Analysis of the promotion of lignin conversion to artificial fulvic acid by hydrothermal humification combined with microbial fermentation

The microbial synergistic hydrothermal humification technology provides a new approach for the preparation of artificial fulvic acid (FA) using biomass as raw material, but the reaction mechanism still needs to be further explored. This study conducted experiments on microbial synergistic hydrothermal humification using rice straw as raw material, solving the problem of difficult sustainable utilization of biomass and proposing a mechanism for biomass conversion to FA synthesis. Through a series of experiments, the chemical properties of organic scaffolds and the types and abundance of oxygen-containing functional groups used for synthesizing FA were revealed. Monitoring of intermediate products also revealed the mode of substance transformation. SEM was used to observe the surface structure of the rice straw, and FTIR was used to demonstrate the hydrolysis of hemicellulases and lignin. XPS and EEM are used to explain the structure of FA. GC-MS and LC-MS analyses of the composition of the pyrolysis mixture revealed that 2,3-dihydroxybenzofan and 4-hydroxy-2-methylacetophenone are precursors for the conversion of lignin to FA as the basic skeleton, whereas 1-stearoylglycol L-α-palmitin and 4-(4-hydroxy-4-methylpentyl) cyclohex-3-ene-1-carboaldehyde are the synthetic basis for the conversion of hydroxyl (OH) functional groups. Hydroxyl and carboxyl dehydrated carbohydrates rich in O and some low molecular weight compounds are the main structural components for preparing FA. The mechanism of microbial synergistic hydrothermal humification proposed is of great significance for the design and synthesis of artificial fulvic acid, and contributes to the development and utilization of agricultural waste, promoting sustainable development. • A green and efficient microbial synergistic hydrothermal reaction system has been constructed. • FA is polymerized from precursors containing benzene rings and hydroxyl groups. • Bacillus exhibits high activity in the pyrolysis solution, promoting the conversion of FA. • Artificial FA exhibits lignin structural characteristics. • The goal of carbon cycle and carbon neutrality has been achieved.