Comparative evaluation of sugarcane leaf biomass pretreatment: Conventional alkali/acid vs. deep eutectic solvent approach for enhanced bioethanol production

This work draws insights into comparative efficiency between three binary deep-eutectic solvents (DES) and the sequential alkali/acid pretreatment techniques. The ability of DES to convert sugarcane leaf (SCL) biomass into fermentable sugars was reviewed at different temperatures (25, 80 and 121 °C) and residence time periods (24, 3 and 1 h), respectively. DESs are suitable solvents for solubilizing lignocellulose highlighting their cost-effectiveness and reduced environmental footprint compared to conventional methods. On the other hand, sequential alkali/acid (SAA) pretreatment was carried out at 121 °C and 90 °C for 60 min. After DES pretreatment, the maximum cellulose concentration attained was 0.435 g/g biomass using choline chloride: acetic acid (CA121) mixture at 121 °C for 60 min. The process also indicated 23.29 kWh/kg energy consumption and 15 L/kg biomass as wastewater generated. In comparison to native biomass, evaluation of the pretreated biomass showed that cellulose concentration of 0.902 g/g biomass (2.5-fold increase) resulted from the sequential alkali/acid pretreatment using 1.5M NaOH followed by 1.5M H 2 SO 4 (121 °C for 60 min). Also, the energy consumption and the waste water generation were 53.8 kWh/kg and 53.3 L/kg biomass respectively. Biochemical analysis using FTIR and XRD showed that the sequential alkali/acid pretreatment method was more effective in removing hemicellulose and lignin compared to DES. The optimized enzymatic hydrolysis of pretreated biomass hydrolysate achieved 0.831 g/g biomass glucose concentration attaining an ethanol yield of 487 kg per ton of SCL biomass (equivalent to 106 L/ton) with a cumulative productivity of 14 kg per ton per hour. • Sequential alkali/acid pretreatment boosts cellulose yield 2.5x vs untreated biomass. • DES pretreatment cuts energy/water use by 57 % and 72 % vs conventional methods. • Co-fermentation with dual yeast strains maximizes ethanol yield (0.379 g/g biomass). • SAA yields higher ethanol but DES offers lower carbon footprint (74.8 vs 83.1 kg CO 2 /kg). • FTIR/XRD confirm enhanced delignification and cellulose accessibility post-pretreatment.