Airlift Fermenter Research Articles

Oxygen transfer measurements during yeast fermentations in a pilot scale airlift fermenter

Oxygen transfer measurements during yeast fermentations in a pilot scale airlift fermenter

Dynamic Mixing and Oxygen Transfer in Small, Airlift Loop Bioreactors: Model and Experimental Verification

AbstractA mechanistic model for mixing and mass transfer in both airlift bubble column and loop bioreactors is described. The model is a useful design tool to improve oxygen‐transfer characteristics. It is shown that the model fits mixing and mass‐transfer experimental data closely. The model confirms that the overall oxygen‐transfer coefficient in the riser of a loop airlift fermentor is similar to that in bubble columns and that lower measured transfer rates are due solely to the dead volume in the downcomer. The effects of parameters such as mass‐transfer coefficient, aeration rate, dispersion coefficient, sparger rotation speed, and liquid circulation velocity are presented in terms of both the liquid‐ and gas‐phase oxygen concentrations.

Mucor—a source of cocoa butter and gamma-linolenic acid

Lipid analyses were performed on 28 strains of various species of the genus Mucor. In shake flasks with glucose as carbon source, the gamma-linolenic acid (GLA) content in the neutral lipid (NL) fraction of some Mucor species was up to 38 mg GLA/g dry biomass. Some Mucor species produced more than 20% (w/w) stearic acid (18:0) and more than 60% of their NL content as symmetrical triacylglycerols (SUS-TAGs) which corresponded to those of cocoa butter. Three Mucor species were evaluated in terms of the production of SUS-TAGs and GLA in pH-stat, fed-batch cultures in an air-lift fermenter with acetic acid as titrant and carbon source. Mucor circinelloides f. circinelloides CBS 108.16 accumulated 27% 18:0 in the NL fraction, which constituted approximately 40% of the dry biomass. In this case, the NL fraction contained more than 70% (w/w) SUS-TAGs.

Two‐phase airlift fermentor operation with elicitation for the enhanced production of enzophenanthridine alkaloids in cell suspensions of Escherichia californica

Approaches to increasing the productivity of benzophenanthridine alkaloids in suspension cultures in Escherichia californica were made in an airlift fermentor under different culture conditions. Elicitation with yeast extract elicitor reduced the time required to obtain a certain amount of alkaloid production. In a two-phase airlift fermentor with compounded silicone fluid, total alkaloid concentration in silicone fluid was 153.1 mg/L and that in the aqueous cellular phase was 8.2 mg/L at day 21 from inoculation. The large accumulation capacity of silicone fluid made it possible to store correspondingly large amounts of total alkaloid and increased the alkaloid production. Act day 21 from inoculation, the volumetric alkaloid productivity and the netproduction in a two-phase airlift fermentor were 1.4 and 1.5 times higher than those of normal airlift fermentor operation. This performance was furthermore enhanced by elicitation. Elicitation in two-phase airlift fermentor operation increased the volumetric productivity and the new production 3.3- and 3.5-fold compared to those of normal airlift fermentor operation.

Influence of increased dissolved oxygen concentration on productivity and selectivity in cultures of a colabomycin-producing strain of Streptomyces griseoflavus.

The influence of enhanced O2 concentration on growth and formation of secondary metabolites by Streptomyces griseoflavus (strain Tü 2880) was investigated in a stirred tank and in an air-lift fermentor. At a partial pressure of O2 Po2 = 1880 mbar the growth was lowered by 50% compared to Po2 = 210 mbar, whilst substrate consumption and O2 uptake rate increased markedly. Production of the colabomycin complex reached maximum values at Po2 = 630 mbar. A similar increase of secondary metabolite formation was obtained when glycerol or acetate were fed at Po2 = 220 mbar. The portion of the derivate colabomycin A in the product mixture rose from 43% at Po2 = 210 mbar to 73% at Po2 = 1260 mbar. Since dissolved O2 concentration has a significant influence on productivity and selectivity it may be used to regulate aerobic fermentation processes.

Performance characteristics of yeast growth in a modified airlift fermenter

Two types of airlift fermenters, conventional (UT-ALF) and modified (CDT-ALF) were investigated to evaluate their performance with respect to baker's yeast growth. The riser tube of conventional external loop airlift fermenter is replaced by a converging-diverging tube, which is named as modified airlift fermenter having downcomer to riser cross-sectional area ratio Ad/Ar=1.8.

Characteristics of sisomicin fermentation supplemented with MgSO4 in stirred and air lift fermentors

Sisomicin fermentations were carried out in stirred and air lift fermentors, and various concentrations of MgSO4 were supplemented to improve antibiotic yield. The highest antibiotic yield was obtained at 80 mM in an air lift fermentor due to effective liberation of intracellular sisomicin by MgSO4. The presence of high concentrations of MgSO4, along with shear stress due to strong agitation in the stirred fermentor, resulted in low values of cell activity, rheological parameter(n) and cell viability in the stirred fermentor, compared with the air lift fermentor. The better physiological states of cells grown in the air lift fermentor resulted in improved antibiotic yields.

