A Structured Study on the Dynamic Bifurcation Behavior of a Continuous Ethanol Fermentor

Abstract The oscillatory behavior of a continuous ethanol fermentor, in the high feed sugar concentration region (200 g/L), is analyzed using the bifurcation theory. The mathematical model was solved using the arc-length continuation method including a refinement algorithm based on the Heaviside step function technique. Experimental data for ethanol production using Zymomonas mobillis were fitted to a phenomenological model based on the concept of dynamic specific growth rate and inhibition. Thus, a through connection is defined between model parameters and oscillatory behavior. Our approach shows the rich static and dynamic bifurcation topology of the continuous fermentation reactor, which includes Fold, Hopf, Bautin, and Cusp bifurcations. The four-dimensional model shows that intricate oscillations can occur and that the periodic attractors of the system can have thoughtful consequences on reactor performance. In fact, it is evidenced that, in some conditions, periodic/bifurcation behavior presents higher ethanol productivity than the corresponding steady-state. Bifurcation analysis provides insight into the possible operation conditions and their impact on conversion and productivity of the fermentation process.