Development of two-step pretreatment of Chinese fir sawdust using dilute sulfuric acid followed by sodium chlorite for bioethanol production

Chinese fir sawdust (CFS) is an abundant potential feedstock for bio-ethanol production. However, as a sawdust from this softwood, its high recalcitrance to enzymatic hydrolysis limits its successful application. Herein, a novel two-step pretreatment with dilute sulfuric acid pretreatment followed by sodium chlorite delignification was developed to enhance enzymatic digestibility of CFS. After dilute sulfuric acid pretreatment removed a larger amount of hemicellulose, a simple sodium chlorite treatment demonstrated a remarkable delignification. Under this optimal condition, this pretreatment can yield cellulose-rich (76.8%) pretreated solids and make it possible to achieve high enzymatic hydrolysis yielding cellulose close to 100% by 48 h. Moreover, a high glucose titer of 138.8 g/L and an ethanol titer of 64.6 g/L were obtained by batch-fed enzymatic hydrolysis and subsequent fermentation, which are the highest so far reported for softwood biomass. These results suggest that this pretreatment can significantly improve the enzymatic hydrolysis and bioethanol production of CFS by removing hemicellulose and lignin.