Use of stillage from alcohol production

摘要

The invention relates to a method of comprehensive use of stillage originating from bio alcohol mass production, while the end products of the process are biogas, dried stillage waste with low salt content, granulated sludge from anaerobic digestion, solid fertilizer on the basis of magnesium ammonium phosphate, elementary sulphur, sludge from aerobic final treatment, and waste heat from process water. According to the method, insoluble fraction is removed from the raw stillage by means of centrifugation, while remaining dispersed substances are removed from liquid fraction by air flotation, centrifugation, vacuum filtration, or a combination of these processes in the secondary separation step. Thickened dense fractions from both of these steps, having low salt content, are further processed to feed of high nutritional value. Liquid fractions from both of these steps are blended and acidified under controlled conditions at pH ranging between 4.8 and 9.2. Then, they arc taken to anaerobic digestion to the reactor with granulated biomass, wherein the said liquid fractions enter the reactor in its bottom part. The biomass consists of acidifying and methanogenic bacteria and the anaerobic digestion is performed at the temperature between 25 and 40°C, residence time 2 to 50 hours, and the granulated biomass loading rate between 5 to 105 COD/m -3 .day -1 . The accumulated granulated sludge is removed and dried. Biogas exhausted from the anaerobic reactor head is biologically desulphurized, and elementary sulphur is produced as a by-product. The biogas is then 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. 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. Furthermore, the invention relates to the device needed to perform the method of the invention.