Food waste to hydrochar: A potential approach towards the sustainable development goals, carbon neutrality, and circular economy

Food waste is a common organic solid waste generated worldwide in significant quantities, and its proper treatment and management practices are hindered by high moisture content. However, hydrothermal carbonisation (HTC) technique uses food waste moisture as the reaction medium and converts it into an environmentally friendly coal-like product, i.e. hydrochar. Food waste conversion to hydrochar via HTC has many benefits but a complex mechanism because each component of food waste has its own structural and chemical properties and interacts with the other components/chemical species during the process involving heterogeneous reactions, which significantly impacts the physio-chemical properties of food waste hydrochar (FWH). Due to high surface area, stability, carbon content, and regeneration capability, FWH is an attractive choice for numerous environmental applications, helps to achieve various sustainable development goals (SDGs), and supports carbon neutrality and a circular economy. Given the importance of this topic, this review provides a comprehensive analysis of the advancements in HTC technology for producing hydrochar from food waste, as well as the carbonisation mechanism of each constituent of food waste. The study also highlights the significance of different modification and activation methods used to enhance the primary drawback of FWH. We primarily intend to assess the application of FWH in accomplishing several SDGs, i.e., SDG 6.3 (pollutant removal from wastewater), SDG7 (solid fuel to generate clean energy), SDG 13 (CO2 sequestration), SDG 15.3 (soil abatement and improvement). Our primary focus is to evaluate the future perspective of FWH via CO2 emission assessment, life cycle assessment, and techno-economic assessment, along with challenges in commercializing FWH, and propose significant avenues for future research. These insights are essential for determining the economic viability and environmental advantages of FWH as a valuable resource to accomplish several SDGs, achieve carbon neutrality, and promote a circular economy.