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Power-to-Methane as one part of Power-to-Gas has been recognized globally as one of the key elements for the transition towards a sustainable energy system. While plants that produce methane catalytically have been in operation for a long time, biological methanation has just reached industrial pilot scale and near-term commercial application. The growing importance of the biological method is reflected by an increasing number of scientific articles describing novel approaches to improve this technology. However, these studies are difficult to compare because they lack a coherent nomenclature. In this article, we present a comprehensive set of parameters allowing the characterization and comparison of various biological methanation processes. To identify relevant parameters needed for a proper description of this technology, we summarized existing literature and defined system boundaries for Power-to-Methane process steps. On this basis, we derive system parameters providing information on the methanation system, its performance, the biology and cost aspects. As a result, three different standards are provided as a blueprint matrix for use in academia and industry applicable to both, biological and catalytic methanation. Hence, this review attempts to set the standards for a comprehensive description of biological and chemical methanation processes.

In this study, the possibility of sector coupling with biological Power-to-Methane to support and stabilize the energy transition of the three major sectors of electricity, heat, and gas was addressed. For this purpose, the energy cell simulation methodology and the Calliope tool were utilized for energy system optimization. This combination provides detailed insights into the existing dependencies of consumers and fossil and renewable energy suppliers on a local scale. In this context, Power-to-Methane represents an efficient technology for quickly and effectively exploiting unused electricity potential for various sectors and consumers. It was found that, even in regions with low wind levels, this surplus electricity potential already exists and depends on various influencing factors in very different ways. The solar influence on these potentials was considered in connection with gas-fired cogeneration plants for district heating. It was found that the current heat demand for district heating produces a large amount of electricity and can generate surplus electricity in the winter. However, in the summer, large amounts of usable waste heat are dissipated into the environment, owing to the low consumption of district heat. This problem in the heat sector could be reduced by the expansion of photovoltaics, but this would require further expansion of storage or conversion systems in the electricity sector. This demonstrates that the consideration of several sectors is necessary to reflect the complexity of the sector coupling with Power-to-Methane properly.

Biological methanation is driven by anaerobic methanogenic archaea, cultivated in different media, which consist of multiple macro and micro nutrients. In addition, a reducing agent is needed to lower the oxidation–reduction potential (ORP) and enable the growth of oxygen-sensitive organisms. Until now, sodium sulfide (Na2S) has been used mainly for this purpose based on earlier published articles at the beginning of anaerobic microbiology research. In a continuation of earlier investigations, in this study, the usage of alternative reducing agents like sodium dithionite (Na2S2O4) and L-Cysteine-HCl shows that similar results can be obtained with fewer environmental and hazardous impacts. Therefore, a newly developed comparison method was used for the cultivation of Methanothermobacter marburgensis. The median methane evolution rate (MER) for the alternatives was similar compared to Na2S at different concentrations (0.5, 0.25 and 0.1 g/L). However, the use of 0.25 g/L Na2S2O4 or 0.1 g/L L-Cys-HCl led to stable MER values over consecutive batches compared to Na2S. It was also shown that a lower concentration of reducing agent leads to a higher MER. In conclusion, Na2S2O4 or L-Cys-HCl can be used as a non-corrosive and non-toxic reducing agent for ex situ biological methanation. Economically, Na2S2O4 is cheaper, which is particularly interesting for scale-up purposes.

Biological methanation is driven by anaerobic methanogenic archaea, cultivated in different media, which consist of multiple macro and micro nutrients. In addition, a reducing agent is needed to lower the oxidation–reduction potential (ORP) and enable the growth of oxygen-sensitive organisms. Until now, sodium sulfide (Na[sub.2] S) has been used mainly for this purpose based on earlier published articles at the beginning of anaerobic microbiology research. In a continuation of earlier investigations, in this study, the usage of alternative reducing agents like sodium dithionite (Na[sub.2] S[sub.2] O[sub.4] ) and L-Cysteine-HCl shows that similar results can be obtained with fewer environmental and hazardous impacts. Therefore, a newly developed comparison method was used for the cultivation of Methanothermobacter marburgensis. The median methane evolution rate (MER) for the alternatives was similar compared to Na[sub.2] S at different concentrations (0.5, 0.25 and 0.1 g/L). However, the use of 0.25 g/L Na[sub.2] S[sub.2] O[sub.4] or 0.1 g/L L-Cys-HCl led to stable MER values over consecutive batches compared to Na[sub.2] S. It was also shown that a lower concentration of reducing agent leads to a higher MER. In conclusion, Na[sub.2] S[sub.2] O[sub.4] or L-Cys-HCl can be used as a non-corrosive and non-toxic reducing agent for ex situ biological methanation. Economically, Na[sub.2] S[sub.2] O[sub.4] is cheaper, which is particularly interesting for scale-up purposes.

