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PubMed2006

Municipal solid waste characterization and its assessment for potential methane generation: a case study.

There has been a significant increase in municipal solid waste (MSW) generation in India during the last few decades and its management has become a major issue because the poor waste management practices affect the health and amenity of the cities. In the present study, various physico-chemical parameters of the MSW were analyzed to characterize the waste dumped at Gazipur landfill site in Delhi, India, which shows that it contains a high fraction of degradable organic components. The decomposition of organic components produces methane, a significant contributor to global warming. Based on the waste composition, waste age and the total amount dumped, a first-order decay model (FOD) was applied to estimate the methane generation potential of the Gazipur landfill site, which yields an estimate of 15.3 Gg/year. This value accounts to about 1-3% of existing Indian landfill methane emission estimates. Based on the investigation of Gazipur landfill, we estimate Indian landfill methane emissions at 1.25 Tg/year or 1.68 Tg/year of methane generation potential. These values are within the range of existing estimates. A comparison of FOD with a recently proposed triangular model was also performed and it shows that both models can be used for the estimation of methane generation. However, the decrease of the emission after closure is more gradual in the case of the first-order model, leading to larger gas production predictions after more than 10 years of closure. The regional and global implications of national landfill methane emission are also discussed.

Conservation of Energy Resources↗

PubMed2002

Geologic emissions of methane to the atmosphere.

The atmospheric methane budget is commonly defined assuming that major sources derive from the biosphere (wetlands, rice paddies, animals, termites) and that fossil, radiocarbon-free CH4 emission is due to and mediated by anthropogenic activity (natural gas production and distribution, and coal mining). However, the amount of radiocarbon-free CH4 in the atmosphere, estimated at approximately 20% of atmospheric CH4, is higher than the estimates from statistical data of CH4 emission from fossil fuel related anthropogenic sources. This work documents that significant amounts of "old" methane, produced within the Earth crust, can be released naturally into the atmosphere through gas permeable faults and fractured rocks. Major geologic emissions of methane are related to hydrocarbon production in sedimentary basins (biogenic and thermogenic methane) and, subordinately, to inorganic reactions (Fischer-Tropsch type) in geothermal systems. Geologic CH4 emissions include diffuse fluxes over wide areas, or microseepage, on the order of 10(0)-10(2) mg m(-2) day(-1), and localised flows and gas vents, on the order of 10(2) t y(-1), both on land and on the seafloor. Mud volcanoes producing flows of up to 10(3) t y(-1) represent the largest visible expression of geologic methane emission. Several studies have indicated that methanotrophic consumption in soil may be insufficient to consume all leaking geologic CH4 and positive fluxes into the atmosphere can take place in dry or seasonally cold environments. Unsaturated soils have generally been considered a major sink for atmospheric methane, and never a continuous, intermittent, or localised source to the atmosphere. Although geologic CH4 sources need to be quantified more accurately, a preliminary global estimate indicates that there are likely more than enough sources to provide the amount of methane required to account for the suspected missing source of fossil CH4.

Air Pollutants↗

PubMed2003

Theoretical consideration of methane emission from sediments.

A stationary theory of gas emission from sedimentary (active) layers of wetlands is developed. The theory takes into account methane generation in a sedimentary layer (W1) and its depth dependence, (W1(z)), the solubility, determined by Henry's constant (K1), and the mobility of methane molecules set by the methane diffusion coefficient (D1). The exponential dependence of methane generation rate decay with depth is considered in more detail. The penetration of atmospheric nitrogen into the active layer is also taken into consideration. It is shown that the value of diffusion methane flux from sedimentary layers is proportional to square root(K1D1P0W10) where P0 characterizes the atmospheric pressure and W10 characterizes the maximum generation rate. Coefficients relating the diffusion methane flux to the square root(K1D1P0W10) value are calculated for the different depth dependencies of methane generation rate. The values of these coefficients are not much different from unity for most real cases.

Geologic Sediments↗

PubMed2004

Influence of plants on the methane emission from sediments.

