Sodium lignosulfonate-assisted alkaline hydrothermal pretreatment improves the production of humic-like substances from lignocellulosic biomass waste residues

In order to provide key precursors for humic-like substances formation via alkaline hydrothermal pretreatment (AHP), this study introduced an innovative approach by incorporating sodium lignosulfonate (SL) into the AHP to boost the production of humic-like acid (HLA) and fulvic-like acid (FLA) from biomass wastes. The SL-AHP conditions were optimized, and structural analysis of HLA was performed. The highest HLA yield reached 21.90 %, and FLA content reached 13.38 g/L after SL-AHP at 200 °C for 2 h with 15 g/L SL. The inclusion of SL led to a 19.67 % increase in HLA yield and a 5.25-fold enhancement in FLA content compared to that without SL. The probable reason underlying SL's facilitation of HLA and FLA formation involved the effective dissolution of lignin and hemicelluloses to produce more precursors, as well as the incorporation of SL structure into the HLA molecule. SL acted as both a surfactant and a precursor for the production of HLA and FLA. In addition, an increase in acidic groups improved the quality of HLA.