Elimination of oscillations in fermentation processes



Fermentation processes that are used to produce ethanol exhibit oscillatory behavior and for periods of time during these oscillations, ethanol production decreases substantially and there is considerable loss of residual substrates. There has been a considerable amount of work demonstrating oscillatory behavior in fermentation processes. The aim of this work is to demonstrate simple strategies to eliminate the oscillatory behavior in fermentation processes involving both Zymomonas mobilis and Saccharomyces cerevisiae. The oscillatory behavior is caused by the existence of Hopf bifurcations and it is demonstrated that very minor changes in the input conditions can eliminate the Hopf bifurcation points. In the case of Zymomonasmobilis, it is shown that the addition of a small amount of substrate and/or the key component of the biomass and/or product in the input stream causes the disappearance of the Hopf bifurcation points while in Saccharomycescerevisiae fermentation process, a very minor increase in the input oxygen supply produces the same result. The aim of this work is not only to demonstrate the existence of the Hopf bifurcations in the fermentation problems, but also to provide strategies to eliminate them. © 2010 American Institute of Chemical Engineers AIChE J, 2011