| dc.description.abstract | Das Image der Biogasanlagen als umweltfreundliche Energieerzeuger hat in der jüngsten Vergangenheit gelitten. Neben dem Biomasseanbau (Maismonokulturen), stehen der Transport und die Ausbringung der Gärreste unter öffentlicher Kritik. Gleichzeitig gilt Biogas gilt als umweltfreundlich, da fossile Ressourcen geschont und Kohlendioxidemissionen gemindert werden. Die ökologischen Aspekte der Biogaserzeugung wurden in einer Ökobilanz untersucht, deren Ergebnisse jetzt für die Öffentlichkeit als Informations- und Diskussionsgrundlage zur Verfügung stehen.Durch die Novellierung des Erneuerbare-Energien-Gesetzes im Jahr 2004 wurde ein Investitionsboom bei Biogasanlagen, speziell im Bereich 500 kW und größer, ausgelöst. In Verbindung mit diesem Boom wurde der Anbau von Energiepflanzen für die Biogasproduktion stark erweitert. Im Rahmen der Untersuchung wurden alle Lebenswegabschnitte der Biogasproduktion untersucht und die bedeutendsten Einflussfaktoren ermittelt. Die Untersuchung wurde in Form einer Ökobilanz gemäß EN ISO 14040 ff. als internationaler Standard durchgeführt. Für die Datensammlung wurden Informationen bestehender Anlagen und Ergebnisse eigener Versuche verwendet, so dass in den wichtigsten Bereichen aktuelle Daten zur Verfügung standen. Die Ergebnisse der Datensammlung wurden auf ein Terrajoule elektrische Energie bezogen und nach der Eco indicator `99 Methode gewichtet und bewertet, so dass die Gesamtergebnisse der untersuchten Prozesse miteinander verglichen werden können. Bei Verwendung anderer Bewertungsschlüssel, können die Ergebnisse abweichen. Die vorliegenden Ergebnisse können sowohl für die Öffentlichkeitsarbeit einzelner Anlagen, als auch für die Weiterentwicklung der Biogastechnik verwendet werden.Untersucht wurden mehrere Varianten der Biogasproduktion. Bei den Inputstoffen wurden eine Mais-/Güllemischung und eine Bioabfall-/Güllemischung betrachtet. Bei der BHKW Technik wurde ein Gas-Otto-Motor mit einer Brennstoffzelle verglichen. Zusätzlich wurde die Nutzung der Abwärme betrachtet. Insgesamt wird der Flächenverbrauch für den Energiepflanzenanbau als bedeutendster Einfluss auf das Gesamtergebnis erkannt. Hierbei sind allerdings methodische Fragen zu berücksichtigen, die dieses Ergebnis einschränken (vgl. Hartmann2006). Insgesamt besitzen Energiepflanzen mit hohen Flächenerträgen (z.B. Mais) ökologische Vorteile vor Pflanzen, die weniger Biomasse bilden. Die aktuellen Züchtungsbemühungen gehen in diese Richtung. Da Abfälle als Input der Biogasproduktion ohne ökologischen Rucksack bilanziert werden, werden hierdurch die ökologischen Belastungen der Vorkette der Biogasproduktion vermieden und die Biogasbilanz deutlich verbessert. Durch die Nutzung der Brennstoffzellentechnik können höhere Wirkungsgrade und sehr niedrige Emissionen erreicht werden, so dass das Gesamtergebnis nachhaltig positiv beeinflusst wird. Entwicklungen in diesem Bereich sollten daher gefördert werden. Die Abwärmenutzung kann bedeutende ökologische Gutschriften erzielen, wenn hierdurch der Verbrauch fossiler Ressourcen eingeschränkt wird. Die Schaffung neuer Wärmeabnehmer, z.B. die Hackschnitzeltrocknung, führt zu keinem Einsparpotential und bedingt daher keine ökologischen Vorteile. Als Fazit kann festgehalten werden, dass die Stromerzeugung aus Biogas umweltfreundlich ist und in der Größenordnung den Effekten des gegenwärtigen Strommixes in Deutschland entspricht. Ökologisch wichtigster Punkt ist der Flächen- und Energiebedarf der Biomasseproduktion. Die BHKW- und der Gärrestemissionen haben einen spürbar negativen Einfluss auf das Gesamtergebnis. Das ökologische Ergebnis kann verbessert werden, wenn höhere Flächenerträge erzielt oder biogene Abfälle anstatt Energiepflanzen als Input genutzt werden. Die Nutzung der Abwärme des BHKW zur Einsparung fossiler Energieträger ermöglicht bedeutende Gutschriften auf das Gesamtergebnis. Werden alle Optimierungsmöglichkeiten genutzt, verursacht Strom aus Biogas weniger als ein Fünftel der ökologischen Auswirkungen des üblichen Strommixes. | de |
| dc.description.abstracteng | Sustainable energy supply is considered to be one of the most important worldwide chal-lenges of the future. When concerning energy supply, three aspects have to be taken into account regarding sustainability. The first aspect is the limitation of fossil and nuclear re-sources. It is generally accepted that these resources will run out within the next decades and centuries. As a secondary aspect, due to this limitation, there is a rise in energy prices. This is contrary to the concept that energy should be affordable to every human being. The third aspect involves the emissions of the state of the art energy conversion technology harming the environment. These must therefore be reduced in the future, especially green-house gas emissions.Renewable energy sources are considered an answer to these problems. They are in end-less supply and thought to be environmental friendly. Biomass, e.g. crops and