Insights into hydrothermal deconstruction and humification of vegetable waste by non-catalytic steam explosion

Source minimization and valorization of vegetable waste has attracted considerable interests recently, but has been limited by its distinctive features of high humidity and perishability. To mitigate these challenges and draw upon its features, this study provides a novel non-catalytic hydrothermal process for rapid humification of broccoli waste by steam explosion (SE). The highest humic substance, fulvic acid (FA) and humic acid yields of 23.48 wt%, 18.70 wt% and 6.07 wt% were obtained within 30 min. Thermal-acidic condition and instantaneous decompression action proved to be favorable for substrate deconstruction, precursor production and humus formation. Potential pathways of hydrothermal humification of vegetable waste were revealed after clarifying the molecular level structure of FA by EA, FTIR, XPS, 2D-NMR and Py-GCMS. This work fills the knowledge gap in the mechanism of hydrothermal humification of vegetable waste and provides technical support for enhancing its agronomic value and efficient cycle in clean production.