For the recovery of phosphate from sewage sludge, a number of processes are available in different stages of development, but these are usually very costly and involve considerable effort. AVA GmbH, of Murchin, the University of Hohenheim, of Stuttgart, and the Fraunhofer Institute for Silicate Research (ISC), of Alzenau, are therefore testing a resource-efficient process based on hydrothermal carbonization. Hydrothermal carbonization (HTC) is the carbonization of organic materials in an aqueous phase under elevated pressures and temperatures.
In the current project, HTC is producing a coal sludge from the sewage sludge, whereby the coal particles contain almost all the phosphorus present in the sewage sludge. By digesting the coal with acid, the phosphorus can be brought into the liquid phase and precipitated or crystallized almost completely as a calcium-phosphate compound by adding suitable calcium compounds. The process has now advanced to the semi-industrial scale, and various strategies for the precipitation of phosphorus compounds have been tested. Initial test series showed an average plant availability. The products can be used for the production of higher-quality mineral fertilizers in the fertilizer industry. In the subsequent project step, the targeted precipitation of a high-quality fertilizer product, namely magnesium-ammonium phosphate (struvite), is currently being optimized.
Libnower Landstrasse 1
03971 | 876 90 0
Institut für Agrartechnik der Universität Hohenheim, Stuttgart
Fraunhofer Projektgruppe für Wertstoffkreisläufe und Ressourcenstrategie (IWKS)
am Fraunhofer Institut für Silicatforschung (ISC), Alzenau