Prediction of kLa in yeast broths

Abstract

Oxygen transfer rate, can play an important role in the scale-up and economy of many microbial processes and values of the volumetric oxygen transfer coefficient ( k L a) for specific fermentation culture media need to be evaluated and correlated to obtain the appropriate design tools. The purpose of this work was to determinate the values of k L a in yeast broths ( Trigonopsis variabilis) in a mechanically-stirred, sparger-aerated and baffled reactor, the most common fermenter type, over a wide range of superficial air velocities impeller rotational speeds and geometric parameters. Three different mixing vessels (2, 5 and 15 litres) were used in order to consider the effect of the fermenter scale-up on k L a. Once k L a data are obtained, several empirical and theoretical correlations were used to fit the experimental data. A new correlation is proposed k L a=3.2·10 −3 P V 0.35 U sg 0.41 based on the power input per unit volume of liquid ( P/ V) and the superficial gas velocity ( U sg). The correlation improves the prediction of k L a values in culture media with respect to other generic correlations, mainly because early correlations were developed for strong coalescent and non-coalescent fluids, whereas the medium used in this work and in most the yeast broths behaves as a typical Newtonian, slightly non-coalescence fluid, due to the moderate presence of mineral salts.