Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Inclludes bibliography.

This study was performed to increase knowledge of oxygen mass transfer (kLa) and mixing times in the scale-up of disposable bioreactors.Results of oxygen mass transfer studies showed kLa to increase with increasing agitation and aeration rates. By maintaining a scale-up constant such as gassed power to volume or shear, an almost constant kLa was achieved during scale-up from 50 to 2000 L. Using the scale-up constant Pg/V resulted in statistically higher kLa values at greater reactor volumes. Mixing times were revealed to be significantly affected by agitation, but not by the aeration rates tested. No pattern was recognized in the mixing time data over an increase in volume. Commonly used methods for predicting kLa upon scale-up were compared to experimental data. New coefficients were determined to fit the historic models to the parameters of this study, namely the unique geometry and low agitation and aeration rates used in the single-use systems. Each of the resulting four models was found to have average error rates from 16-23%. Although the error rates are not statistically different, the Moresi and Patete model was determined to be most conceptually accurate. The Moresi and Patete model found kLa to be more dependent on aeration than on the power input. This finding was consistent with the results of the experimental studies. The results of this study were for aeration rates (0.02-0.04 vvm) and agitation rates (Pg/V range of 2-20 W/m3) that are commonly used in single-use bioreactor systems.

While clinical transplantation of islets of Langerhans for the treatment of insulin dependent Diabetes Mellitus has shown significant promise in recent years, there remains a need for procedural optimizations to improve cell viability, functionality and ultimately, graft longevity. One of the most critical factors to islet cell survival is the proper oxygenation of these highly metabolic cellular aggregates. In culture, islets experience suboptimal oxygen profiles delimited by steep gradients across culture media. When retransplanted, they are subjected to extremes of hypoxia and anoxia, resulting in pronounced graft dysfunction and cell loss, which is further exacerbated when these cells are immunoisolated in polymer matrices. This study examined the effects of improving both in-vitro culture and immunoisolation of islet cells by optimizing oxygen mass transfer via oxygen carriers in the form of perfluorocarbons. Specifically, new systems for these applications were developed utilizing perfluoromoeities and conventional culture (polydimethylsiloxane) and immunoisolation (sodium alginate) matrices. During in vitro culture of islet cells, the use of perfluoro-impregnated PDMS culture platforms enhanced cell recovery, viability and function over the culture period. Additionally, marginal mass transplants of the islets cultured in these novel platforms functioned better in recipients than relevant controls. In immunoisolation, the optimization of perfluorocarbon emulsions was performed investigating the effects of combinations of surfactants and perfluorocarbons on oxygen mass transfer and cell viability. Emulsions were well characterized using particle size analysis by dynamic light scattering, perfluorocarbon inclusion by gravimetry and oxygen diffusivity measurements utilizing fluorescent optodes. A novel method was developed for the assessment of dissolved oxygen content of these emulsions. Optimal emulsions, as determined by predicted/measured oxygen transfer enhancement over relevant controls, were utilized in alginate matrices for microencapsulation of cell lines, initially, and then, islets of Langehans. The effects of these potential improvements were assessed by in-vitro potency assays, including a novel method for assessing glucose stimulated insulin release, and in transplantation efficacy in rodent marginal mass models. While the improvements in culture were promising in cell line studies, the observed benefit did not translate in islet culture. The cause was found to be related to permeability impediments generated from the surfactant components utilized in emulsion manufacture. In addition to the development of several new methods for the characterization of oxygen containing solutions and the potency assessment of isolated islets of Langerhans, the impact of these studies is important in the field of polymer engineering. We observed that the use of Polyethylene glycol (PEG) based materials may limit transport of nutrients and oxygen critical to cells. Additionally, we developed cell culture platforms that enhance the viability, number and function of cultured islet cells, potentially impacting the clinical realm where cell preservation is critical to transplant outcome.

