Hydrothermal Treatment of Food Waste for Bio-fertilizer Production: Regulation of Humus Substances and Nutrient (N and P) in Hydrochar by Feedwater pH

The valorization of food waste (FW) in municipal solid waste is a challenging task. Hydrothermal treatment (HTT) is a promising method to produce carbon-rich materials from biomass, including humus substances. In this research, FW containing cellulose, starches, and proteins was treated by HTT with different feedwater pH values (pH 1, 4, 7, 10, 13) to study the regulation of three kinds of humus (i.e., humin, humic acids [HAs], and fulvic acids [FAs]) and nutrient (N and P). The pH values were adjusted by HCl and KOH (1, 4, 7, 10, 13). Three kinds of humus were quantified and N and P were semi-quantified by XPS. Optimal settings of temperature (200 °C) and pH values (13) for production of HAs and absorbable N and P were determined based on HAs yield (19.90%), protein-N (PN) and inorganic phosphorus. In addition, different forms of nitrogen and phosphorus in the water phase were accurately measured and PN was almost completely hydrolyzed with acid. Formation and regulation of humin, HAs, FAs and different form of N/P was discussed according to the FTIR, GC–MS and XPS analyses. Graphical Abstract