The previous theory [Chem. Global Change Sci. 3 (2001) 33; Chemosphere 50 (2003) 191] of methane emission is applied to vegetated sediments. The presence of roots in a sediment is taken into account. It is assumed that methane and nitrogen enter a sediment through channels existing in plants and roots. The rate of methane and nitrogen transport through plants and roots is proportional to the difference in concentrations in the layer and on the upper surface. It is established that as the vegetation density increases, the rate of methane transport increases so that with sufficient vegetation density, almost all methane passes to the atmosphere through plants. In this case, the value of bubble emission decreases to zero. The nitrogen transport rate through plants first increases and then decreases with increasing the vegetation density. The theory qualitatively and quantitatively describes the dependence of methane concentration on depth in the presence of plants. A comparison with the available experimental data on dissolved methane concentration and bubble composition indicates satisfactory agreement.

Geologic Sediments↗

PubMed2002

Measurement of methane oxidation in lakes: a comparison of methods.

Methane oxidation in lakes constrains the methane emissions to the atmosphere and simultaneously enables the transfer of methane carbon to pelagic food webs. Several different methods have been used to estimate methane oxidation, but these methods have not previously been compared. In this study, we present methane oxidation estimates from three different lakes during summer and winter, using methods based on the transformation of added 14CH4, the fractionation of natural methane 13C, and the mass balance modeling of concentration gradients. All methods yielded similar results, including similar differences between lakes and seasons. Average methane oxidation rates varied from 0.25 to 81 mg of C m(-2) d(-1) and indicatethatthethree methods are comparable, although they to some extent take different processes into account. Critical issues as well as drawbacks and advantages with the used methods are thoroughly discussed. We conclude that methods using the stable isotope or mass balance modeling approach represent promising alternatives, particularly for studies focusing on ecosystem-scale carbon metabolism.

Animals↗

PubMed2005

Biofiltration for mitigation of methane emission from animal husbandry.

Removal of methane from exhaust air of animal houses and manure storage has a large potential for the reduction of greenhouse gas emissions from animal husbandry. The aim of this study was to design a biofilter for methane removal at a full-scale livestock production facility. Air from the headspace of a covered 6 m3 liquid manure storage (air flow: 0.75-8.5 m3 m(-3) h(-1); CH4: 500-5500 mg m(-3)) was treated in an experimental biofilter (160 L). The filterbed, a mixture of compost and perlite in a 40:60 (v/v) ratio, was inoculated with activated sludge that had shown a good methane oxidation rate as compared to pure cultures in preceding laboratory tests. Methane removal up to 85% could be achieved in the experimental biofilter. The methane removal (g m(-3) h(-1)) appeared to be proportional to the concentration (g m(-3)) with k = 2.5 h(-1). Relatively low methane concentrations and high air flows, as reported for the exhaust air of animal houses, would require very large biofilter sizes. Extrapolation of the results showed that treatment of air from a 1000 m3 liquid manure storage with a methane concentration of 22 g m(-3) would require a 20 m3 biofilter for a desired emission reduction of 50%. The costs for such a biofilter are USD 26 per t of CO2 equiv reduction.

Animal Husbandry↗

PubMed2001

Excited- and ground-state versions of the tri-pi-methane rearrangement: mechanistic and exploratory organic photochemistry.

