Journal articles on the topic 'CH4 oxidation'
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1
Liu, Shanfu, Sagar Udyavara, Chi Zhang, Matthias Peter, Tracy L. Lohr, Vinayak P. Dravid, Matthew Neurock, and Tobin J. Marks. "“Soft” oxidative coupling of methane to ethylene: Mechanistic insights from combined experiment and theory." Proceedings of the National Academy of Sciences 118, no. 23 (June 1, 2021): e2012666118. http://dx.doi.org/10.1073/pnas.2012666118.
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The oxidative coupling of methane to ethylene using gaseous disulfur (2CH4 + S2 → C2H4 + 2H2S) as an oxidant (SOCM) proceeds with promising selectivity. Here, we report detailed experimental and theoretical studies that examine the mechanism for the conversion of CH4 to C2H4 over an Fe3O4-derived FeS2 catalyst achieving a promising ethylene selectivity of 33%. We compare and contrast these results with those for the highly exothermic oxidative coupling of methane (OCM) using O2 (2CH4 + O2 → C2H4 + 2H2O). SOCM kinetic/mechanistic analysis, along with density functional theory results, indicate that ethylene is produced as a primary product of methane activation, proceeding predominantly via CH2 coupling over dimeric S–S moieties that bridge Fe surface sites, and to a lesser degree, on heavily sulfided mononuclear sites. In contrast to and unlike OCM, the overoxidized CS2 by-product forms predominantly via CH4 oxidation, rather than from C2 products, through a series of C–H activation and S-addition steps at adsorbed sulfur sites on the FeS2 surface. The experimental rates for methane conversion are first order in both CH4 and S2, consistent with the involvement of two S sites in the rate-determining methane C–H activation step, with a CD4/CH4 kinetic isotope effect of 1.78. The experimental apparent activation energy for methane conversion is 66 ± 8 kJ/mol, significantly lower than for CH4 oxidative coupling with O2. The computed methane activation barrier, rate orders, and kinetic isotope values are consistent with experiment. All evidence indicates that SOCM proceeds via a very different pathway than that of OCM.
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Preuss, I., C. Knoblauch, J. Gebert, and E. M. Pfeiffer. "Improved quantification of microbial CH<sub>4</sub> oxidation efficiency in arctic wetland soils using carbon isotope fractionation." Biogeosciences 10, no. 4 (April 16, 2013): 2539–52. http://dx.doi.org/10.5194/bg-10-2539-2013.
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Abstract. Permafrost-affected tundra soils are significant sources of the climate-relevant trace gas methane (CH4). The observed accelerated warming of the arctic will cause deeper permafrost thawing, followed by increased carbon mineralization and CH4 formation in water-saturated tundra soils, thus creating a positive feedback to climate change. Aerobic CH4 oxidation is regarded as the key process reducing CH4 emissions from wetlands, but quantification of turnover rates has remained difficult so far. The application of carbon stable isotope fractionation enables the in situ quantification of CH4 oxidation efficiency in arctic wetland soils. The aim of the current study is to quantify CH4 oxidation efficiency in permafrost-affected tundra soils in Russia's Lena River delta based on stable isotope signatures of CH4. Therefore, depth profiles of CH4 concentrations and δ13CH4 signatures were measured and the fractionation factors for the processes of oxidation (αox) and diffusion (αdiff) were determined. Most previous studies employing stable isotope fractionation for the quantification of CH4 oxidation in soils of other habitats (such as landfill cover soils) have assumed a gas transport dominated by advection (αtrans = 1). In tundra soils, however, diffusion is the main gas transport mechanism and diffusive stable isotope fractionation should be considered alongside oxidative fractionation. For the first time, the stable isotope fractionation of CH4 diffusion through water-saturated soils was determined with an αdiff = 1.001 &pm; 0.000 (n = 3). CH4 stable isotope fractionation during diffusion through air-filled pores of the investigated polygonal tundra soils was αdiff = 1.013 &pm; 0.003 (n = 18). Furthermore, it was found that αox differs widely between sites and horizons (mean αox = 1.017 ± 0.009) and needs to be determined on a case by case basis. The impact of both fractionation factors on the quantification of CH4 oxidation was analyzed by considering both the potential diffusion rate under saturated and unsaturated conditions and potential oxidation rates. For a submerged, organic-rich soil, the data indicate a CH4 oxidation efficiency of 50% at the anaerobic–aerobic interface in the upper horizon. The improved in situ quantification of CH4 oxidation in wetlands enables a better assessment of current and potential CH4 sources and sinks in permafrost-affected ecosystems and their potential strengths in response to global warming.
3
van Grinsven, Sigrid, Kirsten Oswald, Bernhard Wehrli, Corinne Jegge, Jakob Zopfi, Moritz F. Lehmann, and Carsten J. Schubert. "Methane oxidation in the waters of a humic-rich boreal lake stimulated by photosynthesis, nitrite, Fe(III) and humics." Biogeosciences 18, no. 10 (May 20, 2021): 3087–101. http://dx.doi.org/10.5194/bg-18-3087-2021.
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Abstract. Small boreal lakes are known to contribute significantly to global CH4 emissions. Lake Lovojärvi is a eutrophic lake in southern Finland with bottom water CH4 concentrations up to 2 mM. However, the surface water concentration, and thus the diffusive emission potential, was low (< 0.5 µM). We studied the biogeochemical processes involved in CH4 removal by chemical profiling and through incubation experiments. δ13C-CH4 profiling of the water column revealed a methane-oxidation hotspot just below the oxycline and zones of CH4 oxidation within the anoxic water column. In incubation experiments involving the addition of light and/or oxygen, CH4 oxidation rates in the anoxic hypolimnion were enhanced 3-fold, suggesting a major role for photosynthetically fueled aerobic CH4 oxidation. We observed a distinct peak in CH4 concentration at the chlorophyll-a maximum, caused by either in situ CH4 production or other CH4 inputs such as lateral transport from the littoral zone. In the dark anoxic water column at 7 m depth, nitrite seemed to be the key electron acceptor involved in CH4 oxidation, yet additions of Fe(III), anthraquinone-2,6-disulfonate and humic substances also stimulated anoxic CH4 oxidation. Surprisingly, nitrite seemed to inhibit CH4 oxidation at all other depths. Overall, this study shows that photosynthetically fueled CH4 oxidation can be a key process in CH4 removal in the water column of humic, turbid lakes, thereby limiting diffusive CH4 emissions from boreal lakes. Yet, it also highlights the potential importance of a whole suite of alternative electron acceptors, including humics, in these freshwater environments in the absence of light and oxygen.
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Nielsen, Cecilie Skov, Niles J. Hasselquist, Mats B. Nilsson, Mats Öquist, Järvi Järveoja, and Matthias Peichl. "A Novel Approach for High-Frequency in-situ Quantification of Methane Oxidation in Peatlands." Soil Systems 3, no. 1 (December 31, 2018): 4. http://dx.doi.org/10.3390/soilsystems3010004.
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Methane (CH4) oxidation is an important process for regulating CH4 emissions from peatlands as it oxidizes CH4 to carbon dioxide (CO2). Our current knowledge about its temporal dynamics and contribution to ecosystem CO2 fluxes is, however, limited due to methodological constraints. Here, we present the first results from a novel method for quantifying in-situ CH4 oxidation at high temporal resolution. Using an automated chamber system, we measured the isotopic signature of heterotrophic respiration (CO2 emissions from vegetation-free plots) at a boreal mire in northern Sweden. Based on these data we calculated CH4 oxidation rates using a two-source isotope mixing model. During the measurement campaign, 74 % of potential CH4 fluxes from vegetation-free plots were oxidized to CO2, and CH4 oxidation contributed 20 ± 2.5 % to heterotrophic respiration corresponding to 10 ± 0.5 % of ecosystem respiration. Furthermore, the contribution of CH4 oxidation to heterotrophic respiration showed a distinct diurnal cycle being negligible during nighttime while contributing up to 35 ± 3.0 % during the daytime. Our results show that CH4 oxidation may represent an important component of the peatland ecosystem respiration and highlight the value of our method for measuring in-situ CH4 oxidation to better understand carbon dynamics in peatlands.
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Yoshimura, Masahiro, Jun-ichiro Kase, and Shigeyuki Sōmiya. "Oxidation of SiC powder by high-temperature, high-pressure H2O." Journal of Materials Research 1, no. 1 (February 1986): 100–103. http://dx.doi.org/10.1557/jmr.1986.0100.
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The reaction between SiC powder and H2O has been studied at 400°–800 °C under 10 and 100 MPa. Silicon carbide reacted with H2O to yield amorphous SiO2 and CH4 by the reaction SiC + 2H2O→SiO2 + CH4 above 500 °C. Cristobalite and tridymite crystallized from amorphous silica after the almost complete oxidation of SiC above 700 °C. The oxidation rate, as calculated from the weight gain, increased with temperature and pressure. The Arrhenius plotting of the reaction rate based on a Jander-type model gave apparent activation energies of 167–194 kJ/mol. Contrasted with oxidation in oxidative atmosphere, oxidation in H2O is characterized by the diffusion of H2O and CH4 in an amorphous silica layer where the diffusion seemed to be rate determining. Present results suggest that the oxidation of SiC includes the diffusion process of H2O in silica layers when atmospheres contain water vapor.
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Nykänen, H., S. Peura, P. Kankaala, and R. I. Jones. "Recycling and fluxes of carbon gases in a stratified boreal lake following experimental carbon addition." Biogeosciences Discussions 11, no. 11 (November 28, 2014): 16447–95. http://dx.doi.org/10.5194/bgd-11-16447-2014.
