Disposal of wastewater treatment residues

Municipal wastewater disposal by the HTC method (hydrothermal carbonization) is a process that converts wet biomass, including sewage sludge, into high-quality carbon (so-called biochar) by heating it in an aqueous suspension under pressure. This process resembles natural geological processes but is much faster, and the resulting biochar can then be used for energy production—for example, by gasifying it to synthesis gas that powers cogeneration units.

How does HTC work?

• Heating
  Wet wastes, such as sewage sludge, are heated in a sealed reactor under elevated pressure.
• Conversion
  Under elevated temperature (180–250 °C) and pressure, the organic matter in the waste undergoes chemical transformation.
• Biochar formation
  The HTC process yields a solid product—hydrochar, i.e., biochar.
• Energy production
  Optionally, the resulting biochar can be gasified to produce synthesis gas, which is then used in cogeneration to generate electricity and heat.

Key aspects and benefits:

• Waste conversion
  The HTC method enables the conversion of wet organic wastes, such as sewage sludge, into a high value-added product—biochar.
• Biomass upgrading
  This process is analogous to natural geological coal-forming processes, but it occurs in a much shorter time.
• Energy use
  Biochar can be used as a fuel, e.g., via gasification, allowing energy recovery in the form of heat and electricity.
• Functional materials
  Beyond energy use, HTC biochar can have other applications—for example, as carbon materials with specific properties.