Quick Procedure to Evaluate the Oxygen Mass Transfer Resistance in Aerated Laboratory-scale Bioreactors

Oxygen transfer intensity is a major concern whenever conducting enzymatic reactions or bioprocesses, which require air for microbial growth or enzymatic oxidative steps. Agitation in bio-reaction units is directly related to oxygen transport from the gas phase to liquid phase followed by the oxygen uptake by the individual microbial cell or oxygen consumption in enzymatic oxidation reactions. In fact, activity of microorganisms or of the enzyme (oxidase) is monitored by the use of oxygen from supplied air. A limitation in the supplied oxygen, due to mass transport resistance or a consumption rate faster than the transported oxygen rate, may cause a decrease in the cell growing rate or a decrease of the overall enzymatic reaction rate. Consequently, a close control of the available oxygen in the liquid phase is implemented for any type of aerobic bioreactor, the amount of dissolved oxygen (DO) being continuously measured by means of DO-meters. As the solubility of oxygen in water is not very high (ca. 9 mg/L at 20 o C), its overall consumption rate is dependent on a large number of factors, the most important being the diffusion coefficient, temperature, gas-liquid mass transfer coefficient K L a , and the rate of microbial/enzymatic reactions. Oxygen transfer from gas phase to the reaction site (cells, enzyme) takes place in several steps. First, oxygen is transferred through the gas-liquid interface, then it is transported through bulk liquid and finally into the microbial cell. To improve the oxygenation rate, sophisticated mixing and air sparger systems are implemented on both laboratory and industrial scale bioreactors. Air under pressure is supplied through a tube end consisting in 'O' rings with very fine holes or orifices. The size of bubbles, which affects the mass transfer process, depends on the holes' size and type of sparger. For very fine and uniform bubbles with effective gas dispersion, a micro-sparger system is used instead of a sparger, consisting in highly porous ceramic material. Air dispersion in liquid phase is not only related to the sparger, but also on the type of impeller and mixing intensity. The appropriate position and type of the impeller can ensure the even distribution of the gas in the reactor. High agitation is favourable to the mixing, but a very high stirring speed may cause shear forces, damaging the cells and leading to a spotty aeration of the liquid. Special chapters are dedicated to mass transfer evaluation in the framework of bioreactor design and operation with various areas of applicability: industrial biosynthesis To optimise the aeration rate, knowing the gas-liquid mass transfer resistance is essential not only for a theoretical process analysis, but also for practical reasons related to bioprocess development. As the experimental observation can indicate only the overall oxygen uptake by the bioprocess, it is highly important to separate the contribution of the physical gas-liquid transport to its consumption in bio-reactions. Such analysis is possible only from separate determinations of the K L a coefficient and of the (bio)reaction rates. Experiments should be conducted in the absence of reaction, or under operating regimes at high aeration rates, making the whole process kinetically controllable. The volumetric mass transfer coefficient K L a is dependent on a large number of factors. This is why its precise evaluation is difficult due to its strong dependence on the liquid phase properties, mixing, gas solubility, operating conditions (temperature), sparger depth, aeration rate, vessel volume and geometry, baffles, liquid surface tension, etc

Le lien d'attachement mère-enfant à l'épreuve de la violence conjugale

La violence conjugale met en jeu la sécurité d’enfant. Au travers de ce mémoire, nous tentons de mettre en évidence l’impact de la violence sur le lien d’attachement mère-enfants ainsi que les répercussions sur leur développent en nous appuyant sur une revue de la littérature existant sur le sujet. Pour grandir en développant son plein potentiel, un enfant a besoin de la disponibilité de sa mère. L’attachement est essentiel à la création d’une personnalité saine, représentant pour un enfant la base de son plein développement intellectuel (être capable de penser logiquement, développer son conscience, faire face au stress et à la frustration). Les parents en situation de violence ne sont plus une base de sécurité pour leur enfant lorsque leur comportement est une source de stress major. La mère, impuissante par sa propre panique liée à son propre état peut devenir imperméable aux indices donnés par la peur d’enfant. Le besoin non assouvis de parent, voire la mère, sont le focus de la relation au détriment des besoins de l’enfant.Master [120] en sciences de la famille et de la sexualité, Université catholique de Louvain, 2017La diffusion de ce mémoire n'est pas autorisée par l'institutio

<i>Cnicus benedictus</i> Oil as a Raw Material for Biodiesel: Extraction Optimization and Biodiesel Yield

Cnicus benedictus fruits were used as raw material to extract oil, and the resulting oil was converted into biodiesel. Two extraction methods were tested: batch extraction, and ultrasound assisted extraction. Response surface methodology was considered for the optimization of the process efficiency. The selected key independent variables were temperature, extraction time, and solid/liquid ratio for batch extraction and ultrasound intensity, temperature, and extraction time for the ultrasound assisted extraction, respectively. The optimal working conditions are different for the two extraction techniques, with respect to temperature, solid/liquid ratio, and extraction time, respectively, leading to higher extraction efficiency in the case of the ultrasound-assisted extraction. Cnicus benedictus oil obtained under the optimal extraction conditions was further esterified with methanol under acid catalysis to yield biodiesel. The biodiesel was characterized through 1H-NMR and the main fuel properties were determined

Cnicus benedictus Oil as a Raw Material for Biodiesel: Extraction Optimization and Biodiesel Yield

Cnicus benedictus fruits were used as raw material to extract oil, and the resulting oil was converted into biodiesel. Two extraction methods were tested: batch extraction, and ultrasound assisted extraction. Response surface methodology was considered for the optimization of the process efficiency. The selected key independent variables were temperature, extraction time, and solid/liquid ratio for batch extraction and ultrasound intensity, temperature, and extraction time for the ultrasound assisted extraction, respectively. The optimal working conditions are different for the two extraction techniques, with respect to temperature, solid/liquid ratio, and extraction time, respectively, leading to higher extraction efficiency in the case of the ultrasound-assisted extraction. Cnicus benedictus oil obtained under the optimal extraction conditions was further esterified with methanol under acid catalysis to yield biodiesel. The biodiesel was characterized through 1H-NMR and the main fuel properties were determined

The impact of magnesium–aluminum-layered double hydroxide-based polyvinyl alcohol coated on magnetite on the preparation of core-shell nanoparticles as a drug delivery agent

One of the current developments in drug research is the controlled release formulation of drugs, which can be released in a controlled manner at a specific target in the body. Due to the diverse physical and chemical properties of various drugs, a smart drug delivery system is highly sought after. The present study aimed to develop a novel drug delivery system using magnetite nanoparticles as the core and coated with polyvinyl alcohol (PVA), a drug 5-fluorouracil (5FU) and Mg–Al-layered double hydroxide (MLDH) for the formation of FPVA-FU-MLDH nanoparticles. The existence of the coated nanoparticles was supported by various physico-chemical analyses. In addition, the drug content, kinetics, and mechanism of drug release also were studied. 5-fluorouracil (5FU) was found to be released in a controlled manner from the nanoparticles at pH = 4.8 (representing the cancerous cellular environment) and pH = 7.4 (representing the blood environment), governed by pseudo-second-order kinetics. The cytotoxicity study revealed that the anticancer delivery system of FPVA-FU-MLDH nanoparticles showed much better anticancer activity than the free drug, 5FU, against liver cancer and HepG2 cells, and at the same time, it was found to be less toxic to the normal fibroblast 3T3 cells