Improving enzymatic hydrolysis efficiency of highly recalcitrant Chinese fir biomass via hydrogen peroxide/acetic acid pretreatment and alkaline incubation

Breaking the high recalcitrance of softwood biomass under mild conditions to improve its hydrolysability is a challenge. In this work, 93.2 % lignin was removed from fir biomass by hydrogen peroxide/acetic acid (HPAC) solution at 60 °C for 2 h. Alkaline post-incubation (0.5 % NaOH, 22 °C, 1 h) removed 100 % acetyl groups from HPAC-pretreated fir, resulting in a 75 % reduction in cellulase loading and a satisfactory glucose yield of 97.9 % during the enzymatic hydrolysis of alkaline-incubated fir. In the substrate batch feeding hydrolysis with 200 g/L of solid content, the glucose concentration was 124 g/L with yield of 87.6 %. After the first batch pre-hydrolysis-simultaneous saccharification and fermentation (PSSF), the ethanol concentration was 60.3 g/L with a yield of 70.1 %. The fermentation residue of first batch PSSF was recycled for the second batch PSSF process. Half of cellulase and yeast was reduced and the ethanol concentration reached 58.4 g/L with a yield of 67.9 %, which was close to the ethanol production of first batch PSSF process. This work developed a mild and economic process to efficiently produce bioethanol from highly recalcitrant Chinese fir biomass.