Synergistic effect of white-rot fungi and alkaline pretreatments for improving enzymatic hydrolysis of poplar wood

•Combined treatment was used to improve poplar enzymatic digestibility.•Alkaline treatment is the optimized combination with white-rot fungi treatment.•Alkaline treatment dissolved humin and partially degraded residual lignin.•Enzymatic digestibility was increased to 89.3%.

White-rot fungi pretreatment is one of the most environment-friendly pretreatment methods because of low chemical and energy requirement. However, apart from time consuming, white-rot fungi treatment results in inefficient delignification and humin formation, both of which inhibit subsequent enzymatic hydrolysis. Combined alkaline treatment for partial depolymerization of residual lignin and dissolution of humin is an efficient option for the conversion of white-rot pretreated samples. In the work presented, combined treatments increased the enzymatic digestibility to 89.3%, compared with 10.6% for untreated sample and 12.9% for solely white-rot treated samples. Highest digestibility of cellulose was achieved after 8 weeks of white-rot treatment and alkaline treatment at 120 °C, whereas sugar yield was highest from sole alkaline treatment at 160 °C. The efficient conversion can be ascribed to synergistic interaction between white-rot and alkaline treatments, resulting in increased enzymatic accessibility of cellulose. Therefore, white-rot fungi treatment is a green process that can efficiently decrease energy consumption, and in combination with alkaline treatment is highly effective in promoting sugar conversion.