Abstract: A process is described for dewatering sewage sludge consisting of the combination of an acidic oxidative preconditioning with an inorganic post-conditioning, in which case the preconditioning comprises an acidification of the sewage sludge and a catalytic partial oxidation by addition of a substoichiometric amount of hydrogen peroxide and iron ions at a pH≦5 and then an inorganic post-conditioning is carried out in which the acidified and partially oxidized sewage sludge is admixed with alkaline earth, and in which case, in the inorganic post-conditioning, sufficient calcium hydroxide (Ca(OH)2) is supplied so that the pH of the limed sewage sludge is in the range from at least 9 to at most 11, in order thereafter to dewater the conditioned sewage sludge mechanically.