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Abstract. Partly anoxic stratified humic lakes are important sources of methane (CH4) and carbon dioxide (CO2) to the atmosphere. We followed the fate of CH4 and CO2 in a small boreal stratified lake, Alinen Mustajärvi, during 2007–2009. In 2008 and 2009 the lake received additions of dissolved organic carbon (DOC) with stable carbon isotope ratio (δ13C) around 16‰ higher than that of local allochthonous DOC. Carbon transformations in the water column were studied by measurements of δ13C of CH4 and of the dissolved inorganic carbon (DIC). Furthermore, CH4 and CO2 production, consumption and emissions were estimated. Methane oxidation was estimated by a diffusion gradient method. The amount, location and δ13C of CH4-derived biomass and CO2 in the water column were estimated from the CH4 oxidation pattern and from measured δ13C of CH4. Release of CH4 and CO2 to the atmosphere increased during the study. Methane production and almost total consumption of CH4 mostly in the anoxic water layers, was equivalent to the input from primary production (PP). δ13C of CH4 and DIC showed that hydrogenotrophic methanogenesis was the main source of CH4 to the water column, and methanogenic processes in general were the reasons for the 13C-enriched DIC at the lake bottom. CH4 and DIC became further 13C-enriched in the anoxic layer of the water column during the years of DOC addition. Even gradient diffusion measurements showed active CH4 oxidation in the anoxic portion of the water column; there was no clear 13C-enrichment of CH4 as generally used to estimate CH4 oxidation strength. Increase in δ13C-CH4 was clear between the metalimnion and epilimnion where the concentration of dissolved CH4 and the oxidation of CH4 were small. Thus, 13C-enrichment of CH4 does not reveal the main location of methanotrophy in a lake having simultaneous anaerobic and aerobic oxidation of CH4. Overall the results show that organic carbon is processed efficiently to CH4 and CO2 and recycled in the anoxic layer of stratified boreal lakes by CH4 oxidation. In spite of this, increased DOC input led to increased greenhouse gas release, mainly as CO2 but also as CH4. Due to the predominantly anaerobic CH4 oxidation, a relatively small amount of CH4-derived biomass was produced, while a large amount of CH4-derived CO2 was produced in the anoxic bottom zone of the lake.
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Zheng, Jianqiu, Taniya RoyChowdhury, Ziming Yang, Baohua Gu, Stan D. Wullschleger, and David E. Graham. "Impacts of temperature and soil characteristics on methane production and oxidation in Arctic tundra." Biogeosciences 15, no. 21 (November 8, 2018): 6621–35. http://dx.doi.org/10.5194/bg-15-6621-2018.
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Abstract. Rapid warming of Arctic ecosystems accelerates microbial decomposition of soil organic matter and leads to increased production of carbon dioxide (CO2) and methane (CH4). CH4 oxidation potentially mitigates CH4 emissions from permafrost regions, but it is still highly uncertain whether soils in high-latitude ecosystems will function as a net source or sink for CH4 in response to rising temperature and associated hydrological changes. We investigated CH4 production and oxidation potential in permafrost-affected soils from degraded ice-wedge polygons on the Barrow Environmental Observatory, Utqiaġvik (Barrow), Alaska, USA. Frozen soil cores from flat and high-centered polygons were sectioned into organic, transitional, and permafrost layers, and incubated at −2, +4 and +8 ∘C to determine potential CH4 production and oxidation rates. Significant CH4 production was only observed from the suboxic transition layer and permafrost of flat-centered polygon soil. These two soil sections also exhibited highest CH4 oxidation potentials. Organic soils from relatively dry surface layers had the lowest CH4 oxidation potential compared to saturated transition layer and permafrost, contradicting our original assumptions. Low methanogenesis rates are due to low overall microbial activities measured as total anaerobic respiration and the competing iron-reduction process. Our results suggest that CH4 oxidation could offset CH4 production and limit surface CH4 emissions, in response to elevated temperature, and thus must be considered in model predictions of net CH4 fluxes in Arctic polygonal tundra. Future changes in temperature and soil saturation conditions are likely to divert electron flow to alternative electron acceptors and significantly alter CH4 production, which should also be considered in CH4 models.
8
Ren, Tie, John A. Amaral, and Roger Knowles. "The response of methane consumption by pure cultures of methanotrophic bacteria to oxygen." Canadian Journal of Microbiology 43, no. 10 (October 1, 1997): 925–28. http://dx.doi.org/10.1139/m97-133.
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The rates of CH4 oxidation by strains of groups I and II methanotrophs in pure culture were studied at various O2 concentrations from 0 to 63 % v/v. In the presence of nonlimiting dissolved CH4 and inorganic nitrogen, O2 concentrations from 0.45 to 20% v/v supported maximum rates of CH4 oxidation. The critical dissolved O2 concentration under our conditions was about 5.7 μM, below which O2 was limiting for CH4 oxidation. Concentrations of O2 up to 63% v/v depressed the activity of CH4 oxidation by ≥ 23%. We conclude that methanotrophs are not microaerophilic under the conditions of our experiments and that they have a high affinity for O2.Key words: CH4 oxidation, O2 response, Methylosinus trichosporium, Methylobacter luteus.
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Preuss, I., C. Knoblauch, J. Gebert, and E. M. Pfeiffer. "Improved quantification of microbial CH<sub>4</sub> oxidation efficiency in Arctic wetland soils using carbon isotope fractionation." Biogeosciences Discussions 9, no. 12 (December 4, 2012): 16999–7035. http://dx.doi.org/10.5194/bgd-9-16999-2012.
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Abstract. Permafrost-affected tundra soils are significant sources of the climate-relevant trace gas methane (CH4). The observed accelerated warming of the Arctic will cause a deeper permafrost thawing followed by increased carbon mineralization and CH4 formation in water saturated tundra soils which might cause a positive feedback to climate change. Aerobic CH4 oxidation is regarded as the key process reducing CH4 emissions from wetlands, but quantification of turnover rates has remained difficult so far. The application of carbon stable isotope fractionation enables the in situ quantification of CH4 oxidation efficiency in arctic wetland soils. The aim of the current study is to quantify CH4 oxidation efficiency in permafrost-affected tundra soils in Russia's Lena River Delta based on stable isotope signatures of CH4. Therefore, depth profiles of CH4 concentrations and δ13CH4-signatures were measured and the fractionation factors for the processes of oxidation (αox) and diffusion (αdiff) were determined. Most previous studies employing stable isotope fractionation for the quantification of CH4 oxidation in soils of other habitats (e.g. landfill cover soils) have assumed a gas transport dominated by advection (αtrans = 1). In tundra soils, however, diffusion is the main gas transport mechanism, aside from ebullition. Hence, diffusive stable isotope fractionation has to be considered. For the first time, the stable isotope fractionation of CH4 diffusion through water-saturated soils was determined with an αdiff = 1.001 ± 0.000 (n = 3). CH4 stable isotope fractionation during diffusion through air-filled pores of the investigated polygonal tundra soils was αdiff = 1.013 ± 0.003 (n = 18). Furthermore, it was found that αox differs widely between sites and horizons (mean αox, = 1.017 ± 0.009) and needs to be determined individually. The impact of both fractionation factors on the quantification of CH4 oxidation was analyzed by considering both the potential diffusion rate under saturated and unsaturated conditions and potential oxidation rates. For a submerged organic rich soil, the data indicate a CH4 oxidation efficiency of 50% at the anaerobic-aerobic interface in the upper horizon. The improved in situ quantification of CH4 oxidation in wetlands enables a better assessment of current and potential CH4 sources and sinks in permafrost affected ecosystems and their potential strengths in response to global warming.
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Martinez-Cruz, K., A. Sepulveda-Jauregui, K. Walter Anthony, and F. Thalasso. "Geographic and seasonal variation of dissolved methane and aerobic methane oxidation in Alaskan lakes." Biogeosciences Discussions 12, no. 5 (March 9, 2015): 4213–43. http://dx.doi.org/10.5194/bgd-12-4213-2015.
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Abstract. Methanotrophic bacteria play an important role oxidizing a significant fraction of methane (CH4) produced in lakes. Aerobic CH4 oxidation depends on lake CH4 and oxygen (O2) concentrations, temperature, and organic carbon input to lakes, including from thawing permafrost in thermokarst (thaw)-affected lakes. Given the large variability in these environmental factors, CH4 oxidation is expected to be subject to large seasonal and geographic variations, which have been scarcely reported in the literature. In the present study, we measured CH4 oxidation rates in 30 Alaskan lakes along a north–south latitudinal transect during winter and summer with a new field laser spectroscopy method. Additionally, we measured dissolved CH4 and O2 concentrations. We found that in the winter, aerobic CH4 oxidation was mainly controlled by the dissolved O2 concentration, while in the summer it was controlled primarily by the CH4 concentration, which was in deficit compared to dissolved O2. The permafrost environment of the lakes was identified as another key factor. Thermokarst (thaw) lakes formed in yedoma-type permafrost had significantly higher CH4 oxidation rates compared to other thermokarst and non-thermokarst lakes formed in non-yedoma permafrost environments. These results confirm that landscape processes play an important role in lake CH4 cycling.
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Sun, Jintao, Qi Chen, Baoming Zhao, Caohui Guo, Jianyu Liu, Mingming Zhang, and Decai Li. "Temperature-dependent ion chemistry in nanosecond discharge plasma-assisted CH4 oxidation." Journal of Physics D: Applied Physics 55, no. 13 (January 4, 2022): 135203. http://dx.doi.org/10.1088/1361-6463/ac45ac.
