L'objectif de ce travail était d'étudier les trois fonctions d'une colonne airlift sous dépression qui sont le pompage, les transferts gaz-liquide et l'extraction de matières particulaires par moussage-écumage. Le champ d'application ciblé concernait principalement le traitement des eaux aquacoles incluant l'extraction et la concentration de microalgues naturelles ou de culture. Chacune des fonctions a été étudiée séparément afin d'évaluer les capacités de l'airlift dans différentes conditions. L'étude de la fonction pompage a montré l'importance de la nature de l'eau, du type de diffuseur d'air, du débit gazeux injecté et du niveau de dépression appliqué. En eau douce, une forte coalescence des bulles est observée. Elle a pour conséquence une rétention gazeuse plus faible qu'en eau de mer. Le débit d'eau fourni par la colonne apparaît ainsi supérieur en eau douce (30 à 35 m3.h-1 contre seulement 10 à 20 m3.h-1 en eau de mer pour 5 m3.h-1 d'air injecté). A l'inverse, la hauteur de refoulement disponible est plus élevée en eau de mer (jusqu'à 0.8 m) qu'en eau douce (0.6 m maximum). Pour des circuits d'aquaculture où la perte de charge est faible, l'airlift est un système de pompage économique qui permet de réduire d'environ 40 % la consommation d'énergie par rapport à celle de pompes centrifuges. La colonne airlift présente également des capacités de transferts de matière comparables à celles de systèmes conventionnels. Les valeurs de KLa calculées pour la désorption du CO2 et comprises entre 0.002 et 0.01 s-1, sont environ quatre fois inférieures à celles obtenues pour le transfert d'oxygène par aération dans des conditions comparables. Les efficacités de transfert sont comprises entre 0.02 et 0.023 Kg.KW.h-1 pour le CO2 et entre 1.52 et 1.8 Kg.KW.h-1 pour l'O2. Les vitesses de transfert dépendent significativement du débit d'air, de la température, de la taille moyenne des bulles et de la présence d'aliments dans le bassin d'élevage. Elles sont peu affectées par la salinité, le niveau de dépression, la longueur du tube interne d'échange et le débit d'eau. Enfin, les capacités de séparation par moussage-écumage évoluent de façon positive quand le débit d'air et la taille des bulles sont réduits. L'efficacité globale d'extraction diminue avec l'augmentation de la concentration des produits extraits qui peut atteindre 130 fois la concentration initiale. La colonne à dépression apparaît ainsi comme un système multifonctionnel performant, même si l'efficacité maximale, pour chacune des fonctions, correspond à des conditions opératoires différentes. Ce procédé ouvre des perspectives de développement intéressantes dans des secteurs variés (de l'aquaculture au traitement des eaux industrielles). / The aim of this work was to study the three functions of a vacuum airlift, which are water pumping, mass transfer and foam fractionation. The investigations mainly focused on the treatment of fish culture water and on phytoplancton harvesting. Each function was studied separately, in order to assess the performance of the vacuum airlift with specific operating conditions. By studying the airlift pump, the effects of water and diffuser types, air injection conditions and depression level were shown. In fresh water, bubble coalescence was observed, which reduced gas holdup compared to sea water. Consequently, the water flow of the vacuum airlift appeared higher in fresh water than in sea water (30 to 35 m3.h-1 against 10 to 20 m3.h-1) for the same air flow rate (5 m3.h-1). Conversely, the available lift height was higher in sea water (up to 0.8 m) than in fresh water (0.6 m maximum). For low head aquaculture systems, the vacuum airlift may be an economical pumping system which allows a 40 % energy saving compared to centrifugal pumps. The vacuum airlift had a mass transfer efficiency similar to other gas transfer systems. The KLa values calculated for CO2 desorption ranged between 0.002 and 0.01 s-1. They were four times lower than those obtained for oxygen transfer in similar conditions. Mass transfer efficiencies ranged between 0.02 and 0.023 Kg.KW.h-1 for CO2 and between 1.52 and 1.8 Kg.KW.h-1 for O2. Mass transfer velocities significantly depended on air flow rate, water temperature, average bubble size and the presence of feed in the rearing tank. They are weakly depending on salinity, depression level, inner tube length or water flow. At last, foam fractionation increased when air flow and bubble size were reduced. The extraction efficiency decreased when the concentration of the extracted product increased (maximal concentration factor around130). The vacuum airlift appeared to be as a high-performance multifunctional system, even if the maximal efficiency for each of the functions corresponds to different operating conditions. This process could be used in a large scope of fields ranging from aquaculture to industrial water treatment.

