Studies on transfer processes in mixing vessels: effect of gas on solid-liquid hydrodynamics using modified Rushton turbine agitators

The effect of gas on solid-liquid hydrodynamics in mixing vessels was studied to determine the agitation speed required to just completely suspend all the particles under gassed conditions, N _jsg and by measurement of the power consumption associated with this agitation speed. The solid particles have a mean diameter between 15–1000 μm. For their mixing are used standard and modified Rushton turbine agitators positioned singly or doubly on the same shaft. The modified turbine with a surface fraction of the perforations equal to 0.353 (TP3) was obtained through increase in the blade height of the Rushton turbine simultaneously with the perforation of the blade surface. The filled surface of the modified blade is equal to the blade surface of the standard Rushton turbine.     

Studies on transfer processes in mixing vessels: effect of particles on gas-liquid mass transfer using modified Rushton turbine agitators

The influence of carbon dioxide concentration in liquid medium on elemental sulphur oxidation by Thiobacillus thiooxidans bacteria presented in this paper can be divided into 3 differing relationships. First relationship shows increase of sulphur biooxidation rate with increase of carbon dioxide concentration in liquid medium. Second one shows decrease of S⁰ oxidation rate with increase of CO₂ concentration in nutrient and in the third relationship there is no influence of carbon dioxide concentration on sulphur oxidation by Thiobacillus thiooxidans bacteria. The influence of carbon dioxide concentration in liquid nutrient on alive bacteria concentration in liquid medium is similar to those described above.     

Studies on transfer processes in mixing vessels: effect of particles on gas-liquid hydrodynamics using modified Rushton turbine agitators

The work presents the effect of solid particles having a mean diameter between 15–1000?μm, on the gas dispersion in a mechanically agitated vessel with standard and modified Rushton turbine agitators positioned singly or doubly on same shaft. For the dispersing and uniform distribution of the three phase (gas-liquid-solid) through the entire vessel section, the modified blade turbines, with the surface fraction of the perforations equal to 0.353, were found to be more efficient, the power consumption being reduced by approximately 50%in comparison with the standard Rushton turbines. The power number in the turbulent mixing of the three phase system is dependent on the aeration rate, the surface fraction of the perforations, the turbine number and the physical and rheological properties of the suspensions.     

Studies on transfer processes in mixing vessels: suspending of solid particles in liquid by modified Rushton turbine agitators

The modified blade turbines are attractive alternatives to the standard Rushton turbine as they do not require any modification in the electrical engine motor and drive assemblies are simple to manufacture and have a reduced power consumption.The modified blades were obtained through increase in the blade height of the Rushton turbine simultaneously with perforation of the blade surface. The field surface of the modified blade is equal to the blade surface of the standard Rushton turbine.In this study the modified blade turbine with the surface fraction of the perforations equal to 0.353 is used.The complete suspension speed and the power dissipation in transition and turbulent regimes using standard and modified Rushton turbine agitators positioned singly or doubly on same shaft, in five solid-liquid systems were investigated.The solid particles used have the mean diameter between 15–1000 m.The modified blade turbine, noted as TP3, was found to be more efficient than the standard turbine in complete and homogeneous suspension.List of Symbols A distance between turbine and the vessel bottom (m) - c dimensionless constant (-) - d agitator diameter (m) - d _p surface-to-volume mean diameter of the particle (m) - D vessel diameter (m) - (H _L )₁ suspension height for one turbine immersed (m) - (H _L )₂ suspension height for two turbines immersed (m) - K consistency index (Pa s ⁿ ) - l _k eddy-size characteristic (m) - N flow behaviour index (-) - N _p number of blades of the mixing system (-) - N agitator speed (s^–1) - N _js agitator speed that just causes complete suspension (s^–1) - Ne P_L/_LN³d⁵ power number in liquid system (-) - (Ne) _g P_g/_spN³d⁵ power number in solid-liquid system (-) - P _L power consumption in liquid system (W) - P _s power consumption in solid-liquid system (W) - r coefficient of correlation (-) - R distance between turbines (m) - Re _spNd²/ _a Reynolds number (-) - S suspension parameter in Zwietering equation (2) (-) - S _C full surface of the blade (m²) - S _G surface of the perforations applied on the blade (m²) - S _G /S _C surface fraction of the perforations (-) - X particle concentration (g/l) - w baffle width (m) - _js specific power input per mass at the complete suspension state (W/kg) - _a apparent viscosity under mixing conditions (Pa s) - _L kinematic viscosity of the liquid (m²/s) - _L density of liquid (Kg/m³) - _s density of solid (Kg/m³) - _sp density of suspension (Kg/m³)     

