Sustainable resource recovery and process improvement in anaerobic digesters using hydrochar: A circular bio‐economic perspective

Abstract Hydrothermal carbonization (HTC) is a promising technology for waste valorisation and nutrient recovery to achieve sustainability. HTC converts organic waste into hydrochar, a carbon‐rich solid with numerous surface functionalities that can be used for energy and wastewater treatment. In this review, we highlight the potential of hydrochar‐based technology for improving the performance of anaerobic digestion (AD) systems and downstream applications of nutrient‐laden hydrochar. We identify knowledge gaps in hydrochar production, performance in AD systems and nutrient recovery, including the need for larger‐scale production facilities, multielement adsorption studies, and computational modelling. Techno‐economic analysis and life cycle assessment of hydrochar applications are critical to evaluating the commercial viability of this technology. Overall, hydrochar‐based technology offers a sustainable solution for waste management and resource recovery, with potential socioeconomic benefits for developing economies. The deployment of hydrochar‐based technology will directly address key issues highlighted in the United Nations' Sustainable Development Goals such as Clean water and sanitation (SDG 6); Zero hunger (SDG 2); and Climate action (SDG 13) thereby contributing to a more sustainable future.