The di-pi-methane rearrangement with two pi-groups bonded to a single carbon leading to pi-substituted cyclopropanes is now well established. The present research had as its goal the exploration of molecular systems having three pi-moieties attached to an sp(3)-hybridized atom in a search for a tri-pi-methane rearrangement. Indeed, it was found that such systems do rearrange photochemically to afford cyclopentenes. However, it was also established that vinylcyclopropanes ring-expand to cyclopentenes on direct irradiation. Since both three-ring and five-ring photoproducts often are found to be produced, it was important to establish that the observed photochemistry was really the result of a true single-step tri-pi-methane rearrangement and not the consequence of two sequential rearrangements, first to form a vinyl cyclopropane which subsequently ring expanded to the cyclopentene. The general situation has three species-A, B, and C-corresponding to tri-pi-methane reactant A, vinylcyclopropane photoproduct B, and cyclopentene photoproduct C. Three rate constants are involved, k(1) for A --> B, k(2) for A --> C, and k(3) for B --> C. The kinetics were applied to two examples with provision to avoid differential light absorption; this utilized singlet sensitization. It was determined that direct formation of the cyclopentene photoproduct proceeds more rapidly than the ring-expansion route. In contrast to the di-pi-methane rearrangement, the tri-pi-methane reaction was found to be preferred by the singlet, while in these sterically congested systems, the triplet led to di-pi-methane reactivity. Finally, a ground-state counterpart of the reaction was obtained.

Crystallography, X-Ray↗

PubMed2000

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

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.

Bacteria, Aerobic↗

PubMed2006

Methane emissions from terrestrial plants under aerobic conditions.

Methane is an important greenhouse gas and its atmospheric concentration has almost tripled since pre-industrial times. It plays a central role in atmospheric oxidation chemistry and affects stratospheric ozone and water vapour levels. Most of the methane from natural sources in Earth's atmosphere is thought to originate from biological processes in anoxic environments. Here we demonstrate using stable carbon isotopes that methane is readily formed in situ in terrestrial plants under oxic conditions by a hitherto unrecognized process. Significant methane emissions from both intact plants and detached leaves were observed during incubation experiments in the laboratory and in the field. If our measurements are typical for short-lived biomass and scaled on a global basis, we estimate a methane source strength of 62-236 Tg yr(-1) for living plants and 1-7 Tg yr(-1) for plant litter (1 Tg = 10(12) g). We suggest that this newly identified source may have important implications for the global methane budget and may call for a reconsideration of the role of natural methane sources in past climate change.

Aerobiosis↗

PubMed2006

A microbial consortium couples anaerobic methane oxidation to denitrification.

Modern agriculture has accelerated biological methane and nitrogen cycling on a global scale. Freshwater sediments often receive increased downward fluxes of nitrate from agricultural runoff and upward fluxes of methane generated by anaerobic decomposition. In theory, prokaryotes should be capable of using nitrate to oxidize methane anaerobically, but such organisms have neither been observed in nature nor isolated in the laboratory. Microbial oxidation of methane is thus believed to proceed only with oxygen or sulphate. Here we show that the direct, anaerobic oxidation of methane coupled to denitrification of nitrate is possible. A microbial consortium, enriched from anoxic sediments, oxidized methane to carbon dioxide coupled to denitrification in the complete absence of oxygen. This consortium consisted of two microorganisms, a bacterium representing a phylum without any cultured species and an archaeon distantly related to marine methanotrophic Archaea. The detection of relatives of these prokaryotes in different freshwater ecosystems worldwide indicates that the reaction presented here may make a substantial contribution to biological methane and nitrogen cycles.

Anaerobiosis↗

PubMed2006

Novel microbial communities of the Haakon Mosby mud volcano and their role as a methane sink.

Mud volcanism is an important natural source of the greenhouse gas methane to the hydrosphere and atmosphere. Recent investigations show that the number of active submarine mud volcanoes might be much higher than anticipated (for example, see refs 3-5), and that gas emitted from deep-sea seeps might reach the upper mixed ocean. Unfortunately, global methane emission from active submarine mud volcanoes cannot be quantified because their number and gas release are unknown. It is also unclear how efficiently methane-oxidizing microorganisms remove methane. Here we investigate the methane-emitting Haakon Mosby Mud Volcano (HMMV, Barents Sea, 72 degrees N, 14 degrees 44' E; 1,250 m water depth) to provide quantitative estimates of the in situ composition, distribution and activity of methanotrophs in relation to gas emission. The HMMV hosts three key communities: aerobic methanotrophic bacteria (Methylococcales), anaerobic methanotrophic archaea (ANME-2) thriving below siboglinid tubeworms, and a previously undescribed clade of archaea (ANME-3) associated with bacterial mats. We found that the upward flow of sulphate- and oxygen-free mud volcano fluids restricts the availability of these electron acceptors for methane oxidation, and hence the habitat range of methanotrophs. This mechanism limits the capacity of the microbial methane filter at active marine mud volcanoes to <40% of the total flux.

