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Abstract Sustainable biorefinery depends on the development of efficient processes to convert locally abundant, energy-rich renewable biomass into fuels, chemicals, and materials. Hydrothermal processing has emerged as an attractive approach for wet biomass conversion with less environmental burden. Although considerable efforts have been made in sustainable biorefinery by unitizing innovative technologies at a laboratory scale, its scaling-up is still impeded by the biomass heterogeneity. This article critically reviews the recent advances in hydrothermal carbonization and liquefaction technologies for the sustainable production of hydrochar and aromatics from different biomass wastes. Three main aspects, including lignocellulose-/lignin-rich feedstock, operating conditions, and design of liquid/solid catalysts, are critically reviewed and discussed to understand the reaction mechanisms and system designs for increasing the yields of aromatics and improving the properties of hydrochar. The latest knowledge and technological advances demonstrate the importance of identifying the physical and chemical properties of feedstock. The science-informed design of hydrothermal technology and optimization of operational parameters with reference to the biomass properties are crucial for the selective production of value-added chemicals and multifunctional hydrochar. This review identifies current limitations and offers original perspectives for advancing hydrothermal processing of biomass towards carbon-efficient resource utilization and circular economy in future applications.

Anaerobic digestion (AD) is a widely used technology to valorise food waste for biogas production yet a considerable amount of digestate remains under-utilised. Sustainable management and recycling of the nutrient-rich food waste anaerobic digestate (FWD) is highly desirable for closing resource loop and actualising circular economy. This work reviews the distinct properties of FWD and the existing treatment technologies. FWD shows great prospects as a nutrient source for microalgal cultivation and biofuel production. Emerging technologies such as thermal conversion (e.g., pyrolysis and hydrothermal treatment) of FWD into value-added products such as functionalised biochar/hydrochar with diverse applications would be attractive and warrant further research investigation. Integrated AD with subsequent valorisation facilities is highly encouraged to achieve complete utilisation of resources and reduce carbon emissions.