Enhanced Oxygen Transfer Research Articles

Application of membrane tubing aeration and perfluorocarbon To improve oxygen delivery to hairy root cultures

Growth and atropine production by Atropa belladonna hairy roots were studied in bioreactor cultures using porous polypropylene membrane tubing as a supplementary aeration device and with FC-43 perfluorocarbon emulsion added to the medium. Both these treatments were applied to improve oxygen transfer to the roots. Membrane tubing aeration allowed direct delivery of oxygen within the root clump, thus overcoming mass transfer resistances associated with poor intraclump penetration of liquid convective currents. Combined air sparging and membrane tubing aeration in a gas-driven bioreactor supported biomass levels 32-65% higher than sparging only of air or oxygen-enriched air at the same total gas flow rate. The optimal air flow rate ratio between the sparger and membrane tubing giving the maximum final biomass concentration was 0.2:0.4 L min-1. Intraclump dissolved oxygen tensions at high biomass densities were generally greater using air delivered by combined sparger-membrane tubing aeration than with sparging only of air or oxygen-enriched air. Specific atropine levels were not significantly affected by membrane tubing aeration. Indicators of anaerobic metabolism, such as lactic acid, ethanol, and ADH activity levels, were not significantly different in sparged and membrane-aerated systems; A. belladonna hairy roots also did not produce aerenchyma in response to oxygen limitations. Addition of perfluorocarbon emulsion to Murashige and Skoog medium in sparged stirred tank bioreactors did not improve growth, even when the emulsion was continuously recycled for re-aeration in an external vessel. Perfluorocarbons are associated with enhancement of gas-liquid oxygen transfer, so their ineffectiveness in this work most likely reflects the dominance of liquid-solid transfer resistances in hairy root cultures. The results of this investigation highlight the importance of developing new approaches for site-directed aeration of hairy root cultures, targeting oxygen delivery into the zones of highest root density.

Hydrodynamics of Stirred Bioreactors

This review of the hydrodynamics of stirred bioreactors begins with an introduction to the agitation problems of particular concern in such systems. This is followed by a brief review of some basic concepts in turbulence and rheology of relevance to bioreactors. Important aspects of single phase mixing in low viscosity, high viscosity and Theologically complex broths are then covered in some detail including flow patterns, power number versus Reynolds number plots (including the modification of the latter to allow for shear thinning broths), flow numbers, energy dissipation rates and flow close to impellers and between multiple impeller systems. From these basic principles, the problem of homogenization is then covered in depth because of its significance for bioreactor performance. Aeration concepts are then introduced and the behavior of traditional Rushton turbine impellers is then treated in detail, covering the flow patterns, aerated power characteristics, mixing time and scale-up considerations. The weaknesses of the Rushton turbine are then discussed which leads into a section describing how more modern impellers are able to improve on many of these, especially emphasising their ability to introduce more energy dissipation into the broth and handle more air before flooding, both of which enhance oxygen transfer. The improvement in bulk blending found with multiple axial flow agitators is brought out too. Finally, the retrofitting of fermenters originally containing Rushton turbines with these more modern impellers is discussed. In conclusion, it is clear that there have been substantial increases in the understanding of stirred bioreactor hydrodynamics. However, whilst further understanding will occur within the framework discussed here, the expectation must be that computational fluid dynamics will increase in importance in spite of the difficulty of handling complex rheology, multiphase systems and biological responses. This review article has 135 references.

Enhancement of gas-liquid mass transfer rate of apolar pollutants in the biological waste gas treatment by a dispersed organic solvent

Dispersed water-immiscible solvents are known to enhance oxygen transfer rates in oxygen-limited aerobic fermentations. Here, this technique is applied to improve the mass transfer rate of poorly water-soluble gaseous pollutants during the biological treatment of waste gases. In a stirred-tank reactor, the enhancement of mass transfer rates was studied as a function of the pollutant solubility in water. The solvent used was FC40 (up to 10% v/v) and the model gaseous pollutants were toluene and oxygen (moderately and poorly water-soluble, respectively).The overall volumetric mass transfer coefficient from the gas to the bulk liquid (klagl) was measured under nonsteady-state conditions in the absence of micro-organisms. It was found to be essentially constant for the solvent volume fractions tested and for both toluene and oxygen. Using the values of klagl and the partition coefficient gas/liquid (mgl), the enhancement of the mass transfer rate by solvent addition could be predicted theoretically. A good agreement between the theoretical evaluation and the experimental results from experiments in the presence of biological consumption was observed. An enhancement of the mass transfer rate by a factor of 1.1 was found for toluene using a dispersion containing 10% (v/v) FC40 while the oxygen transfer rate increased by a factor of two at the same solvent volume fraction. It was further demonstrated theoretically for other gaseous compounds that the addition of solvent has a more pronounced effect on the enhancement of the transfer rate in the case of poorly water-soluble compounds compared to moderately water-soluble ones.