A comprehensive comparison of mixing, mass transfer, Chinese hamster ovary cell growth, and antibody production using Rushton turbine and marine impellers

Large scale production of monoclonal antibodies has been accomplished using bioreactors with different length to diameter ratios, and diverse impeller and sparger designs. The differences in these physical attributes often result in dissimilar mass transfer, mechanical stresses due to turbulence and mixing inside the bioreactor that may lead to disparities in cell growth and antibody production. A rational analysis of impeller design parameters on cell growth, protein expression levels and subsequent antibody production is needed to understand such differences. The purpose of this study was to examine the impact of Rushton turbine and marine impeller designs on Chinese hamster ovary (CHO) cell growth and metabolism, and antibody production and quality. Experiments to evaluate mass transfer and mixing characteristics were conducted to determine if the nutrient requirements of the culture would be met. The analysis of mixing times indicated significant differences between marine and Rushton turbine impellers at the same power input per unit volume of liquid (P/V). However, no significant differences were observed between the two impellers at constant P/V with respect to oxygen and carbon dioxide mass transfer properties. Experiments were conducted with CHO cells to determine the impact of different flow patterns arising from the use of different impellers on cell growth, metabolism and antibody production. The analysis of cell culture data did not indicate any significant differences in any of the measured or calculated variables between marine and Rushton turbine impellers. More importantly, this study was able to demonstrate that the quality of the antibody was not altered with a change in the impeller geometry.     

Improvement of mixing time,mass transfer,and power consumption in an external loop airlift photobioreactor for microalgae cultures

Longer mixing times and higher power consumption are common problems in the design of photobioreactors. In this study, a vertical triangular external airlift loop photobioreactor was designed, constructed and operated for microalgae production studies. Gas feeding was performed by two spargers: one at the bottom of the hypotenuse (downcomer) and another at the bottom of the vertical side (riser). This configuration provided more effective countercurrent liquid–gas flow in the hypotenuse. The mass transfer coefficient, gas hold-up, mixing time, circulation time, dimensionless mixing time, bubble size, and volumetric power consumption were measured and optimized using response surface methodology. Investigations were carried out on the performance of the riser (the vertical side), downcomer (the hypotenuse), and separator. The countercurrent flow in the hypotenuse provided sufficient contact between gas and liquid phases, and increased mixing and mass transfer rates, in contrast to the results of previous studies. The promising results of this geometry were shorter mixing time and a significant decrease in volumetric power consumption in comparison with other configurations for photobioreactors.     

Studies on mass transfer characteristics of a modified airlift fermenter

An approach to modify external loop airlift bioreactor is presented that examines its performance with respect to mass transfer. There are various designs of airlift fermenter [1]. In the proposed system [2] the riser has been replaced by a tube of irregular geometry, in the form of converging-diverging sections (CDT-ALF), so that better mass transfer may be obtained due to better liquid mixing caused by the bubble flow, pulsation effect and early transition to turbulence. Mass transfer characteristics of the modified airlift fermenter CDT-ALF were studied and compared with those of a conventional one, UT-ALF. Overall volumetric mass transfer coefficient,K _L a, was determined by sulfite oxidation method.K _L a was determined with respect toU _G for differenth _i. HigherK _L a was always observed in CDT-ALF compared to that in UT-ALF under any operating condition ofh _i andU _G. If theK _L a values are compared in both the systems under their optimum conditions ofh _i andU _G, CDT-ALF showed 122.5% higher values ofK _L a compared to UT-ALF. However, when both the systems were operated at the lowest experimental conditions ofU _G, thek _L a in CDT-ALF was found to be 170% higher. In UT-ALF while with the decrease ofU _G,k _L a decreased, in CDT-ALF the reverse was observed i.e. at lowU _G,K _L a was higher. However with the increase ofh _i,K _L a decreased in both the systems. To predict volumetric mass transfer coefficientK _L a, empirical correlations were developed by dimensional analysis for both the reactors. The correlations were experimentally verified to determine their reliability to predict mass transfer coefficient and the deviation was found within reasonable limit.List of abbreviations ALF Airlift Fermenter - UT-ALF Uniform Tube Airlift Fermenter - CDT-ALF Converging-diverging Tube Airlift Fermenter     

