• Journal of Applied Biological Chemistry
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• v.43 no.2
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• pp.86-93
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• 2000

An experiment was conducted to obtain the quantitative data on the transformation and loss of applied urea-N in waterlogged soil columns. The soil columns were pre-incubated for 35 days to develop oxidized and reduced soil conditions prior to urea application. After urea application at the rate of $150kg\;N\;ha^{-1}$(29.5 mg N), the amounts of nitrogen which were volatilized, leached, and remained in soil column were measured during 38 days of incubation period. On 2 and 4 days of incubation, 54.1%(15.9 mg N) and 98.4%(29.0mg N) of the applied urea was hydrolyzed, respectively. Most of the applied urea was completely hydrolyzed within 6 days. After urea application, the rates of ammonia volatilization were increased with the floodwater pH when the floodwater pH were higher than 7.0. The maximum rate of ammonia volatilization was $0.3mg\;d^{-1}$ when pH of the floodwater showed maximum value of 7.6. The total amount of volatilized nitrogen was 6.1% (1.8mg N) of the applied urea-N. A 63.2 % (18.6mg N) of the applied urea was remained in soil as $NH_4{^+}-N$ and 28.0% (8.2mg N) of the applied urea was leached as $NH_4{^+}-N$ at the end of the incubation. Amount of $NO_3{^-}-N$ in soil was smaller than 2.0 mg throughout the incubation period. The total amount of $NO_3{^-}-N$ leached was very small, which value was 1.8 mg. It suggested that nitrification process was not significant in waterlogged soil column of this study due to high infiltration rate of urea solution applied to the soil column. Therefore only small amount of $NO_3{^-}-N$ was lost by denitrification and leaching process.

• Journal of the Korean Chemical Society
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• v.29 no.1
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• pp.52-60
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• 1985

Oxides of nitrogen (NO$_x$) in exhaust gases was determined by absorbing the gas in alkaline peroxide solution containing 0.03${\%}$ H2O2 and 0.1N NaOH. About 100 ppm of NO$_x$ was rapidly oxidized to NO$_2$ or N$_2$O$_5$ by H$_2$O$_2$ and required a contact time of 2 minutes with the absorbing solution for complete absorption. With vigorous shaking including air or oxygen gas, high concentration of NO$_x$ (>200 ppm) can be absorbed within 30 minutes. The remaining H$_2$O$_2$ affect the absorbance of color solution strongly. However, the excess H$_2$O$_2$ was completely decomposed by zinc powder 0.5g and the sample solution should be adjusted to the pH range 6.1∼6.6 before the reduction so that conversion of nitrate to nitrite ion is possible. The absorbed NO$_x$ is determined colorimetrically by the diazotization-coupling method with sulfonilamide and NEDA as the coupling agent. The sensitivity of the new method was 4.48 ${\times}$ 10$^4$ as molar absorptivity which was high sensitive compared with that obtained for the usual zinc reduction NEDA method with O$_3$. This method was far more rapid, brief and accurate than previously published O$_3$-NEDA method in Korean industrial standard.

• Journal of the Korean Institute of Gas
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• v.19 no.5
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• pp.20-28
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• 2015

This work investigated the size and shape effect of ${\gamma}$-alumina-supported metal oxides on the hydrocarbon selective catalytic reduction of nitrogen oxides. Several metal oxides including Ag, Cu and Ru were used as the catalysts, and n-heptane as the reducing agent. For the Ag/${\gamma}$-alumina catalyst, the $NO_x$ reduction efficiency in the range of $250{\sim}400^{\circ}C$ increased as the size of Ag decreased (20 nm>50 nm>80 nm). The shape effect of metal oxides on the $NO_x$ reduction was examined with spherical- and wire-shape nanoparticles. Under identical condition, higher catalytic activity for $NO_x$ reduction was observed with Ag and Cu wires than with the spheres, while spherical- and wire-shape Ru exhibited similar $NO_x$ reduction efficiency to each other. Among the metal oxides examined, the best catalytic activity for $NO_x$ reduction was obtained with Ag wire, showing almost complete $NO_x$ removal at a temperature of $300^{\circ}C$. For Cu and Ru catalysts, considerable amount of NO was oxidized to $NO_2$, rather than reduced to $N_2$, leading to lower $NO_x$ reduction efficiency.

