Browsing by Subject "Biogasanlage"

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    A full-scale study on efficiency and emissions of an agricultural biogas plant
    (2013) Nägele, Hans-Joachim; Jungbluth, Thomas
    In this study we focused on process engineering for the conversion of biomass, and utilization of the gas obtained by fermentation. Several topics regarding efficiency and emissions have been addressed by conducting intensive and long-term measurements. In detail, our objectives were (1) to conduct long-term measurements of the electric energy consumption of the biogas plant and its individual components and examination of energy-saving potentials; (2) to develop a method to measure mixing quality in the digester and to examine the mixing quality by measuring nutrient distribution in the digester with different agitator setups; (3) measure the influence of maintenance strategies on efficiency and emissions at long-term operation in practical application; (4) examine the efficiency of an external biological desulfurization plant under practical conditions to enhance biogas fuel quality. The results of electric energy measurement over a period of two years showed that a percentage of 8.5% (in 2010) and 8.7% (in 2011) of the produced electric energy was required to operate the biogas plant. The consumer unit agitators with 4.3% (in 2010) and 4.0% (in 2011) and the CHP unit with 2.5% (in 2010 and 2011) accounted for the highest electrical power demand, in relation to the electric energy produced by the CHP unit. Calculations show that the agitators consumed 51% (in 2010) and 46% (in 2011) of the total electric energy demand. The results stress the need for further research in the fields of substrate homogenization in biogas plants in order to reduce the demand for electric energy. Based on the results of electric energy consumption, follow-up studies have been conducted on nutrient distribution, which depends on agitator type and agitator regime. The investigation showed that significant differences in local concentrations of organic acids, which are not correlated to DM content, are found in dependence on agitator type and agitation regime. Measurements on electric energy consumption of the different agitator types verified that, depending on the agitator type, the saving potential rises up to 70%. The results for emissions and efficiency of the CHP unit confirm the fact that after readjustment of the air-fuel ratio (Lambda value), the emission values for NOx decline while CO increases. However, the emission-optimized operation mode leads to lower engine efficiency. The permanent measurements proved their legitimacy showing various emission deviations from the limiting values prior and post maintenance. In addition, the results show that by monitoring the lubricating oil quality, the oil change intervals can be maximized, while ensuring that engine performance is not endangered. This allows the operator to reduce maintenance expenditures while minimizing wear. To increase engine efficiency, the reduction of the lambda value combined with exhaust gas scrubbing and exhaust gas power generation is a promising approach. However, that would presuppose a permanent and almost total removal of H2S from the biogas. The fourth part of the study examined the technical and economic feasibility of a Fixed Bed Trickling Bioreactor (FBTB) for external biological desulfurization of biogas. In contrast to well-established biological methods to oxidize H2S, the FBTB allows removal of these from the biogas process, thus ensuring a constant low H2S concentration in the biogas. The FBTB showed H2S removal efficiencies (RE) of 98% at temperatures between 30-40°C. A major decline in RE in a range of 21-45% was observed when temperature in the FBTB dropped to a range of 5-25°C. The results revealed that different pH values of the percolation fluid and air ratios have little effect on RE. The practical use of the investigated FBTB system is an interesting technological alternative as disadvantages of internal biological desulfurization methods are being avoided. Due to high expenditures for operation resources and maintenance for FBTB operation during the research, a technical optimization is necessary to ensure economical operation. The results presented in this thesis show that the scientific instrument ?research biogas plant? is the ideal supplement to methods such as laboratory scale research and measuring programs. Research at full scale offers an entirely new opportunity to determine the interaction of process technique and process biology and to conduct long-term studies of gas utilization. Compared to measuring programs at commercial biogas plants, the research biogas plant has the advantage of being significantly better equipped with measurement technologies and that economic success is not the overall goal.
