Product from the nutrient recovery of biogas fermentation residues. After all organic matter has been separated, phosphorus salts are precipitated by adding lye and milk of lyme. Due to the increased pH value, phosphorus combines with magnesium, calcium, potassium and other elements and forms crystals. After the crystals have sunk, the phosphorus-containing sludge is pressed out in a chamber filter press. The question now is how this phosphorus fertiliser can be used further (pelletisation, granulation, mixing with other materials, etc.).