NOVELTY - Use of stillage from bio alcohol mass production, by centrifugation and subsequent drying of insoluble substances.    USE - The stillage is used as food supplement.    ADVANTAGE - By means of centrifugation and subsequent drying of insoluble substances, cattle feed of high nutritional value is obtained that has lower salt content in comparison to the conventional feed made of thickened stillage.    DETAILED DESCRIPTION - Use of stillage from bio alcohol mass production, comprises removing insoluble fraction from raw stillage by centrifugation, while remaining dispersed substances are removed from liquid fraction by means of air flotation, centrifugation and/or vacuum filtration in the secondary separation stage. Thickened dense fractions from both of these steps, having low salt content, are further processed to feed of high nutritional value. The liquid fractions from both of these steps are blended and acidified under controlled conditions at pH 4.8-9.2 and taken to anaerobic digestion to the reactor with granulated biomass. The liquid fractions enter the reactor in its bottom part. The biomass contains acidifying and methanogenic bacteria, and the anaerobic digestion is carried out at 25-40degreesC for 2-50 hours, and granulated biomass loading at 5-105 chemical oxygen demand (COD)/m-3-day-1. The accumulated granulated sludge is removed and dried and biogas drawn off from the anaerobic reactor head is biologically desulfurized with production of elementary sulfur as a by-product. The biogas is then drawn off to be used energetically. From the liquid fraction, nitrogenous substances are removed by dosing magnesium chloride and phosphoric acid resulting in precipitation of insoluble magnesium ammonium phosphate that is separated and removed as a high-quality fertilizer and the liquid fraction is further taken to the aerobic final treatment where sludge is separated. After having been thickened, the sludge can be utilized in agriculture. From the aerobic final treatment plant treated water having parameters meeting requirements for release to watercourse is taken. It is then discharged or re-used in the process after an optional distillation. An INDEPENDENT CLAIM is included for a device to perform the inventive method.