Abstract: The present invention relates to a method for the treatment of sewage in which the sewage is supplied to an aeration basin and treated therein by a biomass of aerobic microorganisms with simultaneous supply of air and addition of calcium phosphate. Thereafter, the mixture of the biomass and the deteriorations being the substrate of said microorganisms (M. L. S. S.) is forwarded to a clarifier, wherein the biomass and the effluent are separated from each other and withdrawn separately. The calcium super phosphate is advantageously added in an amount of 0.35 mg/g-2 mg/g M. L. S. S. as a 10% aqueous slurry.