SSF of alkali and concentrated-acid treated switchgrass for ABE production

Switchgrass was investigated as a feedstock for production of acetone, butanol and ethanol by SSF. For this purpose, switchgrass was subjected to alkaline pretreatment, and to simultaneous saccharification and fermentation and separate hydrolysis and fermentation applying cellulase (C-tec-2) and Clostridium acetobutylicum (ATCC-824). In order to assess the overall bioconversion efficiency, control tests were performed with Avicel and pure sugars as reference substrates. SSF of alkali-pretreated switchgrass was found to be as efficient as that of Avicel. Addition of small amount of Tween 80 in the SSF was found to enhance the bioconversion yield significantly. It appears that Tween 80 enhances the cellulase enzyme activity by limiting the non-productive binding of enzyme onto the residual lignin. However, the SSF of solid loading above 6% w/v was difficult to achieve due to limitation of enzymatic hydrolysis. With enzyme loading of 15 FPU/g glucan, SSF of 6% well-pretreated switchgrass produced 12.2 g/L of total solvents, the level far below the inhibition threshold for this culture. To further investigate on this, SHF was applied, from which a comparable level of solvents yields were achieved as in ABE fermentation of pure glucose. To investigate the possibility of reducing the enzyme loading, the alkali-treated switchgrass was further treated with concentrated sulfuric acid, decrystallizing the glucan content. The SSF of this substrate have shown that the enzyme loading can be reduced by a factor of 1-5, still achieving acceptable range of product yield. The details of pretreatment conditions, fermentation profiles, the effects of decrystallization are presented.