Showing papers on "Methane published in 2000"

A marine microbial consortium apparently mediating anaerobic oxidation of methane

Abstract: A large fraction of globally produced methane is converted to CO2 by anaerobic oxidation in marine sediments. Strong geochemical evidence for net methane consumption in anoxic sediments is based on methane profiles, radiotracer experiments and stable carbon isotope data. But the elusive microorganisms mediating this reaction have not yet been isolated, and the pathway of anaerobic oxidation of methane is insufficiently understood. Recent data suggest that certain archaea reverse the process of methanogenesis by interaction with sulphate-reducing bacteria. Here we provide microscopic evidence for a structured consortium of archaea and sulphate-reducing bacteria, which we identified by fluorescence in situ hybridization using specific 16S rRNA-targeted oligonucleotide probes. In this example of a structured archaeal-bacterial symbiosis, the archaea grow in dense aggregates of about 100 cells and are surrounded by sulphate-reducing bacteria. These aggregates were abundant in gas-hydrate-rich sediments with extremely high rates of methane-based sulphate reduction, and apparently mediate anaerobic oxidation of methane.

Methane production by ruminants: its contribution to global warming

Abstract: The aim of this paper is to review the role of methane in the global warming scenario and to examine the contribution to atmospheric methane made by enteric fermentation, mainly by ruminants. Agricultural emissions of methane in the EU-15 have recently been estimated at 10.2 million tonnes per year and represent the greatest source. Of these, approximately two-thirds come from enteric fermentation and one-third from livestock manure. Fermentation of feeds in the rumen is the largest source of methane from enteric fermentation and this paper considers in detail the reasons for, and the consequences of, the fact that the molar percentage of the different volatile fatty acids produced during fermentation influences the production of methane in the rumen. Acetate and butyrate promote methane production while propionate formation can be considered as a competitive pathway for hydrogen use in the rumen. The many alternative approaches to reducing methane are considered, both in terms of reduction per animal and reduction per unit of animal product. It was concluded that the most promising areas for future research for reducing methanogenesis are the development of new products/delivery systems for anti-methanogenic compounds or alternative electron acceptors in the rumen and reduction in protozoal numbers in the rumen. It is also stressed that the reason ruminants are so important to mankind is that much of the world's biomass is rich in fibre. They can convert this into high quality protein sources (i.e. meat and milk) for human consumption and this will need to be balanced against the concomitant production of methane.

Biomass Gasification in Supercritical Water

Abstract: Biomass feedstocks, including corn- and potato-starch gels, wood sawdust suspended in a cornstarch gel, and potato wastes, were delivered to three different tubular flow reactors by means of a “cement” pump. When rapidly heated to temperatures above 650 °C at pressures above the critical pressure of water (22 MPa), the organic content of these feedstocks vaporized. A packed bed of carbon within the reactor catalyzed the gasification of these organic vapors in the water; consequently, the water effluent of the reactor was clean. The gas was composed of hydrogen, carbon dioxide, methane, carbon monoxide, and traces of ethane. Its composition was strongly influenced by the peak temperature of the reactor and the condition of the reactor's wall. Extraordinary yields (>2 L/g) of gas with a high content of hydrogen (57 mol %) were realized at the highest temperatures employed in this work. Irrespective of the reactor geometry and method of heating, all three reactors plugged after 1−2 h of use with feedstocks t...

Carbon isotopic evidence for methane hydrate instability during quaternary interstadials

Abstract: Large (about 5 per mil) millennial-scale benthic foraminiferal carbon isotopic oscillations in the Santa Barbara Basin during the last 60,000 years reflect widespread shoaling of sedimentary methane gradients and increased outgassing from gas hydrate dissociation during interstadials. Furthermore, several large, brief, negative excursions (up to -6 per mil) coinciding with smaller shifts (up to -3 per mil) in depth-stratified planktonic foraminiferal species indicate massive releases of methane from basin sediments. Gas hydrate stability was modulated by intermediate-water temperature changes induced by switches in thermohaline circulation. These oscillations were likely widespread along the California margin and elsewhere, affecting gas hydrate instability and contributing to millennial-scale atmospheric methane oscillations.

