Internal Biofilm Heterogeneities Enhance Solute Mixing and Chemical Reactions in Porous Media

Internal heterogeneityof biofilms enhances fluid mixingand reactions and biologically driven reactions, e.g., bioaccumulation,within porous media. Bacterial biofilms can form in porous media that areof interestin industrial applications ranging from medical implants to biofiltersas well as in environmental applications such as in situ groundwaterremediation, where they can be critical locations for biogeochemicalreactions. The presence of biofilms modifies porous media topologyand hydrodynamics by clogging pores and consequently solutes transportand reactions kinetics. The interplay between highly heterogeneousflow fields found in porous media and microbial behavior, includingbiofilm growth, results in a spatially heterogeneous biofilm distributionin the porous media as well as internal heterogeneity across the thicknessof the biofilm. Our study leverages highly resolved three-dimensionalX-ray computed microtomography images of bacterial biofilms in a tubularreactor to numerically compute pore-scale fluid flow and solute transportby considering multiple equivalent stochastically generated internalpermeability fields for the biofilm. We show that the internal heterogeneouspermeability mainly impacts intermediate velocities when comparedwith homogeneous biofilm permeability. While the equivalent internalpermeability fields of the biofilm do not impact fluid-fluidmixing, they significantly control a fast reaction. For biologicallydriven reactions such as nutrient or contaminant uptake by the biofilm,its internal permeability field controls the efficiency of the process.This study highlights the importance of considering the internal heterogeneityof biofilms to better predict reactivity in industrial and environmentalbioclogged porous systems.