Optimizing bioconversion processes of rice husk into value-added products: D-psicose, bioethanol, and lactic acid

[Display omitted] •Investigating the potential of rice husk (RH) as the biorefinery feed crop.•Combined alkali-HPAC pretreatment enhances the removal of lignin and silica from RH.•The hydrolysis process was optimized using the Box–Behnken experimental design.•The hydrolysis efficiency was 87.9% at 11% (wt) substrate concentration.•High efficiency co-production of bioethanol, lactic acid and D-psicose from RH. Rice husk, rich carbon content, is an agricultural waste produced globally at an amount of 120 million tons annually, and it has high potential as a biorefinery feedstock. Herein, we investigated the feasibility of producing various products as D-psicose, bioethanol and lactic acid from rice husk (RH) through a biorefinery process. Alkali-hydrogen peroxide-acetic acid pretreatment of RH effectively removed lignin and silica, resulting in enzymatic hydrolysis yield of approximately 86.3% under optimal hydrolysis conditions. By using xylose isomerase as well as D-psicose-3-epimerase with borate, glucose present in the RH hydrolysate was converted into D-psicose with a 40.6% conversion yield in the presence of borate. Furthermore, bioethanol (85.4%) and lactic acid (92.5%) were successfully produced from the RH hydrolysate. This study confirmed the high potential of RH as a biorefinery feedstock, and it is expected that various platform chemicals and value-added products can be produced using RH.