Long-term production of fuel ethanol by immobilized yeast in repeated-batch simultaneous saccharification and fermentation of cassava

In this study, a fibrous matrix with chemical modification was used as a support material for the immobilization of Saccharomyces cerevisiae 1308. Cassava hydrolysate without filteration was used for ethanol fermentation. An average utilization rate of starch of 83.5% was obtained by the immobilized cells during the first seven repeated simultaneous saccharification and fermentation. The utilization rate of starch of the immobilized cells was 2.1% higher than that of free cells with an inoculation quantity of 15% (v/v) under the same fermentation conditions. In addition, the effects of enzyme feeding strategies on immobilized yeast fermentation were investigated. The highest utilization rate of starch of 85.9% was obtained at 35 °C with the optimal enzyme feeding strategy. Fermentation performed successfully for about 6 months with 87 batches suggests that ethanol production from cassava using immobilized yeast in a fibrous-bed bioreactor is feasible and may meet the demands of industrial production.