The effect of fermentation configurations and FAN supplementation on ethanol production from sorghum grains under very-high-gravity conditions

A 22 experimental plan was implemented to investigate the effect of free amino nitrogen (FAN) supplementation on sorghum fermentation under very-high-gravity (VHG) conditions. A rapid initial FAN uptake rate signified insufficient provision of utilizable nitrogen by sorghum mash alone. The ethanol productivity was 3.03 g/(L h) (equivalent to 146 g/L ethanol in 48 h when FAN was added) as compared to 0.93 g/(L h) (equivalent to 144 g/L ethanol in 156 h when FAN was not added) using configuration of simultaneous saccharification and fermentation (SSF). Whereas, ethanol productivity was 2.18 g/(L h) (equivalent to 139 g/L ethanol in 64 h when FAN was provided) as compared to 0.68 g/(L h) (equivalent to 125 g/L ethanol in 185 h when FAN was not provided) using configuration of saccharification followed by fermentation (S > F). Results indicate that SSF configuration with addition of FAN-containing substances is the most efficient fermentation configuration among investigated cases. Such a configuration results in the highest ethanol yield and the shortest fermentation time. The ethanol productivity of this configuration was increased by 60% as compared to other similar findings reported previously.