LAUSR

Abstract Second generation (2G) ethanol production is facing major research challenges primarily because of an absence of suitable technology for the extraction of maximum fermentable sugars from complex lignocellulosic structure as well as unavailability of suitable fermentation technique and single microorganism to convert these sugars (pentose and hexose) efficiently into ethanol. Present study is focused on the exploration of various lignocellulosic feedstocks using different inorganic acids for the recovery of maximum amount of fermentable sugars as separate fractions, direct from the biomass by a novel process called “fractional hydrolysis” with minimum toxics generation. Different physical and chemical parameters were optimised for the process previously. Four different inorganic acids (HCl, H3PO4, HNO3, and H2SO4) up to 30% concentration (v/v) were used in 7- and 8-stage fractional hydrolysis processes to treat dry biomass in a fractional hydrolysis column. Using kans grass biomass, H2SO4 resulted in maximum extraction of pentose and hexose sugars separately with negligible toxics. Furthermore, the technique was explored using three different wide and easily available lignocellulosic feedstocks, resulting in saccharification (%): Kans grass 84.88; Sugarcane bagasse 82.55; Wheat straw: 81.66. Hydrolysate fractions without any detoxification were taken into a co-culture system containing Zymomonas mobilis (for glucose fermentation) and Candida shehatae (for xylose fermentation) at bioreactor level. 93.28% of the sugar present in xylose-rich fraction (initial total reducing sugar: 59.74 g/L) and 95.44% of glucose-rich fraction (initial total reducing sugar: 100.25 g/L) were utilised to produce 67.28 g/L ethanol from the kans grass biomass hydrolysate; thereby achieving 82.45% of the maximum theoretical ethanol production.