Enhancing enzymatic hydrolysis of Chinese fir sawdust by using the synergistic effect of dilute sulfuric acid and sodium chlorite pretreatment

The biological valorization of cork depends mainly on the weakening of cell wall recalcitrance. As a typical softwood, Chinese fir is more resistant to enzyme and microbial invasion than most biomass. This study compared the efficiency of two single-step pretreatments (dilute sulfuric acid pretreatment (DSA) and acidic sodium chlorite pretreatment (SC)) and their interaction effects on the pretreatment process. Two single pretreatments could selectively remove hemicellulose and some lignin from Chinese fir sawdust (CFS). Combined pretreatments resulted in a remarkable synergistic enhancement in delignification. The hemicellulose-removal-first strategy is favored by softwood delignification, the destruction of fiber morphology, and the redistribution of lignin. Using DSA-SC, more than 90% of lignin and hemicellulose were removed, and complete hydrolysis (99.3%) was obtained. Based on DSA-SC, the CFS biorefinery recovered 41.6% lignin and 52.8% hemicellulose sugar, and 306.1 g lactic acid was produced from 1000.0 g CFS. The integrated pretreatment process with a stepwise separation feature could be effectively applied in softwood destruction and provide more opportunities for softwood waste whole-component utilization.