Two-stage acid-alkali pretreatment of vetiver grass to enhance the subsequent sugar release by cellulase digestion

Abstract

Vetiver grass (VG; Chrysopogon zizanioides) can be used as a potential feedstock for biofuels and biochemical production due to its chemical composition, which is rich in cellulose, hemicellulose, and lignin. However, the complex and recalcitrant nature of a lignocellulosic biomass requires a pretreatment process to disrupt the lignin seal in the cell wall in order to increase the accessibility for enzymatic hydrolysis and to liberate the sugars contained within the cellulose. The sequential acid-base pretreatment of VG using dilute sulphuric acid (H2SO4) followed by sodium hydroxide (NaOH) was found to be optimal when using a 5% (w/v) VG loading in 0.5% (v/v) H2SO4 at 120 °C, 60 min in the first stage followed by 4% (w/v) NaOH at 120 °C, 60 min in the second stage. This gave the highest yield of total reducing sugars (32.6 g/L as 22.0 and 10.6 g/L of hexose and pentose, respectively) in the subsequent cellulase digestion, which was 10.3% and 46.1% higher than that obtained with the single-stage alkali (24.1 g/L) or acid (13.5 g/L) pretreatment, respectively.