• Applied Chemistry for Engineering
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• v.27 no.1
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• pp.92-100
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• 2016

Low-temperature conversion of nitrogen oxides using plasma-assisted hydrocarbon selective catalytic reduction of (HC-SCR) was investigated. Plasma was created in the catalyst-packed bed so that it could directly interact with the catalyst. The effect of the reaction temperature, the shape of catalyst, the concentration of n-heptane as a reducing agent, the oxygen content, the water vapor content and the energy density on $NO_x$ removal was examined. $NO_x$ conversion efficiencies achieved with the plasma-catalytic hybrid process at a temperature of $250^{\circ}C$ and an specific energy input (SIE) of $42J\;L^{-1}$ were 83% and 69% for one-dimensional Ag catalyst ($Ag\;(nanowire)/{\gamma}-Al_2O_3$) and spherical Ag catalyst ($Ag\;(sphere)/{\gamma}-Al_2O_3$), respectively, whereas that obtained with the catalyst-alone was considerably lower (about 30%) even with $Ag\;(nanowire)/{\gamma}-Al_2O_3$ under the same condition. The enhanced catalytic activity towards $NO_x$ conversion in the presence of plasma can be explained by the formation of more reactive $NO_2$ species and partially oxidized hydrocarbon intermediates from the oxidation of NO and n-heptane under plasma discharge. Increasing the SIE tended to improve $NO_x$ conversion efficiency, and so did the increase in the n-heptane concentration; however, a further increase in the n-heptane concentration beyond $C_1/NO_x$ ratio of 5 did not improve the $NO_x$ conversion efficiency any more. The increase in the humidity affected negatively the $NO_x$ conversion efficiency, resulting in lowering the $NO_x$ conversion efficiency at the higher water vapor content, because water molecules competed with $NO_x$ species for the same active site. The $NO_x$ conversion efficiency increased with increasing the oxygen content from 3 to 15%, in particular at low SIE values, because the formation of $NO_2$ and partially oxidized hydrocarbon intermediates was facilitated.

• Journal of the Korean Ceramic Society
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• v.38 no.10
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• pp.928-935
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• 2001

In this study, two kinds of activated carbon fibers were prepared from PAN-based stabilized fibers by physical activation with steam. The variations in specific surface area, amount of iodine adsorption and pore size distribution of the activated carbon fibers after the activation process were discussed. The activated carbon fibers were prepared by two different methods, namely a 1- and 2-step method. For the 2-step method, carbonization of fibers in $N_2$ atmosphere was carried out to make carbon fibers and then activated by steam. In normal two step steam activation, BET surface area of about $1019m^2/g$ was obtained in the study. In the 1-step steam activation process, the carbonization and activation were simultaneously carried out. In the one step steam activation, BET surface area of $1635m^2/g$ was obtained after heat-treatment at $990^{\circ}C$. However, nitrogen adsorption isotherms for oxidized PAN based activated carbon fibers that were prepared by both methods were type I in the Brunauer-Deming-Deming-Teller (BDDT) classification even though they have different BET surface areas, amounts of iodine adsorption and pore size distributions.

• Korean Journal of Microbiology
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• v.39 no.3
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• pp.175-180
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• 2003

Microbial Fe(III) reduction is an important factor for biogeochemical cycle in anaerobic environments, especially sediment of freshwater such as lakes, ponds and rivers. In addition, the Fe(III) reduction serves as a model for potential mechanisms for the oxidation of organic compounds and the reduction of toxic heavy metals, such as chrome or uranium. Shewanella putrefaciens DK-1 was a gram-negative, facultative anaerobic Fe(III) reducer and used ferric ion as a terminal electron acceptor for the oxidation of organic compounds to $CO_{2}$ or other oxidized metabolites. The ability of reducing activity and utilization of various electron acceptors and donors for S. putrefaciens DK-1 were investigated. S. putrefaciens DK-1 was capable of using a wide variety of electron acceptor, including $NO_{3}^{-}$, Fe(III), AQDS, and Mn(IV). However, its ability to utilize electron donors was limited. Lactate and formate were used as electron donors but acetate and toluene were not used. Fe(III) reduction of S. putrefaciens DK-l was inhibited by the presence of either $NO_{3}^{-}$ or $NO_{2}^{-}$. Further S. putrefaciens DK-1 used humic acid as an electron acceptor and humic acid was re-oxidized by nitrate. Environmental samples showing the Fe(III)-reducing activity were used to investigate effects of the limiting factors such as carbon, nitrogen and phosphorus on the Fe(III) reducing bacteria. The highest Fe (III) reducing activity was measured, when lactate as a carbon source and S. putrefaciens DK-1 as an Fe(III) reducer added in untreated sediment samples of Cheon-ho and Dae-ho reservoirs.