In this study, we developed a method for simultaneous bio-methanation of CO2 and CO with H2 in a single bioreactor using a combination of carboxydotrophic bacteria and methanogenic archaea for industrial applications. Methanogenic archaea generally use H2 and CO2 to produce methane, whereas very few methanogenic archaea methanize CO, and these grow slowly and consequently produce low reactant gas turnover rates. Thus, to achieve fast and simultaneous transformation of CO and CO2, we identified a combination of carboxydotrophic and hydrogenogenic bacteria and methanogenic archaea that can produce H2 and CO2 from CO, and then methanize CO2 and H2. The present screening experiments identified carboxydotrophic bacteria and methanogenic archaea that can cohabitate at the same thermophilic temperature and pH ranges and in the same growth medium. In these experiments, combinations of Carboxydocella thermautotrophica (DSM 12326), Carboxydocella sporoproducens (DSM 16521), and three thermophilic rod-shaped methanogenic archaeal cultures from MicroPyros GmbH formed unique microbial co-cultures that transformed CO2, H2, and CO to methane. The successful combination of these microbes could be used to gasify biowastes, such as sewage sludge, as alternative sources of hydrogen for microbial power-to-gas processes. Accordingly, gasification under these conditions produced H2-rich gas containing CO2 and CO, theoretically allowing various types of biowastes to be converted to biomethane, which is CO2-neutral, storable, and widely applicable as an energy source.

Die Immissionsbelastung im östlichen Umland des neuen Münchner Flughafens wurde im Zeitraum von 1992 bis 1995 mit Hilfe einer Reihe unterschiedlicher Messmethoden untersucht. Für die wirkungsbezogene Erfassung von Umwelteinflüssen wurden Bioindikatoren zur Bestimmung der PAK-Belastung und zur Quantifizierung der Photooxidantienbelastung eingesetzt. Darüber hinaus wurde der PAK-Gehalt des Oberbodens bestimmt. Die aktuelle Luftbelastungssituation wurde während photochemisch aktiver Wetterlagen im Sommer im Rahmen von 7 Intensivmesskampagnen untersucht. Die Bodenbelastung mit PAK liegt im Bereich der für ländliche Regionen typischen Hintergrundwerte mit den höchsten Konzentrationen in der Nähe stark befahrener Straßen und weist keinen zeitlichen Trend auf. Auch der aktuelle PAK-Eintrag liegt an allen Standorten in einem für ländliche Regionen in Bayern typischen Bereich. Als Hauptemittent wird im Sommer der Kfz-Verkehr identifiziert, während die deutlich erhöhte Belastung im Winter auf den Hausbrand zurückgeführt werden kann. Die Photooxidantien-belastung zeigt im Flughafenumland keine ausgeprägten Unterschiede, sie ist an den durch Straßenverkehr beeinflussten Standorten jedoch am geringsten. Die Konzentrationen leicht flüchtiger Kohlenwasserstoffe sind an einer verkehrsreichen Straßenkreuzung in Erding deutlich höher als im ländlichen Flughafenumland. Sie zeigen ausgeprägte Tagesgänge, die u.a. auf den luftchemischen Abbau zurückzuführen sind. Die Hydroperoxide als sekundäre Luftschadstoffe weisen einen gegensätzlichen Verlauf auf, der dem des Ozons mit nachmittäglichem Maximum ähnelt. The airborne immissions in the eastern surroundings to the new Munich airport have been investigated by means of different analytical methods between 1992 and 1995. For a detection of environmental impacts, bioindicators were applied to determine the pollution by PAH and to quantify the pollution by photooxidants. In addition, the PAH content in the upper soil layer was determined. During high pressure weather periods in summer the actual air pollution was investigated in the course of seven measuring campaigns. The PAH pollution of the soil is typical for rural background sites with highest concentrations in the close vicinity of busy roads, and exhibits no temporary trend. The actual input of PAH does not differ from the typical situation of rural regions in Bavaria at any measuring sites at all. Road traffic can be identified as the main PAH source in summer, whereas the considerably higher pollution in winter can be related to domestic heating. The pollution by photooxidants was found to be rather homogeneous throughout the eastern surroundings to the airport, being lowest at the sites directly influenced by road traffic. The pollution by volatile hydrocarbons at a busy road junction in the city of Erding is considerably higher than in the rural vicinity of the airport. The concentrations exhibit distinct daily courses which, among other things, can be related to atmospheric photooxidation. The hydroperoxides as secondary air pollutants exhibit an inverse course similar to that of ozone, with maximum values in the afternoon.[PUBLICATION ABSTRACT]

