Browsing by Author "Simkins, Jeffrey W."

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Characterization and quantification of structure and flow in multichannel polymer membranes by MRI
(2019-01) Schuhmann, S.; Simkins, Jeffrey W.; Schork, N.; Codd, Sarah L.; Seymour, Joseph D.; Heijnen, M.; Saravia, F.; Horn, H.; Nirschl, H.; Guthausen, G.
Polymeric multichannel hollow fiber membranes were developed to reduce fiber breakage and to increase the volume-to-membrane-surface ratio and consequently the efficiency of filtration processes. These membranes are commonly used in ultrafiltration and are operated in in-out dead-end mode. However, some of the filtration details are unknown. The filtration efficiency and flow in the multichannel membranes depend on filtration time and are expected to vary along spatial coordinates. In the current work, in-situ magnetic resonance imaging was used to answer these questions. Velocities were quantified in the feed channels to obtain a detailed understanding of the filtration process. Flow and deposits were measured in each of the seven channels during filtration of sodium alginate, which is a model substance for extracellular polymeric substances occurring in water treatment. Volume flow and flow profiles were calculated from phase contrast flow images. The flow in z-direction in the center channel was higher than in the surrounding channels. Flow profiles variate depending on the concentration of Ca2+, which changes the filtration mechanism of aqueous solutions of sodium alginate from concentration polarization to gel layer filtration.
Spatiotemporal mapping of oxygen in a microbially-impacted packed bed using 19F Nuclear magnetic resonance oximetry
(2018-08) Simkins, Jeffrey W.; Stewart, Philip S.; Seymour, Joseph D.
19F magnetic resonance has been used in the medical field for quantifying oxygenation in blood, tissues, and tumors. The 19F NMR oximetry technique exploits the affinity of molecular oxygen for liquid fluorocarbon phases, and the resulting linear dependence of 19F spin–lattice relaxation rate R1 on local oxygen concentration. Bacterial biofilms, aggregates of bacteria encased in a self-secreted matrix of extracellular polymers, are important in environmental, industrial, and clinical settings and oxygen gradients represent a critical determinant of biofilm function. However, measurement of oxygen distribution in biofilms and biofouled porous media is difficult. Here the ability of 19F NMR oximetry to accurately track oxygen profile development in microbial impacted packed bed systems without impacting oxygen transport is demonstrated. Time-stable and inert fluorocarbon containing particles are designed which act as oxygen reporters in porous media systems. Particles are generated by emulsifying and entrapping perfluorooctylbromide (PFOB) into alginate gel, resulting in oxygen-sensing alginate beads that are then used as the solid matrix of the packed bed. 19F oxygenation maps, when combined with 1H velocity maps, allow for insight into the interplay between fluid dynamics and oxygen transport phenomena in these complex biofouled systems. Spatial maps of oxygen consumption rate constants are calculated. The growth characteristics of two bacteria, a non-biofilm forming Escherichia coli and Staphylococcus epidermidis, a strong biofilm-former, are used to demonstrate the novel data provided by the method.