Volumetric oxygen transfer coefficients (kLa) in batch cultivations involving non-Newtonian broths

The oxygen transfer in non-Newtonian fermentation broths of Aspergillus awamori, during batch cultivations in conventional 101 bioreactor has been investigated. Values of the volumetric oxygen transfer coefficient (k(L)a), obtained at various impeller speeds, air flow rates and at distinct initial substrate concentrations were correlated with operational variables, geometric 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 measurements, and the apparent dynamic viscosity was determined from the broth rheograms. In order to measure power requirements, a torque meter was developed and non-Newtonian fluids with rheological characteristics similar to the Aspergillus fermented broths were utilised to obtain reference curves and correlations in the fermentor where the cultivations took place. Gas balancing method and a modified dynamic method were utilised simultaneously to determine k(L)a values. The rigorous methods thus developed allowed adequate evaluation of the oxygen transfer in the cultivations and also permitted good fits of four different traditional correlations for k(L)a to the experimental data. (C) 2001 Elsevier Science B.V. All rights reserved.