Effects of biomass feedstock and hydrothermal temperature on the molecular composition and bioavailability of invasive plant-based hydrochar-derived dissolved organic matter

Hydrothermal carbonization demonstrates a potential for converting invasive plants into multifunctional carbonaceous material. Invasive plant-based hydrochar derived dissolved organic matter (HDOM) becomes an important source of anthropogenic dissolved organic matter, however, the molecular composition and bioavailability of HDOM and the controlling factors were not sufficiently revealed. Thus, in this study, a variety of invasive plants were selected to fabricate hydrochar at different hydrothermal temperatures to investigate the molecular composition via FT-ICR-MS and bioavailability based on microbial fuel cell system. The results indicated dissolved organic carbon (DOC) yield peaked at 200°C and pH fluctuated within a range of 5.0 ‒ 6.0. Along with the increase in hydrothermal temperature, macromolecular humic-like substances promoted via depolymerization, dehydration, and condensation of lignocellulose, likewise unsaturated-reduced molecules as well as the diversity of CHO group in HDOMs. Van Krevelen diagrams demonstrated highly unsaturated and phenolic compounds as lignin-like/CRAMs were the dominant components. Biomass feedstocks did not greatly alter the molecular distribution pattern of HDOMs. HDOMs were introduced into the microbial fuel cell system as the substitute carbon source of sodium acetate, according to the output voltage, HDOMs demonstrated a superior bioavailability, and the effects of biomass feedstocks and hydrothermal temperature were in line with the percentage of labile compounds (MLB_L%). HDOMs may serve as a carbon substrate that upregulated catabolic pathways to enhance the bioavailability, and act as metabolic driver to promote the nitrogen removal efficiency via enhancing denitrification and anammox. Environmental implications of HDOMs based on molecular composition and bioavailability were further discussed. This work provided theoretical foundation for optimizing the hydrothermal carbonization of invasive plants and reducing the ecological risks of invasive plant-based hydrochar.