Simultaneous saccharification and fermentation of sludge-containing cassava mash for batch and repeated batch production of 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 cassava mash, the repeated batch process using Saccharomyces cerevisiae CHFY0321 could exhibited 10-fold higher initial viable cell number (1.7 x 10(7) 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. (c) 2008 Society of Chemical industry