Accurate experimental oxygen mass transfer coefficient, a measure of how quickly oxygen travels from a gas bubble to the bulk liquid, is important for comparing performance and for evaluating the oxygen transfer capability of a fermentor. Delays in probe response and changing gas volumes upon start-up of gassing affect the accuracy of oxygen transfer measurements. To mitigate these inaccuracies, a standard correction procedure for oxygen mass transfer data was established for highly oxygenated, well-mixed fermentation systems. Probe response time correction was generated by applying a second-order response model to dissolved oxygen probes and shown to be effective within 4%. By using a derived model for transient volume rise, the effect of changing gas volume at start-up was shown to cause very minimal error (1-2%) in kLa. The unsteady-state method of kLa determination was used to compare design aspects of a hypothetical fermentor, including gas sparging devices and locations, baffle geometries and quantities, and impeller configurations. It was shown that locating the sparging device in the center of the tank, directly below the drive shaft and bottom impeller, is optimal for oxygen mass transfer. Sparger type was shown to have little effect on oxygen mass transfer values, although an open-pipe sparger was shown to provide slightly more oxygen mass transfer than a ring sparger. The use of rounded baffles in place of traditional rectangular baffles resulted in a 67-80% decrease in oxygen mass transfer coefficient. A comparison of three and four traditional baffles showed that three baffles produced a higher oxygen mass transfer than four. Correlation of baffle ratio and oxygen mass transfer coefficient indicated that the optimum baffle ratio is approximately one. Radial impellers were observed to provide better mixing, and thus higher oxygen mass transfer coefficients than axial impellers. In seven of ten comparisons, an impeller quantity ratio of 1.33 instead of 1.00 provided significant improvement in kLa. Additionally, only two of ten comparisons showed a difference between traditional Rushton turbine impellers and Smith turbine impellers, indicating that the difference in oxygen mass transfer capability of the two is negligible.

This thesis examined the biological treatment of gas streams containing benzene, toluene, ethylbenzene and o-xylene (BTEX) using solid-liquid two-phase partitioning bioscrubbers (SL-TPPBs). SL-TPPBs consist of a cell containing aqueous phase and a polymeric solid phase that sequesters poorly water soluble and/or toxic substrates, mitigating substrate toxicity in the aqueous phase and improving the gas mass transfer during treatment of VOC contaminated gases. An initial investigation of oxygen transport determined that the polymers in a stirred-tank SL-TPPB enhance gas-liquid mass transfer. In addition, a study on biodegradation kinetics of BTEX by a bacterial consortium identified and quantified substrate interactions such as inhibition, enhancement and cometabolism. The stirred-tank SL-TPPB was then experimentally investigated for treatment of BTEX gas streams during steady-state and dynamic step-change operation to determine performance of the system relative to other biotreatment methods. A mathematical model was developed to predict system performance, which included the microbial kinetic model structure and parameters estimated during kinetic and oxygen mass transfer studies. As a less energy intensive alternative, an airlift SL-TPPB was operated and characterized. The airlift SL-TPPB was compared to an airlift liquid-liquid TPPB (silicone oil as sequestering phase) and a single phase airlift over dynamic step-change loadings, which showed that the airlift SL-TPPB outperformed the single phase airlift by >30% and had similar performance to the liquid-liquid airlift. However, the airlift SL-TPPB performance was lower relative to the stirred-tank SL-TPPB by >15%. Steady-state operation of the airlift SL-TPPB identified a range of operating conditions that provided maximum performance and conditions that were not oxygen limited. This prompted a study of oxygen mass transfer and hydrodynamics in the airlift system, which identified that the addition of polymers to an airlift does not cause physical enhancement of the gas-liquid mass transfer coefficient, but improves aqueous phase mixing and enhances overall oxygen transfer rate. A tanks-in-series mathematical model was formulated to predict performance of the airlift SL-TPPB, wherein the number of tanks-in-series to describe mixing in the airlift was obtained from a residence time distribution analysis of the airlift system completed during the hydrodynamic investigation. This thesis contributes a low-energy solution for the effective treatment of gases contaminated with BTEX. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2009-08-18 16:16:22.598

