Browsing by Subject "Flocculation"

Now showing 1 - 3 of 3
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    Chemical and Hydrodynamic Effects in Polymer-Clay Flocculation: Anisotropic particulate size and surface morphology effects in varied and controlled hydrodynamic fields
    (2017-12) Wilkinson, Nikolas
    Polymer-driven flocculation of suspended particles is a critical process for many applications, including composite materials synthesis, paper manufacturing, and water treatment. However, the role of solution physicochemical properties on the polymer-particle assembly dynamics is nontrivial, particularly for non-spherical, polydisperse particulates such as natural clays. Properties including ionic strength and pH affect both the individual particulate aggregates themselves, as well as the polymer – particle flocculation event. In this work, we study the effects of ionic strength and aggregate size and structure on the polymer behavior and flocculation performance with anisotropic bentonite clay particles using traditional jar tests. The final floc structure is largely informed by ionic-strength driven changes to the initial clay aggregate size and surface structure. With increasing bentonite aggregate size, a transition from a networked to a patched polymer − aggregate floc structure is observed, independent of ionic strength during flocculation. Additionally, the clay’s aggregate morphology is a more direct control parameter of optimal polymer dose and final turbidity (turbidity after 5 min sedimentation) than zeta potential for aqueous bentonite systems. Flocculation performance is the same when bentonite aggregate morphology is the same, regardless of a change in zeta potential. Likewise, when bentonite aggregate morphology changes, flocculation performance also changes, regardless of the identical zeta potential. Therefore, initial clay aggregate morphology controls the extent of polymer adsorption and optimal polymer dose, while initial clay aggregate size controls the internal floc structure. While traditional jar tests offer the advantages of experimental simplicity, speed, and mimic treatment geometries, there is limited homogeneity and control over hydrodynamics within the system. Taylor-Couette cells offer a much higher degree of hydrodynamic control and have been shown to improve several industrial processes due to the wide variety of hydrodynamic flow states accessible. Traditional designs, however, limit the ability to introduce new fluids into the annulus during device operation due to geometric confinement and complexity. As a key part of this thesis effort, a co- and counter-rotating Taylor-Couette cell with radial fluid injection has been constructed. The new inner cylinder design does not modify the critical Re for flow instabilities and can precisely inject a desired mass at a desired flow rate. Using the newly designed, modified Taylor-Couette cell, axial mass transport behavior is experimentally determined over two orders of magnitude of Reynolds number. Four different flow states, including laminar and turbulent Taylor vortex flows and laminar and turbulent wavy vortex flows, were studied. Using flow visualization techniques, the estimated dispersion coefficient was found to increase with increasing Re, and a single, unified regression is found for all vortices studied. In addition to mass transport, the vortex structures’ stability to radial injection is also quantified. A new dimensionless stability criterion, the ratio of injection to diffusion timescales, was utilized to capture the conditions under which vortex structures are stable to injection. Using the stability criterion, global and transitional stability regions are identified as a function of Reynolds number, Re. Overall, this thesis examines chemical and hydrodynamic effects in polymer flocculation with natural clays, and shows the importance of initial contaminant properties on flocculation performance. The initial contaminant properties affect both flocculation efficiency and resultant floc structure and are often not considered at treatment plants. Consideration of these properties potentially can improve process predictive capabilities, which improves process performance.
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    Polymer Solutions in Complex Flows: Fibrils, Filaments, and Flocs
    (2020-08) Metaxas, Athena
    The behavior of polymers in solution under complex physicochemical and hydrodynamic flow fields is of interest to a variety of industrial processes, such as polymer processing and water treatment. In this thesis, two main areas are presented: (1) self-association of polymer chains in flow, resulting in the formation of fibrils and filaments, and (2) association of polymer chains with suspended particulate, resulting in the formation of flocs. In the first area, extensional properties of methylcellulose (MC) solutions were characterized using millimeter scale capillary thinning and micrometer scale filament stretching methods. The addition of NaCl to MC solutions results in self-assembly of a fraction of the MC chains into MC fibrils, which imparts elastic characteristics to the solution. Capillary Breakup Extensional Rheometry (CaBER) studies demonstrate the extensional relaxation time and extensional viscosity increased with increasing MC concentration in the presence of salt. Likewise, microfluidic filament stretching studies demonstrate the extensional viscosity increased with increasing NaCl concentration. By reducing the characteristic length scale of the thinning filament, the microfluidic platform enabled new measurements extensional properties for low molecular weight and low viscosity MC solutions. In the second area, the assembly of charged polymers, or polyelectrolytes, with bentonite clay into flocs was studied in complex flow fields using macroscale Taylor-Couette (TC) flows. A custom-built TC cell allowed for injection of the polyelectrolyte solution into the particle-laden flow to investigate in-situ floc nucleation and growth in varied hydrodynamic flow states. Faster floc growth rates and decreased 2-D perimeter-based fractal dimensions were observed for higher order flow states, indicating improved mass transfer of the polymer flocculant and shear rounding of the flocs, respectively. Additionally, the effects of ionic strength and polyelectrolyte molecular weight on flocculation in the TC cell were investigated. Smaller flocs were formed with increasing ionic strength, due to the role of charge screening on the initial bentonite aggregate size and polyelectrolyte chain persistence length and conformation in solution. Overall, this thesis seeks to provide additional understanding of how polymers assemble in solution under a variety of physicochemical conditions and flow, which can inform predictive processing capabilities and performance.
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    Synthesis and characterization of starch-based cationic flocculants for harvesting microalgae.
    (2012-09) Li, Liang
    Harvest of tiny microalgae cells is a technically and economically challenging step in algal biomass production and utilization. Many techniques have been developed and tested, and some of them are used with limited success. However none of these techniques has broad commercial applications, especially in the area of algae based fuels production. The purpose of this thesis project was to develop a novel flocculation process which would be able to concentrate algal biomass, allowing efficient separation and collection of algal biomass from culture broth. The core of the research was to develop a procedure to synthesize starch-based cationic flocculants which would be renewable, biodegradable, and non-toxic with harvest performance comparable with or better than commercial flocculants. The procedure involves cationization reaction between starch and glycidyltrimethylammonium chloride (GTAC), where the hydroxyl groups on starch are substituted by quaternary ammonium cations with the help of alkaline catalyst. In this project, experiments were designed and carried out to study the effects of key reaction variables, namely temperature, time, GTAC dosage, water content, and catalyst dosage on the degree of substitution (DS), an indication of how well GTAC was utilized in the reaction, and reaction efficiency (RE). The DS and RE generally increased and then decreased with increasing temperature, time, water content, and catalyst dosage. An increase in GTAC dosage increased DS but decrease RE. Pretreatments of starch using acid, alkaline, and microwave did not significantly affect the DS and RE. The resultant cationic starch flocculants and cationic polyacrylamide (CPAM), a commercial flocculant, were tested in harvesting experiments involving live algae grown in fresh water or animal manure. The harvest efficiency was affected by DS of the cationic starch, flocculant dosage, pH, and flocculation time. The cationic starch based flocculant performed better than CPAM in all conditions. Pilot scale cationic starch production and harvest tests were conducted. The results agreed well with those obtained from the lab scale experiments. Based on these results, an optimized cationic starch synthesis procedure was proposed. The novel procedure has great potential for commercial production of renewable, biodegrable, and non-toxic starch based flocculants for cost effective and eco-friendly harvest of algal biomass.