Enhanced oxygen transfer in tower bioreactor on addition of liquid hydrocarbons

A mixture of alkanes in the range of C 12 to C 16, byproducts of distillation processes in the petroleum industry, was used as an oxygen-vector. The effect on the oxygen transfer rate of addition of the alkane mixture to the medium in a tower bioreactor was investigated. A concentration of 4% (v/v) of the alkane mixture increased the volumetric oxygen transfer coefficient ( k L a) and yeast production rate by 1.26- and 1.3-fold, respectively, compared with these values in a medium without oxygen-vector.

The effects of cells on oxygen transfer in bioreactors

Cells may affect oxygen transfer rates by three mechanisms: respiration of cells accumulated at the gas/liquid interface, physical presence of cells as solid particles, and modification of the medium by cells. These effects were studied experimentally in bubble-aerated bioreactors using baker's yeast at different cell concentrations, agitation speeds, aeration rates, and specific oxygen uptake rates. The overall effect of cells was to enhance oxygen transfer rates. The physical presence of cells as solid particles was found to retard oxygen transfer, presumably due to the lower oxygen permeability in the cell layer accumulated near the bubble surfaces. Cell respiration and medium modification, on the other hand, enhanced oxygen transfer rates. The retardation by nonrespiring cells and the enhancement due to cell respiration were found stronger at higher agitation speeds and lower aeration rates employed. This was attributed to the higher interfacial cell accumulation associated with the smaller bubbles produced under these conditions in the systems studied.

Biological oxygen transfer enhancement in wastewater treatment systems

The occurrence of biological oxygen transfer enhancement was investigated with samples of influent wastewater and wastewater solids collected from a nearby wastewater treatment plant. The potential mechanisms for the enhancement, namely, cell respiration, physical presence of solids, and wastewater modification, were studied in isolation by careful experimental design. The physical presence of nonrespiring solids was found to retard oxygen transfer, presumably because of the lower oxygen permeability in the solids layer accumulated near the bubble surfaces. On the other hand, cell respiration and wastewater modification enhanced the oxygen transfer rates. Overall oxygen transfer enhancements of approximately 20% were observed.

Enhancement of oxygen transfer in highly viscous non‐newtonian fermentation broths

The influence of short draft tubes covered by perforated plates on gas-liquid mass transfer was examined in external-loop airlift bioreactors. The volumetric mass transfer coefficients in a model external-loop airlift bioreactor were measured with water and non-Newtonian media. It was found that introduction of draft tubes covered with perforated plates in the riser significantly improved the mass transfer rate, particularly in higher viscous non-Newtonian fermentation media. The enhancement of mass transfer rate might be due mainly to an increase in bubble coalescence and redispersion.

Xanthan gum production with pumping Static-mixing Loop Fermentor(PS-Loop Fermentor)

Pumping Static-mixing Loop Fermentor(PS-Loop Ferxnentor) designed to enhance oxygen transfer into highly viscous solution is suitable for santhan fermentation. Equations relating circulation period and aeration with Kia and equations about the optimal operation were obtained. Xanthan gum production was enhanced by this fermentor.

