Optimization of switchgrass and extruder parameters for enzymatic hydrolysis using response surface methodology

Switchgrass is an important biomass that can be hydrolyzed to yield fermentable sugars through pretreatment, which is the primary and expensive step in conversion of biomass to bio-ethanol. Most of the pretreatment operates in batch mode, which is energy intensive, requires high capital, results in decomposition of hemicellulose, and formation of inhibitors. Considering these shortcomings, a novel biomass pretreatment method using a high shear bioreactor could be a viable continuous one. The current study was undertaken to determine the effect of biomass parameters such as moisture content (10, 20, 30, 40, and 50% wb) and particle size (2, 4, 6, 8, and 10 mm) over a range of barrel temperature and screw speed (45-225 °C and 20-200 rpm). Statistical analyses revealed that among the independent variables considered temperature, screw speed, and moisture content had significant effect on sugar recoveries. Proposed quadratic model to predict glucose, xylose, and combined sugar recoveries from switchgrass had a high F and R2 values indicating that the model has the ability to represent the relationship among the independent variables studied. The optimum pretreatment condition of barrel temperature 176 °C, screw speed 155 rpm, moisture content 20% wb, and particle size 8 mm resulted in maximum glucose, xylose, and combined sugar recoveries of 41.4, 62.2 and 47.4%, respectively. The optimum pretreated switchgrass had 50% higher surface area than that of the control.