A Method to Evaluate the Isothermal Effectiveness Factor for Dynamic Oxygen into Mycelial Pellets in Submerged Cultures

Several models have been developed simulating 02 transfer in bioreactors, but three limitations are often found: (i) an inadequate kinetic representation of 02 consumption or wrong boundary conditions, (ii) unrealistic parameter values, and (iii) inadequate experimental systems. In our study we minimized those possible sources of error. Oxygen uptake rate, void fraction of the pellet, and external 02 mass transfer coefficient were experimentally obtained from bioreactor studies in which pellets of Gibberella fujikuroi were naturally formed. Michaelis—Menten kinetics and diffusion equations were used to describe the 02 consumption rate and to evaluate the effectiveness factor in dynamic mode. The nonlinear mathematical model proposed was solved by the orthogonal collocation technique. The 02 consumption rate in pellets ofG. fujikuroi of 1.7—2.0 mm is only marginally inhibited by diffusion constraints under conditions tested. Simulation analysis showed that the effectiveness factor decreased as the Thiele modulus and pellet diameter increased. The proposed model was applied to experimental data reported for other fungal pellets and allowed to predict optimal conditions for 02 transfer into mycelial pellets.