Theoretical Investigation of Bacterial Chemotaxis in Porous Media

Chemotaxis is defined as the self-generated displacement of motile microbes in the direction of an increasing concentration gradient of a chemoattractant or a decreasing concentration gradient of a chemorepellent. This work presents a Monte Carlo computer simulation of the chemotactic response in porous media. The model is based on the idealized Happel cell model underlying the colloid filtration theory (CFT), which describes the physical and chemical forces acting on an inert particle in flow through porous media. The premise of the model presented here is that bacterial chemotaxis in porous media can be successfully modeled by integrating cellular dynamics simulations with CFT particle trajectory analysis. At each time step a stochastic algorithm chooses a chemotactic velocity to be superimposed onto the deterministic velocity obtained by analytical solution for Stokes flow around the Happel sphere. The model calculates a value for the collection efficiency (the fundamental CFT parameter η) with the effects of chemotaxis incorporated. The collection efficiency is defined as the fraction of particles approaching the Happel sphere, termed the collector, that actually collides with the collector. CFT has been used extensively for the modeling of particle deposition in water treatment processes and, more recently, bacterial transport in groundwater. However, there has been little rigorous examination of the theory since it was developed in the mid-1970s. Thus, in addition to the treatment of chemotaxis, this paper provides an analysis of the theoretical underpinnings of CFT. Preliminary results suggest that chemotaxis may significantly affect η under certain conditions.