Thesis (PhD (Chemical Engineering))--Cape Peninsula University of Technology, 2019 / The South African wine industry is constantly facing several challenges which affect the quality of wine, the local/global demand and consequently the revenue generated. These challenges include the ongoing drought, bush fires, climate change and several liquor amendment bills aimed at reducing alcohol consumption and alcohol outlets in South Africa. It is therefore critical for the wine industry to expand and find alternative ways in which sub-standard or surplus wine grapes can be used to prevent income losses and increase employment opportunities. Traditional Balsamic Vinegar (TBV) is a geographically and legislative protected product produced only in a small region in Italy. However, the methodology can be used to produce similar vinegars in other regions. Balsamic-styled vinegar (BSV), as defined in this thesis, is a vinegar produced by partially following the methods of TBV while applying process augmentation techniques. Balsamic-styled vinegar is proposed to be a suitable product of sub-standard quality or surplus wine grapes in South Africa. However, the production of BSV necessitates the use of cooked (high sugar) grape must which is a less favourable environment to the microorganisms used during fermentation. Factors that negatively affect the survival of the microorganisms include low water activity due to the cooking, high osmotic pressure and high acidity. To counteract these effects, methods to improve the survival of the non-Saccharomyces yeasts and acetic acid bacteria used are essential. The primary aim of this study was to investigate several BSV process augmentation techniques such as, aeration, agitation, cell immobilization, immobilized cell reusability and oxygen mass transfer kinetics in order to improve the performance of the microbial consortium used during BSV production. The work for this study was divided into four (4) phases. For all the phases a microbial consortium consisting of non-Saccharomyces yeasts (n=5) and acetic acid bacteria (n=5) was used. Inoculation of the yeast and bacteria occurred simultaneously. The 1st phase of the study entailed evaluating the effect of cells immobilized by gel entrapment in Ca-alginate beads alongside with free-floating cells (FFC) during the production of BSV. Two Ca-alginate bead sizes were tested i.e. small (4.5 mm) and large (8.5 mm) beads to evaluate the effects of surface area or bead size on the overall acetification rates. Ca-alginate beads and FFC fermentations were also evaluated under static and agitated (135 rpm) conditions. The 2nd phase of the study involved studying the cell adsorption technique for cell immobilization which was carried-out using corncobs (CC) and oak wood chips (OWC), while comparing to FFC fermentations. At this phase of the study, other vinegar bioreactor parameters such as agitation and aeration were studied in contrast to static fermentations. One agitation setting (135 rpm) and two aeration settings were tested i.e. high (0.3 vvm min−1) and low (0.15 vvm min−1) aeration conditions. Furthermore, to assess the variations in cell adsorption capabilities among individual yeast and AAB cells, the quantification of cells adsorbed on CC and OWC prior- and post-fermentation was conducted using the dry cell weight method. The 3rd phase of the study entailed evaluating the reusability abilities of all the matrices (small Ca-alginate beads, CC and OWC) for successive fermentations. The immobilized cells were evaluated for reusability on two cycles of fermentation under static conditions. Furthermore, the matrices used for cell immobilization were further analysed for structure integrity by scanning electron microscopy (SEM) before and after the 1st cycle of fermentations. The 3rd phase of the study also involved the sensorial (aroma and taste) evaluations of the BSV’s obtained from the 1st cycle of fermentation in order to understand the sensorial effects of the Ca-alginate beads, CC and OWC on the final BSV. The 4th phase of the study investigated oxygen mass transfer kinetics during non-aerated and aerated BSV fermentation. The dynamic method was used to generate several dissolved oxygen profiles at different stages of the fermentation. Consequently, the data obtained from the dynamic method was used to compute several oxygen mass transfer parameters, these include oxygen uptake rate ( 𝑟𝑟𝑂𝑂2 ), the stoichiometric coefficient of oxygen consumption vs acid yield (𝑌𝑌𝑂𝑂/𝐴𝐴), the oxygen transfer rate (𝑁𝑁𝑂𝑂2 ), and the