• Environmental Engineering Research
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• v.20 no.2
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• pp.191-197
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• 2015

The first objective of this study was to discuss the applicability of the $CO_2/CH_4$ ratio method in order to assess $CH_4$ oxidation efficiency. To achieve this objective, a comparison between $CO_2/CH_4$ ratios and the mass balance method was conducted. The second objective of this study was to estimate the $CH_4$ oxidation efficiency in an interim landfill soil cover and assess how a $CH_4$ influx influences the $CH_4$ oxidation efficiency. The results showed that despite the $CO_2$ problems brought by respiration, the $CH_4$ oxidation efficiencies obtained by the $CO_2/CH_4$ ratio method led to similar results compared to the mass balance method. In this respect, the $CO_2/CH_4$ ratio method can be an indicator of the $CH_4$ oxidation efficiencies for landfill cover soils. The $CH_4$ oxidation efficiencies derived in this study through the $CO_2/CH_4$ ratio method ranged between 46% and 64%, and between 41% and 62% through the mass balance method. The results imply that the Intergovernmental Panel on Climate Change's (IPCC) default value of 10% for the $CH_4$ oxidation efficiency is an underestimation for landfill cover soils. $CH_4$ oxidation efficiency tends to be negatively correlated with $CH_4$ influx. Therefore, $CH_4$ influx reaching a landfill cover should be limited in order to increase the $CH_4$ oxidation efficiency.

• Asian Journal of Atmospheric Environment
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• v.8 no.1
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• pp.1-14
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• 2014

Migration of methane ($CH_4$) gas from landfills to the surrounding environment negatively affects both humankind and the environment. It is therefore essential to develop management techniques to reduce $CH_4$ emissions from landfills to minimize global warming and to reduce the human risks associated with $CH_4$ gas migration. Oxidation of $CH_4$ in landfill cover soil is the most important strategy for $CH_4$ emissions mitigation. $CH_4$ oxidation occurs naturally in landfill cover soils due to the abundance of methanotrophic bacteria. However, the activities of these bacteria are influenced by several controlling factors. This study attempts to review the important issues associated with the $CH_4$ oxidation process in landfill cover soils. The $CH_4$ oxidation process is highly sensitive to environmental factors and cover soil properties. The comparison of various biotic system techniques indicated that each technique has unique advantages and disadvantages, and the choice of the best technique for a specific application depends on economic constraints, treatment efficiency and landfill operations.

• Korean Journal of Environmental Agriculture
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• v.33 no.4
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• pp.306-313
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• 2014

BACKGROUND: Forest soils contain microbes capable of consuming atmospheric methane ($CH_4$), an amount matching the annual increase in $CH_4$ concentration in the atmosphere. However, the effect of plant residue production by different forest structure on $CH_4$ oxidation is not studied in Korea. The objective of this study was to evaluate the effect of Korean alpine soils having different forestation structure on $CH_4$ uptake rates. METHODS AND RESULTS: the $CH_4$ flux was measured at three sites dominated with pine, chestnut and oak trees in southern Korea. The $CH_4$ uptake potentials were evaluated by a closed chamber method for a year. The $CH_4$ uptake rate was the highest in the pine tree soil ($1.05mg/m^2/day$) and then followed by oak ($0.930mg/m^2/day$) and chestnut trees ($0.497mg/m^2/day$). The $CH_4$ uptake rates were highly correlated to soil organic matter and moisture contents, and total microbial and methanotrophs activities. Different with the general concent, there was no any correlation between $CH_4$ oxidation rates, and soil temperature and labile carbon concentrations, irrespective with tree species. CONCLUSION: Conclusively, the methane oxidation rate was correlated in positive manner with organic matter, abundance of methanotrophs. Methane oxidation was different among tree species. This results could be used to estimate methane oxidation rate in forest of Korea after complementing information about statistical data and methane oxidation of other site.

• Applied Chemistry for Engineering
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• v.23 no.3
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• pp.253-258
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• 2012

The effects of active sites and valence states were investigated over $Pd/TiO_2$ catalyst on simultaneous oxidation of $CH_4$ and CO. The Pd species (PdO) crystallite size increased with increasing Pd loadings, which results in enhancement of the activity of $CH_4$ oxidation. Different results from the activity of $CH_4$ and CO oxidation were shown to be dependent on the Pd valence state on the surface of the catalyst prepared through a thermal treatment. XRD and $H_2-TPR$ analysis confirmed that $Pd^{2+}$species was predominated in the calcination catalyst, while $Pd^0$species was predominated in the reduction catalyst. Additionally, it could be found that the valence state of Pd was a more important factor on the catalytic activity than that of factors as the surface area and pore volume. The reaction mechanism of $CH_4$ and CO followed by the valence state of Pd could be identified using FT-IR analysis.

• Journal of Wetlands Research
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• v.21 no.2
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• pp.95-101
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• 2019

In tidal flats that lack plants, methane ($CH_4$) fluxes are both positive (gas emission) and negative (gas "sinking") in nature. The levels of methanotroph populations significantly affect the extent of $CH_4$ sinking. This preliminary study examined $CH_4$ flux in tidal flats using a circular closed-chamber method to understand the effects of macroinvertebrate burrowing activity. The chamber was deployed over decapods (mud shrimp, Laomedia astacina and crab, Macrophthalmus japonicus) burrows for ~ 2 h, and the $CH_4$ and $CO_2$ concentrations were continuously monitored using a closed, diffuse $CH_4/CO_2$ flux meter. We found that Laomedia astacina burrow (which is relatively long) site afforded higher-level $CH_4$ production, likely due to diffusive emission of $CH_4$ in deep-layer sediments. In addition, the large methanotrophic bacteria population found in the burrow wall sediments has $CH_4$ oxidation (consumption) potential. Especially, nitrite-driven anaerobic oxidation of methane (AOM) may occur within burrows. The proposed $CH_4$-oxidation process was supported by the decrease in the ${\delta}^{13}C$ of headspace $CO_2$ during the chamber experiment. Therefore, macroinvertebrate burrows appear to be an important ecosystem environment for controlling atmospheric $CH_4$ over tidal flats.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.2
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• pp.134-139
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• 2003

