Contact person: Daniela Polag
In cooperation with the Chair of Urban Water Systems Engineering of Technical University München (Dr. Konrad Koch) and the Bavarian State Research Center for Agriculture in Freising (Dr. Michael Lebuhn).
In recent years, the demand for renewable energy and the reduction of greenhouse gases such as CO2 has become increasingly important within the framework of energy transition. Besides possible energy savings and increased energy recovery, the CO2 footprint of wastewater treatment is still an issue that needs to be addressed. In case of wastewater treatment plants, every year about 3 million tons of CO2 are being emitted in Germany. Thus, coupling CO2 utilization with energy recovery for better overall utilization would be a great benefit.
Recent studies involving conventional digester processes reported increased CH4 production when CO2 was provided as flush gas for the digester headspace. Bioconversion from CO2 into CH4 has the advantage of (i) reducing CO2 emissions and (ii) transformation of CO2 into energetically usable CH4. Although describing the process in dependence of various parameters (i.e., substrate composition, temperature, microbial composition), none of the few recently published studies was able to elucidate the basic effects leading to the bioconversion of CO2 to CH4.
Thus, 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 of sewage sludge.
To achieve the mentioned goal an interdisciplinary approach is required including the use of stable isotope methods as the key parameter for process identification (RKU), know-how of process engineering including the supply of a fully-equipped laboratory with expertise in the performance of continuous flow-through experiments (TUM), and accompanying microbial analyses (LfL).
To identify the basic mechanisms of the observed bioconversion from CO2 into CH4 we aim to establish 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 from a municipal wastewater treatment plant in Garching. 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 (RKU). With this powerful technique it is possible to reconstruct precursors and specific pathways during CO2 addition.
Set-up of continuous anaerobic digestions tests
Contact person: Tobias Anhäuser
Stable hydrogen isotope ratios of lignin methoxyl groups (δ²HLM values) in wood have been shown to mirror the δ²H signature of precipitation δ²Hprecip values). Thus, δ²HLM values were suggested to serve as a potential paleotemperature proxy since δ²Hprecip values are dominantly controlled by air temperature in the mid-latitudes. A recent study where a significant δ²HLM-temperature relationship was found for a European transect with mean annual temperatures ranging from −4 to 17 °C strengthened this assumption (Anhäuser et al., 2016). However, using δ²HLM values as a paleotemperature proxy requires quantification of noise from site and species-specific influences to determine the significance of recording smaller temperature changes. This issue has been evaluated in the course of DFG project KE884/6-2 (see below). We measured δ²HLM values of tree-ring sections covering 1981-1990 and 1991-2011 of four different tree species, Norway spruce, European beech, English oak and Scots pine, at 15 sampling sites across Germany. The maximum difference in mean annual temperature between sample sites was 5 °C and all sites showed small temperature increases from 1981-1990 to 1991-2011 (mean ∆ = 0.7° C). For all species investigated, the maximum difference of δ²HLM within the tree was < 10 mUr or ‰ (median values) and between trees at a single site was ≤ 28 mUr (median values). The general pattern of the spatial δ²HLM-temperature relationship found for the European transect was confirmed here although a significant correlation was lacking. This can be explained by the lower spatial δ²Hprecip-temperature correlation (R² = 0.39) found for sampling sites in this study and the δ²HLM differences between trees. Nevertheless, the temporal changes in δ²HLM values of European beech trees correctly reflected within ± 2 °C the temperature change at every sampling site. Therefore, we suggest that δ²HLM values of European beech trees have considerable potential for reconstructing temperature changes when applied on tree-ring chronologies and consider this approach particularly suited for Late Holocene climate studies.
To further test the paleoclimatic potential of this isotope proxy we will collect a sample set of beech trees to establish a high-resolution (annual) tree-ring chronology of the past 150 years. The δ²HLM values will be compared to observed temperature and δ²Hprecip data to characterize its exact temperature significance (Figure below).
Mean annual temperatures (DWD) and weighted mean annual δ²Hprecip values (GNIP) at Hohenpeißenberg. a) Both values at biennially resolution from 1971-2008. b) Mean annual temperatures of the envisaged coverage of the dendrochronology of sampled European beech trees.
The project CHLOROFILTER is an interdisciplinary consortium of two French and two German partners who combine expertizes and knowledge to address the impact of microorganisms on the global budget of chloromethane (CH3Cl). Anthropogenic emissions of ozone-depleting compounds have been strongly reduced since the Montreal Protocol came into force in 1989. As a consequence, compounds released from natural sources, have become increasingly relevant in stratospheric ozone depletion. CH3Cl is the most abundant halogenated compound in the atmosphere, and originates primarily from terrestrial ecosystems. Future warmer climates will likely lead to increased CH3Cl emissions. Current estimates of its global budget are uncertain but suggest that microorganisms play a more important role in degradation of atmospheric CH3Cl than previously thought. Methylotrophic microbes, some with the capability to degrade CH3Cl, occur in soils, the phyllosphere of many plants, and have recently been reported to be active in water droplets of clouds. The main objective of CHLOROFILTER is to provide quantitative information on process-level and in depth genetic insights into these microbes.
The investigations focus on kinetic and isotope effects upon CH3Cl degradation by methylotrophs associated with soils, plants, and clouds to resolve the quantitative relevance of microbial sinks for the global CH3Cl budget. The microbial community will be characterized in selected various environmental samples using a taxonomical (16S RNA genes) and a functional gene marker for CH3Cl degradation (cmuA). Furthermore, selected samples of soil, plants, and cloud water will be subjected to 13CH3Cl in order to label the biomass of CH3Cl degrading microbes and to retrieve 13C-labeled metagenomes via DNA stable isotope probing to assess the diversity of microbial pathways for CH3Cl-degradation.
An improved quantitative understanding of the sources and sinks of atmospheric CH3Cl will be invaluable for our understanding the stratospheric chlorine chemistry and predict ozone layer stability.
Contact person: Thomas Klintzsch
The oceans are considered to be a source of CH4 to the atmosphere although the magnitude of total net emissions is highly uncertain and sources are not well described. To explain the source of CH4 in surface waters, it has been suggested that methanogenesis takes place in anoxic microenvironments of organic aggregates. Other sources such as in-situ formation of CH4 by algae have also been suggested, however, a direct evidence of algae-derived CH4 formation from lab experiments with (axenic) algae cultures is still missing, and thus so far the accumulation of CH4 in the upper water layer has not yet been related to a direct production by algae. The overall aim of this research project is the verification (proof of principle) and quantification of CH4 production by several species of marine algae such as haptophytes (e.g. Emiliania huxleyi). Potential precursors such as (e.g. methyl sulfides and sulfoxides) of algae-derived CH4 will be identified by using stable isotope techniques. Several environmental factors will be investigated with respect to their effect of algae-derived CH4 production. Furthermore, we will apply various microbiological tests to screen for methanogenic Archaea or bacteria potentially involved in CH4 formation. We will also focus on factors sensitive to climate change such as temperature, oxygen concentration and nutrient availability. An interdisciplinary approach requiring the interaction of several disciplines is envisaged to realize the aims of the project. The results are expected to improve our understanding of biogeochemical cycling of CH4 formation in the oceans and to better explain the CH4-enrichment of oxygenated surface waters compared to atmospheric concentration, so-called “Oceanic methane paradox”.