Synergistic bio-mechanical pretreatment and fed-batch semi-SSF strategy for enhanced cellulosic ethanol production from ramie straw.

The recalcitrant lignocellulosic matrix impedes biorefinery efficiency‌‌. This study developed a mechanical-biological pretreatment combined with fed-batch high-solids semi-simultaneous saccharification and fermentation (S-SSF) strategy for ethanol production from ramie straw. Results showed that dual fungal pretreatment with Pleurotus ostreatus (PO) and Ganoderma lucidum (GL) achieved selective lignin (59.8 ± 0.85 %) and hemicellulose (41.0 ± 0.52 %) removal through hydrolase secretion during 14-day cultivation. The glucose yield and recovery rates were 27.9 ± 0.25 % and 21.8 ± 0.20 %, respectively. Ball milling pretreatment enhanced enzymatic digestibility, yielding 71.7 ± 1.28 % glucose (5.48-fold and 2.09-fold increase versus raw material and biologically pretreated residue). Sophorolipid-assisted fed-batch enzymatic hydrolysis‌ (solid loading of 25 % w/v) achieved 88.7 ± 0.57 g/L glucose titer, ‌24.8 % higher than batch processing‌‌. By pre-enzyme hydrolyzing the substrate for 72 h followed by simultaneous saccharification and fermentation (SSF), efficient conversion of the substrate to ethanol (43.0 ± 0.28 g/L) was achieved. The proposed approach enabled clean production of ethanol from ramie straw without the use of harmful chemicals, achieving an ethanol conversion rate of 115 g/kg of raw material, and thus offering a promising direction for the sustainable development of lignocellulosic biorefining.