Optimisation of biogas production from sugar beet pulp

During the processing of sugar beets, by-products as sugar beet pulp (SBP) and sugar beet tail (SBT) are coming out of production process. The SBP is coming out during the sugar extraction process whilst the SBT will be produced during cleaning and cutting sugar beet. Until now the most of them were used as an animal food, but unfortunately the consumption of such by-products as food fed to livestock is continuously reducing, that allows the usage of SBP and SBT for energy production through anaerobic digestion in biogas plants. Aims of the research project: To determinate a specific methane yield of sugar beet pulp (SBP) and sugar beet tail (SBT) in mono digestion. To identify the most suitable mix of sugar beet by-products with a mixture composed of cattle manure, maize silage, sudan grass, clover grass. To explore the influence of drying on specific methane yield of sugar beet pulp Methods: Substance and energy turnover during anaerobic digestion were measured in eudiometer batch experiments at 37.5 °C that was conducted according to DIN 38414/Teil 8 (1985) bzw. VDI 4630 (2006). Results: The results of the present experiments demonstrate that mesophilic fermentation of by-products from sugar beet processing with the aim of producing biogas is viable and sensible. The development of the cumulative specific methane yield showed that the micro organisms were not inhibited and were well adapted to the new substrates. In the present project, high values for the specific methane yield were achieved ranging between 430 and 480 lN kg-1 VS. Supplementation of by-products to the mixture of energy crops and animal manure: The supplementation of 70 % SBT to the mixture of energy crops and animal manure resulted in an increasing of specific methane yield of the mixture at 6%. The addition of 30% and 50% SBT to this mixture showed only a little increasing of specific methane yield at 1-2%. The added methane yield of the mixture was calculated as difference between calculated methane yield on the basis of methane yield of mono digested substrates and measured methane yield of the mixture. The additional methane yield could be a result of reciprocal complementation of used substrates. The supplementation of SBP to the mixture of energy crops and animal manure produced no additional methane compared to calculated specific methane yield of the mixture, whereas the total methane yield of the mixture is rising. Drying of by-products: It was also demonstrated that drying of sugar beet pulp and sugar beet tail significantly reduced the achieved methane yield at 30 to 43 % respectively. A cause of the decreasing of specific methane yield could be an outgassing of volatile fatty acids from beet pulp and sugar beet tail silage during the drying process.