biodegradable waste, is one kind of renewable energy sources. Biogas production is one possibility to pro-duce electricity and heat from this biomass. Within the biogas process bacteria in an anaer-obe atmosphere degrade carbon-hydrogen compounds. Methane, carbon dioxide, some trace gases, and a nutrient rich slurry result from this biogas process. The originated meth-ane can finally be used for heating, electricity generation or fuel production. Within the last years, the government has assisted the energy production from renewable energy sources, especially biogas. This has led to a particular increase in industrial-scale biogas plants using energy crops as input.The utilisation of renewable energies aims at the protection of human health, nature, and resources. However, like any other kind of energy conversion, the biogas process causes effects on the environment. Energy conversion plants using renewable energy sources such as biomass are considered to be environmentally friendly by a wide public. Considerations of the environmental friendliness of renewable resources consuming processes are based on the one hand, on the conservation of fossil resources on the input side of the system and on the other hand on the emission of carbon dioxide, which is not enhancing the green house effect due to its renewable sources offspring on the output side of the process. In this case environmental friendliness is solely seen as a question of sustainability in the fields of fossil resources and climate. Here, it is not considered that the production and transport of energy crops consumes mass and energy flows, uses land and produces emissions.All of these effects have to be taken into account, when assessing the environmental effects of electricity generation from biogas produced by an industrial scale biogas plant. Further-more, manure and organic waste must be transported, leading to fuel consumption and emissions. The production and consumption of biogas lead to gaseous emissions, which threatens human health and the environment. Mass and energy flows are caused for the construction and demolishing of the biogas plant itself. Ultimately, waste is generated by the biogas plant, which has to be disposed of. This is why, for the further development of energy technologies, it is important to know the kind and amount of ecological effects caused.The object under investigation is a hypothetical biogas plant with a capacity of 1.0 MW elec-tric power, fed by biomass from energy crops and manure. The ecological effects shall be determined from start to finish and are determined by mass and energy balances resulting in a life-cycle-assessment (LCA). This assessment is done according to the rules of ISO 14040-14043, which gives a universally valid plan for this method. Data for the mass and energy balances are taken from measured data of existing biogas plants, calculations from similar objects, and estimations where no adoptable data are available. The object under investiga-tion is the biogas plant itself as well as up- and downstream processes related to the power plant. The scope of the data collection will be determined and adjusted within the LCA; also all single unit processes will be defined in the life-cycle-assessment.The only purpose of this study is to give information on the composition of the ecological ef-fects from biogas production in industrial scaled biogas plants. Thereby ecological hot spots are determined and suggestions for ecological improvements are made. The results of this study should not be used for comparisons with results from LCA studies of different energy production systems e.g. electricity from lean coal, as the scope of this study is not designed for such a comparison.As the results of a LCA study are very complex and hard to interpret, due to the variety of impact categories, an additional interpretation step is included. At this stage, the Eco Indica-tor `99 approach of [GOEDKOPP&SPRIENSMA2001] will be used. This step is not part of the rules of ISO14040-43 and must be acknowledged as an additional interpretation tool. The use of such interpretation methods is hardly discussed among experts, due to its social sci-ence based background. The results gained from the LCA done according to the ISO rules are therefore clearly separated from the results of the further interpretation, so that the influ-ence of the interpretation method can be regarded separately. The results of the ecological assessment are given for each unit process, per module, and for the overall process. All re-sults are related to the generation of one Terra Joule of electric energy from the biogas plant.Beginning with the production of energy crops, it can be seen that energy plants with a high productivity per area unit e.g. maize and forage beets have a better ecological performance than crops like rye or grass. The ecological effects of the crop production are mainly caused by energy inputs e.g. fuels and artificial nitrogen fertiliser