Simultaneous saccharification and fermentation of sludge-containing cassava mash for batch and repeated batch productionof bioethanol by Saccharomyces cerevisiae CHFY0321

Background: The aim of this study was to examine the repeated batch production of bioethanol from sludge-containing cassava mash as starchy substrate by flocculating yeast to improve volumetric bioethanol productivity and to simplify the process of a pre-culture system. Results: For the repeated batch production of bioethanol using cassava mash, the optimal recycling volume ratio was found to be 5%. The repeated batch fermentation was completed within 36 h, while the batch fermentation was completed after 42 h. Volumetric productivity, final ethanol concentration, and ethanol yield were attained to 2.15 g L^-1 h^-1, 83.64 g L^-1, and 85.15%, respectively. Although cell accumulation in the repeated batch process is difficult due to the cassavamash, the repeated batch process using Saccharomyces cerevisiae CHFY0321 could exhibited 10-fold higher initial viable cell number (1.7 × 10⁷ CFU mL^-1) than that of the batch process. Conclusion: The liquefied cassava powder was directly used for the repeated batch process without removal of sludge. Repeated batch bioethanol production by simultaneous saccharification and fermentation using self-flocculating yeast could reduce process costs and accelerate commercial applications. This result was probably due in part to the effect of the initial viable cell density.