Batch and continuous ethanol fermentation by saccharomyces cerevisiae NP 01 using cell recycling technique

Abstract

The aims of this research were to compare batch ethanol production efficiency of Saccharomyces cerevisiae NP 01 between using sweet sorghum juice (230 g/l of total sugar) and three synthetic media (230 g/l of sucrose) as substrates and to study the effects of nitrogen supplementation on the ethanol fermentation from the juice. Continuous ethanol fermentation with and without cell recycling system were also studied. In the batch fermentation at 30 o C, the results showed that nitrogen supplementation obviously improved cell growth, sugar consumption and ethanol production. The juice supplemented with 6 g/l of yeast extract gave the highest ethanol concentration (P, 111.57 g/l) and ethanol productivity (Q P , 2.32 g/l.h). For the synthetic media, the modified Melzoch’s medium containing 6 g/l of yeast extract gave the highest P(109.71 g/l) and Q P (1.31 g/l.h). When the continuous ethanol fermentation without cell recycling system using the modified Melzoch’s medium was operated at the dilution rate of 0.02 h -1 , it was found that the aeration rate of 0.2 vvm promoted yeast growth but it did not improve sugar consumption and ethanol production. At the steady state, the cell and residual sugar concentrations were 1.76x10 8 cells/ml and 107.03 g/l, respectively corresponding to Pand Q P of 45.51 g/l and 0.90 g/l.h, respectively. When the continuous fermentation with cell recycling system was performed at the recycled ratio of 2, almost sugar was utilized. At the steady state, the cell and residual sugar concentrations were 2.86x10 8 cells/ml and 16.59 g/l, respectively corresponding to Pand Q P of 75.43 g/l and 1.49 g/l.h, respectively.