A sustainable bio-circular way for biorefinery of rice straw into bioproducts based on energy-efficient pretreatment

Lignocellulosic biorefinery faces challenges associated with high energy input during pretreatment and high enzyme cost for enzymatic hydrolysis of cellulose, as well as the intricate valorization of lignin and hemicellulose. This study applied KOH-urea pretreatment to obtain maximum lignin removal of 68.93 % from rice straw at 80 °C for 60 min. The pretreatment consumed only 10.49 % of the total energy input. Five-time dilution of neutral black liquor can optimally stimulate the plant growth. Enzymatic conversion of KOH-urea-treated rice straw attained 92.02 % at 20 % solid concentration with 10 FPU cellulase/g substrate. The ethanol concentration achieved 37.02 g/L at a yield of 75.89 %. The solid residue after fermentation contained 42.40 % dietary fiber and 16.70 % protein, which is suitable as animal feed. This study developed a simple bio-circular way to concurrently produce liquid fertilizer, bioethanol, and animal feed from rice straw. [Display omitted] •KOH-urea pretreatment shared only 10.49 % of total energy consumption.•Enzymatic conversion of rice straw reached 92.02 % at 20 % solid concentration.•Black liquor can be prepared as fertilizer after pH adjustment and proper dilution.•Solid residues after fermentation are suitable as animal feed.•A feasible bio-circular way of lignocellulosic biorefinery is constructed.