Comparative study on the mild pretreatment processes for enzymatic hydrolysis of wheat straw with high-solid loading

Efficient pretreatment of wheat straw (WS) under mild conditions facilitates its further enzymatic hydrolysis and conversion. Three pretreatment processes with mild conditions including formic acid pretreatment (FAP), sodium chlorite pretreatment (SCP), and alkaline hydrogen peroxide (AHP) pretreatment were investigated in this study. The chemical components of WS before and after pretreatment were compared, and the samples were characterized by scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The lignin removal by FAP, SCP, and AHP pretreatment was 55.79%, 99.33%, and 94.97%, and the enzymatic hydrolysis yields (EHY) were 68.03%, 75.52%, and 90.76%, respectively. The results showed that AHP pretreatment had a better performance on enzyme accessibility thus improving the EHY. Meanwhile, lignin can be separated from the AHP pretreatment liquid, which helps to improve the economics of the process. The effects of enzymes and additives on enzymatic hydrolysis were further optimized by response surface methodology. Under the conditions of 20.37 FPU/g cellulase, 32.14 IU/g xylanases, and 19.15 mg/g Tween 80, the experimental result showed that the maximum EHY was 94.15%, which was close to the predicted EHY (96.19%). The experiments on fed-batch mode after AHP pretreatment with high-solid loadings (20% w/v) were conducted, and the EHY reached 86.05%. These results contributed to improving the economic feasibility of WS pretreatment and enzymatic hydrolysis process.

Automated summary

This study compared three mild pretreatment methods (formic acid pretreatment, sodium chlorite pretreatment, and alkaline hydrogen peroxide pretreatment) for wheat straw. The results showed that alkaline hydrogen peroxide pretreatment had better enzyme accessibility and higher enzymatic hydrolysis yield, and lignin can be separated from the liquid, improving the process's economics. Furthermore, response surface methodology was used to optimize the enzyme and additive conditions, achieving a maximum enzymatic hydrolysis yield of 94.15%. Fed-batch experiments with high-solid loadings achieved an enzymatic hydrolysis yield of 86.05%. These results contribute to improving the economic feasibility of wheat straw pretreatment and enzymatic hydrolysis process.