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PubMed2001

Methane emissions from wastewater management.

Greenhouse gas emissions in the form of methane and carbon dioxide are produced when municipal and industrial wastewater and their residual solid by-product (sludge) are handled under or subject to anaerobic conditions, thus contributing to the global warming potential or the greenhouse effect. This paper presents estimation methods used for determining methane emissions from the management of wastewater. Applications for estimating countrywide methane gas emissions from wastewater management are presented with the country of Lebanon as an example. The relative significance of these emissions is assessed in comparison with methane emissions from developing and developed countries. Uncertainty associated with the estimation process and mitigation measures to reduce potential impacts of methane emissions from wastewater management are also discussed.

Bacteria, Anaerobic↗

PubMed2001

Methane and hydrogen exhalation in normal children and in lactose malabsorption.

UNLABELLED: Methane (CH4) and hydrogen (H2) are gases produced in the colon by the breakdown of carbohydrates, due to the action of anaerobic methanogenic bacteria. No papers have been published in pediatrics concerning these gases production and exhalation. Understanding of the pattern of H2, CH4, carbon dioxide (CO2), butyrates, indolellipsis,etc., production and exhalation, which may differ in gastrointestinal diseases, may be helpful as far as the diagnosis and treatment of some gastrointestinal conditions is concerned. Exhalation of H2, CH4 and CO2 by breath air was studied in basal conditions in 338 normal infants and in 27 lactose malabsorbers. Moreover, stools collected and stored for 10-12 h in anaerobic and aerobic conditions were incubated in anaerobiosis at 38 degrees C. After a 4-h incubation period, H2, CH4 and CO2 were determined. RESULTS: Methane production is independent of hydrogen production; the number of children producing CH4 increases from 0% at 12 months of age to 44% at the age of 9 years. In lactose malabsorption, we found 26 children producing increased quantities of H2 and no methane, and only one producing methane but no hydrogen, which proves that methanogenic bacteria are independent of H2-producing bacteria, and that CH4 determination is compulsory in the study of lactose malabsorption. The incubation of stools in an anaerobic milieu at 38 degrees C for 4 h, in an attempt to imitate the human colon, showed a great production of methane and less of H2 in the stools collected and stored in anaerobic conditions. The same incubation method was applied to the stools collected and stored in aerobic conditions: production of H2 and CH4 was much lower than in the collected and stored anaerobic group. The appearance of CH4 in the stools of the aerobic group proves that methanogenic bacteria are, to a small degree, resistant to oxygen. CONCLUSIONS: The study of gas exhalation in pediatrics merits more study by researchers, with a view to defining a special pattern of gas production in pathological conditions. The anaerobic stool incubation method is a good model for studying gas production under the effect of different diets and the gas production pattern in gastrointestinal diseases.

Aerobiosis↗

PubMed2002

Development of a purpose built landfill system for the control of methane emissions from municipal solid waste.

In the present paper, a new system of purpose built landfill (PBLF) has been proposed for the control of methane emissions from municipal solid waste (MSW), by considering all favourable conditions for improved methane generation in tropical climates. Based on certain theoretical considerations multivariate functional models (MFMs) are developed to estimate methane mitigation and energy generating potential of the proposed system. Comparison was made between the existing waste management system and proposed PBLF system. It has been found that the proposed methodology not only controlled methane emissions to the atmosphere but also could yield considerable energy in terms of landfill gas (LFG). Economic feasibility of the proposed system has been tested by comparing unit cost of waste disposal in conventional as well as PBLF systems. In a case study of MSW management in Mumbai (INDIA), it was found that the unit cost of waste disposal with PBLF system is seven times lesser than that of the conventional waste management system. The proposed system showed promising energy generation potential with production of methane worth of Rs. 244 millions/y ($5.2 million/y). Thus, the new waste management methodology could give an adaptable solution for the conflict between development, environmental degradation and natural resources depletion.

Air Pollution↗

PubMed2003

Simulation model for gas diffusion and methane oxidation in landfill cover soils.

