Coupling of mixing and microbial kinetics for evaluating the performance of bioreactors

The effect of the dynamics of the mixing process in mechanically stirred bioreactors upon their performance has been investigated by using a circulation-model for flow of fluid and a two-environment-model to account for the extent of micromixing in the vessel. With the help of an empirical kinetic model to depict the oxidative and the fermentative growth of bakers' yeast, experimentally observed effects of initial sugar concentrations upon critical dilution rates in continuous cultures of this system could be explained. Effect of different scales of operation upon productivities of fed-batch cultures of bakers' yeast could also be satisfactorily predicted. A discrete simulation procedure was found to be a convenient tool in coupling the two-environment circulation-model of mixing with kinetics of microbial reactions. On a etudie l'effet de la dynamique du processus de melange, dans les bioreacteurs agites mecaniquement, sur leurs performances; on a employe a cette fin un modele de circulation pour l'ecoulement du fluide et un modele comportant deux milieux pour representer le degre de micromelange dans le recipient. On a pu expliquer, grǎce a l'emploi d'un modele cinetique empirique de la croissance de la levure de boulangerie par oxydation et fermentation, les effets observes de la concentration initiale du sucre sur les vitesses de dilution critiques dans les cultures continues du systeme en question. On a pu aussi prevoir d'une maniere satisfaisante l'effet de l'operation a differentes echelles, sur les productivites des cultures de levure de boulangerie alimentees de maniere discontinue. On a trouve qu'une procedure de simulation discrete constituait un moyen approprie pour associer le modele de melange impliquant deux milieux, a la cinetique des reactions microbiennes.