Use of ethanol production and stillage processing residues for biogas production
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In Latvia, ethanol is produced mainly from wheat grains. The production process involves the formation of the by-products of wheat bran, grains residues and stillage. By-products from production of alcohol distilling dregs (stillage) contain much organic matter therefore could be useful for the production of the biogas The product with high protein content usable for feed can be produced from the stillage too. A liquid residue is formed during the production process. Purpose of study is the assessment of the methane volume obtainable from the stillage processing residue mixed with wheat brans and grains residues in anaerobic fermentation process and from wheat brans and grains residues mixed only with inoculum. Investigation was provided in 16 bioreactors operated in batch mode at 38°C. Stillage processing residues mixed with the wheat brans and inoculum were filled into 4 bioreactors, mixed with grains residues were filled into 4 bioreactors and only inoculum was filled into two bioreactors for control. Wheat brans with inoculum were filled into 3 bioreactors. Into others 3 bioreactors were filled grains residues with inoculum. The yield of biogas from wheat brans was 1.151 L g -1 DOM and methane 0.593 L g -1 DOM after 30 days of anaerobic digestion. The yield of biogas from wheat brans with stillage processing residue was 1.098 L g -1 DOM and methane 0.600 L g -1 DOM. The yield of biogas from grains residues was 0.915 L g -1 DOM and methane 0.451 L g -1 DOM. The yield of biogas from grains residues with stillage processing residue was 1.01 L g -1 DOM and methane 0.523 L g -1 DOM. The study demonstrates that the investigated products are very good raw material for the production of methane. Stillage processing residue acted as a catalyst for the process.