• Journal of the Korean Society of Combustion
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• v.22 no.4
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• pp.51-56
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• 2017

The decomposition of tetrafluoromethane has been investigated with the reaction mechanism proposed for freely propagating $CH_4/CF_4/O_2/N_2$ premixed flames on the oxygen enrichment. The factors affecting on the removal efficiency of tetrafluoromethane were analyzed. The increase in flame temperature due to oxygen enrichment has a great influence on the removal efficiency of tetrafluoromethane. At the same oxygen enrichment condition, the removal efficiency in the rich flame is higher than one in the lean flame. The increase of the F/H ratio leads to decrease the flame temperature and the removal efficiency of tetrafluoromethan is decreased at the flame temperature of 2600 K or lower, The elementary reactions that dominate the consumption of tetrafluoromethane are (R1) $CF_4+M=CF_3+F+M$ and (R2) $CF_4+H=CF_3+HF$. (R1) has the greatest effect on the consumption of tetrafluoromethane under the oxygen enhanced flames.

• Journal of environmental and Sanitary engineering
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• v.19 no.2
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• pp.7-14
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• 2004

This paper was investigated to clarify the possibility of ammonia-gas removal by essential oil. First of all, the chemical analysis was performed to analyze the composition of an essential oil by GC-MS. The monoterpenes in an essential oil react with ammonia by neutralization and their reaction mechanism was elucidated. Based on their chemical neutralized reaction, the removal efficiencies of ammonia gas were studied to derive the optimal conditions in the scrubber tower such as optimal temperature and pH. The experimental result shows that the removal efficiency of ammonia gas was achieved over 80 % by the misty aerosol dispersion of scrubber tower.

• Journal of the Korean Applied Science and Technology
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• v.32 no.1
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• pp.78-84
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• 2015

The purpose of this study is to evaluate the removal efficiency of phosphorus from synthetic waste water by reduction and oxidation reaction of Cu-Zn metal alloy. Cu-Zn metal alloy applied in this study is composed of 40% of Zn and 60% of Cu, which is so called Muntz metal. And the fibrous type of metal alloy has approximately $200{\mu}m$ of thickness. Metal is oxidized in an aqueous solution to generate electron and metal ion. The mechanism of phosphate treatment is co-precipitation of metal ion and phosphorous ion at various pH and temperature. The treatment efficiency showed the maximum at a one cycle treatment. This result means that the surface area of reaction material is sufficient enough to get reaction equilibrium. Experiment is conducted at various pH from 5 to 9, and showed the maximum efficiency at pH 8. Phosphorous is dominated as a type of $H_2PO_4{^-}$ and $HPO_4{^{2-}}$ at this pH condition. We could not consider the temperature effect independently, because phosphorous removal efficiency showed such a complex mechanism. We could get high efficiency at lower temperature in this research.

• Environmental Engineering Research
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• v.24 no.3
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• pp.389-396
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• 2019

The electrical energy consumption (EEC) in removal of NO by a $UV/H_2O_2$ oxidation process was introduced and related to removal efficiency of this gas. The absorption-reaction of NO was conducted in a bubble column reactor in the presence of $SO_2$. The variation in NO removal efficiency was investigated for various process parameters including NO and $SO_2$ inlet concentrations, initial concentration of $H_2O_2$ solution and gas flow rate. EEC values were obtained in these different conditions. The removal efficiency was increased from about 22% to 54.7% when $H_2O_2$ concentration increased from 0.1 to 1.5 M, while EEC decreased by about 70%. However, further increase in $H_2O_2$ concentration, from 1.5 to 2, had no significant effect on NO absorption and EEC. An increase in NO inlet concentration, from 200 to 500 ppm, decreased its removal efficiency by about 10%. However, EEC increased from $2.9{\times}10^{-2}$ to $3.9{\times}10^{-2}kWh/m^3$. Results also revealed that the presence of $SO_2$ had negative effect on NO removal percentage and EEC values. Some experiments were conducted to investigate the effect of $H_2O_2$ solution pH. The changing of pH of oxidation-absorption medium in the ranges between 3 to 10, had positive and negative effects on removal efficiency depending on pH value.

• Journal of Environmental Health Sciences
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• v.23 no.1
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• pp.74-80
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• 1997

This study was performed to estimate the ozonation characteristics of phenol wastewater with increasing pH in the continuous packed column reactor (PCR) and the bubble column reactor (BCR). Among various influencing factors that affect phenol on decomposition through the ozonation, pH was chosen as reaction parameter. Upon increasing pH from 3 to 9, the phenol removal efficiency in PCR was improved approximately by 17% while in BCR approximately by 19.2%. The improvements in the phenol removal efficiency by increasing pH caused the enhancements in ozone utilization efficiency reaching almost 100% in PCR at pH 9. In conclusions, ozone has latent power for phenol wastewater treatment, and the performance of PCR was superior to that of BCR in the aspects of phenol removal and ozone utilization efficiency.

