Humic acid-assisted autohydrolysis of waste wheat straw to sustainably improve enzymatic hydrolysis

Humic acid (HA), considered the main component of organic matter in the ash of waste wheat straw (WWS), has the potential to improve autohydrolysis through its function as a surfactant. In this work, a pre-washed WWS (PWWS) was subjected to autohydrolysis with addition of HA to explore whether its surfactant properties can provide benefit to biorefinery operations. Acquired results showed that HA acted as delignification agent likely due to its surfactant properties. Delignification was more than doubled at the maximum HA dosage (30 g/L) relative to the control, which allowed for enzymatic hydrolysis efficiency to also increase from 64.9% to 81.8%. The pretreated materials were further subjected to analysis structure characterization. The results showed that HA effectively reduced the surface lignin area of PWWS, lowering non-specific adsorption of lignin to enzymes. The autohydrolysis with HA was an effective technique to improve the subsequent cellulose enzymatic digestion by enhancing the delignification.