Volumetric oxygen transfer coefficients (k(L)a) in batch cultivations involving non-Newtonian broths

The oxygen transfer in non-Newtonian fermentation broths of Aspergillus awa mori, during batch cultivations in conventional 101 bioreactor has been inv estigated. Values of the volumetric oxygen transfer coefficient (k(L)a), ob tained at various impeller speeds, air flow rates and at distinct initial s ubstrate concentrations were correlated with operational variables, geometr ic parameters of the system and physical properties of the broths utilising rigorous techniques in order to obtain a set of reliable and accurate data . An experimental device was constructed for on-line rheological measuremen ts, and the apparent dynamic viscosity was determined from the broth rheogr ams. In order to measure power requirements, a torque meter was developed a nd non-Newtonian fluids with rheological characteristics similar to the Asp ergillus fermented broths were utilised to obtain reference curves and corr elations in the fermentor where the cultivations took place. Gas balancing method and a modified dynamic method were utilised simultaneously to determ ine k(L)a values. The rigorous methods thus developed allowed adequate eval uation of the oxygen transfer in the cultivations and also permitted good f its of four different traditional correlations for k(L)a to the experimenta l data. (C) 2001 Elsevier Science B.V. All rights reserved.