Prediction of oxygen mass transfer coefficients in stirred bioreactors for bacteria, yeasts and fungus broths

The oxygen mass transfer represents the most important parameter implied on the design and operation of mixing-sparging equipment of the bioreactors. It can be described and analyzed by means of mass transfer coefficient, k(1)a. The k(1)a values are affected by a lot of factors, such as geometrical and operational characteristics of the vessels, media composition, type, concentration and microorganisms morphology, biocatalysts properties. The aim of these experiments is to study the oxygen mass transfer rate through the mass transfer coefficient, for a stirred bioreactor and different fermentation broths, using a large domain of operating variables. For quantifying the effects of the considered factors (concentration and morphology of biomass, specific power input, superficial air velocity) on k(1)a for submerged and surface aeration, the experiments were carried out for non-respiring biomass suspensions of Propionibacterium shermanii, Saccharomyces cerevisiae and Penicillium chrysogenum, mycelial aggregates (pellets) and free mycelia morphological structures. By means of the experimental data and using MATLAB software, some mathematical correlations describing the influences of the considered factors on k(1)a have been proposed for each microbial culture. These equations offer a good agreement with the experiment, the maximum deviation being +/-8.4% for submerged aeration, and +/-9.1% for surface aeration, respectively. (C) 2004 Elsevier B.V. All rights reserved.