Proficient bioconversion of rice straw biomass to bioethanol using a novel combinatorial pretreatment approach based on deep eutectic solvent, microwave irradiation and laccase.

Current study is the first report of the combined application of chemical (deep eutectic solvent), physical (microwave irradiation) and biological (laccase) pretreatment strategies for enhancing the enzymatic digestibility of rice straw biomass. Pretreated rice straw biomass was saccharified by cellulase/xylanase from Aspergillus japonicus DSB2 to get a sugar yield of 252.36 mg/g biomass. Design of Experiment based optimization of pretreatment and saccharification variables increased the total sugar yield by 1.67 times (421.5 mg/g biomass, saccharification efficiency 72.6%). Sugary hydrolysate was ethanol-fermented by Saccharomyces cerevisiae and Pichia stipitis to achieve an ethanol yield of 214 mg/g biomass (bioconversion efficiency 72.5%). Structural/chemical aberrations induced in the biomass due to pretreatment were elucidated by X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, and H nuclear magnetic resonance techniques to unravel the pretreatment mechanisms. Combined application of various physico-chemical/biological pretreatment may be a promising approach for proficient bioconversion of rice straw biomass.