The influence of vessel height and top‐section size on the hydrodynamic characteristics of airlift fermentors

Fermentations of the yeast Saccharomyces cerevisiae were carried out in a 90 to 250-L working volume concentric tube airlift fermentor. Measurements of liquid circulation velocity, gas hold-up, and liquid mixing were made under varying conditions of gas flowrate, vessel height, and top-section size. Both liquid circulation velocity and mixing time increased with vessel height. Liquid velocity varied approximately in proportion to the square root of column height, supporting a theoretically based relationship. The effect of vessel height on gas hold-up was negligible. The height of the top-section had a significant effect on liquid mixing. Mixing time decreased with increasing size of the top-section up to a critical height. As the top-section was expanded beyond this height, little improvement in mixing was seen. This indicated the presence of a two-zone flow pattern in the top-section. Liquid velocity and gas hold-up were essentially independent of top-section height. (c) 1994 John Wiley & Sons, Inc.

Performance characteristics of yeast growth in a modified airlift fermenter

Performance characteristics of yeast growth in a modified airlift fermenter

Enhanced Expression, Secretion, and Large-Scale Purification of Recombinant HIV-1 gp120 in Insect Cells Using the Baculovirus egt and p67 Signal Peptides

The expression of glycosylated and secreted recombinant mammalian proteins in baculovirus-infected insect cells is often much less efficient than that of other foreign proteins in this system. In an effort to improve the expression and secretion of such proteins we have constructed baculovirus vectors which contain the signal peptide coding regions from two baculovirus proteins, an ecdysteroid UDPglucosyltransferase (egt) and the envelope glycoprotein gp67. We used these vectors to express HIV-1 gpl2O, inserting the baculovirus signal peptides in place of the HIV-1 envelope signal peptide. When Sf9 cells infected with recombinant baculoviruses made from these vectors (vegt120 and vp67120) were compared with cells infected with the normal gpl2O baculovirus a 6- to 20-fold increase in expression and secretion of gpl2O was observed. When the HIV-1 signal peptide was used only 40% or less of the total gpl2O produced in Sf9 cells was secreted. However, using the egt or p67 signal peptides, up to 70% of the total gpl2O produced was secreted. Therefore, not only was more gp120 produced from these modified viruses but secretion of gpl2O was more efficient. Large-scale expression and purification of egt-gp 120 from a 5-liter airlift fermenter or a 6-liter spinner flask resulted in a yield of 10 to 15 mg of purified protein per liter. Using these baculovirus-derived signal peptides in baculovirus expression vectors is thus likely to aid in increasing expression and yield of heterologous secreted proteins in insect cells.

Gas hold-up in converging-diverging tube airlift fermenter

Fractional gas holdup study was carried out in two airlift fermenters: one having of conventional design, the other having an asymetric riser arm. Air flow rate was varied from 1.5 to 9.0 cm/sec and gas hold-up values compared. Fractional gas holdup, ɛG, was strongly dependent on superficial gas velocity and initial liquid height. The modified fermenter always showed a higher gas holdup than the conventionally designed one.

Xanthan production in an external‐circulation‐loop airlift fermenter

AbstractA preliminary study of xanthan production by Xanthomonas campestris was performed in an external‐circulation‐loop airlift (ECL‐AL) fermenter. An average of 25 g/L xanthan of good viscosity characteristics was obtained in a total fermentation time of 49 hours. Oxygen limitation was observed after 36 hours of fermentation time. It is conclusively demonstrated that the ECL‐AL fermenter can be used to economically produce xanthan. The key operating and design features are the liquid height, downcomer‐to‐riser cross‐sectional area ratio (AD/AR) and the orfice diameter of the air sparger.

Development of a new commercial-scale airlift fermentor for rapid growth of yeast

To grow yeast rapidly, it is necessary to supply sufficient oxygen to the yeast and to effectively remove the heat of the fermentation. We succeeded in developing a commercial-scale fermentor for growing a food yeast ( Candida utilis) to produce RNA rapidly. This fermentor is an internal-loop airlift type with vertical heat transfer tubes between inner and the outer columns. The volume of the fermentor is 145 m 3 (working volume 75 m 3). The oxygen transfer rate (OTR) was 9.9 kg-O 2/m 3/h using a superficial gas velocity of 30 cm/s based on the outer column. Much of the heat of fermentation and the energy resulting from aeration could be removed effectively by the heat transfer tubes. This unique airlift fermentor was driven at a dilution rate of 0.43 h −1 for about 70 d, with the yeast concentration being maintained at 22.8 kg-dry cell/m 3. The yeast production rate was 9.79 kg-dry cell/m 3/h. Compared with a traditional stirred-type fermentor, two Vogelbush-type fermentors and another airlift fermentor, our fermentor was far superior with respect to OTR and yeast productivity.