Thesis (Ph. D.)--Ohio State University, 2007. / Full text release at OhioLINK's ETD Center delayed at author's request

Techn. Universiẗat, Diss., 2004--Berlin.

The ensuing chaos and power struggles between the East and West following the end of the Second World War in Germany set the stage for the creation of a unique radio station that would broadcast from behind the iron curtain for the duration of the cold war. RIAS, or Radio in the American Sector, would play a key role in the battle over ideology between the West and the Soviet Union. The story of RIAS' birth and development is a unique narrative of unintended consequences as the efforts of the Soviet Union to gain a monopoly over the airwaves of Berlin actually contributed to ensuring a permanent Western radio presence in the city. This paper draws in part upon oral history, personal papers, government documents and the archives of the New York Times to tell the story of the development of RIAS and its role during the Berlin blockade and influence on the cold war.

Bubble columns and airlift reactors were modeled numerically to better understand the hydrodynamics and analyze the mixing characteristics for each configuration. An Eulerian-Eulerian approach was used to model air as the dispersed phase within a continuous phase of water using the commercial software FLUENT. The Schiller-Naumann drag model was employed along with virtual mass and the standard k-e turbulence model. The equations were discretized using the QUICK scheme and solved with the SIMPLE coupling algorithm. The flow regimes of a bubble column were investigated by varying the column diameter and the inlet gas velocity using two-dimensional simulations. The typical characteristics of a homogeneous, slug, and heterogeneous flow were shown by examining gas holdup. The flow field predicted using two-dimensional simulations of the airlift reactor showed a regular oscillation of the gas flow due to recirculation from the downcomer and connectors, whereas the bubble column oscillations were random and resulted in gas flow through the center of the column. The profiles of gas holdup, gas velocity, and liquid velocity showed that the airlift reactor flow was asymmetric and the bubble column flow was symmetric about the vertical axis of the column. The average gas holdup in a 10.2 cm diameter bubble column was calculated and the results for the two-dimensional simulation of varying inlet gas velocities were similar to published experimental results. The average gas holdup in the airlift reactor for the three-dimensional simulations compared well with the experiments, and the two-dimensional simulations underpredicted the average gas holdup. / Master of Science

As microalgas têm sido objeto de diversos estudos visando-se à produção de biocombustíveis ou outros produtos de interesse dentro do conceito de biorrefinaria. Na produção de biocombustíveis, as microalgas têm sido utilizadas por apresentarem elevada produtividade em lipídeos e carboidratos. Para viabilização de seu uso como matéria prima, é fundamental o desenvolvimento de processos com elevada produção de biomassa. Os fatores que influenciam no crescimento e composição da biomassa microalgal incluem a seleção do biorreator, a concentração e natureza da fonte de nitrogênio e o tipo de cultivo com relação às fontes de carbono e energia (autotrófico, heterotrófico ou mixotrófico). Neste trabalho, a microalga Chlorella minutissima 26a foi cultivada em fotobiorreatores do tipo tanque de bolhas em modo batelada ou airlift de tubos concêntricos em modo contínuo. Em cultivo autotrófico, estes fotobiorreatores foram empregados para avaliação da influência da concentração de nitrato de sódio no meio de cultivo no crescimento microalgal, na composição química da biomassa e na produtividade em lipídeos, carboidratos, proteínas e biomassa seca. Foi analisado também o uso de lixiviado proveniente de aterro sanitário na composição do meio de cultivo em fotobiorreator airlift em processo mixotrófico contínuo, promovendo concomitante biorremediação do lixiviado empregado. Os resultados demonstraram que a concentração de nitrato no meio de cultivo influenciou o crescimento e a composição química da biomassa e, consequentemente, os