2000 Volume 26 Issue 6 Pages 861-868
Unstructure models were developed for a mixed culture where one microorganism assimilates the metabolite produced by another microorganism. The model system was a mixed culture using Lactobacillus delbrueckii and Ralstonia eutropha where the former assimilates glucose and produces lactic acid, and the latter assimilates lactate and produce poly-β-hydroxy butyrate (PHB). Performance improvement is shown for the mixed culture over a single culture for chemostat using the model developed. Since the optimal dissolved oxygen (DO) concentration is different for each microorganism, we developed another model which takes into account the effect of DO concentration on the dynamic behavior. Then the optimal DO concentration is obtained for chemostat. Moreover, we developed another model which takes into account NH3 concentration on the cell growth and PHB production by R. eutropha. Then the optimal time-profile for NH3 concentration is derived using the Maximum principle. It is found that high PHB production could be attained even if NH3 concentration is not controlled if initial NH3 concentration is appropriately selected.