• Korean Chemical Engineering Research
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• v.50 no.6
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• pp.1008-1014
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• 2012

The amount of domestic carbon dioxide emissions is more than 600 million tons/year. The emitted $CO_2$ should be captured and stored, however, suitable storage sites have not been found yet. A lot of researches on the conversion of captured carbon dioxide to useful carbon source have been conducted. The purpose of this study is to convert stable carbon dioxide to useful resources using less energy. For this purpose reducing gas and metallic oxide (activator) are required. Hydrogen was used as reducing gas and cobalt ferrite was used as activator. Considering that activator has different physical properties depending on synthesis methods, activator was prepared by hydrothermal synthesis and solid method. Decomposition characteristics of carbon dioxide were investigated using synthesized powders. Temperature programmed reduction/oxidation (TPR/TPO) and thermogravimetric analyzer (TGA) device were used to observe the decomposition characteristics of carbon dioxide. Activator prepared by solid method with 5 and 10 wt% CoO content showed an excellent performance. In TGA experiments with samples prepared by the solid method, reduction by hydrogen was 29.0 wt% and oxidation by $CO_2$ was highest in 27.5 wt%. 95% of adsorbed $CO_2$ was decomposed with excellent oxidation-reduction behaviors.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.462-462
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• 2011

1994년에 발효된 기후변화협약에서 우리나라는 선발 개도국으로 분류되어 온실가스 의무감축 대상국에서 제외되었으나 제2차 공약기간 (2013~2017년)부터는 온실가스 감축 의무이행이 불가피할 것으로 예상되어 그 대응책 마련이 시급한 실정이다. 현재 국내에서는 국제기준에 부합하는 온실가스 배출량 통계자료 구축을 위한 기초연구가 다양하게 수행되고 있으나 온실가스 감축을 위한 시나리오 설정이나 모의실험 연구는 계획 중이거나 시작 단계에 있다. 이 중 농경지에서의 온실가스 배출은 환경조건에 따라 온실가스를 배출하거나 흡수할 수 있는 양면성을 갖기 때문에 미래의 온실가스 배출을 예측하고 국내 실정에 맞는 저감방안을 수립하기 위해서는 다양한 조건을 적용하여 온실가스 배출량을 모의할 필요가 있다. 따라서 본 연구에서는 작물생육과 토양환경의 상호작용을 고려하여 농업생태계 내에서의 온실가스 배출을 모의하는 DNDC (Denitrification-Decomposition)를 이용하여 다양한 물관리 방식을 적용하여 벼 재배시 논에서의 온실가스 배출량을 산정하고 그 결과를 비교하고자 하였다. 물관리 방식에 따른 온실가스 배출 모의를 위해 관개시기를 조정하여 상시담수와 간단관개시의 시나리오를 적용하고, 담수심의 깊이에 따라 심수관개시와 최소 담수심 시나리오를 적용하여 온실가스 배출량을 산정하였다. 이는 향후 농경지를 대상으로 관개 방식 개선을 통해 온실가스 배출량을 감축하고 지속가능한 토지이용방안을 모색하는데 기초자료로 활용할 수 있을 것이라 판단된다.

• Journal of Korean Society of Disaster and Security
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• v.16 no.4
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• pp.45-59
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• 2023

The global focus on mitigating climate change has traditionally centered on carbon dioxide, but recent attention has shifted towards methane as a crucial factor in climate change adaptation. Natural settings, particularly aquatic environments such as wetlands, reservoirs, and lakes, play a significant role as sources of greenhouse gases. The accumulation of organic contaminants on the lake and reservoir beds can lead to the microbial decomposition of sedimentary material, generating greenhouse gases, notably methane, under anaerobic conditions. The escalation of methane emissions in freshwater is attributed to the growing impact of non-point sources, alterations in water bodies for diverse purposes, and the introduction of structures such as river crossings that disrupt natural flow patterns. Furthermore, the effects of climate change, including rising water temperatures and ensuing hydrological and water quality challenges, contribute to an acceleration in methane emissions into the atmosphere. Methane emissions occur through various pathways, with ebullition fluxes-where methane bubbles are formed and released from bed sediments-recognized as a major mechanism. This study employs Biochemical Methane Potential (BMP) tests to analyze and quantify the factors influencing methane gas emissions. Methane production rates are measured under diverse conditions, including temperature, substrate type (glucose), shear velocity, and sediment properties. Additionally, numerical simulations are conducted to analyze the relationship between fluid shear stress on the sand bed and methane ebullition rates. The findings reveal that biochemical factors significantly influence methane production, whereas shear velocity primarily affects methane ebullition. Sediment properties are identified as influential factors impacting both methane production and ebullition. Overall, this study establishes empirical relationships between bubble dynamics, the Weber number, and methane emissions, presenting a formula to estimate methane ebullition flux. Future research, incorporating specific conditions such as water depth, effective shear stress beneath the sediment's tensile strength, and organic matter, is expected to contribute to the development of biogeochemical and hydro-environmental impact assessment methods suitable for in-situ applications.

