A method to evaluate the isothermal effectiveness factor for dynamicoxygen into mycelial pellets in submerged cultures

摘要

Several models have been developed simulating O-2 transfer in bioreactors, but three limitations are often found: (i) an inadequate kinetic representation of O-2 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 O-2 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 O-2 consumption rate and to evaluate the effectiveness factor in dynamic mode. The nonlinear mathematical model proposed was solved by the orthogonal collocation technique. The O-2 consumption rate in pellets of G. 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 O-2 transfer into mycelial pellets.