Hydrodynamic Influences on the Transport of Motile Bacteria in Porous Media

Authors

Marc Berghouse¹, Lazaro Perez¹, Rishi Parashar¹* (rishi@dri.edu), Andy Plymale²

Institutions

¹Desert Research Institute, Reno, NV; ²Pacific Northwest National Laboratory, Richland, WA

Abstract

The transport of motile bacteria in porous media is relevant to many fields, but gaps remain in the understanding of the impacts of hydrodynamics and pore structure on bacterial transport. Two dimensional micromodels, designed with staggered arrays of equal diameter grains (cylinders), were used to visualize behavior of different motile species of metal-reducing bacteria under variable flow rate and porosity conditions. The team’s observation and analysis of the videos of individual cell trajectories showed that at higher flow rates, motility is less important to the transport of bacteria, and that reduced motility results in reduced dispersion. Spatial variations in flow velocities (and shear) add another level of complexity to bacterial transport. Movement of bacteria from low-shear to high-shear regions located near surfaces (termed shear trapping) is generally thought to be one of the mechanisms that drives initial colonization of curved surfaces and of microfluidic pore channels. Interestingly, the team observed that the transition from a motile to a shear-dominated transport regime occurs at similar flow speeds for all species, regardless of their motility type. Furthermore, for the flow rate and porosity conditions tested, researchers did not see evidence of shear trapping causing motile bacteria to accumulate in low velocity regions in porous media. Instead, the results show that irrespective of porosity, flow rate or motility type, bacteria tend to accumulate in the medium velocity regions. This work thus aids in development of a revised picture of bacterial transport in confined porous media under dynamic flow field conditions.