Effects of Biofilms on the Flow and Colloid Transport in Porous Media Inside Microfluidic Channels

When bacteria attach to a surface and start growing into assemblies, they excrete a slimy layer known as extracellular polymeric substances (EPS). The EPS holds bacteria together, acts as a nutrient reservoir, and protects the cells. Such complicated assemblies of bacteria and EPS are called biofilms. One of the major factors that add substantial complexities to the porous media characteristics is the formation and growth of biofilms. Biofilms can modify the physical, chemical, and biological properties of porous systems, and the effect of biofilms on flow in porous media is still a matter of debate between researchers. This dissertation integrated lab experiments and mathematical modeling to explore the impacts of biofilms on the flow and colloid transport in porous media inside a microfluidic channel. For this purpose, evolving E. coli biofilms were grown in a microfluidic channel packed with glass beads, and two-dimensional biofilm structures and distributions in the porous medium were modeled by digitizing confocal images from three different growth stages of biofilms. Two simplified biofilm geometries which can provide reasonable approximations of permeability (k) were also presented. Moreover, the impacts of imaging/modeling domain size and grain size on flow in porous media covered with evolving biofilms were separately studied. Although key parameters, such as biofilm properties, imaging/modeling domain size, grain size, biofilm ratio, and the spatial distribution of biofilms, were found to individually affect the overall permeability, we proved that the extent of their effect on k depends on one another. Finally, the effects of biofilms on the retention of colloidal particles with different sizes in porous media inside microfluidic channels were investigated. We showed that the retention of all colloids, regardless of their size, occurred in the areas where biofilms were present. Furthermore, we showed that although it is generally accepted that the opposite electrostatic forces are the main factors in particle-biofilm interactions, the negatively charged colloidal particles can be retained by the negatively charged biofilms due to other factors