Process optimization for chemical pretreatment of rice straw for bioethanol production

Pretreatment of rice straw was optimized by physical and chemical methods. Among all the pretreatment methods followed by saccharification, autoclaved ammonia pretreatment significantly enhanced the liberation of reducing sugars i.e. 233.76 ± 1.23 mg/g substrate as compared to other methods. Further statistical optimization by response surface methodology (RSM) including ammonia concentration, substrate concentration and autoclaving time, enhanced the saccharification rate by 1.9-fold i.e. 451.96 mg/g substrate at 5 % rice straw, 12 % ammonia and autoclave time of 30 min after saccharification of 6 h. Maximum liberation of reducing sugars (635.37 mg/g substrate) was attained under these optimized conditions at 60 °C after 48 h. Fourier-transform infrared spectroscopy, X-ray diffraction and scanning electron microscope analysis clearly confirmed the removal of lignin in pretreated biomass. Ammonia pretreated enzymatic hydrolysate was fermented by Saccharomyces cerevisiae at 30 °C, pH 7.0, 150 rpm and 20 % hydrolysate, resulted in 24.37 g/L bioethanol after 72 h.