Greenhouse warming by CH4 in the atmosphere of early Earth

Abstract: Earth appears to have been warm during its early history despite the faintness of the young Sun. Greenhouse warming by gaseous CO 2 and H 2 O by itself is in conflict with constraints on atmospheric CO 2 levels derived from paleosols for early Earth. Here we explore whether greenhouse warming by methane could have been important. We find that a CH 4 mixing ratio of 10 -4 (100 ppmv) or more in Earth's early atmosphere would provide agreement with the paleosol data from 2.8 Ga. Such a CH 4 concentration could have been readily maintained by methanogenic bacteria, which are thought to have been an important component of the biota at that time. Elimination of the methane component of the greenhouse by oxidation of the atmosphere at about 2.3 - 2.4 Ga could have triggered the Earth's first widespread glaciation.

Reverse microemulsion synthesis of nanostructured complex oxides for catalytic combustion

Abstract: Catalysts play an important role in many industrial processes, but their use in high-temperature applications-such as energy generation through natural gas combustion, steam reforming and the partial oxidation of hydrocarbons to produce feedstock chemicals--is problematic. The need for catalytic materials that remain stable and active over long periods at high operation temperatures, often in the presence of deactivating or even poisoning compounds, presents a challenge. For example, catalytic methane combustion, which generates power with reduced greenhouse-gas and nitrogen-oxide emissions, is limited by the availability of catalysts that are sufficiently active at low temperatures for start-up and are then able to sustain activity and mechanical integrity at flame temperatures as high as 1,300 degrees C. Here we use sol-gel processing in reverse microemulsions to produce discrete barium hexa-aluminate nanoparticles that display excellent methane combustion activity, owing to their high surface area, high thermal stability and the ultrahigh dispersion of cerium oxide on the their surfaces. Our synthesis method provides a general route to the production of a wide range of thermally stable nanostructured composite materials with large surface-to-volume ratios and an ultrahigh component dispersion that gives rise to synergistic chemical and electronic effects, thus paving the way to the development of catalysts suitable for high-temperature industrial applications.

Modeling trace gas emissions from agricultural ecosystems

Abstract: A computer simulation model was developed for predicting trace gas emissions from agricultural ecosystems. The denitrification-decomposition (DNDC) model consists of two components. The first component, consisting of the soil climate, crop growth, and decomposition submodels, predicts soil temperature, moisture, pH, Eh, and substrate concentration profiles based on ecological drivers (e.g., climate, soil, vegetation, and anthropogenic activity). The second component, consisting of the nitrification, denitrification, and fermentation submodels, predicts NH3, NO, N2O, and CH4 fluxes based on the soil environmental variables. Classical laws of physics, chemistry, or biology or empirical equations generated from laboratory observations were used in the model to parameterize each specific reaction. The entire model links trace gas emissions to basic ecological drivers. Through validation against data sets of NO, N2O, CH4 and NH3 emissions measured at four agricultural sites, the model showed its ability to capture patterns and magnitudes of trace gas emissions.

Stimulation by ammonium-based fertilizers of methane oxidation in soil around rice roots

Abstract: Methane is involved in a number of chemical and physical processes in the Earth's atmosphere, including global warming. Atmospheric methane originates mainly from biogenic sources, such as rice paddies and natural wetlands; the former account for at least 30% of the global annual emission of methane to the atmosphere. As an increase of rice production by 60% is the most appropriate way to sustain the estimated increase of the human population during the next three decades, intensified global fertilizer application will be necessary: but it is known that an increase of the commonly used ammonium-based fertilizers can enhance methane emission from rice agriculture. Approximately 10-30% of the methane produced by methanogens in rice paddies is consumed by methane-oxidizing bacteria associated with the roots of rice; these bacteria are generally thought to be inhibited by ammonium-based fertilizers, as was demonstrated for soils and sediments. In contrast, we show here that the activity and growth of such bacteria in the root zone of rice plants are stimulated after fertilization. Using a combination of radioactive fingerprinting and molecular biology techniques, we identify the bacteria responsible for this effect. We expect that our results will make necessary a re-evaluation of the link between fertilizer use and methane emissions, with effects on global warming studies.

New perspectives on anaerobic methane oxidation

Abstract: Anaerobic methane oxidation is a globally important but poorly understood process. Four lines of evidence have recently improved our understanding of this process. First, studies of recent marine sediments indicate that a consortium of methanogens and sulphate-reducing bacteria are responsible for anaerobic methane oxidation; a mechanism of 'reverse methanogenesis' was proposed, based on the principle of interspecies hydrogen transfer. Second, studies of known methanogens under low hydrogen and high methane conditions were unable to induce methane oxidation, indicating that 'reverse methanogenesis' is not a widespread process in methanogens. Third, lipid biomarker studies detected isotopically depleted archaeal and bacterial biomarkers from marine methane vents, and indicate that Archaea are the primary consumers of methane. Finally, phylogenetic studies indicate that only specific groups of Archaea and SRB are involved in methane oxidation. This review integrates results from these recent studies to constrain the responsible mechanisms.