valores de produtividade obtidos. Nos ensaios usando fotobiorreator de tanque de bolhas em batelada, a variação da concentração de nitrato de sódio no meio de 37,5 mg L-1 para 150 mg L-1 promoveu aumento da produtividade em lipídeos e carboidratos, com valores máximos de 105,2 ± 1,7 mg L-1 d-1 e 36,7 ± 0,6 mg L-1 d-1, respectivamente, obtidos com a maior concentração de nitrato avaliada. No cultivo usando o fotobiorreator airlift em processo contínuo, o aumento da concentração de nitrato de sódio de 75 mg L-1 para 225 mg L-1 resultou nos maiores valores de produtividade média no estado estacionário para biomassa, lipídeos, proteínas e carboidratos, os quais foram, respectivamente, de 188,6 ± 11.2 mg L-1 d-1, 92,8 ± 5,5 mg L-1 d-1, 37,7 ± 2,2 mg L-1 d-1 e 29,1 ± 1,7 mg L-1 d-1. Neste caso, quando a concentração de nitrato de sódio aumentou de 75 mg L-1 para 150 mg L-1, observou-se aumento no teor de lipídeos e redução no teor de carboidratos da biomassa, sem modificação composicional apreciável quando a concentração de nitrato de sódio foi elevada para 225 mg L-1. O emprego do lixiviado diluído como meio de cultivo da Chlorella minutissima 26a resultou em elevados valores de produtividade em lipídeos, carboidratos, proteínas e biomassa, correspondendo a valores máximos de 232,0 ± 7,6, 95,3 ± 5,2, 33,4 ± 2,1 e 69,2 ± 3,0 mg L-1 d-1, respectivamente, dependendo da concentração de lixiviado no meio. O cultivo microalgal em lixiviado diluído resultou ainda em remoção de até 92,8% da demanda química de oxigênio, 90,5% do carbono orgânico total e 100% do nitrato presente no meio. Além disso, metais presentes foram removidos do meio durante o cultivo, resultando na remoção de até 63%, 72%, 100% e 67% para Cr, Fe, Al e Ba, respectivamente. O fotobiorreator airlift de tubos concêntricos demonstrou grande potencial para o cultivo da microalga C. minutissima em processo contínuo, incluindo a possibilidade de uso de lixiviado diluído na composição do meio para cultivo mixotrófico com sua concomitante biorremediação. / Microalgae have been the subject of different studies aimed at the production of biofuels or other products of interest within the concept of biorefinery. In the production of biofuels, microalgae have been used because they present high productivity in lipids and carbohydrates. In order to enable its use as a raw material, the development of processes with high biomass production is fundamental. Variables influencing the growth and composition of microalgal biomass include the selection of the bioreactor, the concentration and kind of the nitrogen source and the type of cultivation with respect to carbon and energy sources (autotrophic, heterotrophic or mixotrophic). In this work, the microalgae Chlorella minutissima 26a was cultivated in photobioreactors of two different kinds: bubble tank in batch mode or airlift of concentric tubes in continuous mode. In autotrophic cultivation, these photobioreactors were used to evaluate the influence of sodium nitrate concentration in the culture medium on microalgal growth, chemical composition of biomass and productivity in lipids, carbohydrates, proteins and dry biomass. The use of landfill leachate was also analyzed as a component of the culture medium in continuous airlift photobioreactor in a mixotrophic process, promoting concomitant bioremediation of the used leachate. The results showed that the concentration of nitrate in the culture medium influenced the growth and chemical composition of the biomass and, consequently, the productivity values obtained. In the assays using batch bubble tank photobioreactor, the variation in the sodium nitrate concentration in the medium from 37.5 mg L-1 to 150 mg L-1 promoted an increase of the productivity in lipids and in carbohydrates, with maximum values of 105.2 ± 1.7 mg L-1 d-1 and 36.7 ± 0.6 mg L-1 d-1, respectively, obtained with the highest evaluated nitrate concentration. In the cultivation using continuous airlift photobioreactor, the increase in sodium nitrate concentration from 75 mg L-1 to 225 mg L-1 resulted in higher values of average productivity in steady-state for biomass, lipids, proteins and carbohydrates, which were, respectively, of 188.6 ± 11.2 mg L-1 d-1, 92.8 ± 5.5 mg L-1 d-1, 37.7 ± 2.2 mg L-1 d-1 and 29.1 ± 1.7 mg L-1 d-1. In this case, when the sodium nitrate concentration increased from 75 mg L-1 to 150 mg L-1, there was an increase in lipid and a reduction in the carbohydrate content of the biomass, with no appreciable compositional modification when the sodium nitrate concentration was increased to 225 mg L-1. The use of diluted leachate as a culture medium of Chlorella minutissima 26a resulted in high productivity values in lipids, carbohydrates, proteins and biomass, corresponding to maximum values of 232.0 ± 7.6, 95.3 ± 5.2, 33. 