Optimization of Fed-Batch Fermentation with in Situ Ethanol Removal by CO2 Stripping

One way of overcoming the substrate and ethanol inhibition effects in the industrial ethanol production process is to use fed-batch fermentation coupled with an ethanol removal technique. This work describes the optimization and experimental validation of sugar cane ethanol production by fed-batch fermentation with in situ ethanol removal by CO2 stripping. The optimization employing a genetic algorithm (GA) was used to find the optimum feed flow rate (F) and the ethanol concentration (C E0) in the medium at which to initiate stripping, in order to obtain maximum ethanol productivity. Conventional ethanol fermentation employing the optimum feed flow rate was performed with must containing 257.1 g L–1 of sucrose (180 g L–1 of total sucrose concentration), resulting in achievement of an ethanol concentration of 82.2 g L–1. The stripping fed-batch fermentation with high total sucrose concentration (260–300 g L–1) or 371.4–428.6 g L–1 in the must feeding was performed with optimal values of the feed flow rate and the ethanol concentration (C E0) in the medium at which to initiate stripping. At the highest sucrose feed (total concentration of 300 g L–1), the total ethanol concentration reached 136.9 g L–1 (17.2 °GL), which was about 65% higher than the value obtained in fed-batch fermentation without ethanol removal by CO2 stripping. This strategy proved to be a promising way to minimize inhibition by both the substrate and ethanol, leading to increased sugar cane ethanol production, reduced vinasse generation, and lower process costs.