Microwave-assisted acid pretreatment for enhancing enzymatic saccharification of sugarcane trash

Sugarcane trash (ST) is an abundant but underused biomass left in the field when the sugarcane is harvested. However, there are only a few studies to evaluate pretreatment of the residual bioresources for enzymatic saccharification. In this study, we aimed to explore the effects of combined severity factor (CSF), resulted from the use of different acids (phosphoric, maleic, and oxalic acids) on the pretreatment efficiency in microwave (MW)-accelerated process. The effects of acids and CSF on pretreated biomass properties and sugars obtained in the pretreatment soluble fraction and in enzymatic hydrolysate were evaluated. The degree of crystallinity of biomass pretreated at the same CSF is different due to different of acids used, and it did not correlate with the sugars obtained in the hydrolysate after enzymatic saccharification. MW-assisted acid pretreatment of ST at CSF of 2.05 affected functional groups and morphology of the biomass significantly. ST exposed to the same severity (CSF 2.05) using different acids resulted in reducing sugars yield 25.3–30.8% (based on initial biomass) from the pretreatment soluble fraction and 26.1–28.8% (based on initial biomass) from enzymatic hydrolysis, with the highest (30.8% and 28.8%) when used maleic acid. We succeeded in the production of total reducing sugars by 59.6% yield (of initial biomass) from recalcitrant sugarcane trash by applying MW-assisted maleic acid pretreatment at CSF of 2.05. The work provided insights into the use of organic acid as the catalyst in MW-accelerated process and can be further developed for application in pretreatment of ST in industry.