Landfill cover soils oxidize a considerable fraction of the methane produced by landfilled waste. Despite many efforts this oxidation is still poorly quantified. In order to reduce the uncertainties associated with methane oxidation in landfill cover soils, a simulation model was developed that incorporates Stefan-Maxwell diffusion, methane oxidation, and methanotrophic growth. The growth model was calibrated to laboratory data from an earlier study. There was an excellent agreement between the model and the experimental data. Therefore, the model is highly applicable to laboratory column studies, but it has not been validated with field data. A sensitivity analysis showed that the model is most sensitive to the parameter expressing the maximum attainable methanotrophic activity of the soil. Temperature and soil moisture are predicted to be the environmental factors affecting the methane oxidizing capacity of a landfill cover soil the most. Once validated with field data, the model will enable a year-round estimate of the methane oxidizing capacity of a landfill cover soil.

Diffusion↗

PubMed1985

Determination of methane in ambient air by multiplex gas chromatography.

A multiplex gas chromatographic technique for the determination of methane in ambient air over extended periods is reported. A modest gas chromatograph which uses air as the carrier gas was modified by adding a silver oxide sample modulator for multiplex operation. The modulator selectively catalyzes the decomposition of methane in air. The resulting analytical systems requires no consumables beyond power. A profile of the methane concentration in this laboratory was obtained for an 8-day period. During this period, methane concentration varied with an approximately daily period from a low of 1.53 +/- 0.60 ppm to a high of 4.63 +/- 0.59 ppm over the entire 8 days. Some of the measured concentrations are higher than those reported elsewhere indicating the presence of some local source or sources for methane. This work has demonstrated the utility of a relatively simple multiplex gas chromatograph for the analysis of environmental samples. The technique should be applicable to other trace components in air through use of other selective modulators.

Air↗

PubMed2006

Regulation of methane monooxygenase catalysis based on size exclusion and quantum tunneling.

The hydroxylase component (MMOH) of the soluble form of methane monooxygenase (sMMO) isolated from Methylosinus trichosporium OB3b catalyzes both the O2 activation and the CH4 oxidation reactions at the oxygen-bridged dinuclear iron cluster present in its buried active site. During the reaction cycle, the diiron cluster forms a bis-mu-oxo-(Fe(IV))2 intermediate termed compound Q (Q) that reacts directly with methane. Many adventitious substrates also react with Q, most at a relatively slow rate. We have proposed that Q reacts preferentially with CH4 because the sMMO regulatory component MMOB induces a size selective pore into the MMOH active site as the two components form a complex. Support for this proposal has come through the observation of a nonlinear Arrhenius plot for the CH4 oxidation, presumably due to a shift in rate-limiting step from substrate binding at low temperature to C-H bond cleavage at high temperature. Reactions of all substrates other than CH4 fail to exhibit a break in the Arrhenius plot because binding is always rate limiting in the temperature range explored. Here we show that it is possible to induce a break in the Arrhenius plot for the ethane reaction with Q by using an MMOB mutant termed DBL2 (S109A/T111A) in which residues at the MMOH-MMOB interface are reduced in size. We hypothesize that this increases the ethane binding rate and shifts the Arrhenius breakpoint into the observable temperature range. As a result of this shift, the kinetic and activation parameters of the C-H bond breaking reaction for both methane and ethane can be observed using the DBL2 mutant. A 2H-KIE is observed for both substrate oxidation reactions when using DBL2, whereas only CH4 oxidation exhibits an effect when using wild type MMOB, consistent with the C-H bond cleaving reaction becoming at least partially rate limiting for ethane. Analysis of the temperature dependence of the 2H-KIE for ethane and methane for reactions using both mutant and wild type forms of MMOB suggests that quantum tunneling plays a significant role in methane oxidation but not ethane oxidation.

Binding Sites↗

PubMed2006

Thermal lens spectroscopy in liquid argon solutions: (Deltav = 6) C-H vibrational overtone absorption of methane.