Enhancement of glucose oxidase fermentation by addition of hydrocarbons

Addition of a hydrocarbon to fermentation medium has been recognized as a means of enhancing oxygen transfer. However, the mechanism involved has not been clarified. We investigated the glucose oxidase fermentation using Aspergillus niger in the presence of n-dodecane, n-hexadecane and soybean oil. The hydrocarbons had positive influences on the formation of both intra- and extracellular glucose oxidases. Moreover, the fermentation time needed to achieve the maximum enzyme yield was reduced. The increase in the yield of glucose oxidase was due to an increase in the efficiency of enzyme synthesis in the cells for cases of n-dodecane or n-hexadecane, while it was due to an increase in cell concentration for soybean oil. The increase in the level of extracellular glucose oxidase arose from increased enzyme secretion. However, it was interesting to find that the hydrocarbons delayed the cell growth as well as the production of glucose oxidase. This fact implies that the hydrocarbons alone do not improve the oxygen transfer. An explanation was made by considering the timing of feeding of the antifoaming agent KM-70 into the fermentation broth. The improved effects of the hydrocarbons on the fermentation are due to their interaction with the antifoaming agent. Accordingly, the timing of addition of the hydrocarbons to the culture is an important determinant for the fermentation. Apparently, the optimal timing is shortly after the start of feeding of the antifoaming agent.

グルコースオキシダーゼとカタラーゼ共存下のグルコース酸化速度の解析

The oxidation of glucose in the presence of glucose oxidase and catalase was employed for studying the oxygen transfer enhancement in an aqueous solution by additions of both n-hexadecane and soybean oil. Like surface-active agents, antifoam agents can decrease the oxygen transfer rate dramatically and thus played an important role in the oxygen transfer process. In the absence of antifoam agents, addition of n-hexadecane or soybean oil to the reaction medium caused decreases in the oxygen transfer rate (OTR). The extent of decrease was greater in soybean oil than in n-hexadecane. The spreading coefficient of the oil on water was found to be adequate for explaining this phenomenon. If the antifoam agent KM-70 was added to the reaction medium, however, an increased OTR could be obtained with addition of n-hexadecane or soybean oil. The enhancement in OTR was thought to be due to the removal of the antifoam-agent molecules away from the air-water interface by the oil added. The enzyme kinetics was verified to be unaffected by additions of KM-70, n-hexadecane and/or soybean oil. The present enzyme system is therefore adequate as a model for studying oxygen-vectors.

Analysis of oxygen transfer enhancement by oxygen carrier in the autotrophic cultivation of Alcaligenes eutrophus under low oxygen partial pressure.

Growth rate of Alcaligenes eutrophus under non-explosive gas mixture of low oxygen partial pressure, where oxygen transfer was rate determining process, was enhanced by adding perfluarocarbon as an oxygen carrier. The trend of enhancement with increase of PFC addition was different across the phase inversion region where continuous phase changes from aqueous medium to PFC. The enhancement was analyzed quantitatively using a mass transfer model, which took into account two cases where either the medium or the PFC was continuous phase. An enhancement factor for the oxygen transfer rate, defined as the ratio of oxygen transfer rate in a medium mixed with PFC to that in a PFC-free medium, was used in evaluating the effect of PFC addition. The factor was a function of the oxygen transfer coefficient and the interfacial area between gas bubble and the medium, and the volume fraction of PFC when the medium was in continuous phase. Also the factor varied with the interfacial area and the oxygen transfer coefficient between the PFC and the medium, the volume fraction of PFC and the dissolved oxygen concentration when the PFC phase became continuous. The model revealed the factors affecting on the observed cell growth rate of A. eutrophus, such that the primary factor contributing to the enhancement of the cell growth in the latter case was the increase of the interfacial area between the PFC and the medium.

Heat transfer in three‐phase fluidization and bubble‐columns with high gas holdups

Bubble column and three-phase fluidized bed reactors have wide applications in biotechnological and petroleum processes (Deckwer, 1985; Fan, 1989). In such biotechnological processes as fermentation and waste water treatment, small bubbles of oxygen and/or nitrogen are introduced in the column to enhance oxygen transfer and to ensure the stability of immobilized cell particles. In addition, tiny bubbles are produced during the biological process due to the production of surface active compounds. The presence of these small bubbles causes an increase in the gas holdup of the system. High gas holdups are also characteristics of industrial processes such as coal liquefaction and hydrotreating of residual oils. Good understanding of the transport properties of three-phase fluidized beds with high gas holdups is essential to the design, control and optimum operations of the commercial reactors employed in the above-mentioned processes. Heat-transfer studies in three-phase fluidized beds have been reviewed recently by Kim and Laurent (1991). Past studies focused primarily on the measurements of time-averaged heat transfer from the column wall to bed (Chiu and Ziegler 1983; Muroyama et al., 1986) or on immersed heating objects to bed (Baker et al., 1978; Kato et al., 1984) in aqueous systems. Recently, Kumar et al. (1992)more » provided a mechanistic understanding of the heat transfer in bubbly-liquid and liquid-solid systems. The purpose of this work is to investigate the heat transfer in a three-phase fluidized bed under high gas holdup conditions. The associated hydrodynamic behavior of the system is also studied.« less