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,KLa, was determined by sulfite oxidation method.KLa was determined with respect toUG for differenthi. HigherKLa was always observed in CDT-ALF compared to that in UT-ALF under any operating condition ofhi andUG. If theKLa values are compared in both the systems under their optimum conditions ofhi andUG, CDT-ALF showed 122.5% higher values ofKLa compared to UT-ALF. However, when both the systems were operated at the lowest experimental conditions ofUG, thekLa in CDT-ALF was found to be 170% higher. In UT-ALF while with the decrease ofUG,kLa decreased, in CDT-ALF the reverse was observed i.e. at lowUG,KLa was higher. However with the increase ofhi,KLa decreased in both the systems. To predict volumetric mass transfer coefficientKLa, 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.

Mixing characteristics of external-loop airlifts: non-Newtonian systems

Mixing time (θ) was measured in a 45 or 60 1 working liquid volume external-circulation-loop airlift (ECL-AL) fermentor, and in a geometrically similar 6 1 prototype, both equipped with perforated-plate spargers (1 mm dia. holes). Carboxymethylcellulose solutions were used to simulate the rheological behaviour non-Newtonian fermentation broths. The specific mixing time (θ/ V) is shown to be highly dependent on the dispersion height and gas superficial velocity in the riser section, as well as on the riser diameter and the effective viscosity of the liquid phase. In the range studied (0.111⩽ A D / A R ⩽0.46), the downcomer-to-riser cross-sectional-area ratio has a relatively minor effect on θ/ V. The superficial velocity of the circulating liquid in the riser ( u LR ) was also measured. The results have been combined with those of a previous investigation, by Popovic and Robinson, to better elucidiate the effect of dispersion height on the rate of liquid circulation. A modified correlation of u LR is presented and discussed.

Modeling and simulation of a large scale air lift fermenter

The paper deals with the modelling of an industrial airlift fermentor used for lactic yeast production on whey substrates. The purpose of this study was to improve the understanding of the interactions between the various parameters that govern the oxygen transfer phenomena in this type of fermentor, and to predict the biomass, lactose and Ethanol profiles inside the fermentor. This is performed through the combination of a knowledge based model of O 2 transfer and a physiological model. We obtain a distributed parameters model. The reliability of the proposed model is demonstrated. The results of the investigations have been put into practice on the industrial scale and have contributed to better monitor the fermentation process.

Modeling and simulation of a large scale air lift fermenter

Modeling and simulation of a large scale air lift fermenter

Effect of inlet oxygen concentration on continuous cultivation of Baker's yeast in a converging-diverging tube airlift fermentor

Continuous cultivation of Baker's yeast was carried out in a converging-diverging tube airlift fermentor. The dilution rate was varied from 0.08 to 0.165 h −1. The residual sugar cone, was maintained below 0.15 g/ l. Pure oxygen was sparged with air to maintain 50% oxygen saturation. The trend of the variation of cell mass, X, with the reciprocal of the dilution rate, D, did not correspond to the Monod chemostat model. The maximum dilution rate was found to be 0.165 h −1 for a cell mass enhancement of 30%.

Bacterial cellulose I. Two-stage fermentation process for cellulose production by Acetobacter aceti

Production of cellulose by Acetobacter aceti AJ12368 was optimized in a two-stage fermentation process. A cell growth stage in an air-lift fermenter (agitated culture) was followed by a cellulose formation stage in production incubators (static culture). The optimal moment of process change was at day 3 of agitated culture when the cell density and intracellular Adenosin triphosphate content peaked; at this time culture broth in the air-lift fermenter could be subdivided to feed four production incubators equipped with nine trays. Surface aeration was effective in producing food-use gelatinous cellulose which is homogeneous and low in syneresis. This process was more economical than the conventional fermentation procedure in the Nata industry.

Characterization of the cellulolytic enzyme system from the brown-rot fungus Coniophora puteana

The cellulolytic enzymes of various strains of the brown-rot fungus Coniophora puteana were studied. The organism was grown in an air-lift fermentor in mineral medium containing glucose, cellobiose or amorphous cellulose. The specific growth rate varied between 0.082 and 0.062 h−1. On amorphous cellulose as sole carbon source, the organism secreted various proteins, some of which were characterized. The mixture contained inter alia four endocellulases, two exo-cellobiohydrolases and a cellobiose dehydrogenase. Three endocellulases (named type I) were active on soluble cellulose derivatives but inactive on p-nitrophenyllactoside (p-NPL), whereas a fourth endocellulase (named type II) was active on both. The two exo-cellobiohydrolases released cellobiose from amorphous cellulose; they were inactive on soluble cellulose derivatives but hydrolyzed p-NPL with strong cellobiose inhibition. A cellobiose dehydrogenase having spectral characteristics compatible with a flavo b-cytochrome was also identified. Neither the exo-cellobiohydrolase nor the type II endocellulase were secreted during growth on cellobiose whereas type I endocellulases and cellobiose dehydrogenase were formed at a reduced rate. No formation of cellulolytic enzymes was observed during growth on glucose alone.