Hydrothermal carbonisation HTC of sewage sludge under high pressures and temperatures causes the carbon compounds in the sludge to be converted into biochar. This carbon can be used both as an energy source and materially as a soil conditioner or as a substitute for fossil carbon products. Compared to the conventional dewatering, drying and incineration of sludge, the HTC process has the advantage of massively improved dewatering and drying of the coal fraction and thus a significant reduction in energy demand and the associated costs and CO2 emissions. The HTC technology therefore has both high economic and ecological potential.The project addresses the hitherto unsolved challenge of treating process water from the HTC process for the carbonisation of sewage sludge in a wastewater treatment plant and develops an innovative, resilient and transferable concept for the purification and utilisation of this problematic wastewater fraction in the context of a wastewater treatment plant.