Catalytic co-hydrothermal carbonization of food waste digestate and yard waste for energy application and nutrient recovery

Hydrothermal carbonization (HTC) provides a promising alternative to valorize food waste digestate (FWD) and avoid disposal issues. Although hydrochar derived from FWD alone had a low calorific content (HHV of 13.9 MJ kg- 1), catalytic co-HTC of FWD with wet lignocellulosic biomass (e.g., wet yard waste; YW) and 0.5 M HCl exhibited overall superior attributes in terms of energy recovery (22.7 MJ kgxfffd; 1), stable and comprehensive combustion behaviour, potential nutrient recovery from process water (2-fold higher N retention and 129-fold higher P extraction), and a high C utilization efficiency (only 2.4% C loss). In contrast, co-HTC with citric acid provided -3-fold higher autogenous pressure, resulting in a superior energy content of 25.0 MJ kgxfffd; 1, but the high C loss (-74%) compromised the overall environmental benefits. The results of this study established a foundation to fully utilize FWD and YW hydrochar for bioenergy application and resource recovery from the process water.

Automated summary

Hydrothermal carbonization (HTC) is a promising alternative for valorizing food waste digestate (FWD) and avoiding disposal issues. Co-HTC of FWD with wet lignocellulosic biomass, such as wet yard waste (YW), and 0.5 M HCl shows superior attributes in terms of energy recovery and nutrient recovery from process water. However, attention should be paid to the carbon loss issue during the process.