Archaea↗

PubMed2000

New perspectives on anaerobic methane oxidation.

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.

Bacteria, Anaerobic↗

PubMed2006

Biogeographical distribution and diversity of microbes in methane hydrate-bearing deep marine sediments on the Pacific Ocean Margin.

The deep subseafloor biosphere is among the least-understood habitats on Earth, even though the huge microbial biomass therein plays an important role for potential long-term controls on global biogeochemical cycles. We report here the vertical and geographical distribution of microbes and their phylogenetic diversities in deeply buried marine sediments of the Pacific Ocean Margins. During the Ocean Drilling Program Legs 201 and 204, we obtained sediment cores from the Peru and Cascadia Margins that varied with respect to the presence of dissolved methane and methane hydrate. To examine differences in prokaryotic distribution patterns in sediments with or without methane hydrates, we studied >2,800 clones possessing partial sequences (400-500 bp) of the 16S rRNA gene and 348 representative clone sequences (approximately 1 kbp) from the two geographically separated subseafloor environments. Archaea of the uncultivated Deep-Sea Archaeal Group were consistently the dominant phylotype in sediments associated with methane hydrate. Sediment cores lacking methane hydrates displayed few or no Deep-Sea Archaeal Group phylotypes. Bacterial communities in the methane hydrate-bearing sediments were dominated by members of the JS1 group, Planctomycetes, and Chloroflexi. Results from cluster and principal component analyses, which include previously reported data from the West and East Pacific Margins, suggest that, for these locations in the Pacific Ocean, prokaryotic communities from methane hydrate-bearing sediment cores are distinct from those in hydrate-free cores. The recognition of which microbial groups prevail under distinctive subseafloor environments is a significant step toward determining the role these communities play in Earth's essential biogeochemical processes.

Archaea↗

PubMed1978

Methane production in the rumen and lower gut of sheep given lucerne chaff: effect of level of intake.

1. Methane production rates were estimated simultaneously in the rumen and caecum of sheep given 200, 400, 600, 800 and 1000 g lucerne (Medicago sativa) chaff/d using isotope dilution techniques. Estimates were also made of volatile fatty acid (VFA) production in the rumen at each level of feeding. In all studies three to four animals were used at each level of intake. 2. Production of VFA and of methane were both related to digestible energy (DE) intake. Regression lines for both VFA production and methane production v. DE intake had significant intercepts indicating an input of endogenous, fermentable organic matter into the rumen in excess of 50 g/d. 3. The values obtained for rates of methane production were compared with those calculated from stoicheiometric equations relating rates of methane and VFA production. Comparisons of methane production with that predicted from DE intake were also made. 4. Balances for digestion of food determined for the rumen indicated that the energies in the end-products were more than 100% of the DE intakes of lucerne chaff. Correction for fermentation of apparent endogenous materials resulted in more realistic values. Endogenous materials appeared to make a significant contribution to VFA and methane production, particularly at low levels of intake.

Animals↗

PubMed2001

The global methane cycle: isotopes and mixing ratios, sources and sinks.

A review of the global cycle of methane is presented with emphasis on its isotopic composition. The history of methane mixing ratios, reconstructed from measurements of air trapped in ice-cores is described. The methane record now extends back to 420 kyr ago in the case of the Vostok ice cores from Antarctica. The trends in mixing ratios and in delta13C values are reported for the two Hemispheres. The increase of the atmospheric methane concentration over the past 200 years, and by 1% per year since 1978, reaching 1.7 ppmv in 1990 is underlined. The various methane sources are presented. Indeed the authors describe the methane emissions by bacterial activity under anaerobic conditions in wet environments (wetlands, bogs, tundra, rice paddies), in ruminant stomachs and termite guts, and that originating from fossil carbon sources, such as biomass burning, coal mining, industrial losses, automobile exhaust, sea floor vent, and volcanic emissions. Furthermore, the main sinks of methane in the troposphere, soils or waters via oxidation are also reported, and the corresponding kinetic isotope effects.