This study was carried out to investigate the aging and conversion characteristics of oxidation catalysts for a natural gas vehicle with lean-bum system. The conversion of $CH_4$ was observed over the various composition ratio of PMs(Precious metals) and washcoating methods. On the fresh catalysts, Pd affected on the activity of $CH_4$ at low temperature more than other PMs in Pd-only and Rh/Pd/Pt catalysts. The activity at low temperature increased as a mount of Pd increases. On the aged catalysts, the $CH_4$ conversion efficiency of Pd-only catalyst with mono-layer washcoat decreased more than that of the other catalysts of $CH_4$ conversion. It was observed that the thermal durability of Rh/Pd/Pt catalysts with double-layer washcoat was better than the single washcoat catalyst.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.6
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• pp.511-517
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• 2002

The complex 1 $([Cp*Fe(CO)_2]_2-(\mu-CH=CH-CH=CH))$ which have butadiene as a bridge were synthesized from $Cp*(CO)_2FeK$ and cis-3,4-dichlorocyclobutene. The derivatives of complex 1 where one or two carbonyl groups are replaced by phosphine ligands have been prepared by photochemical substitution. The new derivatives $([Cp*Fe(L)_2]_2-(\mu-CH=CH-CH=CH))$ where L = $(Ph_2PCH_2CH_2PPh_2)$ and $([Cp*Fe(CO)(L)]_2-(\mu-CH=CH-CH=CH))$ where L : $PPh_3$ have been characterized from $^^1H-$, $^^13C-$,$^^31P-NMR$ and elemental analysis. Obtained complexes have been studied in electrochemical experiment and UV/VIS-near-IR. The mixed-valence radical cation forms of complex 2, 3 species were found to be delocalized as the Class III. Based on the separation of the waves ($\triangle E$ : 0.470 ~ 0.605 V), the efficiency of electronic communication between two metal centers of cation species leading to stabilization relative to neutral species. The phosphine-substitute complexes (2, 3) displays two reversible oxidation waves and oxidation state of metal centers-dependent color change, electrochromism, was observed from yellow to orange and deep blue in methylene chloride.

• Bulletin of the Korean Chemical Society
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• v.23 no.6
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• pp.799-803
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• 2002

Partial oxidation of methane has been conducted over $CeO_2$and it has been found that $CeO_2$has an extraordinary catalytic activity in the reaction. Its activity was strongly dependent on the $CH_4/CO_2$ ratio. Total combustion was dominant with stoichiometric feed ratio$(CH_4/O_2=$ 2.0) but partial oxidation was achieved between the $CH_4/O_2$ ration of 3.8 4.3 and the period depended upon the feed composition. The proposed raaction mechanism it that oxygen vacancies in raduced deria are supplied with oxygen molecules from the reactant, and then activate adsorbed oxygen, followed by releasing activated axygen species reacting with methane to produce $H_2$ and CO.

• Journal of Microbiology and Biotechnology
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• v.25 no.4
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• pp.423-430
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• 2015

Aerobic CH₄ oxidation is an important CH₄ sink in landfills. To investigate the distribution and community diversity of methanotrophs and link with soil characteristics and operational parameters (e.g., concentrations of O₂, CH₄), cover soil samples were collected at different locations and depths from the Mengzi semi-aerobic landfill (SAL) in Yunnan Province of southern China. Specific PCR followed by denaturing gradient gel electrophoresis and realtime PCR were used to examine methanotrophs in the landfill cover soils. The results showed that different locations did harbor distinct methanotroph communities. Methanotrophs were more abundant in areas near the venting pipes because of the higher O₂ concentrations. The depth of 20-25 cm, where the ratio of the CH₄ to O₂ was within the range from 1.3 to 8.6, was more conducive to the growth of CH₄-oxidizing bacteria. Type II methanotrophs dominated in all samples compared with Type I methanotrophs, as evidenced by the high ratio of Type II to Type I methanotrophic copy numbers (from 1.76 to 11.60). The total copy numbers of methanotrophs detected were similar to other ecosystems, although the CH₄ concentration was much higher in SAL cover soil. Methylobacter and Methylocystis were the most abundant Type I and Type II methanotrophs genera, respectively, in the Mengzi SAL. The results suggested that SALs could provide a special environment with both high concentrations of CH₄ and O₂ for methanotrophs, especially around the vertical venting pipes.

• Applied Chemistry for Engineering
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• v.16 no.5
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• pp.641-647
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• 2005

The partial oxidation of methane is one of important processes for hydrogen production. As a membrane reactor, palladium-silver (Pd-Ag) alloy membrane prepared by electroless plating technique was employed for partial oxidation of methane. The experimental variables were reaction temperature, $O_2/CH_4$ mole ratio, $CH_4$ feed rate, and $N_2$ sweep gas flow rate. The methane conversions increased with the reaction temperatures in the range of 350 to $730^{\circ}C$. The highest methane conversion and CO selectivity were obtained at the condition of $O_2/CH_4$ mole ratio of 0.5 and $730^{\circ}C$ using commercially available nickel/alumina catalyst. The Pd-Ag membrane reactor showed higher methane conversions, 10~40% higher, compared to those in a traditional reactor.