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Abstract Ion chemistry with temperature evolution in weakly ionized plasma is important in plasma-assisted combustion and plasma-assisted catalysis, fuel reforming, and material synthesis due to its contribution to plasma generation and state transition. In this study, the kinetic roles of ionic reactions in nanosecond discharge (NSD) plasma-assisted temperature-dependent decomposition and oxidation of methane are investigated by integrated studies of experimental measurements and mathematical simulations. A detailed plasma chemistry mechanism governing the decomposition and oxidation processes in a He/CH4/O2 combustible mixture is proposed and studied by including a set of electron impact reactions, reactions involving excited species, and ionic reactions. A zero-dimensional model incorporating the plasma kinetics solver ZDPlasKin and the combustion chemical kinetics solver CHEMKIN is used to calculate the time and temperature evolution of the ion density. Uncertainty analysis of ionic reactions on key species generation is conducted by using different referenced data, and insignificant sensitivity is found. The numerical model is consistent with experimental data for methane consumption and generation of major species including CO, CO2, and H2. By modeling the temporal evolution of key ions, it is observed that O2 + presents the largest concentration in the discharge stage, followed by CH4 +, CH3 +, and CH2 +, which is in accordance with the traditional ion chemistry in hydrocarbon flames and agrees well with molecular-beam mass spectrometer investigations. The path flux shows that the concentrations of key species, including electrons, O, OH, H, O(1D), O2(a1Δg), O2 +, CH3 +, and CH4 +, change within 1–2 orders of magnitude and that the transition from a homogeneous state to a contracted/constricted state does not occur. The path flux and sensitivity analysis reveal the significant roles of cations in the stimulation of active radical generation, including CH, O, OH, and O(1D), thus accelerating methane oxidation. This work provides a deep insight into the ion chemistry of temperature-dependent plasma-assisted CH4 oxidation.
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Detweiler, Angela M., Brad M. Bebout, Adrienne E. Frisbee, Cheryl A. Kelley, Jeffrey P. Chanton, and Leslie E. Prufert-Bebout. "Characterization of methane flux from photosynthetic oxidation ponds in a wastewater treatment plant." Water Science and Technology 70, no. 6 (July 14, 2014): 980–89. http://dx.doi.org/10.2166/wst.2014.317.
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Photosynthetic oxidation ponds are a low-cost method for secondary treatment of wastewater using natural and more energy-efficient aeration strategies. Methane (CH4) is produced during the anaerobic digestion of organic matter, but only some of it is oxidized in the water column, with the remaining CH4 escaping into the atmosphere. In order to characterize the CH4 flux in two photosynthetic oxidation ponds in a wastewater treatment plant in northern California, the isotopic compositions and concentrations of CH4 were measured in the water column, in bubbles and in flux chambers, over a period of 12 to 21 months to account for seasonal trends in CH4 emissions. Methane flux varied seasonally throughout the year, with an annual average flux of 5.5 g CH4 m−2 d−1 Over half of the CH4 flux, 56.1–74.4% v/v, was attributed to ebullition. The oxidation efficiency of this system was estimated at 69.1%, based on stable carbon isotopes and a calculated fractionation factor of 1.028. This is the first time, to our knowledge, that a fractionation factor for CH4 oxidation has been empirically determined for oxidation ponds. Quantifying CH4 emissions from these systems is essential to properly identify their contribution and to mitigate their impact on global warming.
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Li, Jing, Xiaoqing Xu, Changling Liu, Nengyou Wu, Zhilei Sun, Xingliang He, and Ye Chen. "Active Methanotrophs and Their Response to Temperature in Marine Environments: An Experimental Study." Journal of Marine Science and Engineering 9, no. 11 (November 12, 2021): 1261. http://dx.doi.org/10.3390/jmse9111261.
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Aerobic methane (CH4) oxidation plays a significant role in marine CH4 consumption. Temperature changes resulting from, for example, global warming, have been suggested to be able to influence methanotrophic communities and their CH4 oxidation capacity. However, exact knowledge regarding temperature controls on marine aerobic methane oxidation is still missing. In this study, CH4 consumption and the methanotrophic community structure were investigated by incubating sediments from shallow (Bohai Bay) and deep marine environments (East China Sea) at 4, 15, and 28 °C for up to 250 days. The results show that the abundance of the methanotrophic population, dominated by the family Methylococcaceae (type I methanotrophs), was significantly elevated after all incubations and that aerobic methane oxidation for both areas had a strong temperature sensitivity. A positive correlation between the CH4 oxidation rate and temperature was witnessed in the Bohai Bay incubations, whereas for the East China Sea incubations, the optimum temperature was 15 °C. The systematic variations of pmoA OTUs between the Bohai Bay and East China Sea incubations indicated that the exact behaviors of CH4 oxidation rates with temperature are related to the different methanotrophic community structures in shallow and deep seas. These results are of great significance for quantitatively evaluating the biodegradability of CH4 in different marine environments.
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Michaelis, Tamara, Anja Wunderlich, Ömer K. Coskun, William Orsi, Thomas Baumann, and Florian Einsiedl. "High-resolution vertical biogeochemical profiles in the hyporheic zone reveal insights into microbial methane cycling." Biogeosciences 19, no. 18 (September 21, 2022): 4551–69. http://dx.doi.org/10.5194/bg-19-4551-2022.
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Abstract. Facing the challenges of climate change, policy making relies on sound greenhouse gas (GHG) budgets. Rivers and streams emit large quantities of the potent GHG methane (CH4), but their global impact on atmospheric CH4 concentrations is highly uncertain. In situ data from the hyporheic zone (HZ), where most CH4 is produced and some of it can be oxidized to CO2, are lacking for an accurate description of CH4 production and consumption in streams. To address this, we recorded high-resolution depth-resolved geochemical profiles at five different locations in the stream bed of the river Moosach, southern Germany. Specifically, we measured pore-water concentrations and stable carbon isotopes (δ13C) of dissolved CH4 as well as relevant electron acceptors for oxidation with a 1 cm vertical depth resolution. Findings were interpreted with the help of a numerical model, and 16S rRNA gene analyses added information on the microbial community at one of the locations. Our data confirm with pore-water CH4 concentrations of up to 1000 µmol L−1 that large quantities of CH4 are produced in the HZ. Stable isotope measurements of CH4 suggest that hydrogenotrophic methanogenesis represents a dominant pathway for CH4 production in the HZ of the river Moosach, while a relatively high abundance of a novel group of methanogenic archaea, the Candidatus “Methanomethyliales” (phylum Candidatus “Verstraetearchaeota”), indicate that CH4 production through H2-dependent methylotrophic methanogenesis might also be an important CH4 source. Combined isotopic and modeling results clearly implied CH4 oxidation processes at one of the sampled locations, but due to the steep chemical gradients and the close proximity of the oxygen and nitrate reduction zones, no single electron acceptor for this process could be identified. Nevertheless, the numerical modeling results showed potential not only for aerobic CH4 oxidation but also for anaerobic oxidation of CH4 coupled to denitrification. In addition, the nitrate–methane transition zone was characterized by an increased relative abundance of microbial groups (Crenothrix, NC10) known to mediate nitrate and nitrite-dependent methane oxidation in the hyporheic zone. This study demonstrates substantial CH4 production in hyporheic sediments, a potential for aerobic and anaerobic CH4 oxidation, and underlines the high spatiotemporal variability in this habitat.
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Zhang, G. B., Y. Ji, J. Ma, G. Liu, H. Xu, and K. Yagi. "Pathway of CH<sub>4</sub> production, fraction of CH<sub>4</sub> oxidized, and <sup>13</sup>C isotope fractionation in a straw incorporated rice field." Biogeosciences Discussions 9, no. 10 (October 15, 2012): 14175–215. http://dx.doi.org/10.5194/bgd-9-14175-2012.
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Abstract. Straw incorporation generally increases CH4 emission from rice fields, but its effects on the mechanism of CH4 emission, especially on the pathway of CH4 production and the fraction of CH4 oxidized are not well known. To investigate the methanogenic pathway, the fraction of CH4 oxidized as well as the stable carbon isotope fractionation during the oxidation and transport of CH4 as affected by straw incorporation, production and oxidation of CH4 in paddy soil and rice roots and δ13C-values of produced CH4 and CO2, and emitted CH4 were observed in incubation and field experiments. Straw incorporation significantly enhanced CH4 production potentials of the paddy soil and rice roots. However, it increased the relative contribution of acetate to total CH4 production (Fac) in the paddy soil by ~ 10–30%, but decreased Fac-value of the rice roots by ~ 5–20%. Compared with rice roots, paddy soil was more important in acetoclastic methanogenesis, with Fac-value being 6–30% higher. Straw incorporation highly decreased the fraction of CH4 oxidized (Fox) by 41–71%, probably attributed to the fact that it increased CH4 oxidation potential whereas CH4 production potential was increased to a larger extent. There was little CH4 formed during aerobic incubation, and the produced CH4 was more 13C-enriched relative to that of anaerobic incubation. Assuming δ13C-values of CH4 aerobically produced in paddy soil to be the δ13C-values of residual CH4 after being oxidized, Fox-value still appeared to be 45–68% lower when straw was incorporated. Oxidation fractionation factor (αox) was higher with straw incorporation (1.033) than without straw incorporation (1.025). The δ13C-values of CH4 emitted after cutting of the plants (−50–−43‰) were more positive than those of before (−58–−55‰), suggesting a transport fractionation factor (&varepsilon;transport) was −8.0‰ with straw incorporation and −12.0‰ without straw incorporation. Reasons for this difference may be related to the decrease in growth of the rice crop as a result of straw incorporation. The experiment shows that straw incorporation increases the contribution of acetate to total methanogenesis in paddy soil but decreases it on rice roots, and it significantly decreases the fraction of CH4 oxidized in the field, and expands oxidation fractionation while reducing transport fractionation.
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Martinez-Cruz, K., A. Sepulveda-Jauregui, K. Walter Anthony, and F. Thalasso. "Geographic and seasonal variation of dissolved methane and aerobic methane oxidation in Alaskan lakes." Biogeosciences 12, no. 15 (August 4, 2015): 4595–606. http://dx.doi.org/10.5194/bg-12-4595-2015.
