Enhanced Glucose Recovery from Reed Straw (Phragmites australis) via Cascade Microwave–Alkali and Ultrasound–H2O2 Pretreatment with Sophorolipid/BSA Supplementation

The growing demand for renewable fuels has led to lignocellulosic biomass being turned to as a feedstock for fermentable sugars, yet its hierarchical structure severely limits enzymatic saccharification. In this study, a cascade of microwave-assisted alkali and ultrasound-assisted H2O2 pretreatment, combined with sophorolipid and BSA supplementation, was established to enhance glucose recovery from reed straw under mild conditions while substantially reducing enzyme and chemical inputs. The cascade pretreatment selectively removed lignin and hemicellulose, increasing the apparent cellulose crystallinity index from 58.77% to 69.16%. This apparent increase is attributed to the removal of non-cellulosic components rather than to enhanced cellulose crystallinity. This structural modification boosted glucose yield by 1.28-fold over single-stage alkali pretreatment and 6.29-fold over raw material. Supplementation with β-glucosidase, sophorolipid, and BSA further enhanced the yield by 20.34% at a reduced cellulase loading of 12 FPU/g. Fractal kinetic analysis showed that the combined addition increased the rate constant from 0.0067 to 0.0111 while reducing the fractal dimension from 0.7136 to 0.6787. Fed-batch hydrolysis at 25% solids achieved 128.71 g/L glucose, recovering 31.22 g per 100 g raw material. This integrated strategy offers a viable route for converting reed straw into high-titer fermentable sugars under mild conditions with substantially reduced enzyme and chemical inputs.