HYDROTHERMAL CARBONIZATION – A CRITICAL OVERVIEW OF ITS ENVIRONMENTAL AND ECONOMIC SUSTAINABILITY

Circular economy and waste valorization are intertwined concepts crucial for sustainable development. From this perspective, the search for environmentally friendly processes that supply energy and materials from waste is growing. Hydrothermal carbonization (HTC) is a promising thermochemical process that converts waste into a solid product named hydrochar. Hydrochar, given its physicochemical characteristics, has the potential for several applications (e.g., energy production, soil amendment, and adsorption of water pollutants), which has boosted the research interest in HTC. Several studies have focused on optimizing HTC conditions and evaluating the environmental and economic aspects of this process through life cycle assessment (LCA) and techno-economic analysis (TEA), respectively. However, despite the increasing number of review articles about feedstocks, optimal conditions, and reaction mechanisms of HTC, a critical review focused on HTC sustainability is lacking in the literature. Therefore, this review provides a critical outlook on LCA and TEA studies concerning HTC to verify its environmental and economic sustainability from a broad perspective. Overall, some studies have demonstrated the environmental and economic feasibility of HTC, as evidenced by the current technology readiness level (TRL) of this thermochemical process, which has reached industrial implementation in the last decade. Moreover, this waste valorization approach can evolve into a multi-product biorefinery, in addition to becoming a potential contributor to the achievement of some Sustainable Development Goals (SDGs).