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Abstract. Methanotrophic bacteria play an important role oxidizing a significant fraction of methane (CH4) produced in lakes. Aerobic CH4 oxidation depends mainly on lake CH4 and oxygen (O2) concentrations, in such a manner that higher MO rates are usually found at the oxic/anoxic interface, where both molecules are present. MO also depends on temperature, and via methanogenesis, on organic carbon input to lakes, including from thawing permafrost in thermokarst (thaw)-affected lakes. Given the large variability in these environmental factors, CH4 oxidation is expected to be subject to large seasonal and geographic variations, which have been scarcely reported in the literature. In the present study, we measured CH4 oxidation rates in 30 Alaskan lakes along a north-south latitudinal transect during winter and summer with a new field laser spectroscopy method. Additionally, we measured dissolved CH4 and O2 concentrations. We found that in the winter, aerobic CH4 oxidation was mainly controlled by the dissolved O2 concentration, while in the summer it was controlled primarily by the CH4 concentration, which was scarce compared to dissolved O2. The permafrost environment of the lakes was identified as another key factor. Thermokarst (thaw) lakes formed in yedoma-type permafrost had significantly higher CH4 oxidation rates compared to other thermokarst and non-thermokarst lakes formed in non-yedoma permafrost environments. As thermokarst lakes formed in yedoma-type permafrost have been identified to receive large quantities of terrestrial organic carbon from thaw and subsidence of the surrounding landscape into the lake, confirming the strong coupling between terrestrial and aquatic habitats and its influence on CH4 cycling.
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Wu, Beibei, Beidou Xi, Xiaosong He, Xiaojie Sun, Qian Li, Quanyi Ouche, Hongxia Zhang, and Chennan Xue. "Methane Emission Reduction Enhanced by Hydrophobic Biochar-Modified Soil Cover." Processes 8, no. 2 (February 1, 2020): 162. http://dx.doi.org/10.3390/pr8020162.
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The microbial oxidation of CH4 in biochar-modified soil cover is considered a potent option for the mitigation of emissions from old landfills or sites containing wastes full of low CH4 generation rates. The mechanism of methane oxidizing bacteria (MOB) can be enhanced by amending the landfill cover soil with biochar, which is recalcitrant to biological degradation and can adsorb CH4 while facilitating the growth and activity of MOB within its porous structure. However, the increase in the permeability coefficient and water content of the cover due to the addition of biochar also affects the methane removal efficiency. A hydrophobic biochar modified by KH-570 was employed to reduce the water content and to promote the diffusion and oxidation of CH4 in the cover. Several series of small-scale column tests were conducted to quantify the CH4 oxidation properties of the landfill cover soil amended with biochar and hydrophobic biochar under different levels of exposed CH4 concentrations (5% and 15%), heights (10–66 cm), and temperatures (15–40 °C). After 30 days of domestication, the removal rate of the hydrophobic biochar-modified soil cover reached 98.8%. The water holding capacity of the cover and the CH4 oxidation efficiency under different moisture contents were investigated in different columns. The hydrophobic biochar-modified soil cover has a weak water holding capacity, low saturated water content, and optimal CH4 oxidation efficiency at this time.
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Rose, Juliana Lundgren, Cláudio Fernando Mahler, and Ronaldo Luis dos Santos Izzo. "Comparison of the methane oxidation rate in four media." Revista Brasileira de Ciência do Solo 36, no. 3 (June 2012): 803–12. http://dx.doi.org/10.1590/s0100-06832012000300011.
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Landfill gas emissions are one of the main sources of anthropogenic methane (CH4), a major greenhouse gas. In this paper, an economically attractive alternative to minimize greenhouse gas emissions from municipal solid waste landfills was sought. This alternative consists in special biofilters as landfill covers with oxidative capacity in the presence of CH4. To improve the quality/cost ratio of the project, compost was chosen as one of the cover substrates and soil (Typic red yellow-silt-clay Podzolic) as the other. The performance of four substrates was studied in laboratory experiments: municipal solid waste (MSW) compost, soil, and two soil-compost at different proportions. This study aimed to evaluate the suitability and environmental compatibility as a means of CH4 oxidation in biofilters. Four biofilters were constructed in 60 cm PVC tubes with an internal diameter of 10 cm. Each filter contained 2.3 L of oxidizing substrate at the beginning of the experiment. The gas used was a mixture of CH4 and air introduced at the bottom of each biofilter, at a flow of 150 mL min-1, by a flow meter. One hundred days after the beginning of the experiment, the best biofilter was the MSW compost with an oxidation rate of 990 g m-3 day-1 , corresponding to an efficiency of 44 %. It can be concluded that the four substrates studied have satisfactory oxidative capacity, and the substrates can be used advantageously as cover substrate of MSW landfills.
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Price, Sally J., Francis M. Kelliher, Robert R. Sherlock, Kevin R. Tate, and Leo M. Condron. "Environmental and chemical factors regulating methane oxidation in a New Zealand forest soil." Soil Research 42, no. 7 (2004): 767. http://dx.doi.org/10.1071/sr04026.
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Tropospheric methane (CH4) is oxidised by soil microbes called methanotrophs. We examined them in soil samples from a pristine Nothofagus forest located in New Zealand. Laboratory incubations indicated the presence of high-affinity methanotrophs that displayed Michaelis–Menton kinetics (Km = 8.4 µL/L where Km is the substrate concentration at half the maximal rate). When the soil was dried from its field capacity water content of 0.34 to 0.16 m3/m3, CH4 oxidation rate increased nearly 7-fold. The methanotrophs were thus metabolically poised for very high activity, but substrate availability was commonly limiting. When water content was held constant, CH4 oxidation rate nearly doubled as temperature increased from 5 to 12°C, a range found in the forest. By contrast, CH4 oxidation rate did not change much from 12 to 30°C, and it was zero at 35°C. When water content and temperature were held constant, the optimal soil pH for CH4 oxidation was 4.4, as found in the forest. Soil disturbance by nitrogen (N) and non-N salt amendment decreased CH4 oxidation rate, but this depended on the amendment species and concentration. The methanotrophs were adapted to native conditions and exhibited a great sensitivity to disturbance.
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Zhang, G. B., Y. Ji, J. Ma, G. Liu, H. Xu, and K. Yagi. "Pathway of CH<sub>4</sub> production, fraction of CH<sub>4</sub> oxidized, and <sup>13</sup>C isotope fractionation in a straw-incorporated rice field." Biogeosciences 10, no. 5 (May 22, 2013): 3375–89. http://dx.doi.org/10.5194/bg-10-3375-2013.
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Abstract. Straw incorporation generally increases CH4 emission from rice fields, but its effects on the mechanism of CH4 emission, especially on the pathway of CH4 production and the fraction of CH4 oxidized, are not well known. To investigate the methanogenic pathway, the fraction of CH4 oxidized as well as the stable carbon isotope fractionation during the oxidation and transport of CH4 as affected by straw incorporation, observations were conducted of production and oxidation of CH4 in paddy soil and rice roots and δ13C-values of produced CH4 and CO2, and emitted CH4 in incubation and field experiments. Straw incorporation significantly enhanced CH4 production potentials of the paddy soil and rice roots. However, it increased the relative contribution of acetate to total CH4 production (Fac) in the paddy soil by ∼10–30%, but decreased Fac-value of the rice roots by ∼5–20%. Compared with rice roots, paddy soil was more important in acetoclastic methanogenesis, with Fac-value being 6–30% higher. Straw incorporation highly decreased the fraction of CH4 oxidized (Fox) by 41–71%, probably attributed to the fact that it increased CH4 oxidation potential whereas CH4 production potential was increased to a larger extent. There was little CH4 formed during aerobic incubation, and the produced CH4 was more 13C-enriched relative to that of anaerobic incubation. Assuming δ13C-values of CH4 aerobically produced in paddy soil to be the δ13C-values of residual CH4 after being oxidized, (Fox-value still appeared to be 45–68% lower when straw was incorporated. Oxidation fractionation factor (αox) was higher with straw incorporation (1.033) than without straw incorporation (1.025). The δ13C-values of CH4 emitted after cutting of the plants (−50 to −43‰) were more positive than those of before (−58 to −55‰), suggesting a transport fractionation factor (&varepsilon;transport) was −8.0‰ with straw incorporation and −12.0‰ without straw incorporation. Causes of this difference may be related to the diffusion process in transport as affected by growth of rice plants and pressure in the rhizosphere. The experiment shows that straw incorporation increases the contribution of acetate to total methanogenesis in paddy soil but decreases it on rice roots, and it significantly decreases the fraction of CH4 oxidized in the field and expands oxidation fractionation while reducing transport fractionation.
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Zhang, G. B., Y. Ji, J. Ma, H. Xu, and Z. C. Cai. "Case study on effects of water management and rice straw incorporation in rice fields on production, oxidation, and emission of methane during fallow and following rice seasons." Soil Research 49, no. 3 (2011): 238. http://dx.doi.org/10.1071/sr10117.
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To investigate production, oxidation, and emission of methane (CH4) in rice fields during the fallow and following rice seasons as affected by water management and rice straw incorporation in the fallow season, field and incubation experiments were carried out from November 2007 to November 2008. Four treatments, i.e. two water managements (flooded and drained) and two rates of rice straw application (0 and 4.8 t/ha), were laid out in a randomised block design. Results show that obvious CH4 production occurred in flooded fields in the late fallow season; consequently, fallow CH4 emission contributed 9.6–33.1% to the annual total emission. However, emission mainly occurred during the rice season. During the rice season, the mean CH4 production potential in flooded fields was 2.6–3.8 times that in drained fields, making the total CH4 emission 2.1–2.5 times that in drained fields. Rice straw incorporated in flooded fields significantly increased production and emission of CH4 during both the fallow and the following rice seasons (P < 0.05), but in drained fields, no significant effect was observed (P > 0.05). There was no significant difference in mean CH4 oxidation potential between the treatments (P > 0.05), indicating that water management and rice straw incorporation in the fallow season have little influence on CH4 oxidation during the fallow and following rice seasons. Based on the findings, water management and rice straw incorporation in the fallow season significantly affected CH4 emission during the fallow and the following rice seasons by influencing CH4 production rather than CH4 oxidation in fields.