The airborne immissions in the eastern surroundings to the new Munich airport have been investigated by means of different analytical methods between 1992 and 1995. For a detection of environmental impacts, bioindicators were applied to determine the pollution by PAH and to quantify the pollution by photooxidants. In addition, the PAH content in the upper soil layer was determined. During high pressure weather periods in summer the actual air pollution was investigated in the course of seven measuring campaigns. The PAH pollution of the soil is typical for rural background sites with highest concentrations in the close vicinity of busy roads, and exhibits no temporary trend. The actual input of PAH does not differ from the typical situation of rural regions in Bavaria at any measuring sites at all. Road traffic can be identified as the main PAH source in summer, whereas the considerably higher pollution in winter can be related to domestic heating. The pollution by photooxidants was found to be rather homogeneous throughout the eastern surroundings to the airport, being lowest at the sites directly influenced by road traffic. The pollution by volatile hydrocarbons at a busy road junction in the city of Erding is considerably higher than in the rural vicinity of the airport. The concentrations exhibit distinct daily courses which, among other things, can be related to atmospheric photooxidation. The hydroperoxides as secondary air pollutants exhibit an inverse course similar to that of ozone, with maximum values in the afternoon.Original Abstract: Die Immissionsbelastung im oestlichen Umland des neuen Muenchner Flughafens wurde im Zeitraum von 1992 bis 1995 mit Hilfe einer Reihe unterschiedlicher Messmethoden untersucht. Fuer die wirkungsbezogene Erfassung von Umwelteinfluessen wurden Bioindikatoren zur Bestimmung der PAK-Belastung und zur Quantifizierung der Photooxidantienbelastung eingesetzt. Darueber hinaus wurde der PAK-Gehalt des Oberbodens bestimmt. Die aktuelle Luftbelastungssituation wurde waehrend photochemisch aktiver Wetterlagen im Sommer im Rahmen von 7 Intensivmesskampagnen untersucht. Die Bodenbelastung mit PAK liegt im Bereich der fuer laendliche Regionen typischen Hintergrundwerte mit den hoechsten Konzentrationen in der Naehe stark befahrener Strassen und weist keinen zeitlichen Trend auf. Auch der aktuelle PAK-Eintrag liegt an allen Standorten in einem fuer laendliche Regionen in Bayern typischen Bereich. Als Hauptemittent wird im Sommer der Kfz-Verkehr identifiziert, waehrend die deutlich erhoehte Belastung im Winter auf den Hausbrand zurueckgefuehrt werden kann. Die Photooxidantien-belastung zeigt im Flughafenumland keine ausgepraegten Unterschiede, sie ist an den durch Strassenverkehr beeinflussten Standorten jedoch am geringsten. Die Konzentrationen leicht fluechtiger Kohlenwasserstoffe sind an einer verkehrsreichen Strassenkreuzung in Erding deutlich hoeher als im laendlichen Flughafenumland. Sie zeigen ausgepraegte Tagesgaenge, die u.a. auf den luftchemischen Abbau zurueckzufuehren sind. Die Hydroperoxide als sekundaere Luftschadstoffe weisen einen gegensaetzlichen Verlauf auf, der dem des Ozons mit nachmittaeglichem Maximum aehnelt.