Response surface methodology (RSM) for optimization of thermochemical pretreatment method and enzymatic hydrolysis of deodar sawdust (DS) for bioethanol production using separate hydrolysis and co-fermentation (SHCF)

Abstract

In the present work, Cedrus deodara (deodar) sawdust abbreviated as DS was subjected to thermochemical pretreatment followed by enzymatic hydrolysis and fermentation for bioethanol production. Response surface methodology (RSM) based on central composite design (CCD) tool was employed to optimize dilute acid pretreatment method (at 121 °C temperature and 1-bar pressure) and enzymatic hydrolysis processes. Factorial design of experiments used chemical concentration, incubation time, and biomass loading to optimize thermochemical pretreatment method using dilute acid concentration. Maximum total reducing sugar (TRS) concentration (13.62 g/L) was obtained using optimized conditions (1.5% HCl concentration, 10% biomass loading and 30-min incubation time). These significant studies were subjected to optimize enzymatic hydrolysis process using the CCD tool of the RSM where cellulase loading, xylanase loading, pH, and temperature were taken into consideration. TRS concentration obtained was 29.20 g/L after 48 h with enzyme loading of 9 U/g biomass, each for cellulase and xylanase enzyme at pH 5.0 and 30 °C temperature. Fermentation conditions for enzymatically hydrolyzed DS revealed that at 10% (v/v) yeast inoculum concentrations (Saccharomyces cerevisiae (MTCC-36) and Pichia stipitis (NCIM-3498)) after 24-h fermentation time and pH 5.0, bioethanol concentration was 14.25 g/L with 95.68% conversion efficiency. Characterization studies for native and pretreated DS by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM) analyses revealed delignification rate of 30.93% of DS biomass under optimized thermochemical pretreatment conditions. Statistical studies for optimization of pretreatment and enzymatic hydrolysis for bioethanol production stated DS sawdust (a furniture industry waste) as a potential substrate for biofuel production.