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Rigby, Matthew, Stephen A. Montzka, Ronald G. Prinn, James W. C. White, Dickon Young, Simon O’Doherty, Mark F. Lunt, et al. "Role of atmospheric oxidation in recent methane growth." Proceedings of the National Academy of Sciences 114, no. 21 (April 17, 2017): 5373–77. http://dx.doi.org/10.1073/pnas.1616426114.
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The growth in global methane (CH4) concentration, which had been ongoing since the industrial revolution, stalled around the year 2000 before resuming globally in 2007. We evaluate the role of the hydroxyl radical (OH), the major CH4 sink, in the recent CH4 growth. We also examine the influence of systematic uncertainties in OH concentrations on CH4 emissions inferred from atmospheric observations. We use observations of 1,1,1-trichloroethane (CH3CCl3), which is lost primarily through reaction with OH, to estimate OH levels as well as CH3CC3 emissions, which have uncertainty that previously limited the accuracy of OH estimates. We find a 64–70% probability that a decline in OH has contributed to the post-2007 methane rise. Our median solution suggests that CH4 emissions increased relatively steadily during the late 1990s and early 2000s, after which growth was more modest. This solution obviates the need for a sudden statistically significant change in total CH4 emissions around the year 2007 to explain the atmospheric observations and can explain some of the decline in the atmospheric 13CH4/12CH4 ratio and the recent growth in C2H6. Our approach indicates that significant OH-related uncertainties in the CH4 budget remain, and we find that it is not possible to implicate, with a high degree of confidence, rapid global CH4 emissions changes as the primary driver of recent trends when our inferred OH trends and these uncertainties are considered.
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Chi, Zi-Fang, Wen-Jing Lu, Huai Li, and Hong-Tao Wang. "Dynamics of CH4 oxidation in landfill biocover soil: Effect of O2/CH4 ratio on CH4 metabolism." Environmental Pollution 170 (November 2012): 8–14. http://dx.doi.org/10.1016/j.envpol.2012.06.005.
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Otsuka, Kiyoshi, Masaharu Hatano, and Takayuki Komatsu. "Synthesis of C2H4 by partial oxidation of CH4 over LiCl/NiO." Catalysis Today 4, no. 3-4 (February 1989): 409–19. http://dx.doi.org/10.1016/0920-5861(89)85037-0.
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Tveit, Alexander Tøsdal, Tilman Schmider, Anne Grethe Hestnes, Matteus Lindgren, Alena Didriksen, and Mette Marianne Svenning. "Simultaneous Oxidation of Atmospheric Methane, Carbon Monoxide and Hydrogen for Bacterial Growth." Microorganisms 9, no. 1 (January 12, 2021): 153. http://dx.doi.org/10.3390/microorganisms9010153.
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The second largest sink for atmospheric methane (CH4) is atmospheric methane oxidizing-bacteria (atmMOB). How atmMOB are able to sustain life on the low CH4 concentrations in air is unknown. Here, we show that during growth, with air as its only source for energy and carbon, the recently isolated atmospheric methane-oxidizer Methylocapsa gorgona MG08 (USCα) oxidizes three atmospheric energy sources: CH4, carbon monoxide (CO), and hydrogen (H2) to support growth. The cell-specific CH4 oxidation rate of M. gorgona MG08 was estimated at ~0.7 × 10−18 mol cell−1 h−1, which, together with the oxidation of CO and H2, supplies 0.38 kJ Cmol−1 h−1 during growth in air. This is seven times lower than previously assumed necessary to support bacterial maintenance. We conclude that atmospheric methane-oxidation is supported by a metabolic flexibility that enables the simultaneous harvest of CH4, H2 and CO from air, but the key characteristic of atmospheric CH4 oxidizing bacteria might be very low energy requirements.
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Bradford, M. A., P. Ineson, P. A. Wookey, and H. M. Lappin-Scott. "Role of CH4 oxidation, production and transport in forest soil CH4 flux." Soil Biology and Biochemistry 33, no. 12-13 (October 2001): 1625–31. http://dx.doi.org/10.1016/s0038-0717(01)00078-5.
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Prajapati, Aditya, Brianna A. Collins, Jason D. Goodpaster, and Meenesh R. Singh. "Fundamental insight into electrochemical oxidation of methane towards methanol on transition metal oxides." Proceedings of the National Academy of Sciences 118, no. 8 (February 17, 2021): e2023233118. http://dx.doi.org/10.1073/pnas.2023233118.
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Electrochemical oxidation of CH4 is known to be inefficient in aqueous electrolytes. The lower activity of methane oxidation reaction (MOR) is primarily attributed to the dominant oxygen evolution reaction (OER) and the higher barrier for CH4 activation on transition metal oxides (TMOs). However, a satisfactory explanation for the origins of such lower activity of MOR on TMOs, along with the enabling strategies to partially oxidize CH4 to CH3OH, have not been developed yet. We report here the activation of CH4 is governed by a previously unrecognized consequence of electrostatic (or Madelung) potential of metal atom in TMOs. The measured binding energies of CH4 on 12 different TMOs scale linearly with the Madelung potentials of the metal in the TMOs. The MOR active TMOs are the ones with higher CH4 binding energy and lower Madelung potential. Out of 12 TMOs studied here, only TiO2, IrO2, PbO2, and PtO2 are active for MOR, where the stable active site is the O on top of the metal in TMOs. The reaction pathway for MOR proceeds primarily through *CHx intermediates at lower potentials and through *CH3OH intermediates at higher potentials. The key MOR intermediate *CH3OH is identified on TiO2 under operando conditions at higher potential using transient open-circuit potential measurement. To minimize the overoxidation of *CH3OH, a bimetallic Cu2O3 on TiO2 catalysts is developed, in which Cu reduces the barrier for the reaction of *CH3 and *OH and facilitates the desorption of *CH3OH. The highest faradaic efficiency of 6% is obtained using Cu-Ti bimetallic TMO.
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Morana, C., A. V. Borges, F. A. E. Roland, F. Darchambeau, J. P. Descy, and S. Bouillon. "Methanotrophy within the water column of a large meromictic tropical lake (Lake Kivu, East Africa)." Biogeosciences 12, no. 7 (April 7, 2015): 2077–88. http://dx.doi.org/10.5194/bg-12-2077-2015.
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Abstract. The permanently stratified Lake Kivu is one of the largest freshwater reservoirs of dissolved methane (CH4) on Earth. Yet CH4 emissions from its surface to the atmosphere have been estimated to be 2 orders of magnitude lower than the CH4 upward flux to the mixed layer, suggesting that microbial CH4 oxidation is an important process within the water column. A combination of natural abundance stable carbon isotope analysis (δ13C) of several carbon pools and 13CH4-labelling experiments was carried out during the rainy and dry season to quantify (i) the contribution of CH4-derived carbon to the biomass, (ii) methanotrophic bacterial production (MBP), and (iii) methanotrophic bacterial growth efficiency (MBGE), defined as the ratio between MBP and gross CH4 oxidation. We also investigated the distribution and the δ13C of specific phospholipid fatty acids (PLFAs), used as biomarkers for aerobic methanotrophs. Maximal MBP rates were measured in the oxycline, suggesting that CH4 oxidation was mainly driven by oxic processes. Moreover, our data revealed that methanotrophic organisms in the water column oxidized most of the upward flux of CH4, and that a significant amount of CH4-derived carbon was incorporated into the microbial biomass in the oxycline. The MBGE was variable (2–50%) and negatively related to CH4 : O2 molar ratios. Thus, a comparatively smaller fraction of CH4-derived carbon was incorporated into the cellular biomass in deeper waters, at the bottom of the oxycline where oxygen was scarce. The aerobic methanotrophic community was clearly dominated by type I methanotrophs and no evidence was found for an active involvement of type II methanotrophs in CH4 oxidation in Lake Kivu, based on fatty acids analyses. Vertically integrated over the water column, the MBP was equivalent to 16–60% of the average phytoplankton particulate primary production. This relatively high magnitude of MBP, and the substantial contribution of CH4-derived carbon to the overall biomass in the oxycline, suggest that methanotrophic bacteria could potentially sustain a significant fraction of the pelagic food web in the deep, meromictic Lake Kivu.
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Morana, C., A. V. Borges, F. A. E. Roland, F. Darchambeau, J. P. Descy, and S. Bouillon. "Methanotrophy within the water column of a large meromictic tropical lake (Lake Kivu, East Africa)." Biogeosciences Discussions 11, no. 11 (November 7, 2014): 15663–91. http://dx.doi.org/10.5194/bgd-11-15663-2014.