Anodes for Direct Oxidation of Dry Hydrocarbons in a Solid-Oxide Fuel Cell

Abstract: The manufacture of fuel cells that can operate directly on various hydrocarbon fuels, without the need for reforming, has the potential of greatly speeding the application of fuel cells for transportation and distributed-power applications. This paper will briefly review the literature in this area and describe recent developments in solid-oxide fuel cells (SOFCs) that demonstrate that direct-oxidation fuel cells are possible with Cu-based anodes. A new method for synthesizing thin-electrolyte, anode-supported cells is described that is based on tape casting with graphite pore formers (see Figure), followed by impregnation with aqueous solutions of Cu(NO3)2 and Ce(NO3)3. The performance of model SOFCs for direct conversion of n-butane and methane is shown. Finally, future developments that are needed for this technology to be commercialized are discussed.

A process-based, climate-sensitive model to derive methane emissions from natural wetlands : Application to five wetland sites, sensitivity to model parameters, and climate

Abstract: Methane emissions from natural wetlands constitutes the largest methane source at present and depends highly on the climate. In order to investigate the response of methane emissions from natural wetlands to climate variations, a 1-dimensional process-based climate-sensitive model to derive methane emissions from natural wetlands is developed. In the model the processes leading to methane emission are simulated within a 1-dimensional soil column and the three different transport mechanisms diffusion, plant-mediated transport and ebullition are modeled explicitly. The model forcing consists of daily values of soil temperature, water table and Net Primary Productivity, and at permafrost sites the thaw depth is included. The methane model is tested using observational data obtained at 5 wetland sites located in North America, Europe and Central America, representing a large variety of environmental conditions. It can be shown that in most cases seasonal variations in methane emissions can be explained by the combined effect of changes in soil temperature and the position of the water table. Our results also show that a process-based approach is needed, because there is no simple relationship between these controlling factors and methane emissions that applies to a variety of wetland sites. The sensitivity of the model to the choice of key model parameters is tested and further sensitivity tests are performed to demonstrate how methane emissions from wetlands respond to climate variations.

Biomarker evidence for widespread anaerobic methane oxidation in Mediterranean sediments by a consortium of methanogenic archaea and bacteria

Abstract: Although abundant geochemical data indicate that anaerobic methane oxidation occurs in marine sediments, the linkage to specific microorganisms remains unclear. In order to examine processes of methane consumption and oxidation, sediment samples from mud volcanoes at two distinct sites on the Mediterranean Ridge were collected via the submersible Nautile. Geochemical data strongly indicate that methane is oxidized under anaerobic conditions, and compound-specific carbon isotope analyses indicate that this reaction is facilitated by a consortium of archaea and bacteria. Specifically, these methane-rich sediments contain high abundances of methanogen-specific biomarkers that are significantly depleted in 13C (δ13C values are as low as −95‰). Biomarkers inferred to derive from sulfate-reducing bacteria and other heterotrophic bacteria are similarly depleted. Consistent with previous work, such depletion can be explained by consumption of 13C-depleted methane by methanogens operating in reverse and as part a consortium of organisms in which sulfate serves as the terminal electron acceptor. Moreover, our results indicate that this process is widespread in Mediterranean mud volcanoes and in some localized settings is the predominant microbiological process.

