Critical assessment of the steady‐state Na2SO3 feeding method for kla measurement in fermentors

Abstract

Important aspects of k_la measurement in agitated aerated vessels are briefly characterized from the standpoint of reliability of the measured data. It seems that most of the k_la data, based on a number of variants of the steady‐state and dynamic methods in noncoalescent liquids, do not have a clear physical meaning, because they are affected by the differences between the actual driving force and the driving force assumed by the model used for its evaluation. A reliability test is given for the Na₂SO₃ feeding steady‐state method (FSM), by comparing the results of air and pure oxygen absorption in a noncoalescent liquid (0.5M Na₂SO₄ solution) with the results obtained by the independent pressure step dynamic method (RDM). The RDM is one of a few variants of the dynamic method which gives correct k_la data unaffected by nonideal mixing of the gas phase in the reactor. It was found that the FSM yields correct k_la values only when pure oxygen is used for absorption. When air is absorbed, the FSM gives k_la values in the region of k_la > 0.1 s⁻¹ substantially (to 55%) lower than those for pure oxygen absorption.