Integrated production of humic-like acid, fulvic-like acid, and fermentable sugars from industrial xylooligosaccharides manufacturing waste residues via hydrothermal pretreatment

Commercial humic substances (HS) are usually extracted from non-renewable resources such as lignite and coal. In this study, artificial HS (mainly humic-like acid (HLA) and fulvic-like acid (FLA)) was produced from renewable biomass-alkaline xylooligosaccharides manufacturing waste residue (XOR) of corncob via hydrothermal pretreatment (HP), as well as fermentable sugars were coproduced. The HLA yield was highest at 1.5% and the content of FLA was 9.6 g/L after HP at 210 °C for 8 h. The glucose yield of HP-pretreated XOR reached 98.8% at CTec 2 dosages of 20 FPU/g glucan. Structural characterization analysis proved that the structures and compositions of HLA were similar to those of commercial humic acid. The results of mass balance indicated that 100 g of XOR yielded 1.5 g of HLA, 9.6 g of FLA, and 60.4 g of monosaccharides (46.9 g of glucose and 13.5 g of xylose). Therefore, this work provides a promising strategy for valorization of lignocellulosic biomass in producing HLA, FLA, and fermentable sugars.