Through the process of hydrothermal carbonization (HTC), biomass and other residues are subjected to high temperature and pressure in the presence of water which results in two main products: a coal-like product (hydrochar) and water-soluble products. In essence, the HTC process allows different wet biomass streams, such as sewage sludge, to be easily converted into fuels and substances with high market value, including a nearly 100% recovery of phosphorus.
The economic benefits of the HTC process are clear: not only does the process allow for a clean, environmentally-safe disposal of biomass and mixed waste, but also produces biocoal that serves as fuels and recovers phosphorus, which can be used in fertilizers and the separation of heavy metals. In fact, during the hydrothermal carbonization process, over 95% of the heavy metals are embedded in the coal which makes it easier to remove them during the liquid phase. The heavy metal-enriched HTC coal can then be separated, activated and recycled into the sewage treatment plant.