Comparison between free cells and immobilized cells of Candida shehatae in ethanol production from rice straw hydrolysate using repeated batch cultivation

Ethanol production by xylose-fermenting Candida shehatae ATCC 22984 was studied in repeated batch fermentations of rice straw hydrolysate using both free cells and immobilized cells. Terracotta beads, coconut bract and corncob were investigated as supporting materials for cell immobilization. Ethanol production was stable at least 5 cycles when using cells immobilized on coconut bract. Average ethanol concentrations obtained from each batch were 16.7 g/L in free-cell system and 17.2 g/L in immobilized-cell system. Repeated batch using free cell system resulted in a slightly higher volumetric productivity than the use of immobilized cells. Ethanol that could be produced per ton of dried rice straw was 120 L using free cell system and 117 L using immobilized cell on coconut bract in glass column system.