Model analysis of biological oxygen transfer enhancement in surface‐aerated bioreactors

A model was developed to evaluate the effects of cells and surfactants on oxygen transfer in surface-aerated bioreactors. The model assumed the presence of serial layers of adsorbed surfactants and microorganisms directly adjacent to the gas-liquid interface due to their surface activities, followed by a stagnant liquid layer to account for the oxygen transfer resistance in the liquid phase. The interfacial surfactant film, although posing as an additional resistance, was found to have negligible effect on the oxygen transfer rate because of its extremely small thickness as compared to the cell monolayer and the stagnant liquid layer. On the other hand, cells affect oxygen transfer by two mechanisms: the biological enhancement due to the respiration of interfacial cells and the physical blocking resulting from the semipermeable nature of cell bodies. Due to the low specific oxygen uptake rates of the sludges, the two mechanisms were found to be of comparable importance in activated-sludge systems; the oxygen transfer enhancement factor, E, varied from about 0.97 to 1.10 depending on the operating conditions. The biological enhancement effect, however, predominated in fermentations of actively growing bacteria. At relatively low agitation speed (e. g., 300 rpm), the value of E could reach about 3 to 5 in fermentations with high cell concentrations. Effects of other operating variables, such as the agitation intensity, the oxygen content in the mixed liquor, and the bulk cell concentration, on biological oxygen transfer enhancement were also studied.

Oxygen transfer properties of bubbles in animal cell culture media

Oxygen transfer rates were determined in a bubble aerated animal cell bioreactor. It was found that the oxygen transfer rates increased in the following order: large bubbles ( approximately 5 mm diameter) < intermediate bubbles ( approximately 1 mm diameter) < micron-sized bubbles ( approximately 100 microm diameter). Under certain conditions, the micron-sized bubbles were capable of achieving oxygen transfer rate up to 100 h(-1), a 10-20-fold higher transfer rate than the large bubbles. The effects of medium composition on oxygen transfer rates were different for the three ranges of bubbles studied. For the large bubbles, oxygen transfer rates decreased with increasing medium complexity. The lowest oxygen transfer rate was found in new-born calf serum (NBCS) and/or Pluronic F-68 supplemented media. For the intermediate and micron-sized bubbles, supplementation with NBCS into the culture media resulted in decreased oxygen transfer rate. However, further supplementation with Pluronic F-68 enhanced oxygen transfer rate greatly for both types of bubbles. The highest oxygen transfer rate was found for micron-sized bubbles in Pluronic F-68 supplemented media containing antifoam agent and NBCS.

Multi-Center Trial with a Modified Design of the Sarns Membrane Oxygenator

A redesigned hollow fiber bundle was incorporated into an existing oxygenator that underwent clinical trials at seven cardiovascular surgery centers. Clinical investigators were asked to assess gas transfer performance under clinical conditions that could be considered challenging to any microporous membrane oxygenator, i.e., with large body weight patients, long bypass times, or normothermic bypass and surgery. Sixty-six patients, ranging in weight from 54.5 kg to 143 kg, constituted the initial evaluation population. Enhanced oxygen transfer was noted by all of the investigators. FiO2 requirements for patients weighing 100 kg or more never exceeded .85, despite oxygen consumption levels reaching as high as 396. mL/min. Two centers documented a 15% to 18% reduction in FiO2 requirements compared to their standard oxygenator.

Enhancing Oxygen Transfer in Bioreactors by Perfluorocarbon Emulsions

AbstractThis work aims to investigate the capability of perfluorocarbon (PFC) emulsions in enhancing oxygen transfer in bioreactors. Based on the penetration theory, a model has been derived for evaluating the potential oxygen transfer enhancement effects of PFC emulsions with very fine PFC particles. Defined as the ratio between the maximum oxygen transfer rates in systems with and without the emulsions, the enhancement factor achievable with dilute PFC emulsions can be estimated as the square root of the product of ratios of oxygen permeability and solubility in media with and without the emulsions. The effect of PFC emulsions on oxygen transfer in low‐shear cultivation systems was further studied experimentally with direct measurements of volumetric oxygen transfer coefficients, 𝔨Lα, in bioreactors and with microbial fermentations conducted under low‐shear conditions. It was found that significantly higher cell populations could be maintained at an aerobic state by using systems supplemented with the investigated emulsions. The experimentally determined values of oxygen transfer enhancement factor compare well with the theoretical values for emulsions with up to 15% (v/v) PFC. The feasibility of enhancing oxygen transfer in bioreactors by introduction of adequate amounts of PFC emulsions was clearly demonstrated.

