directed migration toward a contaminant source), attachment-detachment, growth and decay influence bacterial transport phenomena and need to be quantified and considered carefully in order to predict bacterial transport accurately. The aim of this study is to quantify the role of chemotaxis in bacterial transport through a two-dimensional micromodel with a contaminant source. In this study a novel bi-layer polydimethylsiloxane (PDMS) micro-fluidic device was fabricated using photolithography and soft lithography techniques to simulate contamination of groundwater due to leakage from an underground storage tank. This device consists of a porous channel through which a bacterial suspension is flown and another channel for injecting contaminant into the porous channel. The device facilitates visualization of both bacteria and a chemical tracer flowing through porous media and is therefore useful in determining their mutual spatial distribution in porous media. The study focuses on studying enhancement of contaminant mixing in porous media due to the presence of bacterial motility. FITC (fluorescein isothiocyanate) was used as a tracer and changes in the fluorescence intensity profiles at different locations downstream from the injection point was used to evaluate the enhancement in the contaminant mixing. Results indicate a two-fold increase in the effective dispersion coefficient of FITC in the presence of bacteria. This device may also be used for determination of Escherichia. coli HCB33 (wild type) chemotaxis toward L-aspartic acid by imaging bacterial and contaminant (tracer) flow at different cross-sections downward of the injection point. Data obtained from this study will fit into the advection-dispersion equation with an additional term form chemotaxis, to calculate chemotactic sensitivity parameters in the microfludic device.