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Abstract. The permanently stratified Lake Kivu is one of the largest freshwater reservoirs of dissolved methane (CH4) on Earth. Yet CH4 emissions from its surface to the atmosphere has been estimated to be 2 orders of magnitude lower than the CH4 upward flux to the mixed layer, showing that microbial CH4 oxidation is an important process within the water column. A combination of natural abundance carbon stable isotope analysis (δ13C) of several inorganic and organic carbon pools and 13CH4-labelling experiments was carried out during rainy and dry season to quantify (i) the contribution of CH4-derived carbon to the biomass, (ii) methanotrophic bacterial production (MBP), and (iii) methanotrophic bacterial growth efficiency (MBGE), defined as the ratio between MBP and gross CH4 oxidation. We also investigated the distribution and the δ13C of specific phospholipid fatty acids (PLFA), used as biomarkers for aerobic methanotrophs. Data revealed that methanotrophic organisms oxidized within the water column most of the upward flux of CH4 to the mixed layer and a significant amount of CH4-derived carbon was incorporated into the microbial biomass in the oxycline. Maximal MBP rates were measured in the oxycline, suggesting that CH4 oxidation was mainly driven by oxic processes. The MBGE was variable (2–50%) and negatively related to CH4 : O2 molar ratios. Thus, a comparatively smaller fraction of CH4-derived carbon was incorporated into the cellular biomass in deeper waters, at the bottom of the oxycline where oxygen was scarce. The aerobic methanotrophic community was clearly dominated by type I methanotrophs and no evidence was found for an active involvement of type II methanotrophs in CH4 oxidation in Lake Kivu. Vertically integrated over the water column, the MBP was equivalent to 16–58% of the average phytoplankton primary production. This relatively high magnitude of MBP, and the substantial contribution of CH4-derived carbon to the overall biomass in the oxycline, suggest that methanotrophic bacteria could potentially sustain a significant fraction of the pelagic food-web in the deep oligotrophic Lake Kivu.
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Dote, Yutaka. "Kinetics of CH4 oxidation in mixed culture." Waste Management & Research 20, no. 6 (December 2002): 494–500. http://dx.doi.org/10.1177/0734242x0202000603.
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Wu, Yo-ping G., and Ya-Fen Lin. "High temperature oxidation of C2Cl4/CH4 mixtures." Journal of Hazardous Materials 91, no. 1-3 (April 2002): 239–56. http://dx.doi.org/10.1016/s0304-3894(01)00393-4.
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Giannikos, A., A. D. Frantzis, C. Pliangos, S. Bebelis, and C. G. Vayenas. "Electrochemical promotion of CH4 oxidation on Pd." Ionics 4, no. 1-2 (January 1998): 53–60. http://dx.doi.org/10.1007/bf02375780.
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Du, Jin, Wei Chen, Gangfeng Wu, Yanfang Song, Xiao Dong, Guihua Li, Jianhui Fang, Wei Wei, and Yuhan Sun. "Evoked Methane Photocatalytic Conversion to C2 Oxygenates over Ceria with Oxygen Vacancy." Catalysts 10, no. 2 (February 6, 2020): 196. http://dx.doi.org/10.3390/catal10020196.
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Direct conversion of methane to its oxygenate derivatives remains highly attractive while challenging owing to the intrinsic chemical inertness of CH4. Photocatalysis arises as a promising green strategy which could stimulate water splitting to produce oxidative radicals for methane C–H activation and subsequent C–C coupling. However, synthesis of a photocatalyst with an appropriate capability of methane oxidation by water remains a challenge using an effective and viable approach. Herein, ceria nanoparticles with abundant oxygen vacancies prepared by calcinating commercial CeO2 powder at high temperatures in argon are reported to capably produce ethanol and aldehyde from CH4 photocatalytic oxidation under ambient conditions. Although high-temperature calcinations lead to lower light adsorptions and increased band gaps to some extent, deficient CeO2 nanoparticles with oxygen vacancies and surface CeIII species are formed, which are crucial for methane photocatalytic conversion. The ceria catalyst as-calcinated at 1100 °C had the highest oxygen vacancy concentration and CeIII content, achieving an ethanol production rate of 11.4 µmol·gcat−1·h−1 with a selectivity of 91.5%. Additional experimental results suggested that the product aldehyde was from the oxidation of ethanol during the photocatalytic conversion of CH4.
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He, Haijie, Tao Wu, Zhanhong Qiu, Chenxi Zhao, Shifang Wang, Jun Yao, and Jie Hong. "Enhanced Methane Oxidation Potential of Landfill Cover Soil Modified with Aged Refuse." Atmosphere 13, no. 5 (May 13, 2022): 802. http://dx.doi.org/10.3390/atmos13050802.
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Aged refuse with a landfill age of 1.5 years was collected from a municipal solid waste landfill with high kitchen waste content and mixed with soil as biocover material for landfill. A series of laboratory batch tests was performed to determine the methane oxidation potential and optimal mixing ratio of landfill cover soil modified with aged refuse, and the effects of water content, temperature, CO2/CH4, and O2/CH4 ratios on its methane oxidation capacity were analyzed. The microbial community analysis of aged refuse showed that the proportions of type I and type II methane-oxidizing bacteria were 56.27% and 43.73%, respectively. Aged refuse could significantly enhance the methane oxidation potential of cover soil, and the optimal mixing ratio was approximately 1:1. The optimal temperature and water content were about 25 °C and 30%, respectively. Under the conditions of an initial methane concentration of 15% and an O2/CH4 ratio of 0.8–1.2, the measured methane oxidation rate was negatively correlated with the O2/CH4 ratio. The maximum methane oxidation capacity measured in the test reached 308.5 (μg CH4/g)/h, indicating that the low-age refuse in the landfill with high kitchen waste content is a biocover material with great application potential.
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Ngo, Phuong Linh. "THE METHANE UPTAKE CAPACITY OF SOIL GARDEN." Vietnam Journal of Science and Technology 55, no. 4C (March 24, 2018): 122. http://dx.doi.org/10.15625/2525-2518/55/4c/12140.
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Aerobic CH4 oxidation through methanotrophic bacteria is the only terrestrial sink and the only sink that can be altered directly or indirectly by human so far. However, the capacity of this sink is highly variable in different ecosystems depending on four key factors which are soil diffusivity, soil temperature, soil nitrogen status and soil moisture. While many studies in Australia experience the significant inverse correlation between soil moisture and CH4 flux magnitude in temperate forests in Victoria and New South Wales, there is a lack of research about the methane uptake capacity of garden soil. Consequently, we hypothesise that there is a similar pattern of CH4 uptake by garden soil. The aim of this study is to determine the capacity of CH4 oxidation along the soil garden profile. Our study was conducted at a native garden in Burnley Campus of the University of Melbourne, Victoria, Australia. Our results show three main findings. Firstly, garden soil can become a significant sink of CH4. Secondly, there was a significant correlation between soil moisture and the soil CH4 uptake rates. Finally, there was an expansion of the CH4 oxidation layer to deeper soil layers as the soil dries at the surface.
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Friberg, Ida, Aiyong Wang, and Louise Olsson. "Hydrothermal Aging of Pd/LTA Monolithic Catalyst for Complete CH4 Oxidation." Catalysts 10, no. 5 (May 7, 2020): 517. http://dx.doi.org/10.3390/catal10050517.
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Palladium-based catalysts are known to provide high CH4 oxidation activity. One drawback for these materials is that they often lose activity in the presence of water vapor due to the formation of surface hydroxyls. It is however possible to improve the water vapor tolerance by using zeolites as support material. In this study, we have investigated Pd supported on thermally stable LTA zeolite with high framework Si/Al ratio (Si/Al = ~44) for CH4 oxidation and the effect of hydrothermal aging at temperatures up to 900 °C. High and stable CH4 oxidation activity in the presence of water vapor was observed for Pd/LTA after hydrothermal aging at temperatures ≤ 700 °C. However, aging at temperatures of 800–900 °C resulted in catalyst deactivation. This deactivation was not a result of structural collapse of the LTA zeolite as the LTA zeolite only showed minor changes in surface area, pore volume, and X-ray diffraction pattern after 900 °C aging. We suggest that the deactivation was caused by extensive formation of ion-exchanged Pd2+ together with Pd sintering. These two types of Pd species appear to have lower CH4 oxidation activity and to be more sensitive to water deactivation compared to the well dispersed Pd particles observed on the LTA support prior to the hydrothermal aging. By contrast, Pd/Al2O3 was generally sensitive to water vapor no matter of the aging temperature. Although the aging caused extensive Pd sintering in Pd/Al2O3, only minor deterioration of the CH4 oxidation activity was seen. The results herein presented show that Pd/LTA is a promising CH4 oxidation catalyst, however Pd rearrangement at high temperatures (≥800 °C) is one remaining challenge.
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Smemo, K. A., and J. B. Yavitt. "Anaerobic oxidation of methane: an underappreciated aspect of methane cycling in peatland ecosystems?" Biogeosciences Discussions 7, no. 5 (October 29, 2010): 7945–83. http://dx.doi.org/10.5194/bgd-7-7945-2010.
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Abstract. Despite a large body of literature on microbial anaerobic oxidation of methane (AOM) in marine sediments and saline waters and its importance to the global methane (CH4) cycle, until recently little work has addressed the potential occurrence and importance of AOM in non-marine systems. This is particularly true for peatlands, which represent both a massive sink for atmospheric CO2 and a significant source of atmospheric CH4. Our knowledge of this process in peatlands is inherently limited by the methods used to study CH4 dynamics in soil and sediment and the assumption that there are no anaerobic sinks for CH4 in these systems. Studies suggest that AOM is CH4-limited and difficult to detect in potential CH4 production assays against a background of CH4 production. In situ rates also might be elusive due to background rates of aerobic CH4 oxidation and the difficulty in separating net and gross process rates. Conclusive evidence for the electron acceptor in this process has not been presented. Nitrate and sulfate are both plausible and favorable electron acceptors, as seen in other systems, but there exist theoretical issues related to the availability of these ions in peatlands and only circumstantial evidence suggests that these pathways are important. Iron cycling is important in many wetland systems, but recent evidence does not support the notion of CH4 oxidation via dissimilatory Fe(III) reduction or a CH4 oxidizing archaea in consortium with an Fe(III) reducer. Calculations based on published rates demonstrate that AOM might be a significant and underappreciated constraint on the global CH4 cycle, although much about the process in unknown, in vitro rates may not relate well to in situ rates, and projections based on those rates are fraught with uncertainty. We suggest electron transfer mechanisms, C flow and pathways, and quantifying in situ peatland AOM rates as the highest priority topics for future research.
