Integrated hydrothermal carbonization to enhance resource and energy recovery from food waste

Abstract

Food wastage has significant repercussions, such as hindering efforts to combat hunger, contributing to unsustainable resource exploitation, and accounting for approximately half of the greenhouse gas emissions from the entire agri-food system. Converting food waste (FW) into valuable resources and energy provides significant environmental, social, and economic benefits, which are crucial for establishing a circular bioeconomy. Traditional methods of FW valorization, such as landfilling, incineration, and anaerobic digestion, have advanced, with current research and policies increasingly focusing on more sophisticated techniques like hydrothermal carbonization (HTC). HTC involves carbonizing wet biomass at high temperatures and pressures to produce hydrochar, a solid phase, and a nutrient-rich liquid phase. Transforming food waste into useful products like biochar, syngas, and nutrient recovery (e.g., phosphates from waste) addresses the role of HTC in supporting the circular economy and emphasizes the shift from waste disposal to resource recovery. This state-of-the-art review explores how HTC can be integrated with other technologies such as anaerobic digestion, aiming to optimize energy and material recovery with improved properties. The latest advancements in the optimization of HTC process variables, catalytic enhancements, and downstream applications are discussed. Besides, by highlighting the latest life cycle assessments and techno-economic analyses, the economic viability, scalability, and environmental benefits of HTC integration are assessed. Presenting emerging research on novel conversion pathways and potential synergies between HTC and other industries (e.g., agriculture, energy storage) would highlight how the field is evolving to create more versatile uses for HTC byproducts.