Reutilization of green liquor chemicals for pretreatment of whole rice waste biomass and its application to 2,3-butanediol production

• NaC–NaS pretreatment for whole rice waste biomass (RWB) was investigated.
• Intensified delignification of RWB facilitates enzymatic saccharification.
• Reusability of NaC–NaS spent wash to treat RWB and its hydrolysis were evaluated.
• Obtained RWB hydrolysates were used for BDO production by K. pneumonia.
• Developed pretreatment strategy performed well for saccharification and biorefinery.

The performance of green liquor pretreatment using Na2CO3 and Na2SO3 and its optimization for whole rice waste biomass (RWB) was investigated. Incubation of Na2CO3–Na2SO3 at a 1:1 ratio (chemical charge 10%) for 12% RWB at 100 °C for 6 h resulted in maximum delignification (58.2%) with significant glucan yield (88%) and total sugar recovery (545 mg/g of RWB) after enzymatic hydrolysis. Recovery and reusability of the resulting chemical spent wash were evaluated to treat RWB along with its compatibility for enzymatic digestibility. Significant hydrolysis and lignin removal were observed for up to three cycles; however, further reuse of Na2CO3 and Na2SO3 lowered their performance. Significant 2,3-butanediol (BDO) was produced by Klebsiella pneumoniae KMK-05 with the RWB enzymatic hydrolysate from each pretreatment cycle. BDO yield achieved using RWB-derived sugars was similar to those using laboratory-grade sugars. This pretreatment strategy constitutes an ecofriendly, cost-effective, and practical method for utilizing lignocellulosic biomass.