Ethanol production from starch by co-immobilized amyloglucosidase - zymomonas mobilis cells in a continuously-stirred bioreactor

Abstract

Continuous ethanol production from starch was studied in a continuously-stirred bioreactor using co-immobilized amyloglucosidase (AMG) and Zymomonas mobilis cells. In this process, saccharification of starch and fermentation to ethanol were carried out in a single reactor. The experiments were carried out at three sets of conditions for which temperature and centrifuged cell weight were 35 °C and 20.3 g; 30 °C and 19.0 g; 35 °C and 29.2 g, respectively. The maximum volumetric ethanol productivity (7.6 g·L-1·h-1) was achieved with 0.45 g·g-1 yield at the 0.20 h-1 dilution rate at 35 °C, with the initial centrifuged cell concentration of 29.2 g. The maximum ethanol concentration (43.5 g·L-1) was obtained at the 0.15 h-1 dilution rate with a 96 % conversion of substrate. When experimental conditions in the reactor were compared to each other, the initial concentration of immobilized cells was found to have a significant positive influence on the kinetic parameters of ethanol fermentation.