Valorization of rice straw into high-purity lactic acid with reduced enzyme cost and waste footprint

Rice straw, an abundant agricultural residue, represents an underutilised lignocellulosic resource to produce bio-based platform chemicals. In this study, an integrated and scalable process was developed for the valorisation of dilute acid-pretreated rice straw into high-purity L -lactic acid (LA) using a modified simultaneous saccharification and fermentation (MSSF) strategy coupled with adsorption-based downstream purification. The process employed a mesophilic strain, Lactobacillus casei , operating at 42 °C, as opposed to conventional energy-intensive processes utilising thermophilic strains. A low cellulase loading of 5 FPU g⁻¹ of pretreated biomass was sufficient to achieve an LA yield of 0.40 g g⁻¹ of pretreated biomass and a productivity of 0.63 g L⁻¹ h⁻¹ with a reduced process time of 48 h. The hemicellulose-derived xylose stream was simultaneously recovered, supporting a biorefinery approach for comprehensive biomass utilization. Downstream processing protocol was established using mechanically robust ion-exchange resins (Indion 225 H and Indion 860S), without the production of solid waste unlike the conventional precipitation method, resulting in 93% LA purity with an overall recovery of 74%. By integrating low-enzyme SSF with sustainable adsorption-based purification, the present study demonstrates a cost-effective and environmentally favourable pathway for converting rice straw into value-added chemicals, contributing to the economic viability of second-generation biorefineries. • Modified SSF of rice straw at 42 °C using low enzyme loading of 5 FPU/g biomass. • A high lactic acid yield (0.4 g/g) and productivity (0.63 g/L h) were achieved. • Lactobacillus casei , a mesophilic strain, was used for SSF at 42 °C. • Downstream processing with Indion 860 S resin yielded 93% pure lactic acid. • The integrated end-to-end process resulted in 74% overall recovery of lactic acid.