4 ± 2.1 and 69.2 ± 3.0 mg L-1 d-1, respectively, depending on the landfill leachate concentration in the medium. The microalgal cultivation in diluted leachate also resulted in the removal of up to 92.8% of the chemical oxygen demand, 90.5% of the total organic carbono and 100% of the nitrate present in the medium. In addition, present metals were uptake from the medium during cultivation, resulting in a removal of up to 63%, 72%, 100% and 67% for Cr, Fe, Al and Ba, respectively. The airlift photobioreactor of concentric tubes demonstrated great potential for the cultivation of C. minutissima microalgae in a continuous process, including the possibility of using landfill leachate diluted in the medium composition for mixotrophic cultivation with its concomitant bioremediation.

As microalgas têm sido objeto de diversos estudos visando-se à produção de biocombustíveis ou outros produtos de interesse dentro do conceito de biorrefinaria. Na produção de biocombustíveis, as microalgas têm sido utilizadas por apresentarem elevada produtividade em lipídeos e carboidratos. Para viabilização de seu uso como matéria prima, é fundamental o desenvolvimento de processos com elevada produção de biomassa. Os fatores que influenciam no crescimento e composição da biomassa microalgal incluem a seleção do biorreator, a concentração e natureza da fonte de nitrogênio e o tipo de cultivo com relação às fontes de carbono e energia (autotrófico, heterotrófico ou mixotrófico). Neste trabalho, a microalga Chlorella minutissima 26a foi cultivada em fotobiorreatores do tipo tanque de bolhas em modo batelada ou airlift de tubos concêntricos em modo contínuo. Em cultivo autotrófico, estes fotobiorreatores foram empregados para avaliação da influência da concentração de nitrato de sódio no meio de cultivo no crescimento microalgal, na composição química da biomassa e na produtividade em lipídeos, carboidratos, proteínas e biomassa seca. Foi analisado também o uso de lixiviado proveniente de aterro sanitário na composição do meio de cultivo em fotobiorreator airlift em processo mixotrófico contínuo, promovendo concomitante biorremediação do lixiviado empregado. Os resultados demonstraram que a concentração de nitrato no meio de cultivo influenciou o crescimento e a composição química da biomassa e, consequentemente, os valores de produtividade obtidos. Nos ensaios usando fotobiorreator de tanque de bolhas em batelada, a variação da concentração de nitrato de sódio no meio de 37,5 mg L-1 para 150 mg L-1 promoveu aumento da produtividade em lipídeos e carboidratos, com valores máximos de 105,2 ± 1,7 mg L-1 d-1 e 36,7 ± 0,6 mg L-1 d-1, respectivamente, obtidos com a maior concentração de nitrato avaliada. No cultivo usando o fotobiorreator airlift em processo contínuo, o aumento da concentração de nitrato de sódio de 75 mg L-1 para 225 mg L-1 resultou nos maiores valores de produtividade média no estado estacionário para biomassa, lipídeos, proteínas e carboidratos, os quais foram, respectivamente, de 188,6 ± 11.2 mg L-1 d-1, 92,8 ± 5,5 mg L-1 d-1, 37,7 ± 2,2 mg L-1 d-1 e 29,1 ± 1,7 mg L-1 d-1. Neste caso, quando a concentração de nitrato de sódio aumentou de 75 mg L-1 para 150 mg L-1, observou-se aumento no teor de lipídeos e redução no teor de carboidratos da biomassa, sem modificação composicional apreciável quando a concentração de nitrato de sódio foi elevada para 225 mg L-1. O emprego do lixiviado diluído como meio de cultivo da Chlorella minutissima 26a resultou em elevados valores de produtividade em lipídeos, carboidratos, proteínas e biomassa, correspondendo a valores máximos de 232,0 ± 7,6, 95,3 ± 5,2, 33,4 ± 2,1 e 69,2 ± 3,0 mg L-1 