Multi-objective Optimization of a Fermentation Process Integrated with Cell Recycling and Inter-stage Extraction

Bio-fuels are clean, renewable energy with potential to replace fossil fuels. Bio-ethanol is the widely used bio-fuel, which can be produced from a variety of agricultural feedstocks. Its production from fermentable sugars is well established. Production of bioethanol from starchy and cellulosic materials requires hydrolysis as an additional step to produce fermentable sugars. In SHF (separate hydrolysis and fermentation) process, hydrolysis and fermentation are performed at their respective optimal temperatures, but end products (i.e., glucose and cellobiose) inhibit hydrolysis. SSF (simultaneous saccharification and fermentation) process removes product inhibition by immediate consumption of end products of hydrolysis. Ethanol concentration also inhibits glucose to ethanol conversion in the fermentor, which results in low ethanol productivity and yield. To avoid this, ethanol can be continuously removed from the fermentor using either extraction or perm-selective membrane. In this study, a three-stage fermentation process integrated with cell recycling and inter-stage extraction is considered, for producing ethanol from the lignocellulosic feed-stocks. The integrated process is optimized using a multi-objective differential evolution algorithm for two objectives simultaneously. Finally, improvement in the performance of the fermentation process due to inter-stage extraction is evaluated quantitatively.