Green alkaline fractionation of sugarcane bagasse at cold temperature improves digestibility and delignification without the washing processes and release of hazardous waste.

A response surface design was used to pretreat sugarcane bagasse (SB) with urea (U)/potassium hydroxide (K) at low temperatures. Alkaline pretreatment can increase the digestibility of biomass by removing lignin. However, this pretreatment has common issues, such as high-water consumption and liquid waste generation. To address these issues, this study was conducted to perform the UK pretreatment without washing steps. Under optimized pretreatment condition (−20 °C, 7.5 % UK), hemicellulose and lignin removal were increased approximately by 1.4 (26.18–18.86 %) and 1.7 folds (21.25 % to 12.43 %), respectively, while cellulose increased by 1.6-fold (42.39–68.34 %) as compared to control. This enhanced the enzymatic hydrolysis by 3.16-fold (75.15 %). In addition, physicochemical analyses revealed that U facilitates fiber opening, reduces the crystallinity index of cellulose (55.06–49.03 %), and prevents lignin droplet formation from adhering to cellulose. Hence, UK pretreatment can be a promising pretreatment technology for lignocellulosic valorization towards biorefinery without any washing in restoring the liquid substances. [Display omitted] • Urea/KOH pretreatment effectively depolymerize and dissolve lignin. • Direct enzymatic hydrolysis of unwashed UK-treated SB was achieved. • The enzymatic hydrolysis efficiency increased to 76.1 % with delignification rate 41.50 %. • This method explains the role and mechanism of urea in alkali treatment. [ABSTRACT FROM AUTHOR]