Increasing methane productivity in anaerobic digesters by addition of CO2

该项目的主要目标是确定在厌氧消化过程中添加CO2导致CH4形成增加的机制。虽然各种研究已经提供了足够的证据证明这种影响，但到目前为止，其潜在机制只是假设，而且还远未被理解。为了重现这些影响并利用废物流产生能源的巨大潜力，必须充分揭示其机制。为了实现上述目标，需要采用跨学科的方法，包括使用稳定同位素方法作为工艺鉴定的关键参数，工艺工程的专业知识，包括提供一个设备齐全的实验室，该实验室具有连续流通实验的专业知识，以及伴随的微生物分析。为了确定所观察到的生物转化的基本机制，详细描述，我们的目标是建立两个连续的厌氧消化试验系统在TUM。一个系统富含二氧化碳，而另一个系统用作对照。这些反应器将用污水污泥进料，因为它似乎是最有可能富集CO2的基质。试验将在不同的负荷率下进行，表明不同的应力状态可能对CH4-形成机制产生重大影响。在测试过程中，将监测标准工艺参数（TS、VS、COD、VFA、碱度、pH值、气体量和质量）。此外，还将采用最先进的分子生物学方法，如在DNA和mRNA水平上的Guild-specific定量实时PCR和群落测序方法，对该地区的生物群落进行表征。作为该项目的一个特别重点，为了追溯CO2转化为CH4的过程，将在消化试验中应用同位素技术，包括同位素标记实验。有了这种强大的技术，就有可能重建CO2添加过程中的前体和特定途径。一旦了解了潜在的机制，就为在实践中实施该方法提供了基础。

The major goal of this project is the identification of the mechanisms leading to increased CH4 formation by the addition of CO2 during anaerobic digestion. While enough evidence of the effect has already been provided by various studies, the underlying mechanisms have only been hypothesized so far and are still far from being understood. In order to reproduce the effects and to utilize this great potential for energy production from waste streams, the mechanisms had to be fully uncovered. To achieve the above mentioned goals an interdisciplinary approach is required including the use of stable isotope methods as the key parameter for process identification, know-how of process engineering including the supply of a fully-equipped laboratory with expertise in the performance of continuous flow-through experiments, and accompanying microbial analyses. To identify the basic mechanisms of the observed bioconversion described in detail, we aim at establishing two continuous anaerobic digestion test systems at TUM. One system is enriched with CO2 while the other serves as the control. The reactors will be fed with sewage sludge, since it seems to be the substrate with the highest potential for CO2 enrichment. Tests will be carried out at various loading rates indicating different stress regimes which might have a significant influence on the mechanism of CH4-formation. During the tests, standard process parameters (TS, VS, COD, VFA, Alkalinity, pH value, gas quantity and quality) will be monitored. Additionally, the biocenosis in the digestate will be characterized by state-of-the-art molecular biological methods such as guild-specific quantitative real-time PCR on DNA and mRNA levels, and community sequencing approaches.As a special focus of the project, in order to retrace CO2 conversion to CH4, isotope techniques including isotope labeling experiments will be applied during the digestion tests. With this powerful technique it is possible to reconstruct precursors and specific pathways during CO2 addition.Once the underlying mechanisms are understood, the basis for implementing the approach in practice is provided.