d-1, respectivamente, dependendo da concentração de lixiviado no meio. O cultivo microalgal em lixiviado diluído resultou ainda em remoção de até 92,8% da demanda química de oxigênio, 90,5% do carbono orgânico total e 100% do nitrato presente no meio. Além disso, metais presentes foram removidos do meio durante o cultivo, resultando na remoção de até 63%, 72%, 100% e 67% para Cr, Fe, Al e Ba, respectivamente. O fotobiorreator airlift de tubos concêntricos demonstrou grande potencial para o cultivo da microalga C. minutissima em processo contínuo, incluindo a possibilidade de uso de lixiviado diluído na composição do meio para cultivo mixotrófico com sua concomitante biorremediação. / Microalgae have been the subject of different studies aimed at the production of biofuels or other products of interest within the concept of biorefinery. In the production of biofuels, microalgae have been used because they present high productivity in lipids and carbohydrates. In order to enable its use as a raw material, the development of processes with high biomass production is fundamental. Variables influencing the growth and composition of microalgal biomass include the selection of the bioreactor, the concentration and kind of the nitrogen source and the type of cultivation with respect to carbon and energy sources (autotrophic, heterotrophic or mixotrophic). In this work, the microalgae Chlorella minutissima 26a was cultivated in photobioreactors of two different kinds: bubble tank in batch mode or airlift of concentric tubes in continuous mode. In autotrophic cultivation, these photobioreactors were used to evaluate the influence of sodium nitrate concentration in the culture medium on microalgal growth, chemical composition of biomass and productivity in lipids, carbohydrates, proteins and dry biomass. The use of landfill leachate was also analyzed as a component of the culture medium in continuous airlift photobioreactor in a mixotrophic process, promoting concomitant bioremediation of the used leachate. The results showed that the concentration of nitrate in the culture medium influenced the growth and chemical composition of the biomass and, consequently, the productivity values obtained. In the assays using batch bubble tank photobioreactor, the variation in the sodium nitrate concentration in the medium from 37.5 mg L-1 to 150 mg L-1 promoted an increase of the productivity in lipids and in carbohydrates, with maximum values of 105.2 ± 1.7 mg L-1 d-1 and 36.7 ± 0.6 mg L-1 d-1, respectively, obtained with the highest evaluated nitrate concentration. In the cultivation using continuous airlift photobioreactor, the increase in sodium nitrate concentration from 75 mg L-1 to 225 mg L-1 resulted in higher values of average productivity in steady-state for biomass, lipids, proteins and carbohydrates, which were, respectively, of 188.6 ± 11.2 mg L-1 d-1, 92.8 ± 5.5 mg L-1 d-1, 37.7 ± 2.2 mg L-1 d-1 and 29.1 ± 1.7 mg L-1 d-1. In this case, when the sodium nitrate concentration increased from 75 mg L-1 to 150 mg L-1, there was an increase in lipid and a reduction in the carbohydrate content of the biomass, with no appreciable compositional modification when the sodium nitrate concentration was increased to 225 mg L-1. The use of diluted leachate as a culture medium of Chlorella minutissima 26a resulted in high productivity values in lipids, carbohydrates, proteins and biomass, corresponding to maximum values of 232.0 ± 7.6, 95.3 ± 5.2, 33. 4 ± 2.1 and 69.2 ± 3.0 mg L-1 d-1, respectively, depending on the landfill leachate concentration in the medium. The microalgal cultivation in diluted leachate also resulted in the removal of up to 92.8% of the chemical oxygen demand, 90.5% of the total organic carbono and 100% of the nitrate present in the medium. In addition, present metals were uptake from the medium during cultivation, resulting in a removal of up to 63%, 72%, 100% and 67% for Cr, Fe, Al and Ba, respectively. The airlift photobioreactor of concentric tubes demonstrated great potential for the cultivation of C. minutissima microalgae in a continuous process, including the possibility of using landfill leachate diluted in the medium composition for mixotrophic cultivation with its concomitant bioremediation.

