Optimisation of combined acid and enzymatic hydrolysis of paddy straw to produce fermentable hydrolysate

Abstract

Paddy straw (PS), a by-product of rice production, has a large volume, low economic value, and environmental impact due to burning, contributing to pollution and health hazards. This manuscript highlights the combined effect of acid treatments and enzymatic hydrolysis of paddy straw to produce fermentable hydrolysate, a potential biofuel. This study uses response surface methodology (RSM) with a Box–Behnken design to optimize process parameters (acid concentration, temperature, and duration of hydrolysis), thereby improving the efficiency of converting paddy straw into fermentable sugars. The efficacy of pretreatment was evaluated based on cellulose content and lignin reduction. The optimal conditions of 1% H₂SO₄, 80 °C, and 20 min resulted in effective cellulose enrichment (95.4%) and lignin reduction (38.2%), promoting efficient enzymatic hydrolysis. The enzymatic hydrolysis used cellulase from Trichoderma reesei, yielding high glucose concentrations of 225.2 mg glucose ml⁻¹ g⁻¹ paddy straw. Using Brunauer–Emmett–Teller (BET) analysis and morphology of pretreated and raw PS samples, the surface modification was validated for the optimized hydrolysis conditions. Surface area and pore volume for optimized condition decreased by 58.6% and 25% respectively. However, mean pore diameter increased by 87.9%. Herein, this study offers a more efficient, optimized, and sustainable pathway for converting paddy straw into biofuel using cellulase, with broader implications for agricultural waste management and renewable energy production.

Graphical Abstract