Application of Saccharomyces Cerevisiae ATCC 9763 Immobilised Cells in Nanocellulose Based Matrix for Bioethanol Production

Attempts to improve the bioethanol productivity of S. cerevisiae ATCC 9763 were made using the entrapment method of cell immobilisation for its culture fermentation. The cells were entrapped using several types of matrix (beads) materials including alginate/cellulose, alginate/CMC and alginate/nanocellulose, which had the potential to differ in their mechanical strength charge and particle size and thus affect the value of water absorption of beads and the viability of the cells within them. To evaluate the productivity of the yeast, fermentation studies were carried out under repeated-batch fermentation using free and immobilised cells systems. Despite the relative similarity of the concentration of bioethanol produced by the yeast in both the free cell and immobilised systems (approximately 1 % w/v higher in immobilised culture), the two culture systems had different productivities. The highest bioethanol productivity (1.38 g/L/h) was observed for the immobilised culture system using alginate/nanocellulose as beads. This was higher than the productivity of the free cells culture system, which reached only 0.76 g/L/h. Furthermore, cell reusability was maintained in the immobilised culture system for up to nine fermentation cycles, with only 26 % of the beads damaged after nine such cycles. Interestingly, there was a lower breakage rate among the alginate/nanocellulose beads (18 %), which may indicate the greater mechanical strength of this nanomaterial.