production. Relevant effects are also caused from heavy metals inserted into the system by phosphate fertilisers. A specific effect from crop production is the impact category land use. More than 80% of the ecological effects of the crop production and more than 60% of the overall effects are related to this category. As this category is a qualitative and not a quantitative indicator like the other mass and energy flows, its implementation into the overall assessment is quite complicated.For the production of energy crops, mainly crops with a high yield of organic dry matter mass per unit area should be used in order to reduce the ecological effects from this module. Whenever possible, biodegradable waste should be used instead of specially produced crops to reduce the ecological effects on the input side of the system, as this waste is taken into account without any ecological burden. Within the agricultural production system the influence of the impact category land use is very strong, in comparison to all other ecological effects in their influences on the overall re-sult. On the one hand, large areas are needed for the production of energy crops. This has a multiplying effect on the results per unit area. The intensive arable production leads to a de-crease in biodiversity, which is close to the decrease caused by a sealed surface. Therefore this form of production is calculated with heavy ecological burdens. On the other hand it must be recognised that there would also be arable production, even if no energy crops would be produced. Hence, stopping the production of energy crops would not lead to an overall re-duction of ecological effects from arable farming. Therefore this impact category should be taken into account, showing that improvements of the ecological effect from biogas produc-tion are mainly improvements of the biodiversity in the energy crop production. But they should not be accounted for, if the ecological effects of the biogas production are compared to other kinds of electricity generation.The transport caused by the input and output flows of the biogas plant have only a small in-fluence on the overall ecological effects. Most ecological effects are herein derived from the consumption of fossil fuels. From a theoretical analysis the result gained can show that larger biogas plants do not cause an equivalent increase of transport efforts as two smaller biogas plants would cause. When biogas plants and related areas for energy crop production in-crease, the transport efforts increase subproportionally due to the circular area/radius nature of the area around the biogas plant. Therefore, the crops in areas around a biogas plant al-ways grow faster, however transport distances have yet to be covered.The construction and demolition of installations in a biogas plant produce hardly any dam-ages to the environment. Only two ecological hot spots occur at the biogas plant: the emis-sions of the CHP plant and the consumption of electricity from the grid. Gas engines with oxidising converters are calculated as CHP plants, which emit the lowest emission rates out of all conventional CHP plants. Lower emissions rates can only be realised with a change of technology e.g. use of fuel cells. The share of ecological effects from electricity consumption is related to the fact that biogas plants, which use energy crops, need up to 10% of the en-ergy that they generate to run the process. Facilities using less energy can be helpful to re-duce this influence on the overall ecological effect from this hot spot. The biogas slurry is applied to fields, where it is used as an organic fertiliser. The application of biogas slurry has two different ecological effects. The nutrient content of the slurry leads to a reduced consumption of artificial fertiliser. The emissions from the biogas slurry the influ-ence of the change in input material can be seen contribute mainly to the impact categories acidification/eutrophication and greenhouse effect. These negative effects, especially the acidification from gaseous NH3 emissions, contribute to around 25% of the total ecological effects. This threat to the environment can be reduced through application and incorporation methods in keeping with good agricultural practice. Thereby, very low emission levels of the applied biogas slurry can be achieved. These emissions levels are below the emissions from manure, which is used as input to the plant, and would alternatively spread to the fields, where it would cause emissions.In brief, electricity generation from biogas produced in industrial scale biogas plants can be regarded as a durable way of generating electricity. On considering the biogas production from start to finish, it is shown that most ecological effects are related to the agricultural pro-duction system. Just some parts of these effects can be manipulated. Qualitative aspects, e.g. land use, cannot be influenced and will always occur, even if no energy crops were to be produced. | de |