Synergistic Optimal Integration of Continuous and Fed-Batch Reactors for Enhanced Productivity of Lignocellulosic Bioethanol

With significant technological advances in metabolic engineering, there are currently available efficient recombinant yeast strains capable of fermenting lignocellulosic sugars (i.e., glucose and xylose) to bioethanol. Conventional batch fermentation, preferred in most bioprocesses, may not provide the most appropriate environments for those engineered strains to perform their best. In this article, we consider new reactor configurations integrating different types of reactors to examine their maximal productivity of lignocellulosic bioethanol. Among various possible scenarios, the highest performance was acquired from a synergistic operation of continuous and fed-batch reactors. In a chemostat, glucose is fermented alone by the hexose-only fermenting (wild-type) yeast, and unconverted xylose is fed to a batch reactor where mixed sugars are fermented by recombinant yeast. The optimization of the feed rate is a critical issue in order to maximize the productivity in a fed-batch reactor. It is shown that the proposed idea is able to increase the bioethanol productivity by up to 50% in comparison to a simple batch operation. Obviously, these considerations must be integrated with a more comprehensive cost benefit analysis before a clear choice of reactor configuration can emerge.