| Lignocellulose-to-ethanol conversion is a promising technology to supplement corn-based ethanol production. However, the recalcitrant structure of lignicellulosic materials necessitates a pretreatment step to break up the lignocellulosic matrix, thus improving the accessibility of carbohydrates to hydrolytic enzymes for fermentable sugar production. Switchgrass (Panicum virgatum L.) is regarded as a potential feedstock for ethanol production because of its excellent growth in various soil and climate conditions, and low requirements for agricultural inputs. The general objective of this research is to explore alkaline pretreatment of switchgrass for improved enzymatic hydrolysis.;Sodium hydroxide (NaOH) pretreatment of switchgrass was investigated at 121, 50, and 21 °C respectively for 0.25-1 h, 1-48 h, and 1-96 h at different NaOH concentrations (0.5, 1.0, and 2.0%, w/v). At the best pretreatment conditions (50 °C, 12 h, and 1.0% NaOH), the yield of total reducing sugars in the subsequent enzymatic hydrolysis reached 453.4 mg/g raw biomass, which was 3.78 times that of untreated biomass. Although using reduced temperatures resulted in lower carbohydrate and higher lignin percentages of the pretreated biomass, better carbohydrate preservations achieved at such milder conditions contributed to high sugar productions that were comparable with those obtained using elevated pretreatment temperatures. The optimum cellulase and cellobiase loadings applied in enzymatic hydrolysis were respectively 15 FPU/g and 20 CBU/g.;Lime pretreatment of switchgrass was investigated at 121, 50, and 21 °C respectively for 0.25-1 h, 1-48 h, and 1-168 h, and the effects of lime loading (0.05-0.20 g/g raw biomass) and biomass washing (100 and 300 ml water/g raw biomass) on the sugar production efficiency were also studied. At the best pretreatment conditions (50 °C, 24 h, 0.10 g Ca(OH)2 /g raw biomass, and wash intensity of 100 ml water/g raw biomass), the yield of total reducing sugars reached 433.4 mg/g raw biomass, which was 3.61 times that of untreated biomass. Calcium ions from Ca(OH)2 dissociation could extensively crosslink lignin molecules within the biomass, resulting in low lignin reductions. However, as long as the chemical bonds stiffening lignocellulose were disrupted and biomass porosities increased, the enzymatic digestibilities of biomass could still be substantially improved even in the presence of great lignin contents. The optimum cellulase and cellobiase loadings applied in enzymatic hydrolysis were respectively 20 FPU/g and 20 CBU/g.;Pretreatment of switchgrass using the combination of sodium hydroxide and lime was invented to improve the cost-effectiveness of alkaline pretreatment at room temperature (21 °C). The effects of residence time (3, 6, and 9 h), NaOH loading (0.05, 0.10, and 0.20 g/g raw biomass), time point for NaOH addition (adding NaOH after 0, 1/3, or 2/3 of the residence time elapses), lime loading (0-0.10 g/g raw biomass), and biomass washing (100 and 200 ml water/g raw biomass) on the sugar production efficiency were investigated. At the best pretreatment conditions (6 h, 0.10 g NaOH/g raw biomass, start point NaOH addition, 0.02 g Ca(OH)2/g raw biomass, and wash intensity of 100 ml water/g raw biomass), the yield of total reducing sugars reached 386.4 mg/g raw biomass, which was 3.22 times that of untreated biomass. The sugar production of the pretreatment using the combination of 0.10 g NaOH/g raw biomass and 0.02g Ca(OH)2/g raw biomass was comparable with that of using 0.20 g NaOH/g raw biomass, while its cost was barely higher than that of using 0.10 g NaOH/g raw biomass only, considering the low cost of lime and the minor loading required. The optimum cellulase and cellobiase loadings applied in enzymatic hydrolysis were respectively 20 FPU/g and 10 CBU/g. |
