Hydrothermal treatment of food waste for bio-fertilizer production: Formation and regulation of humus substances in hydrochar.

Food waste (FW) poses serious challenges to incineration and composting. Hydrothermal treatment (HTT) is a promising method to produce carbon-rich materials from biomass, including humus substances. In this study, FW containing cellulose, starches, and proteins was treated by HTT to study the formation and regulation of three kinds of humus (i.e., humin, humic acids [HAs], and fulvic acids [FAs]). Ultimate analysis and proximate analyses were conducted to explore the material composition, which was very similar to natural humus. Three kinds of humus were quantified. Optimal temperature (200 °C) and residence time (30 min) for production of HAs were determined based on HAs yield (14.60%). In addition, formation and regulation of humin, HAs and FAs was discussed. The amino acids, peptides, monosaccharides, and HMF obtained by hydrolysis of FW produced important precursors of humus. Moreover, the transfer of nutrient elements was revealed. Nearly 90% of K was dissolved in water. Recovery of N (60%) was relatively stable in hydrochar. Up to 67.61% of P deposited in hydrochar with 12 h.