• Korean Journal of Microbiology
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• v.51 no.2
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• pp.97-107
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• 2015

Wetlands constitute a transitional zone between terrestrial and aquatic ecosystems and have unique characteristics such as frequent inundation, inflow of nutrients from terrestrial ecosystems, presence of plants adapted to grow in water, and soil that is occasionally oxygen deficient due to saturation. These characteristics and the presence of vegetation determine physical and chemical properties that affect decomposition rates of organic matter (OM). Decomposition of OM is associated with activities of various extracellular enzymes (EE) produced by bacteria and fungi. Extracellular enzymes convert macromolecules to simple compounds such as labile organic carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) that can be easily taken up by microbes and plants. Therefore, the enzymatic approach is helpful to understand the decomposition rates of OM and nutrient cycling in wetland soils. This paper reviews the physical and biogeochemical factors that regulate extracellular enzyme activities (EEa) in wetland soils, including those of ${\beta}$-glucosidase, ${\beta}$-N-acetylglucosaminidase, phosphatase, arylsulfatase, and phenol oxidase that decompose organic matter and release C, N, P, and S nutrients for microbial and plant growths. Effects of pH, water table, and particle size of OM on EEa were not significantly different among sites, whereas the influence of temperature on EEa varied depending on microbial acclimation to extreme temperatures. Addition of C, N, or P affected EEa differently depending on the nutrient state, C:N ratio, limiting factors, and types of enzymes of wetland soils. Substrate quality influenced EEa more significantly than did other factors. Also, drainage of wetland and increased temperature due to global climate change can stimulate phenol oxidase activity, and anthropogenic N deposition can enhance the hydrolytic EEa; these effects increase OM decomposition rates and emissions of $CO_2$ and $CH_4$ from wetland systems. The researches on the relationship between microbial structures and EE functions, and environmental factors controlling EEa can be helpful to manipulate wetland ecosystems for treating pollutants and to monitor wetland ecosystem services.

• Journal of the Korean Institute of Gas
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• v.25 no.2
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• pp.1-12
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• 2021

MILD(Moderate or Intense Low-oxygen Dilution) combustion has attracted attention as the clean thermal energy technology due to the lower emissions of unburnt carbon and NO_x. MILD combustion aims to enlarge the combustion reaction zone using the spontaneous ignition phenomenon of the reactants. In this study, the ignition delay time of CH₄ according to the initial temperature of reactants and the addition of CO, H₂ was investigated using a numerical approach. Ignition delay time became shorter as the increases of initial temperature and H₂ addition. But, CO addition to the fuel increase the ignition delay time. In case of H₂ addition to the fuel, the ignition delay time decreased because the higher fraction of HO₂ promotes the decomposition of methyl radical(CH₃) and produce OH radical. However, in case of CO addition to the fuel, ignition delay time inceased because a high proportion of HCO consumes H radical. There was no significant effect of HCO on the reduction of ignition delay time. Also, the increase rates of NO emissions by the addition of CO and H₂ were approximately 7% and 1%, respectively. A high proportion of NCO affects the increase in NO production rate.

• Journal of Korean Society of Forest Science
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• v.107 no.2
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• pp.140-150
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• 2018

For the estimation of greenhouse gas dynamics in forests, it is useful to use a model which simulates both carbon (C) and nitrogen (N) cycle simultaneously. A forest C model, called FBDC, was developed and validated in Korea. However, studies on development of forest N model are insufficient. This study aimed to suggest a development process of a forest C and N model. We analyzed the general features, structures, ecological processes, input data, output data, and methods of integrating C and N cycles of the VISIT, Biome-BGC, Forest-DNDC, and O-CN. The structure and features of the FBDC were also analyzed. The VISIT was developed by integrating forest C model with a N cycle module, and the new model also could be designed by combining the FBDC with a N cycle module. The VISIT and Forest-DNDC could estimate soil $N_2O$ emissions, and the integrated model should include the processes shared by these models. Especially, the overseas models linked C and N cycles based on N absorption, C absorption, and decomposition of dead organic matter. Therefore, the integration of the FBDC with N cycle module should apply this linkage of structures between C and N cycles. Climate, soil texture, and species distribution data, which are essential for the model development, were available in Korea. However, parameter data associated with N cycle and validation data for soil $N_2O$ emissions need to be obtained by field studies.

• Korean Journal of Ecology and Environment
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• v.51 no.2
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• pp.160-167
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• 2018

The role played by reservoirs in the biogeochemical cycles of elements is a subject of ongoing debate. Recent research has revealed that reservoirs emit significant levels of greenhouse gases. To assess the importance of reservoirs in monsoon climate areas as a source of methane gas into the atmosphere, we investigated variations in organic carbon (OC) input into the reservoir, oxic state changes, and finally the amount of methane emitted (focusing on the ebullition pathway) in Lake Soyang, which is the largest reservoir in South Korea. Total organic carbon (TOC) concentrations were higher during summer after two years of heavy rainfall. The sedimentation rates of particulate organic carbon (POC) and particulate organic nitrogen (PON) were higher in the epilimnion and hypolimnion than the metalimnioin, indicating that autochthonous and allochthonous carbon made separate contributions to the TOC. During stratification, oxygen depletion occurred in the hypolimnion due to the decomposition of organic matter. Under these conditions, $H_2S$ and $CH_4$ can be released from sediment. The methane emissions from the reservoir were much higher than from other natural lakes. However, the temporal and spatial variations of methane ebullition were huge, and were clearly dependent on many factors. Therefore, more research via a well-organized field campaign is needed to investigate methane emissions.