volumetric mass transfer coefficients (𝐾𝐾𝐿𝐿𝑎𝑎). During all the phases of the study samples were extracted on weekly intervals to evaluate pH, sugar, salinity, alcohol and total acidity using several analytical instruments. The 4th phase of the study involved additional analytical tools, i.e. an oxygen µsensor to evaluate dissolved oxygen and the ‘Speedy breedy’ to measure the respiratory activity of the microbial consortium used during fermentation. The data obtained from the 1st phase of the study demonstrated that smaller Ca-alginate beads resulted in higher (4.0 g L-1 day−1) acetification rates compared to larger (3.0 g L-1 day−1) beads, while freely suspended cells resulted in the lowest (0.6 g L-1 day−1) acetification rates. The results showed that the surface area of the beads had a substantial impact on the acetification rates when gel entrapped cells were used for BSV fermentation. The 2nd phase results showed high acetification rates (2.7 g L-1 day−1) for cells immobilized on CC in contrast to cells immobilized on OWC and FFC, which resulted in similar and lower acetification rates. Agitated fermentations were unsuccessful for all the treatments (CC, OWC and FFC) studied. Agitation was therefore assumed to have promoted cell shear stress causing insufficient acetification during fermentations. Low aerated fermentations resulted in better acetification rates between 1.45–1.56 g L-1 day−1 for CC, OWC and FFC. At a higher aeration setting, only free-floating cells were able to complete fermentations with an acetification rate of 1.2 g L-1 day−1. Furthermore, the adsorption competence data showed successful adsorption on CC and OWC for both yeasts and AAB with variations in adsorption efficiencies, whereby OWC displayed a lower cell adsorption capability compared to CC. On the other hand, OWC were less efficient adsorbents due to their smooth surface, while the rough surface and porosity of CC led to improved adsorption and, therefore, enhanced acetification rates. The 3rd phase results showed a substantial decline in acetification rates on the 2nd cycle of fermentations when cells immobilized on CC and OWC were reused. While cells entrapped in Ca-alginate beads were able to complete the 2nd cycle of fermentations at reduced acetification rates compared to the 1st cycle of fermentations. The sensory results showed positive ratings for BSV’s produced using cells immobilized in Ca-alginate beads and CC. However, BSV’s produced using OWC treatments were neither ‘liked nor disliked’ by the judges. The SEM imaging results further showed a substantial loss of structural integrity for Ca-alginate beads after the 1st cycle fermentations, with minor changes in structural integrity of CC being observed after the 1st cycle fermentations. OWC displayed the same morphological structure before and after the 1st cycle fermentations which was attributed to their robustness. Although Ca-alginate beads showed a loss in structural integrity, it was still assumed that Ca-alginate beads provided better protection against the harsh environmental conditions in contrast to CC and OWC adsorbents due to the acetification rates obtained on both cycles. The 4th phase data obtained from the computations showed that non-aerated fermentations had a higher 𝑌𝑌𝑂𝑂/𝐴𝐴, 𝑟𝑟𝑂𝑂2 , 𝑁𝑁𝑂𝑂2 and a higher 𝐾𝐾𝐿𝐿𝑎𝑎 . It was clear that aerated fermentations had a lower aeration capacity due to an inappropriate aeration system design and an inappropriate fermentor. Consequently, aeration led to several detrimental biochemical changes in the fermentation medium thus affecting 𝐾𝐾𝐿𝐿𝑎𝑎 and several oxygen mass transfer parameters which serve as a driving force. Overall, it was concluded that the best method for BSV production is the use of cells entrapped in small alginate beads or cells adsorbed on CC under static and non-aerated fermentations. This conclusion was based on several factors such as cell affinity/cell protection, acetification rates, fermentation period and sensorial contributions. However, cells entrapped in Ca-alginate beads had the highest acetification rates. The oxygen mass transfer computations demonstrated a high 𝐾𝐾𝐿𝐿𝑎𝑎 when Ca-alginate beads were used under static-non-aerated conditions compared to fermentations treated with CC. Therefore, a fermentor with a high aeration capacity needs to be designed to best suit the two BSV production systems (Ca-alginate beads and CC). It is also crucial to develop methods which can increase the robustness of Ca-alginate beads in order to improve cell retention and reduce the loss of structural integrity for subsequent cycles of fermentation. Studies to define parameters used for upscaling the BSV production process for large scale productions are also crucial.

