Bioethanol production from cassava starch by enzymatic hydrolysis, fermentation and ex-situ nanofiltration.

Cassava starch were liquefied and saccharified by alpha-amylase and gluco-amylase, respectively, before fermentation for bioethanol production. Response surface methodology (RSM) was used to optimize the condition of liquefaction and saccharification on sugar concentrations. The effects of amount of enzyme, liquefaction temperature and liquefaction time on dextrin concentrations and the effects of amount of enzyme, saccharification temperature and saccharification time on glucose concentrations were measured and studied. Maximum glucose content was 273.1g/l when cassava starch (30 %w/v) was liquefied by 0.9 mg/g of alpha-amylase/starch at 85 °C for 180 min and saccharified by 1.5 mg/g of gluco-amylase/starch at 60 °C for 90 min. Saccharomyces cerevisiae (S. cerevisiae) and Zymomonas mobilis (Z. mobilis) were studied in batch mode to prove ethanol efficiency. The batch culture was inoculated at 30±1 °C and agitated at 70 rpm with a Rushton turbine in 2-liter and 10-liter working volume baffled bioreactors. Microbial cells and ethanol solutions were then separated from fermentation broths using microfiltration (membrane Model M-M1812PS20) and nanofiltration (membrane Model M-N1812A5 and M-N1812A9), respectively. The batch mode results showed that the log phase was approximately 16h. Maximum ethanol produced after 72h period of fermentation by S. cerevisiae in 10-liter bioreactor was 43.5 g/l, resulted in an ethanol yield of 0.44 with a fermentation efficiency of 85.4 %.