Biobutanol production from sugarcane straw: Defining optimal biomass loading for improved ABE fermentation

Key objective of this work was to evaluate the use of cellulosic fraction from sugarcane straw pretreated by liquid hot water (LHW) for butanol production via acetone-butanol-ethanol (ABE) fermentation. Separated hydrolysis and fermentation (SHF), and pre-saccharification and simultaneous saccharification and fermentation (PSSF) were investigated at 10 and 15 % w/v biomass loading. For 15 % w/v, the synergistic effect of weak acids and phenolic compounds made the sugarcane straw hydrolysate poorly fermentable. The 10 % w/v solid load was more favorable (similar to 4-fold higher) in both SHF and PSSF strategies with respect to the ABE production, without including a detoxification step. However, PSSF achieved higher ABE titer (10.5 g/L - SHF; 13.5 g/L - PSSF) and productivity (0.09 g/(L.h) - SHF; 0.14 g/(L.h) - PSSF) when compared with SHF. Using best condition (PSSF at 10 % w/v), it would be possible to estimate a yield of 169 L ABE per ton pretreated sugarcane straw (or 84.5 L ABE per ton of raw sugarcane straw), containing 65 L acetone, 95 L butanol, and 9 L ethanol. This result represents a process efficiency of 28 %, based on carbohydrates content in raw material.