Effects of Tween 80 on fermentative butanol production from alkali-pretreated switchgrass

In this study, switchgrass was investigated as a renewable feedstock for fermentative production of acetone, butanol and ethanol (ABE). For this purpose, switchgrass was first subjected to alkaline pretreatment, which reduces its recalcitrance and increases enzyme accessibility. Both simultaneous saccharification and fermentation (SSF) and separate hydrolysis and fermentation (SHF) were applied. The pretreated switchgrass solids inhibit ABE fermentation, presumably due to the residual lignin portion, as evidenced by the toxicity test of various model phenolic compounds. Addition of a non-ionic surfactant, Tween 80, alleviated the phenol-induced inhibition. As constrained by the “solid effects”, the upper limit of solid loading that SSF could process was in the range of 5-6%. SSF with 5% solid loading produced a total of 12.3 g/L ABE solvents with 7.8 g/L of butanol. SHF was further applied to process higher solid loadings. A total of 14.3 g/L ABE solvent with 8.5 g/L of butanol was produced from SHF with 7% solid loading. SSF gave an overall bioconversion yield close to that of pure sugar control, whereas SHF was able to avoid the “solid effects” with a slightly lower overall bioconversion yield.