Laboratory scale optimization of alkali pretreatment for improving enzymatic hydrolysis of sweet sorghum bagasse

Sweet sorghum has been identified as a promising feedstock for biological conversion to fuels as well as other chemicals. The lignocellulosic stalk of sweet sorghum, called sweet sorghum bagasse (SSB) is a potential source of lignocellulosic biofuel. The primary goal of this study was to determine optimal alkali (lime: Ca(OH)₂ and lye: NaOH) pretreatment conditions to obtain higher yield of total reducing sugar while reducing the lignin content for biofuel production from SSB. Biomass conversion and lignin removal were simultaneously optimized through four quadratic models analyzed by response surface methodology (RSM). The optimal conditions for lime pretreatment was 1.7% (w/v) lime concentration, 6.0% (w/v) SSB loading, 2.4h pretreatment time with predicted yields of 85.6 total biomass conversion and 35.5% lignin reduction. For lye pretreatment, 2% (w/v) alkali, 6.8% SSB loading and 2.3h duration were the optimal levels with predicted biomass conversion and lignin reduction of 92.9% and 50.0%, respectively. More intensive pretreatment conditions removed higher amounts of hemicelluloses and cellulose. Fourier transform infrared spectroscopy (FTIR) spectrum and scanning electron microscope (SEM) image revealed compositional and microstructural changes caused by the alkali pretreatment.