A comparative study on enhanced enzymatic hydrolysis of diverse herbaceous and woody wastes by promising dilute acid and alkaline pretreatments

Biomass recalcitrance makes pretreatment process a key step for efficient bioconversion process. In this study, differential effects of promising acid (AP) and alkaline pretreatments (ALP) on enzymatic hydrolysis of diverse herbaceous and woody wastes were systematically investigated. Four biomass samples were separately pretreated and sugar recovery was then recorded in the subsequent hydrolysis. Results showed that both dilute AP and ALP exhibited efficacy in the removal of hemicellulose. Specifically, soybean straw AP demonstrated the highest recovery of soluble sugars at the pretreatment stage [270 mg/g raw stalk (RS)], against 71-212 mg/g RS achieved in AP and ALP of other wastes. Compared with herbaceous soybean straw, both AP and ALP of more recalcitrant woody biomass (e.g., bamboo and poplar) showed much lower enzymatic sugar yields. Among tested samples, ALP soybean straw produced stronger structure modification, morphological changes and higher delignification, which increased its availability to cellulases. As a result, the sugar yield of ALP soybean straw using 1.5% NaOH reached 787 mg/g, which is much higher than those of other tested AP & ALP biomass wastes. The present study revealed differential responses of diverse biomass wastes to AP & ALP, hence providing valuable information for the development of effective bioconversion process of these promising biomass. Looking ahead, these classic AP and ALP will be further investigated together with other potential and emerging pretreatments (e.g., green solvent pretreatments) to provide a foundation for high value utilization of biomass.