Sodium sulfite-formaldehyde pretreatment of mixed hardwoods and its effect on enzymatic hydrolysis

► Sodium sulfite-formaldehyde (SF) was used as pretreatment on mixed hardwoods. ► The result indicated that pretreatment temperature is a key factor. ► Sugar yield of mixed hardwoods was greatly improved after SF pretreatment. ► 74% of the original polysaccharides could be converted into fermentable sugars.