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

随着时间的推移，垃圾填埋场中的有机成分被细菌活动转化。由此产生的垃圾填埋气体由40%的二氧化碳和60%的甲烷组成。如果没有安装收集系统，垃圾填埋气体可以随意排放到大气中。不幸的是，甲烷是一种特别有害的温室气体，对大气的污染是二氧化碳的23倍以上。因此，政界、科学界和工业界都在寻找能够永久减少甲烷排放的技术。正常的程序是用所谓的气井主动提取垃圾填埋气体，然后最后对气体进行热处理。然而，一个尚未解决的问题是，从细菌活性降低到产气量减少的时间。这一时期被称为被动的护理后阶段，可能持续100年或更长时间，这是一种困境。一方面，在几十年的时间里，积极地提取垃圾填埋气体在经济上和技术上都是非常昂贵的。另一方面，通过垃圾填埋气体对大气的长期污染是不负责的，也是不合理的。因此，需要一种解决方案：1)导致合理的成本，2)技术上可行，3)在故障或故障方面显示足够的可靠性。关于前两个方面，甲烷氧化层似乎是一个有希望的解决方案。甲烷氧化过程是基于甲烷营养细菌将从垃圾填埋场提取的甲烷转化为危害较小的二氧化碳和水。由此产生的问题是甲烷氧化层是否能够完全转化来自垃圾填埋场的进入气体。此外，层的性能很容易受到外部边界条件的影响，例如温度、衬底含量、湿度或氧饱和度。最后，这甚至可能导致甲烷氧化层完全失效。因此，本项目的目的是对甲烷氧化层中扩散-对流-反应-生物-化学耦合过程进行基础研究和预测。在研究项目的第一部分，从模型和仿真两个方面对正常条件下的层的功能进行了实验分析。在项目的第二部分，该模型将得到加强，以便它也考虑到由于长期缺乏营养或极端高温、寒冷、潮湿和干旱而发生的极限和失效状态。主要关注的问题是，在这种极端环境条件下，甲烷氧化层是否能够恢复，以何种方式恢复，以及在接下来的一段时间内，甲烷氧化层的性能如何发展。

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.