• Journal of Environmental Health Sciences
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• v.24 no.3
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• pp.124-130
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• 1998

This study was to examine the utilization of waste egg snells for removal of heavy metals in laboratory wastewater. It was estimated that pH increasing formed heavy metals into a hydroxide and then settled to remove them. Removal rate of heavy metals were increased as increased dosage, low adsorbate concentration and passed reaction time. Average adsorption volumes of Cr, Cu, Mn and Pb per g were about 1.21 mg, 1.1 mg, 0.96 mg and 1.04 mg, respectively. If we reflected the adsorption capacity(k) and adsorption intensity(1/n) of Freundlich isotherm, we couldn't consider waste egg shells as a good adsorbent. It seemed that heavy metals contained in complex wastewater was removed to be influenced by inital pH, solubilities with passed reaction rime and competitive reaction.

• Resources Recycling
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• v.16 no.4
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• pp.27-32
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• 2007

The characteristics of fluorine removal from wastewater have been investigated by precipitation method using calcium as a precipitant for the purpose of the reuse of treated wastewater. In the conditions of 10 mM of the initial concentration of fluorine and pH 4, the precipitation of fluorine was rapidly progressed within a few minutes after the precipitant was added and the precipitation of fluorine was observed to follow a second order reaction. Also, as the addition of precipitant was increased, the reaction rate constant of fluorine precipitation was found to rise. Postulating that the maximum fluorine removal was attained at pH 4, about 70% of fluorine was precipitated compared with the maximum removal when 10 times of equivalent amount of calcium was employed at pH 2 and the fluorine removal was about 96% compared with its maximum value at pH 3 under the same addition of precipitant. The fluorine precipitation reaction was found to be endothermic and the coexistence of $SiF_6{^{2-}}$ with fluorine resulted in its less removal. Finally, the isoelectric point of the precipitate was examined to be ca. pH 5.

• Applied Chemistry for Engineering
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• v.28 no.6
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• pp.619-625
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• 2017

In this study, the formation of hydroxyl radical and decomposition characteristics of bisphenol A (BPA) was investigated by quantifying hydrogen peroxide formed as a reaction by-product during the formation stage of hydroperoxyl radical. The direct oxidation reaction by ozone only decomposed BPA just like the Criegee mechanism under the condition where radical chain reactions did not occur. Non-selective oxidation reactions occurred under the conditions of pH 6.5 and 9.5 where radical chain reactions do occur, confirming indirectly the formation of hydroxyl radical. The decomposition efficiency of BPA by the added catalysts appeared in the order of $O_3$/PAC ${\geq}$ $O_3/H_2O_2$ > $O_3$/high pH > $O_3$ alone. 0.03~0.08 mM of hydrogen peroxide were continuously measured during the oxidation reactions of ozone/catalyst processes. In the case of $O_3$/high pH process, BPA was completely decomposed in 50 min of the oxidation reaction, but reaction intermediates formed by oxidation reaction were not oxidized sufficiently with 29% of the removal ratio for total organic carbon (TOC, selective oxidation reaction). In the case of $O_3/H_2O_2$ and $O_3$/PAC processes, BPA was completely decomposed in 40 min of the oxidation reaction, and reaction intermediates formed by the oxidation reaction were oxidized with 57% and 66% of removal ratios for TOC, respectively (non-selective oxidation reactions).

• Journal of environmental and Sanitary engineering
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• v.12 no.3
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• pp.73-79
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• 1997

This research was intended as an investigation of applying Reduced Pressure Evaporation as efficient treatment method for landfill leachate. According to the variance of time, temperature, pressure and pH in experiments, the properties of leachate treatment are follows. The removal efficiencies of COD, NH$_{3}$-N, TOC, Conductivity and SS on the basis of reaction time was 96.4%-97.5%, -1.4%-53.7%, 81.7%-89.0%, 92.0%-95.3% and 99.86%-99.97%, respectively. When the pH of Influent was 7.5, the pH of effluent was increased to 10-11 with time elapse. It is concluded that the orgin of pH increase may be ammonia. When the properties of concentrate were investigated at the concentration ratio 90%(V/V), concentration difficiency represented in the ratio of experimental value/calculated value had following orders ; COD>TOC>NH$_{3}$-N>Conductivity>SS. Concentrate had good precipitation because of additive thermal treatment in the process. When evaporation experiments with pH adjustment of 4.0, 6.0, 7.5, 9.0 and 10.0 were performed ; Acidic evaporation experiments(pH 4.0, 6.0) showed low removal efficiency(81.6, 87.6%) of COD and high removal efficiency (97.5%. 84.6%) of NH$_{3}$-N at initial evaporation. Basic evaporation(pH 9.0, 10.0) showed high removal efficiency (97.2%, 98.9%) of COD and very low removal efficiency (-7.4%, -27.2%) of NH$_{3}$-N at initial evaporation.

• 한국신재생에너지학회:학술대회논문집
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• 2008.10a
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• pp.238-241
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• 2008

In this study, absorption behaviors of absorbents and additives were measured for removing of $H_2S$ and COS from syn-gas in IGCC process, such as MDEA and HMDA. The experimental variables were concentration of absorbents and reaction temperature. From these experiments, the loading ratios of $H_2S$ were decreased with increasing of concentration of absorbents and absorption temperatures. These results will be applied to basic data for designing of $H_2S$ removal process in IGCC.