Chapter 3: Trends of Food Waste Treatment/Resources Recovery with the Integration of Biochemical and Thermochemical Processes

Urgent efforts and appropriate measures to utilise food waste (FW) for holistic exploitation of resources are needed. This chapter briefly reviews the global FW generation scenario among several selected high economic and low developing countries. It further highlights the common globally adopted treatment techniques, such as landfilling, composting, heat–moisture reaction, and anaerobic digestion, their challenges, and associated merits for FW treatment. This review discusses considerations for optimal resource generation from FW and highlights the selection of three conceptual routes. The first route proposes anaerobic digestion and pyrolysis, where valuable products such as biochar can serve as additives in anaerobic digestion for optimal biogas production and stabilised digestates. In addition, in the upstream coupling section, pyro-oil and syngas can be used in anaerobic digestion for biomethanation enhancement. The performance of the syngas biomethanation in anaerobic digestion reflects on hydrogen and carbon monoxide concentrations. A higher concentration of hydrogen could accelerate the carbon monoxide degradation rate and vice versa. The second route offers a direction for high water content FW valorisation via hydrothermal carbonation (HTC) combined with anaerobic digestion and vice versa to obtain hydrochar and valuable products, such as hydro-oil, high biogas, and enriched digestates. Previous studies showed that hydrochar could mitigate ammonia in anaerobic digestion and enhance methane generation compared with pyrochar. For high hydrogen syngas generation, the gasification technique coupled with anaerobic digestion was proposed for FW and associated residues in the third route, thus offering sustainability towards increased bioenergy production. This review stimulates the possibility for the development of the baseline approach on FW and associated residues in different technology (anaerobic digestion, pyrolysis, HTC, and gasification) combinations for optimal resource recovery.