Ethanol fermentation characteristics of Pichia stipitis yeast from sugar beet pulp hydrolysate: Use of new detoxification methods

This study investigates the ethanol production characteristics of adapted Pichia stipitis yeast in growth media containing various sugar sources, namely, synthetic xylose, sulfuric acid hydrolyzed sugar beet pulp and sugar beet pulp hydrolysate-synthetic xylose mixture. In synthetic growth media, the xylose concentration range of 10-75 g l−1 did not exhibit substrate inhibition and at an initial xylose concentration of 75.1 g l−1, 37.1 g l−1 ethanol was obtained after 75 h with productivity of 0.494 g l−1 h−1. Prior to fermentation, the inhibitory components of the sugar beet pulp hydrolysate was detoxified using three different treatments: commercial activated charcoal with overliming, activated charcoal obtained from sugar beet pulp with overliming and fly ash treatment. Phenolics and furan compounds were significantly adsorbed with activated charcoal treatments and overliming with CaO showed to enhance their reduction. A significant amount of furan was removed by fly ash treatment due to its high CaO content. Neither case demonstrated a noticeable decrease in acetic acid concentration. Ethanol concentrations and productivities ranged between 10.8-12.2 g l−1 and 0.119-0.286 g l−1 h−1 respectively, over 50-121 h, in the detoxified hydrolysate media which contained 48.2 g l−1 of total reducing sugar. Increase in inoculum concentration also improved the ethanol production yield.