Dilute acid pretreatment of rice straw, structural characterization and optimization of enzymatic hydrolysis conditions by response surface methodology

Abstract

Efficient conversion of fermentable sugars from cheap lignocellulosic biomass is a current need in viable ethanol production technology. In the present study, agricultural waste biomass such as rice straw was pretreated by using 0.5% sulfuric acid for 60 min at 121 °C in an autoclave. A statistical experimental design like central composite design (CCD) was used for optimization of the enzymatic hydrolysis conditions to achieve a significant reducing sugar yield using commercial cellulase. The optimal conditions for acid pretreated rice straw were found to be 40 FPU g⁻¹ enzymes loading, 17.50% biomass loading at 50 °C for 72 h. The reducing sugar yield was 0.359 g g⁻¹, achieved at the optimized conditions. Experimental results under optimum conditions fit well with CCD model predictions. The structural and morphological changes in native and dilute acid treated rice straw substrate were evaluated by FTIR, XRD and SEM analysis. The XRD pattern of biomass revealed an increase in the crystallite size and crystallinity index of pretreated biomass. Scanning electron micrography reported surface porosity and a distorted structure due to pretreatment. HPTLC analysis of sugars like glucose and xylose in hydrolysate produced after enzymatic hydrolysis was determined.