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Smemo, K. A., and J. B. Yavitt. "Anaerobic oxidation of methane: an underappreciated aspect of methane cycling in peatland ecosystems?" Biogeosciences 8, no. 3 (March 24, 2011): 779–93. http://dx.doi.org/10.5194/bg-8-779-2011.
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Abstract. Despite a large body of literature on microbial anaerobic oxidation of methane (AOM) in marine sediments and saline waters and its importance to the global methane (CH4) cycle, until recently little work has addressed the potential occurrence and importance of AOM in non-marine systems. This is particularly true for peatlands, which represent both a massive sink for atmospheric CO2 and a significant source of atmospheric CH4. Our knowledge of this process in peatlands is inherently limited by the methods used to study CH4 dynamics in soil and sediment and the assumption that there are no anaerobic sinks for CH4 in these systems. Studies suggest that AOM is CH4-limited and difficult to detect in potential CH4 production assays against a background of CH4 production. In situ rates also might be elusive due to background rates of aerobic CH4 oxidation and the difficulty in separating net and gross process rates. Conclusive evidence for the electron acceptor in this process has not been presented. Nitrate and sulfate are both plausible and favorable electron acceptors, as seen in other systems, but there exist theoretical issues related to the availability of these ions in peatlands and only circumstantial evidence suggests that these pathways are important. Iron cycling is important in many wetland systems, but recent evidence does not support the notion of CH4 oxidation via dissimilatory Fe(III) reduction or a CH4 oxidizing archaea in consortium with an Fe(III) reducer. Calculations based on published rates demonstrate that AOM might be a significant and underappreciated constraint on the global CH4 cycle, although much about the process is unknown, in vitro rates may not relate well to in situ rates, and projections based on those rates are fraught with uncertainty. We suggest electron transfer mechanisms, C flow and pathways, and quantifying in situ peatland AOM rates as the highest priority topics for future research.
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Korkiakoski, Mika, Tiia Määttä, Krista Peltoniemi, Timo Penttilä, and Annalea Lohila. "Excess soil moisture and fresh carbon input are prerequisites for methane production in podzolic soil." Biogeosciences 19, no. 7 (April 13, 2022): 2025–41. http://dx.doi.org/10.5194/bg-19-2025-2022.
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Abstract. Boreal upland forests are generally considered methane (CH4) sinks due to the predominance of CH4 oxidizing bacteria over the methanogenic archaea. However, boreal upland forests can temporarily act as CH4 sources during wet seasons or years. From a landscape perspective and in annual terms, this source can be significant as weather conditions may cause flooding, which can last a considerable proportion of the active season and because often, the forest coverage within a typical boreal catchment is much higher than that of wetlands. Processes and conditions which change mineral soils from acting as a weak sink to a strong source are not well understood. We measured soil CH4 fluxes from 20 different points from regularly irrigated and control plots during two growing seasons. We also estimated potential CH4 production and oxidation rates in different soil layers and performed a laboratory experiment, where soil microcosms were subjected to different moisture levels and glucose addition simulating the fresh labile carbon (C) source from root exudates. The aim was to find the key controlling factors and conditions for boreal upland soil CH4 production. Probably due to long dry periods in both summers, we did not find occasions of CH4 production following the excess irrigation, with one exception in July 2019 with emission of 18 200 µg CH4 m−2 h−1. Otherwise, the soil was always a CH4 sink (median CH4 uptake rate of 260–290 and 150–170 µg CH4 m−2 h−1, in control and irrigated plots, respectively). The median soil CH4 uptake rates at the irrigated plot were 88 % and 50 % lower than at the control plot in 2018 and 2019, respectively. Potential CH4 production rates were highest in the organic layer (0.2–0.6 nmol CH4 g−1 d−1), but some production was also observed in the leaching layer, whereas in other soil layers, the rates were negligible. Potential CH4 oxidation rates varied mainly within 10–40 nmol CH4 g−1 d−1, except in deep soil and the organic layer in 2019, where potential oxidation rates were almost zero. The laboratory experiment revealed that high soil moisture alone does not turn upland forest soil into a CH4 source. However, a simple C source, e.g., substrates coming from root exudates with high moisture, switched the soil into a CH4 source. Our unique study provides new insights into the processes and controlling factors on CH4 production and oxidation, and the resulting net efflux that should be incorporated in process models describing global CH4 cycling.
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Zhan, Liang-tong, Tao Wu, Song Feng, Ji-wu Lan, and Yun-min Chen. "A simple and rapid in situ method for measuring landfill gas emissions and methane oxidation rates in landfill covers." Waste Management & Research 38, no. 5 (December 19, 2019): 588–93. http://dx.doi.org/10.1177/0734242x19893007.
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A newly developed static chamber method with a laser methane detector and a biogas analyser was proposed to measure the landfill gas emissions and methane (CH4) oxidation rates in landfill covers. The method relied on a laser methane detector for measuring CH4 concentration, avoiding gas samplings during test and hence the potential interference of gas compositions inside the chamber. All the measurements could be obtained on site. The method was applied to determine the landfill gas emissions and CH4 oxidation rates in a full-scale loess gravel capillary barrier cover constructed in landfill. Both laboratory calibration and in-situ tests demonstrated that fast (i.e. <20 min) and accurate measurements could be obtained by the proposed method. The method is capable of capturing the significant spatial and temporal variations of the landfill gas emissions and CH4 oxidation rates in landfill site.
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Bykova, Svetlana, Pascal Boeckx, Irina Kravchenko, Valery Galchenko, and Oswald Van Cleemput. "Response of CH4 oxidation and methanotrophic diversity to NH4 + and CH4 mixing ratios." Biology and Fertility of Soils 43, no. 3 (September 7, 2006): 341–48. http://dx.doi.org/10.1007/s00374-006-0114-5.
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Chawla, Jaspreet, Sven Schardt, Sofia Angeli, Patrick Lott, Steffen Tischer, Lubow Maier, and Olaf Deutschmann. "Oxidative Coupling of Methane over Pt/Al2O3 at High Temperature: Multiscale Modeling of the Catalytic Monolith." Catalysts 12, no. 2 (February 2, 2022): 189. http://dx.doi.org/10.3390/catal12020189.
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At high temperatures, the oxidative coupling of methane (OCM) is an attractive approach for catalytic conversion of methane into value-added chemicals. Experiments with a Pt/Al2O3-coated catalytic honeycomb monolith were conducted with varying CH4/O2 ratios, N2 dilution at atmospheric pressure, and very short contact times. The reactor was modeled by a multiscale approach using a parabolic two-dimensional flow field description in the monolithic channels coupled with a heat balance of the monolithic structure, and multistep surface reaction mechanisms as well as elementary-step, gas phase reaction mechanisms. The contribution of heterogeneous and homogeneous reactions, both of which are important for the optimization of C2 products, is investigated using a combination of experimental and computational methods. The oxidation of methane, which takes place over the platinum catalyst, causes the adiabatic temperature increase required for the generation of CH3 radicals in the gas phase, which are essential for the formation of C2 species. Lower CH4/O2 ratios result in higher C2 selectivity. However, the presence of OH radicals at high temperatures facilitates subsequent conversion of C2H2 at a CH4/O2 ratio of 1.4. Thereby, C2 species selectivity of 7% was achieved at CH4/O2 ratio of 1.6, with 35% N2 dilution.
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Weimer, W. A., F. M. Cerio, and C. E. Johnson. "Examination of the chemistry involved in microwave plasma assisted chemical vapor deposition of diamond." Journal of Materials Research 6, no. 10 (October 1991): 2134–44. http://dx.doi.org/10.1557/jmr.1991.2134.
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Chemical reaction products formed in a microwave plasma assisted chemical vapor deposition apparatus for diamond film deposition are detected using mass spectrometry. Carbon source gases CH4, C2H6, C2H4, or C2H2 produce CH4, C2H2, CO, and H2O as major stable reaction products when introduced into a H2/O2 plasma under diamond deposition conditions. The effect of oxygen addition is similar for all carbon source gases with respect to reaction product formation, indicating that a common reaction mechanism is active in all cases. On a qualitative basis, these observations are consistent with a mechanism describing the oxidation of CH4 in flames. No beneficial effects were observed using alternating growth/etch cycles to deposit films. Films grown using CH4 as the carbon source gas consistently produce higher quality diamond films compared to films grown from C2H2.
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Stylianidis, Nearchos, Ulugbek Azimov, and Martin Birkett. "Investigation of the Effect of Hydrogen and Methane on Combustion of Multicomponent Syngas Mixtures using a Constructed Reduced Chemical Kinetics Mechanism." Energies 12, no. 12 (June 25, 2019): 2442. http://dx.doi.org/10.3390/en12122442.
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This study investigated the effects of H2 and CH4 concentrations on the ignition delay time and laminar flame speed during the combustion of CH4/H2 and multicomponent syngas mixtures using a novel constructed reduced syngas chemical kinetics mechanism. The results were compared with experiments and GRI Mech 3.0 mechanism. It was found that mixture reactivity decreases and increases when higher concentrations of CH4 and H2 were used, respectively. With higher H2 concentration in the mixture, the formation of OH is faster, leading to higher laminar flame speed and shorter ignition delay time. CH4 and H2 concentrations were calculated at different pressures and equivalence ratios, showing that at high pressures CH4 is consumed slower, and, at different equivalence ratios CH4 reacts at different temperatures. In the presence of H2, CH4 was consumed faster. In the conducted two-stage sensitivity analysis, the first analysis showed that H2/CH4/CO mixture combustion is driven by H2-based reactions related to the consumption/formation of OH and CH4 recombination reactions are responsible for CH4 oxidation. The second analysis showed that similar CH4-based and H2 -based reactions were sensitive in both, methane- and hydrogen-rich H2/CH4 mixtures. The difference was observed for reactions CH2O + OH = HCO + H2O and CH4 + HO2 = CH3 + H2O2, which were found to be important for CH4-rich mixtures, while reactions OH + HO2 = H2O + O2 and HO2 + H = OH + OH were found to be important for H2-rich mixtures.