Les microalgues sont des organismes photosynthétiques considérés pour la production d'énergie. Les photobioréacteurs sont des systèmes fermés avec des productivités plus importantes que les bassins ouverts. Cette étude concerne l'expérimentation et la modélisation d'un réacteur du type " airlift à circulation interne". Des microparticules sont ajoutées pour modéliser les concentrations d'algues dans le réacteur. Les fractions du gaz et les vitesses du liquide ne sont pas affectées par la présence de microparticules. La distribution de la lumière dans le réacteur est calculée en considérant les concentrations de la biomasse et les propriétés optiques des algues. La lumière est atténuée de la paroi jusqu'au centre du réacteur et cette atténuation augmente avec la concentration de la biomasse. Les productivités de biomasse, estimées en utilisant deux modèles biologiques, montrent que celles obtenues dans les photobioréacteurs sont plus élevées que celles obtenues dans les bassins ouverts. La capacité du réacteur pour absorber du CO2 et produire de l'O2 est évaluée selon les productivités obtenues. A intensités lumineuses modérées, l'O2 dissout n'atteint pas le niveau d'intoxication, même pour de faibles débits d'air. Le CO2 et le CIT deviennent limitant si de l'air naturel est injecté dans le bioréacteur. Il est donc nécessaire d'injecter de l'air enrichi en CO2. L'hydrodynamique d'un réacteur airlift hélicoïdal est également présentée. Deux diamètres de tuyaux sont testés dans la section hélicoïdale. Une corrélation est proposée pour estimer le coefficient de frottement en fonction du Reynolds et le rapport entre le diamètre d'enroulement et le diamètre de tuyau. Pour réaliser la culture de microalgues à l'échelle industrielle, il est indispensable d'obtenir un bilan énergétique positif et de faibles émissions de GES. Pour cela, il faudra intégrer la culture dans des procédés de transformation tels que la production de biodiesel et la digestion anaérobique.

<p>Cilj doktorske disertacije je pobolj&scaron;anje hidrodinamičkih i<br />masenoprenosnih karakteristika airlift reaktora sa<br />spolja&scaron;njom recirkulacijom umetanjem samo-rotirajućih<br />impelera u uzlaznu cev. Uticaj ugradnje samo-rotirajućih<br />impelera na osnovne hidrodinamičke i masenoprenosne<br />osobine ispitivan je pri radu sa različitim tečnostima i<br />distributorima gasa. Rezultati su tumačeni poređenjem<br />vrednosti za sadržaj gasa u uzlaznoj cevi, za brzinu<br />tečnosti u silaznoj cevi, i za zapreminski koeficijent<br />prenosa mase, dobijenih za dve konfiguracije reaktora (sa<br />i bez impelera).<br />Rezultati disertacije ukazuju da ugradnja samo-rotirajućih<br />impelera dovodi do znatnog razbijanja mehurova i<br />smanjenja srednjeg prečnika mehurova gasa, naročito u<br />viskoznim rastvorima karboksimetilceluloze. Prividna<br />brzina gasa, vrsta tečne faze i tip distributora gasa u<br />velikoj meri utiču na efikasnost samo-rotirajućih impelera.<br />Dobijene vrednosti sadržaja gasa u uzlaznoj cevi su do<br />47% veće u konfiguraciji sa impelerima u odnosu na<br />konfiguraciju bez impelera. Iako samo-rotirajući impeleri<br />predstavljaju dodatni otpor proticanju tečnosti, njihovom<br />ugradnjom je u svim ispitivanim sistemima postignuto<br />relativno malo smanjenje brzine tečnosti (oko 10%).<br />Zahvaljujući impelerima, zapreminski koeficijent prenosa<br />mase uvećan je do 82% pri manjim protocima gasa. Pri<br />većim protocima, koji odgovaraju uslovima rada koji se<br />sreću u većini fermentacionih procesa, postignute su oko<br />20-30% veće vrednosti zapreminskog koeficijenta prenosa<br />mase.<br />Pored empirijskih modela, u ovom radu uspe&scaron;no su<br />razvijeni i modeli ve&scaron;tačkih neuronskih mreža kojim se<br />predviđaju sadržaj gasa u uzlaznoj cevi, brzina tečnosti i<br />zapreminski koeficijent prenosa mase za obe konfiguracije<br />airlift reaktora sa spolja&scaron;njom recirkulacijom.