Efficient bioconversion of sugarcane tops biomass into biofuel-ethanol using an optimized alkali-ionic liquid pretreatment approach

Sugarcane tops (SCT) may be an imperative lignocellulosic feedstock for production of renewable energy in view of ever-rising global energy demands. The current study presents the first ever report of combinative pretreatment of sugarcane tops biomass using ionic liquid (1-ethyl-3-methylimidazolium chloride) and alkali (ammonium carbonate) for effective and enhanced saccharification. The enzymatic hydrolysis of combinatorially pretreated SCT biomass resulted in a significantly higher reducing sugar yield (172.34 mg/g biomass) as compared to that obtained after standalone IL (85.9 mg/g biomass) or alkali pretreatment (102.6 mg/g biomass). The saccharification enzymes (cellulase/xylanase) used for hydrolysis of pretreated SCT biomass were in-house produced from an IL-tolerant, newly isolated fungus Penicillium chrysogenum VS4. Optimization of process variables for combined pretreatment was accomplished based on design of experiments, and enhanced reducing sugar yield was obtained. The experimental design for ascertaining optimal level of process variables, i.e., biomass loading (5.33%, w/w), temperature (100 °C), and time (4.50 h) was validated. Optimization of the process parameters resulted in 25.27% increased reducing sugar yield (215.89 mg/g biomass) as compared to that under unoptimized process. Ultrastructural analysis of SCT biomass after combined pretreatment was investigated by scanning electron microscopy and Fourier transform infrared spectroscopy which indicated that the biomass had undergone drastic alterations and substantial disintegration due to pretreatment. The current study highlights the potential of combinative pretreatment strategy for efficient conversion of SCT biomass. Such combined pretreatment approaches may be extended to other biomass feedstocks as well for developing successful biorefineries.