Collaborative Research: Investigation of Chemotaxis in Porous Media -- Visualization Experiments and Modeling

Collaborative Research:

Investigation of Chemotaxis in Porous Media ? Visualization Experiments and Modeling

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

Understanding bacterial transport in the subsurface is critical both in preventing microbial contamination of drinking-water supplies and in successful implementation of bioremediation schemes. Much of the subsurface microbial community is motile and can actively swim due to their flagella. Many motile bacterial species exhibit chemotaxis to chemoattractants, however, chemotaxis is often excluded from bacterial transport models.

Our hypotheses address two scenarios in which chemotaxis has been theoretically predicted to be relevant, but not proven experimentally: (a) Theoretically predicted traveling bands of chemotactic bacteria can be observed experimentally, and correspond to chemical gradients created by bacterial consumption of substrate. (b) Chemotactic bacteria migrate into regions of low permeability in response to chemical gradients created in the freely-flowing media.

Our specific objectives are:

1. To optimize a novel visualization system for simultaneously observing bacterial transport and aqueous chemical concentrations in 2D micromodels whose surfaces are labeled with sensor molecules.

2. To experimentally investigate Hypotheses a and b with the visualization system in the following scenarios: (a) a homogeneous porous medium where the consumable chemoattractant concentration is initially uniform and where traveling bacterial bands should occur; and (b) a dual permeability porous medium in which chemoattractant diffuses from the low permeability region.

3. To develop a pore-scale numerical model to describe the observed transport phenomena. Specifically, a Lattice-Boltzmann model will be generalized to account for cell attachment and Knudsen diffusion.

4. To develop Darcy-scale analytical solutions for chemotaxis and to evaluate the Darcy-scale mobile-immobile zone concept.

We will use the visually appealing imaging techniques employed in this proposal to improve undergraduate education and community outreach, including a science fair for middle school girls and research experience for high school teachers. We will also offer a research opportunity for a mathematics major to work on modeling tasks.