Determination of power consumption and volumetric oxygen transfer coefficient in bioreactors

A torque meter has been developed for determining the power consumption in a bench stirred tank. The device has been bonded in the stirrer shaft inside a commercial bench fermentor, in order to avoid frictional losses in the mechanical seal. Power consumption measurements in ungassed and gassed systems were obtained at different agitation and aeration conditions, for Newtonian and non-Newtonian fluids. Also, a "simple modified sulfite method" for volumetric oxygen transfer coefficient (k_La) determination was developed and the experimental data were correlated with the gassed power (P_g) by using well-known correlations presented in the literature.     

Oxygen transfer efficiency in the biosynthesis of antibiotics in bioreactors with a modified RUSHTON turbine agitator

In this work, the oxygen mass transfer efficiency and power consumption in a non-biological system and an antibiotic biosynthesis process, using a modified RUSHTON turbine agitator, were investigated. It was demonstrated that a simple modification of the blades through the increase of the blade height, simultaneously with the discontinuation of the blade surface, could improve the oxygen transfer efficiency by about 30%. Experiments performed in stirred tank bioreactors with an overall volume of 20 m³, equipped with the modified RUSHTON turbine agitator, showed that the power consumption diminished by a factor of 1.18 to 1.6 during the fermentation processes of Streptomyces erithreus, Streptomyces griseus, Streptomyces noursei, and Nocardia mediaterranei, compared to the witness bioreactor. The use of the modified RUSHTON turbine for the antibiotic biosynthesis process may contribute to the decrease of the overall costs and the obtainment of better productivity, allowing an intensive utilization of power inputs for aeration and agitation.     

Studies on the suitability of alginate-entrapped Chlamydomonas reinhardtii cells for sustaining nitrate consumption processes

Some aspects of the suitability of alginate beads entrapping Chlamydomonas reinhardtii cells for nitrate consumption from nitrate-containing waters were studied and discussed. Among 14 different metal cations tested as gel bead stabilizing agents, only calcium and barium formed beads showing nitrate-consuming activity. Pure calcium alginate cell entrapment resulted in the most suitable method for active cell immobilization compared to alginate-composite-gel beads based on poly-vinylcaprolactam (PVCL) and poly-vinylpyrrolidone (PVP). To perform a continuous nitrate consumption process, calcium alginate-entrapped cells were first grown in a 2.5 l airlift-loop reactor. A cell loading of about 150 microg Chl. g(-1) gel was achieved. Afterwards, five days nitrate consumption processes were performed and three different dilution rates were applied: (i) D < mu; (ii) D = mu; (iii) D > mu, where mu is the specific growth rate (h(-1)). The maximum consumption rates calculated for each dilution rate were: (i) 3.8, (ii) 6.4 and (iii) 7.2 mg nitrate mg(-1) Chl. h(-1). For low dilution rates (D < mu) some nitrite (< 300 microM) was excreted into the culture medium. However, this concentration of nitrite was not high enough to inhibit nitrate consumption.     

Effects of paddle impeller geometry on power input and mass transfer in small-scale animal cell culture vessels

Process scaleup for stirred-tank animal cell cultures such as suspension and microcarrier cultures often begins at the bench scale in small spinner vessels. In order to initiate process development under the proper conditions, it is essential to know the physical conditions under which the cells are grown. In this article, power inputs and surface oxygen transfer rates to culture medium in 500-mL Corning spinner vessels were determined as a function of the impeller geometry, impeller height, and agitation speed. The results obtained indicate that power dissipation dependency differs from literature correlations and may compromise scale up at constant power input from these vessels. These results are of general utility to researchers using small-scale vessels.     