</p> / <p>The aim of this study was intensification of<br />hydrodynamic and mass transfer properties of<br />external-loop airlift reactor by means of self-agitated<br />impellers mounted in the riser section. The influence<br />of impellers&rsquo; insertion on the main hydrodynamic<br />and mass transfer characteristics was investigated for<br />various liquid phases and sparger types. The values<br />of riser gas holdup, downcomer liquid velocity and<br />volumetric mass transfer coefficient obtained in<br />configurations with and without impellers were<br />compared.<br />Results showed that the installment of self-agitated<br />impellers led to a significant bubble breakage and<br />decrease of bubble size, especially in viscous<br />carboxymethylcellulose solutions. The efficiency of<br />self-agitated impellers was immensely influenced by<br />superficial gas velocity, liquid phase, and distributor<br />type. Obtained riser gas holdup values were up to<br />47% higher in the configuration with impellers, in<br />comparison to the configuration wthout impellers.<br />Despite the fact that self-agitated impellers<br />represented an obstacle to liquid flow, relatively low<br />reduction of downcomer liquid velocity was attained<br />(about 10%). Furthermore, the insertion of impellers<br />induced up to 82% higher values of volumetric mass<br />transfer coefficient at lower superficial gas velocities.<br />At higher superficial gas velocities, i.e. conditions<br />mainly operated in various fermentation processes,<br />about 20-30% higher values of volumetric mass<br />transfer coefficient were achieved with impellers.<br />In addition to empirical correlations, artificial neural<br />network models were sucessfully developed to<br />predict riser gas holdup, downcomer liquid velocity<br />and volumetric mass transfer coefficient in both<br />external-loop airlift configurations.</p>

Made available in DSpace on 2016-06-02T19:56:50Z (GMT). No. of bitstreams: 1 5040.pdf: 2753762 bytes, checksum: 183de6a78d0f606bfd3485cc5c3d7711 (MD5) Previous issue date: 2013-03-21 / Universidade Federal de Sao Carlos / The sugarcane sugar (sucrose) is a raw material produced in abundance in Brazil, being attractive to produce high added-value by-products. The gluconic acid (GA) can be obtained by multienzymatic conversion of sucrose, using three enzymes. Invertase, responsible for the inversion of sucrose to glucose and fructose, glucose oxidase (GOD) responsible for the glucose oxidation and catalase (CAT) responsible for decomposition of hydrogen peroxide. In multienzymatic process fructose is obtained as a byproduct, also of great interest to the food, pharmaceutical and chemical industries. In this study, the production of GA from sucrose in airlift reactor is evaluated. Temperature and pH of maximum activity were determined for the enzymes invertase, GOD and CAT , as well as the thermal stability in the absence of substrate. Invertase enzymatic activity was quantified by formation of reducing sugars on a 200 mM sucrose solution at 30 ° C, and pH 4.8. The enzymatic activity of GOD and the CAT were determined by monitoring respectively the formation of H2O2 from a solution of glucose 1 g/L, 25°C, pH 5.0 and the decomposition of H2O2 from a solution of H2O2 35 mM, 25°C, pH 7.5. Invertase showed maximum activity at 45 ºC and pH 5.0; GOD at 55ºC and pH 6.0 and CAT at 25 ° C and pH 8.0, respectively. From the activity profiles as a function of temperature and pH, the operational conditions of 50, 45 and 40°C at pH 5.0 and 6.0 were pre-selected for the multienzymatic process. It was found that the best half-lives times of the soluble enzymes, invertase, GOD and CAT, occurred in the condition of 