Sulfite (SPORL) pretreatment of switchgrass for enzymatic saccharification

► SPORL pretreatment of switchgrass was optimized by Response Surface Methodology. ► SPORL was compared with acid and alkali in pretreating switchgrass. ► Hemicellulose removal and lignin sulfonation in SPORL improved hydrolysability. ► SPORL pretreated switchgrass had better hydrolysability than DA and NaOH ones. ► Removing hemicellulose was more critical than lignin to SPORL substrate hydrolysis.