HTC consists in applying high temperatures and pressures to biomass or other residues in the presence of water, which results in two main products: a coal-like product (hydrochar) and water-soluble products. This process allows converting different wet biomass streams, such as sewage sludge, into fuels and other substances of industrial interest including a nearly 100 % recovery of phosphorus.
The economic benefits of this process consist in the production of biocoal, thus of activated carbon, but also in the recovery of phosphorus, used as fertilizer and the separation of the heavy metals. During the carbonization process, 95% of heavy metals are embedded in the coal, thus offering the possibility to remove them from the liquid phase with its nutrients and valuable materials. The heavy-metal-containing HTC coal obtained by separation is activated and recycled as adsorbent into the sewage treatment plant.