• Journal of Korean Society of Environmental Engineers
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• v.29 no.9
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• pp.1035-1043
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• 2007

A leachate containing an elevated concentration of organic and inorganic compounds has the potential to contaminate adjacent soils and groundwater as well as downgradient areas of the watershed. Moreover high-strength ammonium concentrations in leachate can be toxic to aquatic ecological systems as well as consuming dissolved oxygen, due to ammonium oxidation, and thereby causing eutrophication of the watershed. In response to these concerns landfill stabilization and leachate treatment are required to reduce contaminant loading sand minimize effects on the environment. Compared with other treatment technologies, leachate recirculation technology is most effective for the pre-treatment of leachate and the acceleration of waste stabilization processes in a landfill. However, leachate recirculation that accelerates the decomposition of readily degradable organic matter might also be generating high-strength ammonium in the leachate. Since most landfill leachate having high concentrations of nitrogen also contain insufficient quantities of the organic carbon required for complete denitrification, we combined a shortcut biological nitrogen removal (SBNR) technology in order to solve the problem associated with the inability to denitrify the oxidized ammonium due to the lack of carbon sources. The accumulation of nitrite was successfully achieved at a 0.8 ratio of $NO_2^{-}-N/NO_x-N$ in an on-site reactor of the sequencing batch reactor (SBR) type that had operated for six hours in an aeration phase. The $NO_x$-N ratio in leachate produced following SBR treatment was reduced in the landfill and the denitrification mechanism is implied sulfur-based autotrophic denitrification and/or heterotrophic denitrification. The combined leachate recirculation with SBNR proved an effective technology for landfill stabilization and nitrogen removal in leachate.

• Journal of the Korean Applied Science and Technology
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• v.34 no.1
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• pp.183-188
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• 2017

This study deals with $de-SO_X$ and $de-NO_X$ process of a wet scrubber for small size ship engines. The experiment was conducted according to the E3 mode of the $NO_X$ technical code. In order to discharge the sulfur containing flue gas, ditertiarybutyldusulfide was added to the diesel fuel to increase the sulfur content. NO gas, which occupies most of the nitrogen oxides in the exhaust gas, was oxidized into $NO_2$ and absorbed by a wet scrubber. The developed equipment of this work achieved 100% of removal efficiency for highly soluble $SO_2$ gas in an aqueous solution.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.1
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• pp.93-101
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• 2006

This research makes a new attempt to apply the activated seawater by electrolysis in the development of two-stage wet scrubber system to control the exhaust gas of large marine diesel engines. First, with using only seawater that is naturally alkaline (pH typically around 8.1). the $SO_2\;and\;SO_3$ are absorbed by relatively high solubility compared to other components of exhaust pollutants, and PM (Particulate Matter) is removed through direct contact with sprayed seawater droplets. Besides, the electrolyzed alkaline seawater by electrolysis, which contains mainly NaOH together with alkali metal ions $(i.e.\;Na^+,\;Mg^{2+},\;Ca^{2+})$, is used as the absorption medium of NOx and $CO_2$. Especially, to increase NOx absorption rate into the alkaline seawater. nitric oxide (NO) is adequately oxidized to nitrogen dioxide $(NO_2)$ in the acidic seawater, which means both volume fractions are adjusted to identical proportion. The results found that the strong acidic seawater was a valid oxidizer from NO to $NO_2$ and the strong alkaline seawater was effective in $CO_2$ absorption In the scrubber test, the SOx reduction of nearly $100\%$ could be achieved and also led to a sufficientPM reduction. Hence, the author believes that applying seawater and its electrolyte would bring the marine air pollution control system to an economical measure. Additionally it is well known that NOx and SOx concentration has a considerable influence on the $N_2O$ emission of green house gas. Although the $N_2O$ concentration exhausted from diesel engines is not as high, the green house gas effect is around 300 times greater than an equivalent volume of $CO_2$. Therefore, we investigated the $N_2O$ removal efficiency with using the electrolyzed seawater too. Finally this research would also plan to treat the effluent by applying electro-dialysis and electro-flotation technique s in the future.

• Journal of Korean Society of Water and Wastewater
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• v.24 no.6
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• pp.775-788
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• 2010

The decomposition of 2,4,6-trinitrotoluene (TNT) and the mass balance of nitrogen (N) species as products were investigated in a UV/H2O2system by varying pH, concentrations of $H_2O_2$, and $O_2$. All experiments were conducted in a semi-batch system employing a 50 mL reaction vessel and a coil-type quartz-tube reactor. In contrast with previous studies employing batch mode, TNT decomposition in the semi-batch mode was proportionally enhanced by increasing $H_2O_2$ concentration to 10 mM (0.034%), indicatingthat an inhibitory effect of excess $H_2O_2$on hydroxyl radical (${\cdot}OH$) can be negligible. N compounds are released as $NO_2^-$ in the early stages of the reaction, but $NO_2^-$ is rapidly oxidized to $NO_3^-$ by means of ${\cdot}OH$. $NH_4^+$ was also detected in this study and showed gradually the increase with increasing reaction time. In this study, $NH_4^+$ production can involve the reduction of nitro group of TNT concurrent with the production of $NO_3^-$. Of the N species originating from TNT decomposition, 12 ~ 72% were inorganic forms (i.e. [$NO_3^-$] + [$NO_2^-$] + [$NH_4^+$]). This result suggests that the large remaining N portions indicate that unidentified N compounds can exist.