Fate of nutrients during hydrothermal treatment of food waste

Hydrothermal carbonization was evaluated as a food waste valorization strategy to obtain hydrochar and recover nutrients. In the hydrothermal treatment, the temperature (170-230 degrees C), reaction time (5-60 min), and addition of HCl (0.1-0.5 M) during the reaction were analyzed. Compared to the feedstock, hydrochar showed an increase in fixed carbon (greater than 45%) and a decrease in ash content (<7%), along with a higher heating value (18.6-26.2 MJ/kg), which would allow for its application as a biofuel for industry according to ISO/TS 17225-8. The hydrochar obtained using plain carbonization showed 75% P and 40% N of the feedstock content, whereas the HCl-mediated treatment (0.5 M) solubilized most of the P, K, and N in the process water (98% P as PO4-P, 98% K, and the total N content as NH4-N (16%) and organic-N) operating at 170 degrees C for 60 min.