Agriculture↗

PubMed1992

Breath methane excretion in Hong Kong Chinese children.

The factors which determine whether an individual is a methane excretor or a nonexcretor are not clearly understood. Genetic makeup, ethnic origin, diet, environment, or an interaction of all these factors have been implicated. In order to delineate the incidence, the age of onset, and environmental factors that may influence the excretion of methane in our community, we investigated a total of 425 Chinese children in Hong Kong (204 females, 221 males). End-expiratory breath samples were collected after an overnight fast and measured by gas-chromatography using a flame ionization detector. Thirty one children (7.3%) excreted at least 1 ppm methane above the ambient level (median = 6.4, range = 1.8-26.0 ppm). There was no difference in methane excretion status and pattern between the sexes or between children who lived at home and those who lived at an institution. There was a general increase in the number of methane excretors with age, but a statistically significant increase was reached only after 14 years of age. The amount of methane excreted was unrelated to age and there were no excretors detected under the age of 5 years. It is concluded that the methane excretion pattern of these children was generally similar to those previously reported from other regions, but the incidence is much lower and the age of onset appears to be more gradual.

Adolescent↗

PubMed2005

Response and adaptation of different methanotrophic bacteria to low methane mixing ratios.

Described genera of methanotrophic bacteria are present in most upland soils, but it is not known whether these are sufficiently oligotrophic to oxidize methane at its trace atmospheric mixing ratio of 1.75 ppmv. Members of the genera Methylocystis, Methylosinus, Methylocaldum and Methylobacter were isolated from different upland soils and compared with type strains for growth and activity under low methane mixing ratios. The specific affinity (a0s) varied by about one order of magnitude among different methanotrophs. It was highest in some Methylocystis spp., suggesting that these were the most oligotrophic. In direct tests, the threshold mixing ratio of methane required by most methanotrophs for growth ranged from 100 to greater than 1000 ppmv. However, two Methylocystis strains grew at only 10-100 ppmv of methane and one oxidized atmospheric methane for >3 months with little or no decline in the absolute rate. The results show that some cultivated methanotrophic bacteria are much more oligotrophic than others, and may contribute to atmospheric methane oxidation in soils. However, it is likely that these need additional energy sources for long-term survival, and that uncultivated groups of methanotrophic bacteria are primarily responsible for the process in soils possessing high methane oxidation rates.

Adaptation, Physiological↗

PubMed2006

An anaerobic methane-oxidizing community of ANME-1b archaea in hypersaline Gulf of Mexico sediments.

Sediments overlying a brine pool methane seep in the Gulf of Mexico (Green Canyon 205) were analyzed using molecular and geochemical approaches to identify geochemical controls on microbial community composition and stratification. 16S rRNA gene and rRNA clone libraries, as well as mcrA gene clone libraries, showed that the archaeal community consists predominantly of ANME-1b methane oxidizers; no archaea of other ANME subgroups were found with general and group-specific PCR primers. The ANME-1b community was found in the sulfate-methane interface, where undersaturated methane concentrations of ca. 100 to 250 microM coexist with sulfate concentrations around 10 mM. Clone libraries of dsrAB genes and bacterial 16S rRNA genes show diversified sulfate-reducing communities within and above the sulfate-methane interface. Their phylogenetic profiles and occurrence patterns are not linked to ANME-1b populations, indicating that electron donors other than methane, perhaps petroleum-derived hydrocarbons, drive sulfate reduction. The archaeal component of anaerobic oxidation of methane is comprised of an active population of mainly ANME-1b in this hypersaline sediment.

Anaerobiosis↗