Previous report shows that butanol concentrations from the fermentation with initial sugar of 10 – 20 g/l are 2 – 4 g/l since a low sugar concentration may permits the accumulation of butyrate which
competes with butanol synthesis [9]. These relatively low sugar concentrations in medium B, C, and D are inevitable
due to some restriction in the hydrolysis steps such as the problem in suspending the biomass at a high concentration
before hydrolysis. The butanol yields obtained from the fermentation in medium C and D are close to the theoretical
yield (41 g/100 g glucose). The lower yield in medium B shows that butanol fermentation is not completed.