Studies on three microsomal electron transfer enzyme systems: Specificity of electron flow pathways

The routes of microsomal electron flow to the three terminal oxidative enzymes, the mixed function oxidase, the fatty acyl CoA desaturase, and the lipid peroxidase have been examined by the use of specific antibodies, by alteration of electron transfer enzyme levels, and with the inhibitor NADP⁺. From these studies a number of conclusions are drawn: (1) NADH-supported lipid peroxidation utilizes NADH-cytochrome b₅ reductase, but electron flow does not go via cytochrome b₅. (2) The positive modifier effect of type I substrates on NADPH-driven cytochrome P-450 reduction is seen also with NADH-supported cytochrome P-450 reductase activity. The latter reaction proceeds via cytochrome b₅ while the former does not. (3) Cross-reactivity can occur between NADH-cytochrome b₅ reductase and NADPH-cytochrome c reductase, but at a rate too slow to support most reactions. (4) Cytochrome b₅ appears to exist in two pools; one pool is readily inhibited by antibody and the other pool is either inaccessible to or incompletely inhibited by antibody. The various cytochrome b₅-dependent reactions show different abilities to use the noninhibited hemoprotein. NADH-cytochrome c reductase activity and NADH-synergism appear to utilize only the former pool and are completely inhibitable by antibody. Other NADH-supported reactions (Δ⁹-desaturation and mixedfunction oxidation) utilize the total cytochrome b₅ population. Fortification studies show that the extra bound cytochrome b₅ is distributed in the same manner as the endogenous cytochrome b₅.     

Effect of additives on mass transfer in turbine aeration

Mass transfer coefficients and interfacial areas were determined for the aeration of aqueous solutions in a turbine agitated vessel. The mass transfer coefficients measured for water without additive and for sodium chloride solutions matched very well to measurements in the literature for air bubbles of the same diameter in free rise. Thus the only effect of agitation was to determine the bubble size which then in turn set the coefficient. Two surface active agents were studied: sodium dodecyl sulfate and Dow Corning Antifoam C. The rate of mass transfer increased with the former additive but decreased with the latter; however, the mass transfer coefficient was the exact same function of bubble diameter in both cases and the different rates are attributed to the quite different effects on interfacial area.     

Studies on the fine structure of invertebrate blood vessels

Summary The position, structure and function of the valves within the lateral sinus of the medical leech, Hirudo medicinalis, are described on the basis of vital, light- and electron microscopy. In this species the valvular apparatus consists of multiple elongated fir cone-shaped fibrous villi surrounding the orifices of the latero-lateral and latero-dorsal vessel like a tentacular crest. Each villus is covered by a thin sheet of a continuous endothelium. The valves prevent the backflow of hemolymph during systolic contraction of the lateral sinus.The endothelium contains many small mitochondria and polyribosomes in the perinuclear cytoplasm and it develops deep projections into the underlying connective tissue. Each of these consists of a multilayered system of closely interwoven thin endothelial membranes. The endothelium is anchored to its basement membrane by means of a great number of poorly defined hemidesmosomes. The fibrous tissue of the villi consists mainly of a homogeneous vitreous matrix in which few cellular components and very fine filaments are dispersed. Close to the endothelium this matrix appears to be condensed to form a multilayered framework made out of a basement membrane-like material.Though the valves themselves are devoid of muscle cells, those situated at their base and thus belonging to the vascular wall proper, display some specific morphological features: in particular the nuclei of these cells show a distinct fibrous lamina. Moreover, these muscle cells seem to be innervated only by one type of axon, containing both small, lucent synaptic vesicles as well as some of the dense-core variety.These findings are compared with data from earlier works and are discussed in relation to the hemodynamic functions of this valvular apparatus.     