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    Influence of biogas-digestate processing on composition, N partitioning, and N₂O emissions after soil application
    (2023) Petrova, Ioana; Pekrun, Carola
    The ever-growing need for agricultural products represents a global issue, particularly with a view to the limited availability of cultivable land. According to the latest estimates, the arable land per capita decreases and, in 2050, is expected to account for about 60% less than in the 1960s. In order to meet the demand, agriculture has evolved into industrial-like structures. This development often goes along with nutrient surpluses (e.g., excess of nitrogen and phosphorus) and increased emissions, caused by mismanagement and inappropriate agricultural practices (e.g., over-fertilization). Biogas plants offer a possibility to valorize organic residues and wastes, but potentially aggravate this problem since additional organic residues (referred to as digestates) with considerable nutrient contents are generated as by-products. A simple approach to adjust nutrient levels in the affected regions is the transfer of manures and digestates. However, to make this feasible, a reduction of water content (and consequently of total mass/volume) of digestates is required. Up to now, various techniques for digestate downstream processing are available. Previous research mainly addressed single processing stages or differences between feedstock mixtures. Only limited information was found about the influence of a completed downstream processing on total mass reduction and nitrogen concentration in digestate. Studies about the (gaseous) N losses that occur after the application of the respective intermediate and final products to soils were equally scarce. Therefore, the aims of the current doctoral thesis were to determine (i) the mass reduction achieved by the gradual removal of water within competing processing chains, (ii) the nitrogen partitioning after every single processing step and its recovery in the end products, and (iii) the amount of greenhouse gases (especially N₂O) released after the application of intermediate and end products to soils in comparison to untreated, raw digestate. For that purpose, two commercial, full-scale biogas plants were examined, which completely processed either the solid or the liquid fraction after mechanical screwpress separation of raw digestate. The separated solid fraction was subsequently dried and pelletized, while the liquid fraction was treated by vacuum evaporation with partial NH₃ scrubbing. As final products, digestate pellets and N-enriched ammonium sulfate solution were generated. Calculation of a mass flow balance served as the basis for determining (total) mass reduction, the partitioning of fresh mass and nitrogen during digestate processing, and the recovery of initial N in the products. Additionally, the environmental impact of utilizing digestate as an organic fertilizer was studied by measuring the N₂O release after application to soil under field and laboratory conditions. A further in-depth analysis was performed to observe the main factors influencing the production and release of climate-relevant N₂O from digestate pellets. It was found that the mass reduction caused by water removal during subsequent processing accounted for 6% (solid chain) and 31% (liquid chain) of the total mass of raw digestate. Liquid processing required 40% less thermal energy per ton of water evaporated than solid processing. At the end of the downstream processing, the recovery of initial nitrogen in pellets was 33% lower than in ammonium sulfate solution. Regarding the environmental impact of digestate application to soil, mechanical solidliquid separation showed the potential to reduce N₂O emissions. Contrary to expectations, pelletizing of dry solid boosted the emissions, which was linked to the properties and composition of the pellet. Here, indigenous microbial activity triggered N₂O production and release from denitrification immediately after wetting. Overall, the present work has shown that the subsequent processing of separated solid or liquid digestate generates different products with individual benefits and challenges. Solid digestates are characterized by a high share of recalcitrant organic compounds and therefore can serve, e.g., as soil improver. After processing to pellets, they can be easily transported, stored, and commercialized. However, it is questionable whether the pelletizing process is advisable, since pellets emitted a considerable amount of GHGs during utilization. Liquid processing produces ammonium sulfate solution, which can be utilized as a valuable inorganic fertilizer rich in plant-available N. Besides the discussed advantages, a final decision for or against digestate processing always depends on individual factors, such as local situation and financial means. Smart decision-making must include fertilizer properties, technological performance, and economic feasibility. With a view to future research, additional aspects were identified, such as returning to a laboratory-scale biogas plant for more accurate digestate sampling and analysis, consideration of digestate storage and transport, and economic evaluation of the entire digestate value chain including the assessment of digestate fertilizer value (expressed as e.g., N use efficiency or N fertilizer replacement value).
