Fuel potential and combustion emission characteristics of hydrothermal conversion products from kitchen waste

Hydrothermal technology offers a promising method for resource recovery from kitchen waste (KW). This study developed a model mixture representing KW to investigate the impact of varying hydrothermal conditions (210–270 °C, 30–90 min) on product yield, physicochemical properties, biocrude composition, and organic emissions during combustion. As the temperature increased from 210 to 270 °C, biocrude yield rose from 24% to 35%, HHV from 34.976 to 35.351 MJ/kg, and energy yield from 35.489% to 51.850%. Meanwhile, organic emissions during biocrude combustion decreased from 441 μg/mg to 251 μg/mg. Further analysis using biocrude composition analysis and combustion emission studies revealed that biocrude produced at 210 °C contains low-molecular-weight aldehydes and ketones, which are released during the low-temperature volatilization phase, where emissions peak at 155 μg/mg. In contrast, at 240 °C and 270 °C, enhanced secondary reactions such as the Maillard and amination reactions generate high-molecular-weight nitrogen-containing heterocycles (NHCs) and amides, causing organic emissions to concentrate in the oxidation initiation stage at 280–480 °C. Although emissions from biocrude produced at 270 °C are lower than those at 210 °C, product complexity increased. Biocrude produced at 270 °C exhibits optimal fuel properties and lower pollutant emissions. Nevertheless, subsequent applications should carefully consider the identification and control of complex organic emissions. This study provides a valuable reference for the fuel utilization and pollution control of KW hydrothermal biocrude.