Bench and pilot scale determinations of the volumetric oxygen transfer coefficient, K_La, were performed on an improved A²/O biological nutrient removal (BNR) pilot plant. Effluent from a full scale primary clarifier, used as pilot plant influent, was found to have an alpha (ratio of process to clean water K_La) of 0.71 as determined in a 21 liter bench scale reactor and an alpha of 0.332 as determined in a 0.45 m³ aeration basin of the 2.4 m³ pilot plant. Alpha of a 1:1 mixture of primary clarifier effluent with pilot plant return activated sludge was determined to be 0.94 at bench scale and 0.71 at pilot scale. An assay of alphas through the initial non aerated treatment zones of the pilot plant using the bench scale reactor indicated that alphas peaked in the effluent of the first anaerobic zone (alpha equal to 1.01) and were lower in the second anaerobic zone and first anoxic zone. An assay of alphas in the three pilot plant series sideline aeration basins indicated that alpha was maximum in the first aeration basin (alpha equal to 0.905) and were lower in the second and third aeration basins (0.716 and 0.661 respectively). A consistent increase in average surface tension was noted from the first to second to third aeration basins, however the differences were not statistically significant. A comparison of pilot plant alphas determined in the first aeration basin following anaerobic nominal hydraulic retention times of 0.0, 0.21, 0.43, and 0.64 hours yielded alpha values of 0.71, 0.94, 0.64, and 0.74 respectively. Like the assay using the bench scale reactor, the alpha values at pilot scale peaked following treatment in only one anaerobic zone (nominal HRT of 0.21 hours). The study concludes that short exposures in an initial anaerobic reactor as required for biological phosphorus removal may benefit oxygen transfer efficiency through increased alphas, however the benefits of long periods of anaerobic reaction time (over 0.43 hours) are uncertain. / Master of Science

Un nouveau système d’aération de surface pour le traitement des eaux usées a été étudié. Sa spécificité réside dans sa capacité à fonctionner selon deux modes : aération ou simple brassage, en modifiant uniquement le sens de rotation du système. Un pilote a permis de cibler le travail sur l’étude expérimentale du transfert de matière et de l’hydrodynamique. Les champs d'écoulement et les mesures de vitesse à l'intérieur de la cuve agitée ont été réalisés par vélocimétrie laser à effet Doppler (LDV) et par vélocimétrie par images des particules (PIV) pour le mode monophasique (brassage) et pour le mode diphasique (aération). Le transfert d'oxygène se produit à la fois dans la cuve et dans le spray au-dessus de la surface de l'eau. Il a été étudié dans les deux zones. Différentes configurations et conditions opératoires ont été testées afin de comprendre les phénomènes d’interaction : tube de guidage, hélice complémentaire RTP, vitesse de rotation, niveau de submersion des pales de la turbine. La partie expérimentale sur l’hydrodynamique et les champs d'écoulement montre que le mode de fonctionnement en pompage vers le bas (brassage) avec tube de guidage procure les meilleurs résultats en termes de mélange si on se réfère aux champs d'écoulement et à la mesure du temps de mélange. Pour le mode de fonctionnement en pompage vers le haut (aération), les résultats expérimentaux montrent que la configuration du système complet est la plus efficace si on considère le transfert d’oxygène, les vitesses moyennes, l'intensité de l'écoulement turbulent et le temps de mélange. Il est constaté que la meilleure efficacité d'aération standard est atteinte (SAEb = 2.65 kgO2kw-1h-1) lorsque le système complet est utilisé. L'efficacité d'aération standard à 20°C la plus élevée au niveau du spray d'eau est obtenue ((ESP)20 = 51,3%) avec la configuration du système complet. Plusieurs modèles sont proposés pour calculer le transfert d'oxygène dans la cuve et dans le spray, la consommation énergique et le temps de mélange. Ces relations permettent d’évaluer l’influence des différents paramètres géométriques et de fonctionnement dans des systèmes similaires à une échelle industrielle. / A new surface aeration system for water and wastewater treatment has been studied. Its uniqueness lies in its ability to operate in two modes: aeration or simply blending (mixing) by just reversing the direction of rotation. An experimental plant has enabled to focus on mass transfer performance and hydrodynamics. The flow pattern and the velocity field measurements inside the agitated tank were performed by both the Laser Doppler Velocimetry (LDV) and the Particle Image Velocimetry (PIV) techniques for the single phase (Mixing) mode and for the two phases (Aeration) mode. The oxygen mass transfer occurs both in the water bulk and in the spray above water surface and has been independently investigated. Different configurations and operational conditions were tested during the experimental part in order to interpret phenomenon effect of the draft tube and RTP propeller, rotational speed, turbine blades submergence and else on the flow field and the oxygen mass transfer in the agitated system that produced mainly by a cone shape turbine. The experimental part dealing with hydrodynamics and flow field shows that the down-pumping operation mode with the draft tube has the most convenient results in the mixing mode with respect to turbulent flow field and mixing time. Whilst for the up-pumping aeration mode the hydrodynamics experimental results show the whole system configuration is the most convenient with regarded to mean velocities, turbulent flow intensity and mixing time. For the oxygen mass transfer experimental part, it is found that the highest standard liquid bulk aeration efficiency is achieved (SAEb = 2.65 kgO2 kw-1h-1) when the whole system configuration is used. The highest standard aeration efficiency at 20°C for the water spray zone is accomplished ((Esp)20 = 51.3 %) with the whole system configuration. Several correlations models have been derived for the oxygen mass transfer in water bulk and spray zones, power consumption and mixing time, on the basis of experimental results. They can be used as tools to estimate these parameters for geometrical and dynamical similar systems at industrial scales.