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    Untersuchungen zum Potential biotechnologischer Methoden zur Inaktivierung von tier- und humanmedizinischen Krankheitserregern der Schutzstufe 3
    (2017) Hartmann, Nadja; Hölzle, Ludwig
    With the increasing use of slurry in biogas plants there remains the question of the extent of the potential hazard for human and animal beings due to infectious pathogens which enter biogas plants through contaminated substrates. The aim of this doctoral thesis was to establish a suitable approach for the inactivation of infectious and zoonotic agents. Therefore, the fermentation process itself as well as potential pre- and post-procedures which can contribute to the inactivation of pathogens were analyzed. First of all, a laboratory process was established concerning an increase of temperature and dwelling time to analyze the consequences for the inactivation of the pathogens. Additionally, the possible impact of pasteurization and diverse substrates on the inactivation of different pathogens were investigated. The influence of storage to the contaminated substrates after the biogas process was also considered. Due to the distinctive tenacity of the bovine tuberculosis pathogens M. bovis and M. caprae as well as the paratuberculosis pathogen M. avium ssp. paratuberculosis (MAP). Those pathogens are used within this study. As another major cause of zoonotic, the obligate intracellular bacterium C. burnetii was used. This bacterium occurs also in high concentrations in slurry from animal populations which are tested positively of coxelliosis. Beside bacterial infection and zoonotic pathogens, viral agents are playing a major role, such as the highly contagious foot-and-mouth disease (FMD) and the virus classical swine fever (CSF). FMD was substituted by the equine rhinitis A virus (ERAV) and CSF by the bovine virus diarrhea (BVD). The results can be transferred to FMD and CSF because of the close phylogenetic relation of the surrogate viruses. The inactivation studies of M. bovis through storage over 21 days showed that there are besides the substrate and temperature specific differences also intraspecific differences. This fact should be included in future selection of the inactivation methods. At temperatures of 4 and 20 °C it was possible to detect mycobacteria throughout the entire experimental duration time. At 37 °C already after seven days no pathogens could be detected. Mycobacteria which were suspended in PBS were detectable during the whole experimental time. The storage studies with ERAV and BVDB were performed over 15 days with the different substrates. At low temperatures of 4 and 20 °C there was no significant virus reduction detectable. At higher temperatures (40 – 42 °C) after three days, a significant virus reduction for ERAV was detectable and a complete inactivation for BVD, respectively. Additionally, it could be proven, that the substrate has no impact on the reduction of ERAV. Experiments using ERAV absorbed membranes showed a substrate dependent inactivation at 40 °C. As a consequence, those adsorbed membranes were used for a biogas plant in a laboratory dimension for 24 hours in the style of the Hohenheim biogas yield test. The reduction of the titer could be seen at least after 120 minutes. Furthermore, it could be shown, that there is a significant reduction of the ERAV titer between 120 minutes and 24 hours. In regard to the success of pasteurization dependent on the substrate, no substrate dependency was found for mycobacteria. In experiments with M. bovis and M. caprae no pathogens could be found after 30 minutes incubation time at 60 °C. Investigations with MAP showed after 360 minutes at 70 °C no culturable pathogens. Pasteurization studies with C. burnetii showed no reliable data. The pasteurization studies of ERAV in dependence of three different substrates showed, that the reduction was only caused by temperature. Therefore, BVD was only combined with one substrate which had the most heterogenic composition. Concerning ERAV, after 15 minutes at 55 °C a significant reduction of the titer was detectable. For BVD at 40 °C no significant virus reduction was achieved, but a dependency of the substrate was proven. A significant reduction of the titer was achieved after 60 minutes at 45 °C in the substrate suspended viruses, 30 minutes at 50 °C, and for in cell culture suspended viruses after 60 – 120 minutes at 50 °C. The results of this thesis show the massive effect of the properties of individual pathogens on the duration of inactivation. This subordinate role should be considered within the choice of the suitable biotechnological process. To reduce the infectious risk the procedure should always orientate at the worst case: the pathogen with the highest tenacity.
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    Untersuchungen zur Verwertbarkeit von Pferdemist im Biogasprozess
    (2014) Mönch-Tegeder, Matthias; Jungbluth, Thomas
    The increasing use of energy crops as the main feedstock and the resulting occupancy of arable land is the central point of criticism of the population in biogas production. Although waste and residues provide significant energy potentials, the conversion of these materials in the biogas process has not been established to date. Significant barriers are the widely varying composition of these materials and their substrate properties. In general, the residues contain a high percentage of fiber, which rises great challenges for the existing process technology. This work aimed to address these challenges by investigating the suitability and usability of the fiber-rich substrate horse manure for biogas production in continuously operated agricultural biogas plants. The study was divided into three consecutive 1. Investigation of the composition and usability of horse manure with different bedding materials and determination of the specific methane yields also taking into account the aging process degradation of horse manure; 2. Determination of the impact of mechanical pretreatment of the substrate with the cross-flow grinder on the specific methane yield and degradation kinetics of commonly used energy crops and horse manure in laboratory-scale; 3. Studies on the feasibility of horse manure in full-scale biogas processes and the effects of mechanical treatment at the research biogas plant "Unterer Lindenhof”. The use of straw-based horse manure in the biogas process is feasible. However, contaminations with alternative bedding materials due to their low degradability must be avoided. Furthermore, a substantial loss of methane potential could be detected due to the storage and meanwhile aerobic degradation. As a result of the high dry matter content and low levels of essential micro- and macro-nutrients, horse manure should only be utilized in biogas plants with suitable co - substrates. The mechanical treatment of silage and horse manure with the cross-flow grinder resulted in a significant reduction in particle size and increased substrate surface. However, no significant changes in the specific methane yield of the investigated silages were observed. Due to the increase of the substrate surface the degradation rate of the grass silage and whole crop silage accelerates. The mechanical disintegration of horse manure resulted in a significant increase of the specific methane yield and a significant improvement of the degradation kinetics. When considering the energy balance of the disintegration, a positive result could only be obtained for the processing of the fiber-rich substrates. Accordingly a previous disintegration of silage for biogas production is not recommended. The results from the investigation of the usability of untreated and disintegrated horse manure in the full-scale biogas process show that the use of horse manure without previous treatment causes serious procedural problems and results in insufficient degrees of degradation. The mechanical pretreatment guarantees a plant operation without failures during this trial. Additionally a complete substrate utilization can be achieved due to the treatment. The additional energy expenditure for the operation of the cross flow grinder was overcompensated by the higher gas yield. The results of this study show, that with a suitable treatment technology, the use of straw based horse manure and other high fiber structural materials in agricultural biogas plants is possible. A complete conversion of straw based horse manure provides an energy equivalent of up to 156,000 ha of maize. Thus, this study helps to improve the sustainability and profitability of biogas production and the achievement of the energy policy objectives.
