Unlike other waste conversion systems, hydrothermal carbonization requires wet waste with a higher
than 70% moisture content. This makes it most suitable for organic waste, especially certain types of
food waste and sludges.
Relative to other thermal conversion methods, reactors are kept at relatively low temperatures
(around 400°F). The primary output product is hydrochar as well as byproduct liquids with high COD
(chemical oxygen demand). In addition, some gas is produced, mostly composed of carbon dioxide.
Hydrochar is a solid output and possible lignite-grade coal alternative. Hydrochar may also be able to
be used as a soil amendment and the process may be an effective tool for carbon sequestration,
though many uncertainties remain as hydrothermal carbonization is a relatively nascent conversion
Hydrothermal carbonization has not been used in large-scale projects. It is mostly still used and
studied in laboratory-scale tests.