Bioconversion of sawdust into ethanol using dilute sulfuric acid-assisted continuous twin screw-driven reactor pretreatment and fed-batch simultaneous saccharification and fermentation

Ethanol production from poplar sawdust using sulfuric acid-assisted continuous twin screw-driven reactor (CTSR) pretreatment followed by simultaneous saccharification and fermentation (SSF) was investigated. Pretreatment with high acid concentration increased the cellulose content in the pretreated solid (74.9–76.9% in the range of 4.0–5.5 wt.% H2SO4). The sugar content (XMG; xylan + mannan + galactan) in the treated-solid was 11.1–15.2% and 0.9–5.7% with 0.5 wt.% and 7.0 wt.%, respectively. The XMG recovery yield of the sample treated with 4.0 wt.% H2SO4 at 185 °C was maximized at 88.6%. Enzymatic hydrolysis test showed a cellulose digestibility of 67.1%, 70.1%, and 73.6% with 15, 30, and 45 FPU/g-cellulose, respectively. In the fed-batch SSF tests with initial enzyme addition, the ethanol yield of each stage almost reached a maximum at 28 h, 48 h, and 56 h, respectively, with yields of 63.9% (16.5 g/L), 78.4% (30.1 g/L), and 81.7% (39.9 g/L), respectively.