Towards comprehensive lignocellulosic biomass utilization for bioenergy production: Efficient biobutanol production from acetic acid pretreated switchgrass with Clostridium saccharoperbutylacetonicum N1-4

Abstract

For bioenergy production from lignocellulosic biomass, most biomass pretreatment processes need to use some chemical reagent as the catalyst to overcome the biomass recalcitrance barrier. Such reagents are usually severe inhibitors for the subsequent microbial fermentation process. Therefore, in many cases, the liquid prehydrolysates fraction (LPF) is discarded after the pretreatment, which is a tremendous waste of materials and leads to additional pollution. Biobutanol produced from the acetone, butanol and ethanol (ABE) fermentation process has been of great interests recently due to its high value as a bioenergy source or biochemical. During ABE fermentation, acetic acid (AA) is produced and then re-assimilated as a carbon source. Thus, AA is a substrate rather than an inhibitor for biobutanol production. In this study, we employed AA as the chemical catalyst for the pretreatment of switchgrass which then be used for ABE production through simultaneous saccharification and fermentation (SSF) with hyper-butanol producing Clostridium saccharoperbutylacetonicum N1-4. Through systematic investigation of the pretreatment conditions and fermentation, we concluded that the optimized condition for switchgrass pretreatment was with 3 g/L AA at 170 °C for 20 min. Both LPF and solid cellulosic fraction (SCF) of the pretreated biomass were highly fermentable. In the fermentation with the SCF/LPF mixture as the substrate, 8.6 g/L butanol (corresponding to a yield of 0.16 g/g) was obtained. Overall, here we demonstrated an innovative and tailored biomass pretreatment strategy for comprehensive and efficient carbon source utilization for bioenergy production.