A dual-beam thermal lens technique has been used to obtain the absorption spectrum of the (Deltav = 6) C-H stretch of liquid methane and methane in liquid argon solutions. The lowest concentration detected was 1 x 10(-3) (mole fraction) of CH(4) in liquid Ar with a continuous wave laser power of 20 mW. The thermal lens signal is linear with the mole fraction of methane up to 1 x 10(-2) but not for higher concentrations. Considering the system CH(4)-Ar as an ideal solution, the factors that contribute to the thermal lens signal were calculated as a function of the concentration of methane. A mechanism of energy transfer based on the gas-phase results could explain qualitatively the dependence of the magnitude of the signal on the mole fraction of methane.

Absorption↗

PubMed2006

Nanoscale tubular vessels for storage of methane at ambient temperatures.

Novel carbon nanostructures can serve as effective storage media for methane, a source of "clean energy" for the future. We have used Grand Canonical Monte Carlo Simulation for the modeling of methane storage at 293 K and pressures up to 80 MPa in idealized bundles of (10,10) armchair-type single-walled carbon nanotubes and wormlike carbon pores. We have found that these carbon nanomaterials can be treated as the world's smallest high-capacity methane storage vessels. Our simulation results indicate that such novel carbon nanostructures can reach a high volumetric energy storage, exceeding the US FreedomCAR Partnership target of 2010 (5.4 MJ dm(-3)), at low to moderate pressures ranging from 1 to 7 MPa at 293 K. On the contrary, in the absence of these nanomaterials, methane needs to be compressed to approximately 13 MPa at 293 K to achieve the same target. The light carbon membranes composed of bundles of single-walled carbon nanotubes or wormlike pores efficiently physisorb methane at low to moderate pressures at 293 K, which we believe should be particularly important for automobiles and stationary devices. However, above 15-20 MPa at 293 K, all investigated samples of novel carbon nanomaterials are not as effective when compared with compression alone since the stored volumetric energy and power saturate at values below those of the bulk, compressed fluid.

Methane↗

PubMed2003

Stable isotopic evidence for methane seeps in Neoproterozoic postglacial cap carbonates.

The Earth's most severe glaciations are thought to have occurred about 600 million years ago, in the late Neoproterozoic era. A puzzling feature of glacial deposits from this interval is that they are overlain by 1-5-m-thick 'cap carbonates' (particulate deep-water marine carbonate rocks) associated with a prominent negative carbon isotope excursion. Cap carbonates have been controversially ascribed to the aftermath of almost complete shutdown of the ocean ecosystems for millions of years during such ice ages--the 'snowball Earth' hypothesis. Conversely, it has also been suggested that these carbonate rocks were the result of destabilization of methane hydrates during deglaciation and concomitant flooding of continental shelves and interior basins. The most compelling criticism of the latter 'methane hydrate' hypothesis has been the apparent lack of extreme isotopic variation in cap carbonates inferred locally to be associated with methane seeps. Here we report carbon isotopic and petrographic data from a Neoproterozoic postglacial cap carbonate in south China that provide direct evidence for methane-influenced processes during deglaciation. This evidence lends strong support to the hypothesis that methane hydrate destabilization contributed to the enigmatic cap carbonate deposition and strongly negative carbon isotopic anomalies following Neoproterozoic ice ages. This explanation requires less extreme environmental disturbance than that implied by the snowball Earth hypothesis.

Animals↗

PubMed1967

Methane production from glucose in vitro by mixed rumen bacteria.

1. Methane was produced in vitro by incubating cell suspensions of rumen bacteria with glucose, under nitrogen. The amount of methane produced varied considerably and was lowered by high glucose concentrations. Carbon dioxide, acetic acid, propionic acid, butyric acid and lactic acid were also produced. An oxidation-reduction balance of near unity could be calculated, although carbon recovery was low. Under the experimental conditions, rumen bacteria used most of the metabolic hydrogen produced during the oxidation of glucose to form lactic acid. 2. Lower methane production at high glucose concentrations was balanced by higher lactic acid production. Low pH values due to a high production rate of lactic acid might explain the inhibition of methane production. 3. No lactic acid, less methane, but considerably more propionic acid were formed when nitrogen was replaced by carbon dioxide in the incubation system.

