Hydrothermal carbonization of biomass and waste: A review

The replacement of traditional and non-renewable resources by shifting towards renewable-based strategies is a strategy implemented by the European Union for a circular economy-based society. Among the various methods to produce renewable biofuels, hydrothermal carbonization is promising in terms of waste management. This technology involves thermochemical treatment of wastes at lower emperatures than other common thermal treatments such as pyrolysis or gasification. Here we review hydrothermal carbonization for managing a wide variety of biomass–wastes and obtaining value-added products. Three types of products are obtained: gases, liquids and solids. The solid carbonized product is the main product, which can be used for many applications, highlighting its use as substitute for fossil coal. Nonetheless, actual commercial plants hardly reach profitability by considering only the solid products. Therefore, this review focus on the integration of other processes. For instance, anaerobic digestion, catalytic conversion of gaseous streams and membrane technology for liquid concentration appear as the most interesting options to valorize all the products generated during hydrothermal carbonization.