40°C and pH 6.0, respectively 137, 105 and 98 h. A kinetic study was carried out at 40°C and pH 6.0. The kinetics of the enzyme invertase showed a behavior best predicted by the model of substrate inhibition. Michaelis-Menten model (MM) was fitted to experimental data of GOD and substrate inhibition model best predicted the kinetics behavior of CAT. The proposed kinetic models were used to estimate enzyme/substrate ratio (w/w) used in the production of GA in agitated and aerated and airlift bioreactors. On the other hand, in the batch assays conducted in airlift bioreactor were obtained AG real yields of 80.38 ± 5.69% and global yields of 103.20 ± 13.96% and conversion of sucrose of 98.86 ± 0.97%; obtained after 5 h. A new set of kinetic parameters including volumetric oxygen transfer coefficient (kLa) was based on the experimental data from tests in airlift bioreactor. These showed that Bi-Bi Ping-Pong model both with or without product inhibition correspond satisfactorily to the tendency of the experimental data. / O açúcar de cana (sacarose) é uma matéria-prima produzida em abundância no Brasil, sendo atrativa a produção de derivados com maior valor agregado. O ácido glucônico (AG) pode ser obtido através da conversão multienzimática da sacarose, utilizando como biocatalisadores as enzimas invertase, glicose oxidase (GOD) e catalase (CAT), responsáveis respectivamente pela inversão da sacarose, oxidação da glicose e decomposição de peróxido de hidrogênio (H2O2). No processo multienzimático obtém-se como subproduto a frutose, também de grande interesse para as indústrias alimentícia, farmacêutica e química. No presente trabalho foi avaliada a produção de AG a partir de sacarose em reator airlift. As enzimas invertase, GOD e CAT solúveis foram caracterizadas quanto à temperatura e ao pH de máxima atividade, bem como quanto à estabilidade térmica na ausência de substrato. A atividade enzimática da invertase foi quantificada pela ação da invertase sobre uma solução de sacarose 200 mM a 30ºC, pH 4,8, acompanhando-se a formação de açúcares redutores totais. As atividades enzimáticas da GOD e da CAT foram determinadas monitorando respectivamente a formação de H2O2 a partir de uma solução de glicose 1 g/l, 25ºC, pH 5,0 e a decomposição de H2O2 a partir de uma solução de H2O2 35 mM, 25ºC, pH 7,5. Invertase apresentou máxima atividade a 45ºC e pH 5,0; GOD a 55ºC e pH 6,0 e CAT a 25ºC e pH 8,0, respectivamente. A partir dos perfis de atividade em função da temperatura e do pH, as condições operacionais de 50, 45 e 40ºC em pHs 5,0 e 6,0 foram pré-selecionadas para a bioconversão multienzimática de sacarose a AG. Verificou-se que os melhores tempos de meias-vidas das enzimas invertase, GOD e CAT solúveis ocorreram na condição de 40ºC e pH 6,0, respectivamente 137, 105 e 98 h. Um estudo cinético foi realizado a 40ºC e pH 6,0. A cinética da enzima invertase apresentou comportamento previsto pelo modelo de inibição pelo substrato. O modelo de Michaelis-Menten (MM) foi ajustado aos dados experimentais da GOD e o modelo de inibição pelo substrato foi o que melhor se ajustou à cinética da CAT. Os modelos cinéticos propostos serviram para a estimativa das relações enzima/substrato (m.m-1) empregadas na produção de ácido glucônico em biorreatores agitado e aerado e airlift. Os ensaios em batelada em biorreator airlift apresentaram eficiências real e global em AG de respectivamente 80,40 ± 5,70 % e 103,20 ± 13,96 % e conversão de sacarose de 98,86 ± 0,97 %; obtidas após 5 h. Um novo ajuste dos parâmetros cinéticos incluindo o coeficiente volumétrico de transferência de oxigênio (kLa) foi realizado com base nos dados experimentais dos ensaios em biorreator airlift. Este mostrou que os modelos Bi-Bi Ping-Pong com ou sem inibição pelo produto responderam de forma satisfatória à tendência dos dados experimentais.