Natural gas hydrate : in oceanic and permafrost environments

Abstract: Preface M.D. Max. Part 1: Hydrate as a Material and its Discovery. 1. Introduction, Physical Properties, and Natural Occurrences of Hydrate R.E. Pellenbarg, M.D. Max. 2. Natural Gas Hydrate: Introduction and History of Discovery K.A. Kvenvolden. Part 2: Physical Character of Natural Gas Hydrate. 3. Practical Physical Chemistry and Empirical Predictions of Methane Hydrate Stability E.T. Peltzer, P.G. Brewer. 4. Thermal State of the Gas Hydrate Reservoir C. Ruppel. Part 3: Oceanic and Permafrost-Related Natural Gas Hydrate. 5. Permafrost-Associated Gas Hydrate T.S. Collett, S.R. Dallimore. 6. Oceanic Gas Hydrate W.P. Dillon, M.D. Max. Part 4: Source of Methane and its Migration. 7. The Role of Methane Hydrate in Ocean Carbon Chemistry and Biogeochemical Cycling R.B. Coffin, et al. 8. Deep Biosphere: Source of Methane for Oceanic Hydrate P. Wellsbury, R.J. Parkes. 9. Movement and Accumulation of Methane in Marine Sediments: Relation to Gas Hydrate Systems M.B. Clennell, et al. Part 5: Major Hydrate-related Issues. 10. Natural Gas Hydrate as a Potential Energy Resource T.S. Collett. 11. Climate Impact of Natural Gas Hydrate B.U. Haq. 12. Potential Role of Gas Hydrate Decomposition in Generating Submarine Slope Failures C.K. Paull, et al. Part 6: Some Examples of Natural Gas Hydrate Localities. 13. U.S. Atlantic Continental Margin the Best Known Gas Hydrate Locality W.P. Dillon, M.D. Max. 14. Gas Hydrate in the Arctic and Northern North Atlantic Oceans M.D. Max, et al. 15. Cascadia Margin, Northeast Pacific Ocean: Hydrate Distribution from Geophysical Investigations G.D. Spence, et al. 16. The Occurrence of BSRs on the Antarctic Margin E. Loddo, A. Camerlenghi. 17. Gas Hydrate Potential of the Indian Sector of the NE Arabian Sea and Northern Indian Ocean M.D. Max. 18. Hydrate as a Future Energy Resource for Japan M.D. Max. 19. A Note on Gas Hydrate in the Northern Sector of the South China Sea S. McDonnel, M. Czarnecki. Part 7: How we see Hydrate. 20. Introduction to Physical Properties and Elasticity Models J. Dvorkin, et al. 21. Geophysical Sensing and Hydrate P.R. Miles. 22. Seismic Methods for Detecting and Quantifying Marine Methane Hydrate/Free Gas Reservoirs I.A. Pecher, W.S. Holbrook. 23. Ground Truth: In-Situ Properties of Hydrate D.S. Goldberg, et al. Part 8: Laboratory Studies of Gas Hydrates. 24. GHASTLI -- Determining Physical Properties of Sediment Containing Natural and Laboratory-Formed Gas Hydrate W.J. Winters, et al. 25. Laboratory synthesis of pure methane hydrate suitable for measurement of physical properties and decomposition behavior L.A. Stern, et al. Part 9: The Promise of Hydrate. 26. Economic Perspective of Methane from Hydrate K.J. Bil. 27. Hydrate Resource, Methane, Fuel, and a Gas-Based Economy? M.D. Max. Glossary of Terms. Selected References. List of Contributing Authors.

Measurements of excess O3, CO2, CO, CH4, C2H4, C2H2, HCN, NO, NH3, HCOOH, CH3COOH, HCHO, and CH3OH in 1997 Alaskan biomass burning plumes by airborne Fourier transform infrared spectroscopy (AFTIR)

Abstract: We used an airborne Fourier transform infrared spectrometer (AFTIR), coupled to a flow-through, air-sampling cell, on a King Air B-90 to make in situ trace gas measurements in isolated smoke plumes from four, large, boreal zone wildfires in interior Alaska during June 1997. AFTIR spectra acquired near the source of the smoke plumes yielded excess mixing ratios for 13 of the most common trace gases: water, carbon dioxide, carbon monoxide, methane, nitric oxide, formaldehyde, acetic acid, formic acid, methanol, ethylene, acetylene, ammonia and hydrogen cyanide. Emission ratios to carbon monoxide for formaldehyde, acetic acid, and methanol were 2.2±0.4%, 1.3±0.4%, and 1.4±0.1%, respectively. For each oxygenated organic compound, a single linear equation fits our emission factors from Alaska, North Carolina, and laboratory fires as a function of modified combustion efficiency (MCE). A linear equation for predicting the NH3/NOx emission ratio as a function of MCE fits our Alaskan AFTIR results and those from many other studies. AFTIR spectra collected in downwind smoke that had aged 2.2±1 hours in the upper, early plume yielded ΔO3/ΔCO ratios of 7.9±2.4% resulting from O3 production rates of ∼50 ppbv h−1. The ΔNH3/ΔCO ratio in another plume decreased to 1/e of its initial value in ∼2.5 hours. A set of average emission ratios and emission factors for fires in Alaskan boreal forests is derived. We estimate that the 1997 Alaskan fires emitted 46±11 Tg of CO2.

