Improvement of continuous ethanol fermentation from sweet sorghum juice by Saccharomyces cerevisiae using stirred tank bioreactor coupling with plug flow bioreactor

Abstract

The continuous ethanol production from sweet sorghum juice in a continuous stirred tank bioreactor (STR) and a combined bioreactor was compared. The combined bioreactor comprised an STR and three tubular (plug flow) bioreactors (TB) in series with a total working volume of 3320 ml. The fermentation was carried out at 30°C by Saccharomyces cerevisiae NP 01. The sweet sorghum juice containing 250 g l-1 of total sugar was introduced into the systems at total dilution rates (D) of 0.007, 0.02 and 0.04 h-1. Our results clearly show that the degree of ethanol production depends on the residence time of the fermentation broth in the system. In the STR system at D = 0.007 h-1, the ethanol concentration (P), yield (YP/S) and productivity (QP) were 67.28 ± 0.37 g l-1, 0.52 ± 0.01 g g-1 and 0.47 ± 0.00 g l-1 h-1, respectively. Using the combined bioreactor (CSTR + TB) could improve ethanol production efficiency. The sugar consumption and ethanol production of the combined bioreactor system were markedly higher than those of the STR system. The highest P value (106.01 ± 0.47 g l-1) was obtained when using the combined system at D 0.007 h-1; and under this condition, the YP/S and QP values were 0.50 ± 0.01 g g-1 and 0.76 ± 0.02 g l-1 h-1, respectively.