Optimization of Biomass and High Shear Bioreactor Parameters for Enzymatic Hydrolysis using Response Surface Methodology

Abstract

Abstract: Biomass pretreatment is necessary to open up the biomass structure so that the access to the enzymes can be increased. The literature review indicated that no perfect pretreatment method has been established for the production of biofuels from biomass. Extrusion might be a viable continuous pretreatment due to its advantages over other pretreatment methods. The current study was undertaken to optimize the parameters such as extruder barrel temperature (45-225C), screw speed (20-200 rpm), moisture content (10-50%), and particle size (2-10 mm) for maximum sugar recovery from corn stover and big bluestem. An experiment consisting 36 treatment combinations based on a central composite rotatable design was developed using Design Expert. The ground, moisture-balanced biomass was extruded using a lab scale single screw extruder to vary the barrel temperature and screw speed in a random order. The extruded samples were subjected to enzymatic hydrolysis, and the sugar yield was quantified using HPLC as outlined in NREL LAPs. It was confirmed through statistical analysis that all the independent variables studied had a significant effect on sugar recoveries. A quadratic polynomial model was proposed to predict the glucose, xylose, and combined sugar recovery from corn stover and big bluestem. The optimum pretreatment conditions for corn stover were found to be the following: barrel temperature 180C, screw speed 155 rpm, moisture content 20% wb, and particle size 8 mm resulted in a glucose, xylose, and combined sugar recovery of 85.7, 87.5, and 86.3%, respectively. The optimum pretreatment condition was the same for big bluestem (except 150 rpm) and the maximum glucose, xylose, and combined sugar recovery of 71.3, 78.5, and 56.9%, respectively.