Acetates↗

PubMed1980

Methane production by the membranous fraction of Methanobacterium thermoautotrophicum.

Intact membrane vesicles are required to synthesize methane from CO2 and H2 by disrupted preparations of Methanobacterium thermoautotrophicum cells. When membrane vesicles were removed by high-speed centrifugation at 226 600 g, the remaining supernatant fraction no longer synthesized methane. Alternatively, if vesicle structure was disrupted by passage through a Ribi cell fractionator at very high pressures (345 MPa), the bacterial cell extract, with all the particulate fraction in it, did not synthesize methane. Methyl-coenzyme M, a new coenzyme first described by McBride & Wolfe [(1971) Biochemistry 10, 2317--2324], was shown to stimulate methane production from CO2 and H2, as previously reported, but the methyl group of the coenzyme did not appear to be a precursor of methane in this reaction. No methyl-coenzyme M reductase activity was detected in the cytoplasmic fraction of M. thermoautotrophicum cells.

Adenosine Triphosphate↗

PubMed1983

Methane oxidation by Nitrosomonas europaea.

Methane inhibited NH4+ utilization by Nitrosomonas europaea with a Ki of 2mM. O2 consumption was not inhibited. In the absence of NH4+, or with hydrazine as reductant, methane caused nearly a doubling in the rate of O2 uptake. The stimulation was abolished by allylthiourea, a sensitive inhibitor of the oxidation of NH4+. Analysis revealed that methanol was being formed in these experiments, with yields approaching 1 mol of methanol per mol of O2 consumed under certain conditions. When cells were incubated with NH4+ under an atmosphere of 50% methane, 50 microM-methanol was generated in 1 h. It is concluded that methane is an alternative substrate for the NH3-oxidizing enzyme (ammonia mono-oxygenase),m albeit with a much lower affinity than for methane mono-oxygenase of methanotrophs.

Ammonium Sulfate↗

PubMed1985

The methane mono-oxygenase reaction system studied in vivo by membrane-inlet mass spectrometry.

A membrane-inlet mass spectrometer connected to an open-system cuvette was used for direct measurement of dissolved methane and O2 in bacterial samples of strain OU-4-1, a type II methanotrophic bacterium. A technique was applied for keeping the concentration of dissolved methane or O2 in the sample constant while the concentration of the other dissolved gas was varied. This allowed the reaction mechanism of methane mono-oxygenase to be studied in vivo. The enzyme was found to follow a random bi-reactant mechanism with respect to binding of methane and O2. Binding of one substrate decreased the affinity for the other. The true binding constants were 1 microM for methane and 0.14 microM for O2. Studies of HCN inhibition confirmed the random bi-reactant mechanism. HCN was found to be a non-exclusive inhibitor with a binding constant of 0.4 microM.

Cell Membrane↗

PubMed2003

Methane oxidation and its coupled electron-sink reactions in ruminal fluid.

AIMS: This study was conducted to investigate the occurrence of methane oxidation in the rumen, and to identify the electron-sink reaction coupled to the oxidation if it occurred. METHODS AND RESULTS: Mixed ruminal microbes taken from sheep were incubated with 13CH4. Oxidation of methane, estimated from the flux of 13C to CO2 and microbial cells, occurred, but represented only 0.2-0.5% of the methane produced. Methane oxidation was suppressed by the presence of oxygen, and was also inhibited by 2-bromoethane-sulphonate, and molybdate, but not by tungstate. CONCLUSION, SIGNIFICANCE AND IMPACT OF THE STUDY: Methane could be oxidized anaerobically in the rumen by reverse methanogenesis in consort with sulphate reduction.

Animals↗

PubMed1976

Rates of production of methane in the rumen and large intestine of sheep.

1. An isotope tracer method for estimating methane production in sheep is described. 2. The technique was used to estimate methane produced in both the upper and lower digestive tract and to determine the routes by which it was excreted. 3. Four Merino ewes given lucerne chaff (33 g every hour) were used. 4. Total methane production rate was 21 +/- 1-1 (SE) ml/min; production in the rumen accounted for 87 +/- 1-2% of the total production; 95 +/- 1-4% of the methane produced in the rumen was excreted by eructation. 5. Of the methane produced in the lower digestive tract, 89 +/- 2-3% was excreted through the lungs and 11% through the anus.