Flammability of methane, propane, and hydrogen gases

Abstract: This paper reports the results of flammability studies for methane, propane, hydrogen, and deuterium gases in air conducted by the Pittsburgh Research Laboratory. Knowledge of the explosion hazards of these gases is important to the coal mining industry and to other industries that produce or use flammable gases. The experimental research was conducted in 20 L and 120 L closed explosion chambers under both quiescent and turbulent conditions, using both electric spark and pyrotechnic ignition sources. The data reported here generally confirm the data of previous investigators, but they are more comprehensive than those reported previously. The results illustrate the complications associated with buoyancy, turbulence, selective diffusion, and ignitor strength versus chamber size. Although the lower flammable limits (LFLs) are well defined for methane (CH4) and propane (C3H8), the LFLs for hydrogen (H2) and its heavier isotope deuterium (D2) are much more dependent on the limit criterion chosen. A similar behavior is observed for the upper flammable limit of propane. The data presented include lower and upper flammable limits, maximum pressures, and maximum rates of pressure rise. The rates of pressure rise, even when normalized by the cube root of the chamber volume (V1/3), are shown to be sensitive to chamber size.

Hydrogen production via the direct cracking of methane over Ni/SiO2: catalyst deactivation and regeneration

Abstract: The catalytic cracking of methane over supported nickel catalysts is a potential route to the production of CO-free hydrogen and filamentous carbon. Eventually, however, the catalyst deactivates due to the spatial limitations imposed on the filamentous carbon growth by the reactor. In this study we show that a 15 wt.% Ni/SiO 2 catalyst can be fully regenerated at 923 K with steam for up to 10 successive cracking/regeneration cycles without any significant loss of catalytic activity. XRD analyses indicate no increase in the amount of carbon remaining on the catalyst after successive regenerations and no structural changes in the nickel particles as the catalyst is cycled between cracking and steam regeneration. SEM micrographs are in agreement with the XRD results and show that most of the filamentous carbon is removed during steam regeneration, leaving only small pockets of this material which resist this treatment.

Termination of global warmth at the Palaeocene/Eocene boundary through productivity feedback

Abstract: The onset of the Palaeocene/Eocene thermal maximum (about 55 Myr ago) was marked by global surface temperatures warming by 5–7 °C over approximately 30,000 yr (ref 1), probably because of enhanced mantle outgassing2,3 and the pulsed release of ∼1,500 gigatonnes of methane carbon from decomposing gas-hydrate reservoirs4,5,6,7 The aftermath of this rapid, intense and global warming event may be the best example in the geological record of the response of the Earth to high atmospheric carbon dioxide concentrations and high temperatures This response has been suggested to include an intensified flux of organic carbon from the ocean surface to the deep ocean and its subsequent burial through biogeochemical feedback mechanisms8 Here we present firm evidence for this view from two ocean drilling cores, which record the largest accumulation rates of biogenic barium—indicative of export palaeoproductivity—at times of maximum global temperatures and peak excursion values of δ13C The unusually rapid return of δ13C to values similar to those before the methane release7 and the apparent coupling of the accumulation rates of biogenic barium to temperature, suggests that the enhanced deposition of organic matter to the deep sea may have efficiently cooled this greenhouse climate by the rapid removal of excess carbon dioxide from the atmosphere

Detection and classification of atmospheric methane oxidizing bacteria in soil

Abstract: Well-drained non-agricultural soils mediate the oxidation of methane directly from the atmosphere, contributing 5 to 10% towards the global methane sink1,2. Studies of methane oxidation kinetics in soil infer the activity of two methanotrophic populations: one that is only active at high methane concentrations (low affinity) and another that tolerates atmospheric levels of methane (high affinity). The activity of the latter has not been demonstrated by cultured laboratory strains of methanotrophs, leaving the microbiology of methane oxidation at atmospheric concentrations unclear3,4. Here we describe a new pulse-chase experiment using long-term enrichment with 12CH4 followed by short-term exposure to 13CH4 to isotopically label methanotrophs in a soil from a temperate forest. Analysis of labelled phospholipid fatty acids (PLFAs) provided unambiguous evidence of methane assimilation at true atmospheric concentrations (1.8–3.6 p.p.m.v.). High proportions of 13C-labelled C18 fatty acids and the co-occurrence of a labelled, branched C17 fatty acid indicated that a new methanotroph, similar at the PLFA level to known type II methanotrophs, was the predominant soil micro-organism responsible for atmospheric methane oxidation.