Characterization of non-Newtonian fluids and fluid flow through biofilms in porous media using nuclear magnetic resonance
Edden, Alexis Sanderlin.
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The research presented in this thesis uses nuclear magnetic resonance (NMR) experiments to study biofilm growth in porous media and to characterize the effects of shear forces on a non-Newtonian fluid. An introduction to NMR is given to provide experimental background and an understanding of the data analysis, followed by an overview of polymers and biofilms. The next chapters describe the experiments and results for biofilm growth in two different model porous media. The final chapter provides analysis of shear forces on the non-Newtonian fluid polyacrylamide. Biofilms are formed when bacterial cells attach to a surface and begin to grow in a phenotypically altered state. Observation of biofilm growth in porous media poses significant challenges due to the heterogeneous nature of the biofilm and the opaque nature of the surfaces on which biofilms form. In the experiments presented, displacement-relaxation experiments were performed while a biofilm grew in a model porous media positioned in the magnet. Separate analysis of the flow characteristics of the biofilm phase and the bulk fluid phase was possible within the same data set. The results indicate that convective flow did not occur through the biofilm and that biofouling of the pore space resulted in faster bulk fluid flow through the channels. Natural geological matter contains magnetically susceptible materials such as iron-bearing minerals and cannot be analyzed with a high-field NMR system. A benchtop low-field NMR system was used to perform relaxation measurements on highly magnetic natural geological sand samples mixed with sand and biofilm from a sand column reactor. Shorter relaxation times in the biofouled sample indicated the presence of a biofilm, demonstrating that low-field NMR systems can be used in the natural environment to test for the presence of biofouling. Polyacrylamide is often used in high-shear applications such as enhanced oil recovery and wastewater treatment. These shear forces could affect the structure, and thus the function, of the polymer. Rheo-NMR, a combination of rheology and NMR, was used to study the velocity field for polyacrylamide solutions in a Rheo-NMR Couette device under different shear rates. The data shows that the polymer exhibits shear thinning behavior.