Prediction of k(L)a in yeast broths

Oxygen transfer rate, can play an important role in the scale-up and econom y of many microbial processes and values of the volumetric oxygen transfer coefficient (k(L)a) for specific fermentation culture media need to be eval uated 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 (Trigonop sis variabilis) in a mechanically-stirred, sparger-aerated and baffled reac tor, the most common fermenter type, over a wide range of superficial air v elocities impeller rotational speeds and geometric parameters. Three differ ent 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, se veral empirical and theoretical correlations were used to fit the experimen tal 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 superficia l gas velocity (U-sg). The correlation improves the prediction of k(L)a val ues in culture media with respect to other generic correlations, mainly bec ause early correlations were developed for strong coalescent and non-coales cent fluids, whereas the medium used in this work and in most the yeast bro ths behaves as a typical Newtonian, slightly non-coalescence fluid, due to the moderate presence of mineral salts. (C) 1999 Elsevier Science Ltd. All rights reserved.