Enhanced oxygen transfer rates in fermentation using soybean oil-in-water dispersions

The effect of soybean oil on the volumetric oxygen transfer coefficient during the cultivation ofAerobacter aerogenes cells is presented. For our aeration-agitation conditions (0.278 vvm and 500 rpm), it has been demonstrated that the use 19% (v/v) of soybean oil enabled a 1.85-fold increase of thekl a coefficient (calculated on a per liter aqueous phase basis). For smaller volumetric oil fractions,kL a increased linearly with the oil loading. Because of the oxygen-vector properties of soybean oil, this oil is able to significantly increase thekL a of a bioreactor.

Enhancing penicillin fermentations by increased oxygen solubility through the addition of n‐hexadecane

n-Hexadecane was added to fermentation media to increase the medium oxygen solubilities, thus enhancing oxygen transfer rates in penicillin fermentations. For shake flask fermentations, cells were found to grow faster in the flasks with n-hexadecane than those without. The addition of n-hexadecane to penicillin fermentations was shown to significantly increase cell growth and penicillin production and reduce formation of mycelial pellets. The result was attributed to the enhancement of oxygen transfer in mycelial fermentations due to the higher oxygen solubilities of fermentation media achieved by adding n-hexadecane.

Oxidation of carbon monoxide over palladium on zirconia prepared from amorphous PdZr alloy I. Bulk structural, morphological, and catalytic properties of catalyst

Catalysts highly active for the oxidation of carbon monoxide have been prepared by oxidation of amorphous and crystalline Pd 1Zr 2 metal alloys. The oxidation was carried out in situ; i.e., the fresh metal alloys were exposed to CO-oxidation conditions at temperatures of 473–553 K. Under these conditions, the initially almost inactive metal alloys underwent a series of solid state reactions and were finally transformed into stable and highly active microporous catalysts. Bulk structural characterization using X-ray diffraction and electron microscopy revealed that the final catalysts were made up of small intergrown and poorly crystalline domains of different palladium and zirconia phases. Palladium was present in three forms in the active catalysts, as a solid solution of palladium and oxygen, as metallic palladium, and as PdO. Zirconia existed in monoclinic and tetragonal forms. Comparative kinetic measurements carried out in a differential fixed bed reactor in the temperature range 300–500 K indicated that the activity of the palladium species in the catalysts derived from the metal alloys was more than an order of magnitude higher than the activity of the palladium species in a palladium on zirconia catalyst prepared by impregnation. The comparison of the activities was based on turnover frequencies calculated on the basis of accessible palladium sites determined by CO chemisorption. The higher activity of the catalysts derived from the metal alloys is attributed to their unique structural and chemical properties leading to extremely large interfacial areas and possibly to enhanced oxygen transfer via the solid-solid interphase.

Enhancing oxygen transfer in surface-aerated bioreactors by stable foams.

To enhance oxygen transfer in surface-aeration bioreactors, stabilized foams were generated to increase the gas-liquid interfacial area by slowly introducing coarse bubbles into media containing fetal bovine serum. The bubble sparging rates were so low (i.e., 20 and 50 mL/h) that the contribution to oxygen transfer from these bubbles was due to foaming instead of bubbling. Furthermore, no physical cell damage caused by bubble sparging was observed. Oxygen transfer coefficients, kLa, in the bioreactors were measured in cell-free media. Without the foam-stabilizing agent (i.e., serum), no appreciable change in kLa was observed due to the bubble sparging. On the other hand, with serum, kLa increased with increasing serum content and bubble sparging rate and corresponded well with the degree of foaming. With 10% fetal bovine serum and a bubble sparging rate of 50 mL/h, kLa increased approximately 90% compared with no foaming. The enhancing effect of foam on oxygen transfer in surface aeration bioreactors has been further demonstrated with hybridoma cultures simultaneously grown in three identical bioreactors with and without stabilized foams.