The dynamic gassing-out method using nitrogen for gas–liquid KLa measurements has been modified so that gassing-out is performed with air and gassing-in with oxygen-enriched air. This new method was proven theoretically valid for use in inert model systems and in actual fermentation systems. The KLa values were measured in a 1-m-high bubble column and compared with those obtained from the traditional gassing-in method for three different mixing models in batchwise contacting: mixed gas and liquid (MMB); plug-flow gas and mixed liquid (PMB); and plug-flow gas and plug-flow liquid (PPB). The KLa values obtained from the new method were consistent with those of the method of Bartholomew et al. Discrimination between the models appeared to be not important for the 1-m-high column, but the theoretical analysis revealed that it would become necessary for columns about 10 m and higher.
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