Abstract: A process for treating a waste liquid which is obtained from a fermentation process, e.g., an alcohol fermentation, and contains organic and inorganic substances which are useful as fertilizer, is provided which includes combusting a concentrate of the waste liquid and bringing the combustion products containing the ashes which are formed from the inorganic substances and the hot combustion gases into direct contact with a fresh portion of the waste liquid. Thereby the liquid is concentrated by evaporation and a slurry of the ashes in the concentrated waste liquid is formed. The slurry is separated into a solid sediment containing the minerals and a part of the organic components of the liquid and a concentrates mother liquid, at least a portion of which is combusted as the concentrate. By drying the sediment with agitation, a granulate which can be used as a fertilizer can be produced.