Bioprocess development for enhanced bioethanol production from Saccharum spontaneum biomass using synergistic ionic liquid-metal salt pretreatment and enzymatic catalysis.

Lignocellulosic biomass (LB) is a renewable and abundant feedstock with great potential for biofuel production. The current study is the first demonstration of a synergistic pretreatment strategy that integrates ionic liquid (IL) 1-ethyl-3-methylimidazolium bromide ([Emim][Br]) and metal salt FeSO₄ for next generation bioconversion of kans grass biomass (KGB; Saccharum spontaneum) into bioethanol through a one-pot consolidated bioprocess (OPCB). An indigenously developed IL-stable and efficient cellulase-xylanase enzyme preparation from Bacillus subtilis G2 was employed for saccharification of the pretreated biomass. Combined [Emim][Br] + FeSO₄ pretreatment coupled with enzymatic hydrolysis yielded a significantly higher sugar yield (113.71 mg/g KGB) than the individual pretreatments with FeSO₄ (48.40 mg/g KGB) or [Emim][Br] (50.74 mg/g KGB), thus, demonstrating a clear synergistic enhancement in biomass deconstruction and saccharification efficiency. Optimization of pretreatment and saccharification parameters enhanced the reducing sugar yield considerably (2.42-fold) i.e. 274.77 mg vs. 113.74 mg/g biomass in control. Subsequent fermentation of KGB sugars generated 0.09 g/g biomass of ethanol, with a fermentation efficiency of 66.75%, and a bioconversion efficiency of 32.54%. Detailed characterization of the pretreated biomass using techniques/methods such as, XRD (X-ray Diffraction), FT-IR (Fourier Transform Infrared Spectroscopy), NMR (Nuclear Magnetic Resonance Spectroscopy), SEM (Scanning Electron Microscopy), BET (Brunauer-Emmett-Teller), water retention capacity, and cellulase adsorption isotherm reveals the effectiveness of the combined pretreatment strategy. The current findings highlight the significance of [Emim][Br] and FeSO4 as an effective and synergistic pretreatment system for improving the bioconversion of KGB into bioethanol.