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    Vorbehandlung lignocellulosehaltiger Substrate zur Steigerung des Biogasertrages
    (2019) Baumkötter, Daniel; Jungbluth, Thomas
    There are various approaches for the optimization in biogas technology. One possibility is the pretreatment of the used substrates in order to achieve higher biogas yields, open up new substrates and increase the overall economic viability of biogas plants. For this pretreatment, mechanical treatment technologies are used, which are very different in construction. Therefore, a systematic investigation of the mechanical pretreatment by means of impact with regard to particle size distribution, biogas yield and power consumption for different substrates was carried out for the first time. The aim of this thesis was thus to optimize and eva¬luate the technology “impact reactor” for pretreatment of lignocellulosic substrates for use in an agricultural biogas plant. Substrates with a model character were selected for the experiments, which allow the results to be transferred to comparable substrates. These were triticale straw, oat whole crop silage, maize straw and horse manure. In addition, the substrate mixture of a biogas plant, in which an impact reactor is also used for pretreatment, with a high proportion of grass silage (53 % grass silage, 40 % maize silage and 7 % cattle and horse manure) was examined. Pretreatment of all substrates showed a reduction in particle size. As expected, finer particle sizes also required more effort and therefore higher power consumption. However, no direct correlation could be established between a finer particle size and an increased methane yield. Therefore, an increase in the processing intensity does not necessarily lead to an increase in microbial degradation. In addition to the use of alternative substrates, the main objective of substrate pretreatment was to increase biogas yields. Mechanical pretreatment of triticale straw made it possible to increase methane yield by up to 16 %, horse manure by up to 14 % and substrate mixture by up to 10 %. In contrast, no additional methane yields were recorded for oat whole crop silage and maize straw. Apparently short chopped silages are already sufficiently broken down by the silage. To avoid possible losses due to aerobic degradation, the pretreated substrates must be fed directly into the fermenter. Therefore, the pretreatment should ideally be integrated into the process engineering of the biogas plant between storage and the feed system. In order to classify the results with the impact reactor, additional treatment experiments were carried out with an extruder on a laboratory scale. In principle, the extruder was also suitable for all substrates examined, but liquid had to be added to substrates with a high dry substance content (straw). The results for increasing methane yields were comparable. Besides the investment costs, power consumption had the greatest influence on the costs of pretreatment. These varied significantly depending on the selected settings at the impact reactor. With the help of the determined optimal settings, power consumption of 12.9 kWhel/tFM for triticale and maize straw, 2.6 kWhel/tFM for oat whole crop silage, 10.8 kWhel/tFM for horse manure and 6.1 kWhel/tFM for the substrate mixture could be determined. After combining the results on power consumption and additional methane yield, the mechanical pretreatment of triticale straw, horse manure and the substrate mixture resulted in a gain after energetic balancing. From an economic point of view, horse manure and maize straw showed their potential as an alternative substrate compared to silage maize. Due to their residual material character and the associated lack of market value, these two substrates are economically interesting. By contrast, the market value of cereal straw makes triticale straw more economical than silage maize. However, the results may vary depending on substrate quality and biogas plant, which is why an individual consideration is required for each project. The impact reactor as a method of mechanical pretreatment is basically suitable for various substrates. The pretreatment process increases the biogas yield and opens up previously unused residues for the biogas process, which also improves economic efficiency.