Effects of chemical and biological pretreatments on biobutanol production from Pennisetum purpureum × Pennisetum typhoideum by semi-simultaneous saccharification and fermentation

The conversion of biomass to biofuel is a key strategy for sustainable energy production. Effective pretreatment of lignocellulosic biomass is critical to improving its bioconversion efficiency. Optimum times and temperatures for chemical giant Juncao grass (GJG) pretreatment with sodium hydroxide (NaOH) and N-Methylmorpholine N-oxide (NMMO) were systematically determined. Under the suitable pretreatment conditions, higher percentage of cellulose was remained in NaOH-pretreated GJG (at 81.7 °C, 60.0 min) compared to that pretreated by NMMO (at 138.3 °C, 10.3 min), whereas GJG's properties changed slightly in anaerobic digestion (AD)-pretreated GJG. After the semi-simultaneous saccharification and fermentation (sSSF) process, the highest glucose concentration of 48.3 g L⁻¹ was observed from NaOH-pretreated GJG within the first 24 h and the highest butanol concentration of 8.95 g L⁻¹ was detected after fermentation with Clostridium acetobutylicum ATCC 824 for 96 h. While both chemical pretreatments produced satisfactory acetone-butanol-ethanol (ABE) yields, GJG pretreated with AD was inferior. A suitable conversion sequence of GJG was suggested for butanol followed by methane productions as products provided higher total energy yields with lesser operational complexities. Efficient ABE fermentation of the high-lignin GJG could be achieved using the uncomplicated NaOH treatment with sSSF, which was technically and economically advantageous.