Efficient Bioethanol Production from Glucose-Xylose Mixtures Using Co-Culture of Saccharomyces cerevisiae Immobilized on Canadian Pine Wood Chips and Free Pichia stipitis

To meet the ever increasing demand for energy and fuels, it is essential to produce renewable fuels such as bioethanol at low cost and in reduced time. In the present work, Saccharomyces cerevisiae was immobilized on a novel Pinewood chips (PC) support and the immobilized yeast was used in fermentation with an aim to increase bioethanol yield and productivity in single and mixed sugar fermentation. Different concentrations of glucose or xylose were used to see the effect on ethanol production from S. cerevisiae and P stipitis, separately. With PC immobilized S. cerevisiae, ethanol yield of 0.44 g/g and productivity of 1.11 g/l.h were obtained for 200 g/l initial glucose concentration. This immobilized S. cerevisiae, was then used in co-culture along with free culture of Pichia stipitis for ethanol production from glucose-xylose sugar mixtures (1.5:1 ratio of glucose to xylose; average concentration 50.75 g/l) and compared with co-culture of free S. cerevisiae and free P stipitis. Improvement in ethanol yield (0.47 g/g from 0.45 g/g in case of co-culture of free cells) and productivity (0.73 g/h.h from 0.45 g/l. h in case of co-culture of free cells) were obtained with co-culture of immobilized S. cerevisiae and free P stipitis. Further, PC were treated with a sequential treatment of H2SO4 followed by sodium sulphite and sodium chlorite and used to immobilize S. cerevisiae. Yeast immobilized on treated pine wood chips support (TP) was then used in co-culture with free P stipitis and further improvement in ethanol yield (0.50 g/g) and productivity (0.80 g/l.h) were obtained for 50.8 g/l initial glucose-xylose mixture concentration. This work showed that this novel co-culture scheme of S. cerevisiae immobilized on pine wood chips and free P stipitis can be used for efficient fermentation of mixed sugars to bioethanol.