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Zhou, Mingyang, Zhijun Liu, Xiaomin Yan, Kai Tan, Fengyuan Tian, and Jiang Liu. "Simultaneous Electrochemical Reduction of Carbon Dioxide and Partial Oxidation of Methane in a Solid Oxide Cell with Silver-Based Cathode and Nickel-Based Anode." Journal of The Electrochemical Society 169, no. 3 (March 1, 2022): 034502. http://dx.doi.org/10.1149/1945-7111/ac554d.
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Simultaneous electrochemical reduction of CO2 and partial oxidation of CH4 in a solid oxide cell (CO2/CH4 redox SOC) with Ag-based cathode and Ni-based anode is compared with CO2 reduction in a solid oxide electrolysis cell (CO2-SOEC) and CH4 oxidation in a solid oxide fuel cell (CH4-SOFC). Overpotential losses from different sources and gases products from each electrode are analyzed. Results show that the process of a CO2/CH4 redox SOC is exactly a combination of the cathode process of a CO2-SOEC and the anode process of a CH4-SOFC. With the same CO and syngas obtained, a CO2/CH4 redox SOC consumes less energy because it avoids oxygen evolution reaction (OER) of a CO2-SOEC and oxygen reduction reaction (ORR) of a CH4-SOFC. At 500 mA cm−2, the overall resistance of an electrolyte-supported CO2/CH4 redox SOC is only half of that for separately reducing CO2 in an SOEC and oxidizing CH4 in an SOFC. The conversion of CH4 and yield of H2 in the SOC approach 81% and 63%, respectively. An anode-supported CO2/CH4 redox SOC is operated stably for 110 h at 1 A cm−2 under an applied voltage of ∼0.9 V. Sufficient current density may prevent high performance Ni-based anode from coking.
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Iverach, Charlotte P., Sabrina Beckmann, Dioni I. Cendón, Mike Manefield, and Bryce F. J. Kelly. "Biogeochemical constraints on the origin of methane in an alluvial aquifer: evidence for the upward migration of methane from underlying coal measures." Biogeosciences 14, no. 1 (January 17, 2017): 215–28. http://dx.doi.org/10.5194/bg-14-215-2017.
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Abstract. Geochemical and microbiological indicators of methane (CH4) production, oxidation and migration processes in groundwater are important to understand when attributing sources of gas. The processes controlling the natural occurrence of CH4 in groundwater must be understood, especially when considering the potential impacts of the global expansion of coal seam gas (CSG) production on groundwater quality and quantity. We use geochemical and microbiological data, along with measurements of CH4 isotopic composition (δ13C-CH4), to determine the processes acting upon CH4 in a freshwater alluvial aquifer that directly overlies coal measures targeted for CSG production in Australia. Measurements of CH4 indicate that there is biogenic CH4 in the aquifer; however, microbial data indicate that there are no methanogenic archaea in the groundwater. In addition, geochemical data, particularly the isotopes of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC), as well as the concentration of SO42−, indicate limited potential for methanogenesis in situ. Microbial community analysis also shows that aerobic oxidation of CH4 occurs in the alluvial aquifer. The combination of microbiological and geochemical indicators suggests that the most likely source of CH4, where it was present in the freshwater aquifer, is the upward migration of CH4 from the underlying coal measures.
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Rainer, Edda M., Christophe V. W. Seppey, Caroline Hammer, Mette M. Svenning, and Alexander T. Tveit. "The Influence of Above-Ground Herbivory on the Response of Arctic Soil Methanotrophs to Increasing CH4 Concentrations and Temperatures." Microorganisms 9, no. 10 (October 2, 2021): 2080. http://dx.doi.org/10.3390/microorganisms9102080.
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Rising temperatures in the Arctic affect soil microorganisms, herbivores, and peatland vegetation, thus directly and indirectly influencing microbial CH4 production. It is not currently known how methanotrophs in Arctic peat respond to combined changes in temperature, CH4 concentration, and vegetation. We studied methanotroph responses to temperature and CH4 concentration in peat exposed to herbivory and protected by exclosures. The methanotroph activity was assessed by CH4 oxidation rate measurements using peat soil microcosms and a pure culture of Methylobacter tundripaludum SV96, qPCR, and sequencing of pmoA transcripts. Elevated CH4 concentrations led to higher CH4 oxidation rates both in grazed and exclosed peat soils, but the strongest response was observed in grazed peat soils. Furthermore, the relative transcriptional activities of different methanotroph community members were affected by the CH4 concentrations. While transcriptional responses to low CH4 concentrations were more prevalent in grazed peat soils, responses to high CH4 concentrations were more prevalent in exclosed peat soils. We observed no significant methanotroph responses to increasing temperatures. We conclude that methanotroph communities in these peat soils respond to changes in the CH4 concentration depending on their previous exposure to grazing. This “conditioning” influences which strains will thrive and, therefore, determines the function of the methanotroph community.
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Frasi, Niccolò, Elena Rossi, Isabella Pecorini, and Renato Iannelli. "Methane Oxidation Efficiency in Biofiltration Systems with Different Moisture Content Treating Diluted Landfill Gas." Energies 13, no. 11 (June 4, 2020): 2872. http://dx.doi.org/10.3390/en13112872.
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This study investigates the influence of moisture content on the potential oxidation efficiency of methane (CH4) of biofiltration systems treating landfill gas containing high oxygen concentrations. Column tests filled with compost with different moisture contents (20%, 30%, and 40%) loaded with different methane flows were set up on a laboratory scale. Analyzing the results the following evidences can be summarized: With low methane load (<100 g CH4 m−2 d−1), a moisture content of 20% was not enough to support bacterial activity, while a moisture content of 40% advantaged the compost respiration assisting it to become the dominating process; with higher methane load (100–300 g CH4 m−2 d−1), a moisture content of 30% resulted in an optimal value to support methanotrophic activity showing the highest CH4 concentration reduction; moving on to a CH4 load above 300 g CH4 m−2 d−1, the inhibition of methanotrophic activity emerged independently to the moisture content of the filter media. The optimal configuration is obtained for a moisture content of 30% and in the case of flows below 200 g CH4 m−2 d−1 for which the oxidation efficiency results higher than 80%.
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Bezdek, Máté J., Shao-Xiong Lennon Luo, Kang Hee Ku, and Timothy M. Swager. "A chemiresistive methane sensor." Proceedings of the National Academy of Sciences 118, no. 2 (December 31, 2020): e2022515118. http://dx.doi.org/10.1073/pnas.2022515118.
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A chemiresistive sensor is described for the detection of methane (CH4), a potent greenhouse gas that also poses an explosion hazard in air. The chemiresistor allows for the low-power, low-cost, and distributed sensing of CH4 at room temperature in air with environmental implications for gas leak detection in homes, production facilities, and pipelines. Specifically, the chemiresistors are based on single-walled carbon nanotubes (SWCNTs) noncovalently functionalized with poly(4-vinylpyridine) (P4VP) that enables the incorporation of a platinum-polyoxometalate (Pt-POM) CH4 oxidation precatalyst into the sensor by P4VP coordination. The resulting SWCNT-P4VP-Pt-POM composite showed ppm-level sensitivity to CH4 and good stability to air as well as time, wherein the generation of a high-valent platinum intermediate during CH4 oxidation is proposed as the origin of the observed chemiresistive response. The chemiresistor was found to exhibit selectivity for CH4 over heavier hydrocarbons such as n-hexane, benzene, toluene, and o-xylene, as well as gases, including carbon dioxide and hydrogen. The utility of the sensor in detecting CH4 using a simple handheld multimeter was also demonstrated.
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Chiri, Eleonora, Chris Greening, Rachael Lappan, David W. Waite, Thanavit Jirapanjawat, Xiyang Dong, Stefan K. Arndt, and Philipp A. Nauer. "Termite mounds contain soil-derived methanotroph communities kinetically adapted to elevated methane concentrations." ISME Journal 14, no. 11 (July 24, 2020): 2715–31. http://dx.doi.org/10.1038/s41396-020-0722-3.
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Abstract Termite mounds have recently been confirmed to mitigate approximately half of termite methane (CH4) emissions, but the aerobic CH4 oxidising bacteria (methanotrophs) responsible for this consumption have not been resolved. Here, we describe the abundance, composition and CH4 oxidation kinetics of the methanotroph communities in the mounds of three distinct termite species sampled from Northern Australia. Results from three independent methods employed show that methanotrophs are rare members of microbial communities in termite mounds, with a comparable abundance but distinct composition to those of adjoining soil samples. Across all mounds, the most abundant and prevalent methane monooxygenase sequences were affiliated with upland soil cluster α (USCα), with sequences homologous to Methylocystis and tropical upland soil cluster (TUSC) also detected. The reconstruction of a metagenome-assembled genome of a mound USCα representative highlighted the metabolic capabilities of this group of methanotrophs. The apparent Michaelis–Menten kinetics of CH4 oxidation in mounds were estimated from in situ reaction rates. Methane affinities of the communities were in the low micromolar range, which is one to two orders of magnitude higher than those of upland soils, but significantly lower than those measured in soils with a large CH4 source such as landfill cover soils. The rate constant of CH4 oxidation, as well as the porosity of the mound material, were significantly positively correlated with the abundance of methanotroph communities of termite mounds. We conclude that termite-derived CH4 emissions have selected for distinct methanotroph communities that are kinetically adapted to elevated CH4 concentrations. However, factors other than substrate concentration appear to limit methanotroph abundance and hence these bacteria only partially mitigate termite-derived CH4 emissions. Our results also highlight the predominant role of USCα in an environment with elevated CH4 concentrations and suggest a higher functional diversity within this group than previously recognised.