Continuous ethanol production from sugarcane molasses using a newly designed combined bioreactor system by immobilized Saccharomyces cerevisiae.

Continuous ethanol fermentation using polyvinyl alcohol (PVA), immobilized yeast, and sugarcane molasses (22 and 35°Bx) with 8 g/L urea was run in a combined bioreactor system consisting of three-stage tubular bioreactors in series. The effect of the dilution rate (D) at 0.0037, 0.0075, 0.0117, 0.0145, 0.018, and 0.0282 H(-1) on continuous ethanol fermentation was investigated in this study. The results showed that D had a significant effect on fermentation efficiency, sugar-utilized rate, ethanol yield, and ethanol productivity in this designed continuous fermentation system. The D had a linear relationship with residual sugar and ethanol production under certain conditions. The highest fermentation efficiency of 83.26%, ethanol yield of 0.44 g/g, and the lowest residual sugar content of 6.50 g/L were achieved at 0.0037 H(-1) in the fermentation of 22°Bx molasses, indicating that the immobilization of cells using PVA, sugarcane pieces, and cotton towel is feasible and the established continuous system performs well.