The thickened sludge is mixed with polyelectrolyte. The resulting mixture is then mixed with the Rhenipal A - a non reactive product for pre-conditioning - (average addition rate 20-30% of dry substance) simply to achieve a more economical basis for the later post stabilisation. This pre-conditioned blend is consequently de-watered by means of a centrifuge or belt press. The resulting cake is then mixed with Rhenipal B or C for stabilisation.