Analysis of the Effect of in situ Product Removal on the Stability and Performance of a Continuous Bioreactor with Cell Separator for Ethanol Production

K. Ghosh and K. B. Ramachandran

Abstract
In this study, the behaviour of a continuous membrane bioreactor with in situ removal of product ethanol by pervaporation and cell recycle has been investigated. The kinetic model used is an unstructured growth model taking into account product as well as substrate inhibition and the product formation rate is represented by the Leudeking-Piret model. The effect of pervaporation on the performance of the system with cell separator is evaluated in terms of ethanol productivity and its stability. The stability analysis carried out using elementary principles of bifurcation theory shows that the reactor is characterized by the presence of steady-state multiplicity and hysteresis. The simulation results also demonstrate that the in situ removal of ethanol by pervaporation increases productivity as the ethanol inhibition barrier is overcome. Introduction of both pervaporation and cell recycling increases the region of instability in the system but the instability region moves to higher values of dilution rate. This allows stable operation of a fermentor at higher dilution rates to achieve increased productivity.

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Keywords
Cell recycling, ethanol fermentation, pervaporation, stability, productivity