Bioprocessing of pineapple leaf waste biomass using an integrated ultrasound-deep eutectic solvent pretreatment approach for improved bioethanol production

Abstract

Biorefineries play a crucial role in advancing the circular bioeconomy by integrating the environmental and socio-economic dimensions of the industrial sector. This study investigated the potential of integrated ultrasound (UL)-deep eutectic solvent (DES, choline chloride/glycerol) pretreatment of pineapple leaf (PL) waste for efficient bioethanol production, emphasizing its sustainability and environmental benefits. The pretreatment conditions were optimized using response surface methodology, with variables including ultrasound amplitude (45 %), time (30 min), and solid loading (10 %, w/w). The solid PL biomass was physico-chemically characterized, revealing prominent variations in functional groups, surface morphology, crystallinity, and surface area across samples subjected to individual and integrated pretreatment approaches. A high reducing sugar yield of 324.41 mg/g PL biomass was recovered after enzymatic hydrolysis of integrated UL-ChCl/glycerol pretreated PL samples under optimized conditions. The fermentation of the sugar hydrolysate yielded 121.36 mg/g ethanol with 89.61 % fermentation efficiency. Notably, DES recyclability experiments indicated significant performance up to the third cycle, after which activity marginally declined in correlation with sugar yield. The synergistic UL-ChCl/glycerol pretreatment process supports circular bioeconomy by promoting sustainable biomass conversion and offering a promising approach to reducing environmental impacts by utilizing agricultural waste for renewable energy production.