• Analytical Science and Technology
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• v.31 no.1
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• pp.47-56
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• 2018

Finding the blood left at a crime scene is very important to reconstruct or solve a criminal case. Although numerous reagents have been developed for use at crime scenes, luminol is the most representative. Bluestar Forensic has been used in recent years, but is expensive and cannot be stored after preparation. This study aims to develop a new luminol reagent that can be stored for a long period of time while maintaining the chemiluminescence intensity at the level of Bluestar Forensic. Because luminol dissolves well in aqueous alkaline solutions, the use of sodium hydroxide in the preparation of luminol reagents can promote the decomposition of hydrogen peroxide. Magnesium sulfate, sodium silicate, and potassium triphosphate have been used as hydrogen peroxide stabilizers. The effects of the addition of these substances on the chemiluminescence emission intensity and the storage period of the luminol reagents were confirmed. The addition of a hydrogen peroxide stabilizer was shown to have no significant affect on the chemiluminescence emissions intensity or stabilized pH of the luminol reagent during storage. It also greatly increases the shelf life of the reagents. The use of magnesium sulfate as a hydrogen peroxide stabilizer is the most appropriate. When sodium perborate is used instead of hydrogen peroxide as an oxidizing agent, there is no significant change in the sensitivity and chemiluminescence emissions intensity, but the storage period is shortened. However, after the reaction with blood, the pH of the mixed solution does not increase significantly, and is judged to be more suitable than a reagent made of hydrogen peroxide.

• Korean Journal of Environmental Biology
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• v.31 no.4
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• pp.471-477
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• 2013

Biochar amendment to agricultural soil is regarded as a promising option to mitigate climate change and enhance soil quality. It could sequester more carbon within the soil system and increase plant yield by changing soil physicochemical characteristics. However, sustainable use of biochar requires comprehensive environmental assessment. In this sense, it is important to measure additional greenhouse gas emission from soils after biochar addition. We investigated emissions of $CO_2$, $N_2O$, and $CH_4$ from incubated soils collected from rice paddy and cultivated grassland after amendment of 3% biochar (wt.) produced from rice chaff. During incubation, soils were exposed to three wet-dry cycles ranging from 5~85% soil gravimetric water content (WC) to investigate the changes in effect of biochar when influenced by different water levels. The $CO_2$ emission was reduced in biochar treatment compared to the control at WC of 30~70% both in rice paddy and grassland soils. This indicates that biochar could function as a stabilizer for soil organic carbon and it can be effective in carbon sequestration. The $N_2O$ emission was also reduced from the grassland soil treated with biochar when WC was greater than 30% because the biochar treated soils had lower denitrification due to better aeration. In the rice paddy soil, biochar addition resulted in decrease in $N_2O$ emission when WC was greater than 70%, while an increase was noted when WC was between 30~70%. This increase might be related to the fact that available nutrients on biochar surface stimulated existing nitrifying bacterial community, resulting in higher $N_2O$ emission. Overall results imply that biochar amendment to agricultural soil can stabilize soil carbon from fast decomposition although attention should be paid to additional $N_2O$ emission when biochar addition is combined with the application of nitrogen fertilizer.

• Journal of the Korean Institute of Gas
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• v.27 no.3
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• pp.19-26
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• 2023

Hydrogen, a clean energy source free of COx emissions, is poised to replace fossil fuels, with its usage on the rise. Despite its high energy content per unit mass, hydrogen faces limitations in storage and transportation due to its low storage density and challenges in long-term storage. In contrast, ammonia offers a high storage capacity per unit volume and is relatively easy to liquefy, making it an attractive option for storing and transporting large volumes of hydrogen. While NH₃ decomposition is an endothermic reaction, achieving excellent low-temperature catalytic activity is essential for process efficiency and cost-effectiveness. The study examined the effects of different zeolite types (5A, NaY, ZSM5) on NH₃ decomposition activity, considering differences in pore structure, cations, and Si/Al-ratio. Notably, the 5A zeolite facilitated the high dispersion of Ni across the surface, inside pores, and within the structure. Its low Si/Al ratio contributed to abundant acidity, enhancing ammonia adsorption. Additionally, the presence of Na and Ca cations in the support created medium basic sites that improved N₂ desorption rates. As a result, among the prepared catalysts, the 15 wt%Ni/5A catalyst exhibited the highest NH₃ conversion and a high H₂ formation rate of 23.5 mmol/g_cat·min (30,000 mL/g_cat·h, 600 ℃). This performance was attributed to the strong metal-support interaction and the enhancement of N₂ desorption rates through the presence of medium basic sites.