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Francielo Vendruscolo 1 and Márcio José Rossi 2 and Willibaldo Schmidell 1 and Jorge Luiz Ninow 1
Recommended by G. Bayramoglu and A. Brucato
1, Chemical and Food Engineering Department, Federal University of Santa Catarina (UFSC), P.O. Box 476, 88040-900 Florianópolis, SC, Brazil
2, Microbiology, Immunology and Parasitology Department, Federal University of Santa Catarina (UFSC), P.O. Box 476, 88040-900 Florianópolis, SC, Brazil
Received 23 February 2012; Accepted 26 April 2012
This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1. Introduction
The main purpose of a stirring system is the oxygen supply to keep the cell respiratory activity. Thus, the point is to transfer the oxygen from the gas phase to the liquid phase and let the dissolved oxygen reach the suspended cells, penetrating into the cells and, finally, being consumed in the reaction [1]. The mechanism of oxygen transfer from the gas phase to the liquid phase is controlled by the liquid phase mass transfer resistance. The rate of mass transfer or the rate of oxygen absorption can be stated mathematically. Therefore, for studying both the oxygen transfer and the uptake kinetics of the cells, it is essential to know about the values of saturation oxygen concentration in the liquid phase and concentration of oxygen in the liquid phase [2].
One of the greatest difficulties faced when oxygen transfer and oxygen consumption are used is the determination of Henry's law constant H , which will be used as reference to calculate the saturation concentration and the specific oxygen uptake rates. The O2 concentration in the liquid can be determined by Winkler's method [3], which consists in determining the liquid chlorosity. Galvanic and polarographic electrodes measure the partial pressure of dissolved oxygen or oxygen tension in the fermentation broth, not the dissolved oxygen concentration. Thus, data are in terms of relative fraction saturation . To convert this to dissolved oxygen concentration, it is necessary to know the solubility of oxygen in the liquid at the temperature and pressure of measurement.
Oxygen has a low solubility in aqueous medium. Its solubility in distilled water is only about...