Abstract: In the case of mono sewage sludge incineration, a solution may be created that enables sewage sludge ash, which may still have a low proportion of unburned carbon, to be discharged from a mono sewage sludge incineration plant. This is achieved by a method for the post-combustion of sewage sludge ash obtained in a mono sewage sludge incineration in a rotary kiln by means of a hot and a low oxygen content, such as an oxygen content of 5-10 vol. % oxygen. The gas stream from the rotary kiln may escape the sewage sludge ash and is fed to the gas flow. This sufficiently hot gas flow may cause oxidation or afterburning of unburned carbon contained in the sewage sludge ash.