Anal Canal↗

PubMed1999

Breath hydrogen and methane responses of men and women to breads made with white flour or whole wheat flours of different particle sizes.

OBJECTIVE: While it is well known that consumption of whole grain foods results in beneficial health effects, the great majority of Americans prefer bread made with white flour. Consumption of whole grain foods in high fiber menus may cause undesirable intestinal responses. The purpose of this study was to determine whether consumption of bread made with ultra fine ground whole wheat flour retained beneficial effects while reducing undesirable effects. METHODS: Twenty-six men and women (31 to 55 years of age) consumed glucose solutions or bread made with white, whole wheat or fine ground whole wheat flour (1 g carbohydrate/kg body weight) in a Latin square design after two days of controlled diet. Breath methane and hydrogen were determined over the 24 hours after consumption of test foods. RESULTS: Hydrogen and methane responses of men and women were similar. There were no significant differences in methane responses to the different treatments, but hydrogen response was increased by all breads (p<0.0001). Although the overall mean response values were similar for all three breads, the patterns of hydrogen response differed (treatment*time, p<0.003). Gastrointestinal symptoms were not associated with fiber content or particle size of bread; however, subjects reporting symptoms tended to have higher methane responses (0.05<p<0.10). CONCLUSION: Neither fiber content of bread nor particle size of whole wheat flour substantially affected breath hydrogen or methane responses or gastrointestinal symptoms. Fine ground whole wheat breads may provide a more acceptable food choice than standard whole wheat bread without sacrificing the beneficial health effects of higher fiber.

Adult↗

PubMed2000

An improved inventory of methane emissions from coal mining in the United States.

Past efforts to estimate methane emissions from underground mines, surface mines, and other coal mine operations have been hampered, to different degrees, by a lack of direct emissions data. Direct measurements have been completely unavailable for several important coal mining operations. A primary goal of this study was to collect new methane emissions measurements and other data for the most poorly characterized mining operations and use these data to develop an improved methane emission inventory for the U.S. coal mining industry. This required the development and verification of measurement methods for surface mines, coal handling operations, and abandoned underground mines and the use of these methods at about 30 mining sites across the United States. Although the study's focus was on surface mines, abandoned underground mines, and coal handling operations, evaluations were also conducted to improve our understanding of underground mine emission trends and to develop improved national data sets of coal properties. Total U.S. methane emissions are estimated to be 4.669 million tons, and as expected, emissions from underground mine ventilation and methane drainage systems dominate (74% of the total emissions). On the other hand, emissions from coal handling, abandoned underground mines, and surface mines are significant, and collectively they represent approximately 26% of the total emissions.

Air Pollutants, Occupational↗

PubMed2003

Methane emission from fields with three various rice straw treatments in Taiwan paddy soils.

Flooded rice fields are one of the major biogenic methane sources. In this study, the effects of straw residual treatments on methane emission from paddy fields were discussed. The experimental field was located at Tainan District Agricultural Improvement Station in Chia-Yi county (23 degrees 25'08''N, 120degrees16'26''E) of southern Taiwan throughout the first and the second crop seasons in 2000. The seasonal methane fluxes in the first crop season with rice stubble removed, rice straw burned and rice straw incorporated were 4.41, 3.78 and 5.27 g CH4 m(-2), and the values were 32.8, 38.9 and 75.1 g CH4 m(-2) in the second crop season, respectively. In comparison of three management methods of rice straw residue, the incorporation of rice straw residue should show a significant tendency for enhancing methane emission in the second crop season. Moreover, stubble removed and straw burned treatments significantly reduced CH4 emissions by 28 approximately 56% emissions compared to straw incorporated plot. Concerning for air quality had led to legislation restricting rice straw burning, removing of rice stubble might be an appropriate methane mitigation strategy in Taiwan paddy soils.

Agriculture↗