A novel two-stage xylose-upfront SSCF process for second-generation ethanol production from acid pretreated rice straw at very low enzyme loading and process time

To enhance the cost-effectiveness of bioethanol production from acid-pretreated rice straw, a novel two-stage modified Simultaneous Saccharification and Co-Fermentation (SSCF) process was developed. This process incorporates an initial xylose-upfront (XU) fermentation stage, conducted under low glucose concentrations during enzymatic hydrolysis at 30 °C, followed by a second stage involving continued hydrolysis and glucose fermentation. Under optimized conditions, the modified XU-SSCF process achieved an ethanol concentration of 50  g/L at 20 % (w/v) solid loading within 46 h, using a total enzyme loading of 3.3 FPU/g total solids (TS). In contrast, the conventional SSCF process yielded 46  g/L ethanol over 77 h at the same solid loading, requiring a significantly higher enzyme dose of 7 FPU/gTS. The modified process also demonstrated enhanced ethanol productivity, reaching 1.08  g/L/h, compared to 0.63  g/L/h observed in the conventional SSCF. Furthermore, the implementation of a fractional cellulase dosing strategy—comprising in-house produced enzymes from Penicillium funiculosum MRJ-16 (2.0 FPU/gTS) and commercial CTec3 (0.3 FPU/gTS) enabled a 52.8 % reduction in total enzyme usage relative to the conventional approach, without compromising process efficiency.