Continuous Ethanol Fermentation at Very High Gravity in the Presence of &amp;lt;i&amp;gt;Saccharomyces cerevisiae&amp;lt;/i&amp;gt;: A Bifurcation Analysis

Ghanem-Lakhal Abdelghani

doi:10.4236/jsbs.2018.84009

Abstract

In this paper, a study of the bifurcation analysis of fermentation of sugar to ethanol in presence of Saccharomyces cerivisiae at very high gravity is described. The bifurcation analysis was done for a concentration 280 gl−1 of sugar, and the dilution rate was taken as the parameter of bifurcation. Two Hopf bifurcations (HB) at 280 gl−1 were found. At dilution rate of 0.027 h−1 the system exhibits damped oscillations and not sustained oscillations as previously reported because the system is close to a point of attraction, and we can attenuate these oscillations by the choice of initial conditions. The system exhibits sustained oscillations between the two Hopf Bifurcations, the first at 0.08028 h−1 and the second at 0.04395 h−1. These oscillations are the consequence of synchrony between the daughter and the mother yeast. Indeed, it is better to take a dilution rate between the two Hopf bifurcations (self sustained oscillations), in order to increase the ethanol productivity.

Highlights

The increase of CO2 concentration in the atmosphere, with the possibility of energy deficit, led to an orientation toward biofuels
The bifurcation analysis was done for a concentration 280 gl−1 of sugar, and the dilution rate was taken as the parameter of bifurcation
The dilution rate D was taken as the bifurcation parameter, and the bifurcation analysis was done for a feed concentration of sugar at CS0 = 280 gl−1

Summary

Introduction

The increase of CO2 concentration in the atmosphere, with the possibility of energy deficit, led to an orientation toward biofuels. Very high gravity (VHG) fermentation has been thoroughly studied in [3] where it has been shown that it increases ethanol concentration at the reactor exit and decreases energy consumption for ethanol distillation, some counter effects are induced both at the initial and final phases of the process. When ethanol concentration is over 40 gl−1, it inhibits the yeast metabolism and when it exceeds 90 gl−1 it becomes toxic [4] These effects should be taken into consideration in the design of efficient processes for bioethanol production because they can act negatively on ethanol production [4]. Oscillations are observed that are difficult to eliminate These appear for dilution rates between 0.09 and 0.25 h−1 [5]. The dilution rate was taken as the parameter of bifurcation, and the results are present in the form of diagram of bifurcation for the different variables of the system

The Cell Cycle

Ethanol Effect

Results and Discussion

Conclusions