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    Optimierung der Konservierung und der anaeroben Konversion von Zuckerrüben zur Nutzung in flexiblen Biogassystemen
    (2019) Kumanowska, Elzbieta Joanna; Jungbluth, Thomas
    Biogas production is well suited to balance the fluctuating electricity production from the renewable energy sources sun and wind. Due to the currently unfavorable conditions in the renewable energy supply policy in Germany, time is spent looking for alternatives for electricity production from biogas. The preparation for natural gas quality for fuel production or for natural gas grid injection would be such an alternative but requires process improvements to reduce costs. One approach would be to use two-stage biogas production, as there is a high methane content in the produced biogas, thus reducing the cost of processing to natural gas quality. A suitable substrate for both applications would be sugar beet, due to its fast biodegradability and good methane yields. The preservation of sugar beets for year-round provision has so far been problematic because it can cause high losses. In addition, it can cause process biological problems, if it is used in high proportions. In the context of this work, the use of sugar beets for biogas production was tested using these promising methods. For this purpose, storage experiments were carried out and new storage methods for the practice were developed and tested, all of which are primarily aimed at the use of sugar beet silage effluent. Practice-based point-feeding experiments were used to test its suitability for demand-oriented biogas production. Furthermore, the optimization of the two-stage biogas production from sugar beet was carried out. For this purpose, an experiment was conducted in the biogas laboratory to determine the optimum hydrolysis pH during the fermentation of sugar beet silage. In order to develop a new, optimal method for the storage of sugar beets, further knowledge regarding the process of ensiling sugar beets, the silage effluent formation and the influencing parameters was required. Therefore, mass balances were carried out in the column experiments in the laboratory of the State Institute of Agricultural Engineering and Bioenergy to determine the influence of the parameters stack height and sugar beet chips size on the silage effluent formation during the ensiling process of the chopped sugar beets. Silage effluent was produced in amount about 50% of the stored mass. About half of the silage effluent production took place during the first three weeks of storage. The produced silage effluent was characterized over the entire storage time by extremely high COD-values of 250 g l-1. The parameters stack height and particle size had no significant influence on the mass balance. On the basis of the results of the column experiments, a mobile and a stationary method on a technical scale for the storage of sugar beets were investigated. In the mobile variant, the flexible tanks, washed, chopped sugar beet was ensiled. Considering the goal to maximize silage effluent yield, the ensiling of chopped sugar beet was superior to the ensiling of whole beet. Also, soil removal is advantageous for silage effluent production as well as for silage quality. Storage in the stationary pit silos proved to be technically advantageous, and it promises to be well suited for the intended applications when in combination with washed and chopped beets. The application of produced silage effluent for demand-oriented biogas production was carried out at the research biogas plant of the University of Hohenheim. The system’s response observed as an increase in biogas production took place a few minutes after the point feeding with sugar beet silage effluent. As a result of the point feeding, the produced volumetric biogas flow rate was doubled without endangering the stable biogas plant operation. The maximum gas production was reached after about 1:45 h. In this work, a concept for the use of sugar beet for the production of high calorific biogas was tested, based on the two-stage anaerobic digestion. The experimental plants consisted of a horizontal stirred tank reactor for hydrolysis and two combined fixed bed reactors used as a methane reactor. The influence of the pH value in the hydrolysis stage on the anaerobic digestion of sugar beet silage was tested. High degradation rates and methane yields demonstrated the overall suitability of this system for sugar beet silage digestion. The best compromise of the process parameters degradation rate in complete system and methane yield was achieved at a pH value of 6. The investigation carried out for this work shows, that the concept of a new sugar beet storage method, with a focus on sugar beet silage effluent production, is well suited for demandoriented biogas production as well as for the production of a high calorific biogas by means of the two-stage biogas process.