Description of limit and failure states for biological methane oxidation in landfills: experimental investigation, chemical analysis, mechanical modeling and computational simulation

点击翻译按钮获取中文摘要

Over time the organic components in landfills are converted by bacterial activities. The resulting landfill gas is composed of 40% carbon dioxide and 60% methane. If no collection system is installed, the landfill gas can freely emit into the atmosphere. Unfortunately, methane is an especially harmful greenhouse gas and pollutes the atmosphere over 23 times more than carbon dioxide. Therefore, politics, science and industry are searching for technologies in order to permanently reduce the methane emissions. The normal procedure is to actively extract the landfill gas with so called gas wells and then finally to dispose the gas thermally. However, an unsolved problem remains regarding the time from when the gas production decreases due to reduced bacterial activity.This time period is called passive after-care phase and can last for 100 years or more which presents a predicament. On the one hand, the active extraction of the landfill gas over a period decades is financially as well as technically very costly. On the other hand, the long term pollution of the atmosphere through the landfill gas is socially not responsible or justifiable. Thus, a solution is needed which i) leads to reasonable costs, ii) is technically feasible and iii) shows sufficient reliability in respect to malfunction or failure. Regarding the first two aspects the methane oxidation layer would appear to be a promising solution. The process of methane oxidation is based on the methanotrophic bacteria converting the extracted methane from the landfills into less harmful carbon dioxide and water. The question which arises is whether the methane oxidation layer is capable to entirely convert the incoming gas from the landfill or not. In addition, the performance of the layer can easily be influenced by outer boundary conditions for example temperature, content of substrate, humidity or oxygen saturation. Finally, this could even result in the complete failure of the methane oxidation layer.Therefore, the aim of the project is the fundamental investigation as well as the prediction of the biologically-chemically coupled diffusion-convection-reaction-process in methane oxidation layers. In the first part of the research project the function of the layer was experimentally analyzed under normal conditions with regard to model and simulation aspects. In the second part of the project the model will be enhanced so that it also takes the limit and failure states into account which occur due to long periods without nutrition or extreme heat, cold, clamminess and aridness. The main attention is paid to the answering of the question whether and in what manner methane oxidation layers are able to recover after such extreme environmental conditions and how the performance of the layer develops in the following period.