Optimization of alkali, big bluestem particle size, and extruder parameters for maxium enzymatic sugar recovery using response surface methodology

Abstract

Extrusion can be a viable continuous biomass pretreatment that industry can adopt readily due to its uniqueness (including pretreatment time less than 90 s) over other pretreatment methods. The current study was undertaken to evaluate the combined effect of alkali soaking and extrusion of big bluestem to improve the sugar recovery to nearly quantitative. In order to evaluate the combined effect of alkali soaking and extrusion on the performance of enzymatic saccharification, big bluestem (2-10 mm) was soaked in different alkali concentrations (0.5-2.5 % w/v NaOH) for 30 min at room temperature and then extruded using a lab scale single screw extruder at various barrel temperatures (45-225°C) and screw speeds (20-200 rpm). Statistical analyses confirmed that all the independent variables considered had a significant effect on sugar recovery. A proposed quadratic model to predict sugar recovery had high F and R2 values with a low p value, and adequately represented the relationship among the independent variables on sugar recovery. The optimum pretreatment condition found was the following: 90°C barrel temperature, 155 rpm screw speed, 2.0% alkali concentration, and 4 mm particle size resulted the maximum glucose, xylose, and combined sugar recovery of 90.1, 91.5, and 89.9%, respectively.