Ulfert Onken

Inhibition of bubble coalescence by solutes in air/water dispersions

Measurement of bubble size distributions in bubble column by a photoelectric probe showed that both electrolyte and organic solutes affect coalescence behaviour of aqueous solutions drastically within a narrow concentration range, changing from quick coalescence as in pure water to coalescence restraining. Besides the electrolytes NACl, Na2SO4, Al2(SO4)3, NaOH, organic compounds from homologous series (n-alcohols, diols, ketones, carboxylic acids), detergents, saccharose, and carboxymethylcellulose have been used as solutes. Rough relationships between concentrations for coalescence restraining and molecular properties can be given (ionic strength for electrolytes, number of C-atoms in homologous series of organic compounds), but no exact equations based on a theory of coalescence. For the n-alcohols (C1-C8), specific surface areas were calculated from experimental mean bubble diameters (Sauter diameters) and measured gas hold-up and compared to volumetric mass transfer coefficients from literature. Concentration dependence of the two types of data showed surprisingly good agreement with regard to the fact that the mass transfer data had been obtained in a gas-liquid contacting device (stirred vessel) quite different to the reactor used in this work (bubble column).

Influence of dissolved oxygen concentration and shear rate on the production of pullulan byAureobasidium pullulans

SummaryExperiments were carried out withA. pullulans (ATCC 9348) at constant dissolved oxygen concentration (DO=100 and 50% related to air saturation at 1 bar) and at constant stirrer speeds (n=500 and 150 [min−1]). The highest pullulan yield was achieved at decreased constant DO in connection with decreased shear rate. Biomass production was not affected.

Comparison of airlift and stirred reactors for fermentation with Aspergillus niger

Abstract The design and fabrication of a simple laboratory airlift fermentor are described. This reactor excels in reliability and low power requirement. Its efficiency has been proved for the production of gluconic acid by Aspergillus niger. As in the case of bubble columns, the desired morphology of A. niger, i.e pellet growth, is obtained in the laboratory airlift fermentor as well as in a pilot scale airlift fermentor of 260 l working volume. Thus, pellet formation occurred under rather low stress conditions as compared to stirred tanks where high agitation conditions are expected to be required to achieve similar results.

A simple laboratory airlift fermentor

SummaryA glass airlift fermentor for laboratory use has been constructed and tested. Its design is based on hydrodynamic requirements. Because of its simple construction it can be easily dismantled and reassembled.

THE EFFECT OF SOLUTES ON BUBBLE SIZE IN AIR-WATER DISPERSIONS

Bubble size distributions in a bubble column of 200 mm diameter were measured by means of a photoelectric probe. The gas-liquid dispersion was generated by distributing air with a porous plate into aqueous solutions of electrolytes and of organic compounds (alcohols, glycols, ketones, carboxylic acids, saccharose, carboxymethyl-cellulose, detergents). For all these solutes there exists a rather narrow concentration range in which the change from quick coalescence in pure water to coalescence suppression takes place. Though rough relationships between concentrations for coalescence suppression and molecular properties can be found (ionic strength for electrolytes, number of carbon atoms in a homologous series of organic compounds), exact equations based on a theory of coalescence cannot be given. The bubble size distributions obtained in the experiments have also been used to show the impact of coalescence phenomena on gas-liquid mass transfer. For this purpose, surface areas were calculated from measured ...

Hydrodynamics and Mass Transfer in an Airlift Loop Fermentor

SummaryThe hydrodynamics and mass transfer behaviour of an airlift fermentor with an external loop (height 10m) has been investigated by measuring gas and liquid velocities, gas hold-up, liquid mixing and oxygen transfer coefficients. Liquid phase properties, i.e., ionic strength, viscosity and surface tension have been varied by altering the fermentation media. Results are compared with those from bubble column experiments performed in the same unit. It is shown, that more uniform two-phase flow in the airlift leads to advantages in scale-up and operation.

DIKETO-GLUCONATE FERMENTATION BY GLUCONOBACTER OXYDANS

Abstract Production of 2,5-diketogluconate by Gluconobacter oxydans (ATCC9937) in two types of reactors, namely, airlift and stirred fermentors, is described. Accumulation of diketo-acid is shown to be dependent on the pH of the medium. Oxidation of gluconate to 2,5-diketogluconate in Gluconobacter oxydans is described as a specific reaction carried out through an intermediate of 2-ketogluconate rather than 5-ketogluconate. The enzyme profile of the culture depicting two distinct phases, i.e. direct glucose oxidation and gluconate oxidation, is described.

Extractive Fermentation of Gibberellic Acid by Gibberella fujikuroi

Microbial production of metabolites is often limited by product inhibition, decomposition or bio-degadation during the process of fermentation. If the product can be removed from the broth, e.g. by liquid/liquid extraction, these losses can be reduced. The production of gibberellic acid (GA3), a secondary metabolite of the ascomycete Gibberella fujikuroi, was studied with respect to product inhibition and kinetics of decomposition under fermentation conditions. A two-fold increase in the yield of GA3 as a result of on-line extraction of the product by polyalkoxylate (Genapol 2822) is described. For this extractive fermentation, a stirred tank fermentor was used. The biomass was separated by cross-flow filtration and recycled. The filtrate was extracted in a mixer/settler unit with the extraction solvent. The raffinate was recycled to the fermentor. The influences of product inhibition, chemical decomposition of the product and possible bio-degradation on the product yield are discussed.

PROFILE OF LIQUID FLOW IN BUBBLE COLUMNS

Equations for the liquid velocity profile and the average gas hold-up in bubble columns including cocurrent flow are proposed. It is shown that the inversion point of liquid flow can be used as the characteristic parameter for calculating the liquid flow profiles and gas hold-up. A tracer method was developed to measure the inversion point of liquid flow in bubble column reactors. For water as the liquid phase this inversion point was found at a distance from the column axis of 0·70 0·73 times the column radius. Besides, bubble velocities and bubble diameters in water and methanol-water solutions were determined, using a 5-point conductivity microprobe. It was found that in dilute solutions of methanol the bubble velocity is lower than in pure water. With increasing superficial gas velocity, the bubble velocity steadily increases in pure water, whereas in methanol-water solution it first decreases and, after reaching a minimum, increases too.

Influence of bovine serum albumin on the growth of hybridoma cells in airlift loop reactors using serum-free medium

SummaryHybridoma cells were grown in serum-free media using different culture systems: stationary culture, spinner flask and a laboratory-scale airlift loop reactor. Influence of bovine serum albumin (BSA) on growth and product formation was only found in the airlift loop reactor.