Influence of impeller type on mass transfer in fermentation vessels

Radial flow Rushton impellers were compared qualitatively with axial flow hydrofoil impellers (Maxflo T and A315) at the pilot scale. Six types of impellers were compared for qualitative differences in mass transfer. Measurements were conducted using three model systems: water, glycerol and Melojel (soluble starch). Power measurements were obtained using watt transducers, which although limited in accuracy and prone to interferences, were able to provide useful qualitative monitoring results. While there was little effect of impeller type on mass transfer as measured by the rapid pressure increase technique, significant qualitative differences were observed using the rapid temperature increase technique specifically for the Melojel and glycerol model systems. The Miller correlation, relating gassed-to-ungassed power, was used effectively to qualitatively evaluate the power drop upon gassing for both the model systems and a Streptomyces fermentation for the various impeller types. A high oxygen demand Streptomcyes fermentation then was conducted in fermenters possessing each type of impeller. Performance was not adequate with the A315 impellers pumping upwards and the small diameter Maxflo T impellers. Peak titers and profiles of the estimated apparent broth viscosity varied depending upon the impeller type. Mass transfer rates generally declined with higher viscosities when other fermentation operating conditions where held constant. Overall, values for OUR, k _L a, P _g /V _L and other calculated mass transfer and power input quantities for the A315 pumping upwards and undersized Maxflo T (D _T /D _I ?=?2.3) impellers were at the lower end of the range obtained for the larger Maxflo T (D _T /D _I ?=?1.8–2.0) and A315 impellers pumping downwards. Rushton impellers generally behaved qualitatively similar to hydrofoil impellers based on these calculated quantities.     

Influence of impeller type on power input in fermentation vessels

Prior investigations comparing radial flow Rushton impellers with axial flow hydrofoil impellers (Maxflo T and A315) were extended at the pilot scale. Six types of impellers (disk-style Rushton, Prochem Maxflo T hydrofoils of three diameters pumping downwards and A315 hydrofoils pumping upwards and downwards) were compared for qualitative differences in power number behavior with Reynolds' number, single versus double impeller power draw, gassed power reduction with aeration number and gas hold-up. Power measurements were obtained using watt transducers which, although limited in accuracy and prone to interferences, were able to provide useful qualitative monitoring results. Measurements were conducted using three model liquid systems: water, glycerol and Melojel (soluble starch). Apparent viscosities for actual Streptomyces cultivations were estimated using measured gassed power values and the experimental relationships obtained for gassed/ungassed power to aeration number and power number to Reynolds' number for the glycerol model system. Results confirmed the lower power number and lower shear environment for hydrofoil impellers, yet suggested useful trends for various process parameters and process fluids.     

Effect of the alcohol consumption on osteocyte cell processes: a molecular imaging study

We have previously shown microarchitectural tissue changes with cellular modifications in osteocytes following high chronic alcohol dose. The aim of this study was to assess the dose effect of alcohol consumption on the cytoskeleton activity, the cellular lipid content and modulation of differentiation and apoptosis in osteocyte. Male Wistar rats were divided into three groups: Control (C), Alcohol 25% v/v (A25) or Alcohol 35% v/v (A35) for 17 weeks. Bone mineral density (BMD) was assessed by DXA, osteocyte empty lacunae, lacunae surface, bone marrow fat with bright field microscopy. Osteocyte lipid content was analysed with transmission electron microscopy (TEM) and epifluorescence microscopy. Osteocyte apoptosis was analysed with immunolabelling and TEM. Osteocyte differentiation and cytoskeleton activity were analysed with immunolabelling and real time quantitative PCR. At the end of the protocol, BMD was lower in A25 and A35 compared with C, while the bone marrow lipid content was increased in these groups. More empty osteocyte lacunae and osteocyte containing lipid droplets in A35 were found compared with C and A25. Cleaved caspase‐3 staining and chromatin condensation were increased in A25 and A35 versus C. Cleaved caspase‐3 was increased in A35 versus A25. CD44 and phosphopaxillin stainings were higher in A35 compared with C and A25. Paxillin mRNA expression was higher in A35 versus A25 and C and sclerostin mRNA expression was higher in A35 versus C. We only observed a dose effect of alcohol consumption on cleaved caspase‐3 osteocyte immunostaining levels and on the number of lipid droplets in the bone marrow.