• Journal of Korean Society of Water and Wastewater
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• v.37 no.5
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• pp.253-259
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• 2023

Bioreactors are devices used by sewage treatment plants to process sewage and which produce active sludge, and sediments separated by solid-liquid are treated in anaerobic digestion tanks. In anaerobic digestion tanks, the volume of active sludge deposits is reduced and biogas is produced. After dehydrating the digestive sludge generated after anaerobic digestion, anaerobic digested wastewater, which features a high concentration of organic matters, is generated. In this study, the decomposition of organic carbon and nitrogen was studied by advanced oxidation process. Ozone-microbubble flotation process was used for oxidation pretreatment. During ozonation, the TOC decreased by 11.6%. After ozone treatment, the TOC decreased and the removal rate reached 80.4% as a result of the Ultra Violet-Advanced Oxidation Process (UV-AOP). The results with regard to organic substances before and after treatment differed depending on the organic carbon index, such as CODMn, CODCr, and TOC. Those indexes did not change significantly in ozone treatment, but decreased significantly after the UV-AOP process as the linkage treatment, and were removed by up to 39.1%, 15.2%, and 80.4%, respectively. It was confirmed that biodegradability was improved according to the ratio of CODMn to TOC. As for the nitrogen component, the ammonia nitrogen component showed a level of 3.2×10² mg/L or more, and the content was maintained at 80% even after treatment. Since most of the contaminants are removed from the treated water and its transparency is high, this water can be utilized as a resource that contains high concentrations of nitrogen.

• Applied Chemistry for Engineering
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• v.24 no.4
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• pp.433-437
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• 2013

Electrical discharge plasma created in a multi-channel porous ceramic membrane-supported catalyst was applied to the decomposition of a volatile organic compound (VOC). For the purpose of improving the oxidation capability, the ceramic membrane used as a low-pressure drop catalyst support was loaded with zinc oxide photocatalyst by the incipient wetness impregnation method. Alternating current-driven discharge plasma was created inside the porous ceramic membrane to produce reactive species such as radicals, ozone, ions and excited molecules available for the decomposition of VOC. As the voltage supplied to the reactor increased, the plasma discharge gradually propagated in the radial direction, creating an uniform plasma in the entire ceramic membrane above a certain voltage. Ethylene was used as a model VOC. The ethylene decomposition efficiency was examined with experimental variables such as the specific energy density, inlet ethylene concentration and zinc oxide loading. When compared at the identical energy density, the decomposition efficiency obtained with the zinc oxide-loaded ceramic membrane was substantially higher than that of the bare membrane case. Both nitrogen and oxygen played an important role in initiating the decomposition of ethylene. The rate of the decomposition is governed by the quantity of reactive species generated by the plasma, and a strong dependence of the decomposition efficiency on the initial concentration was observed.

• Applied Chemistry for Engineering
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• v.9 no.6
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• pp.829-834
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• 1998

Concerned with environmental issue, a new decomposition method for CFCs that caused the destruction of ozone layer was proposed. Using thermal plasma process, CFC113 decomposed completely. In order to quantify the tendency in decomposition and recombination of CFC113, thermodynamic equilibrium calculations were performed. The calculation was conducted with CFC113, $H_2$, $O_2$ at 1 atm and 300 K~5000 K. In the experiment, products which are generated after decomposition in the plasma were examined by varying reacting gases($H_2$, $O_2$) flow rates and the changes of inside diameters of quenching tubes. Decomposition products were analyzed using Gas Chromatograph. The results are very promising with a decomposition efficiency greater than 99.99%. As to CFC113/$H_2$=1/3, conversion to CO decreased with increasing $O_2$ ratio. When CFC113/$O_2$=1/1, 1/1.5 and 1/2, conversion to CO increases above $H_2$ ratio of 3. The change of CO conversion is not sensitive to power changes. As total flow rate increased, CO conversion was slightly decreased. When the inside diameter of the quenching tube was changed from 8mm into 4mm, CO conversion was increased due to enhanced quenching rate.

• Journal of Korean Society for Atmospheric Environment
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• v.20 no.5
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• pp.625-632
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• 2004

Perfluorocompounds ($PFC_s$), such as tetrafluoromethane ($CF_4$) and hexafluoroethane ($C_2F_6$), have been widely used as plasma etching and chemical vapor deposition (CVD) gases for semiconductor manufacturing processes. Since these $PFC_s$ are known to cause a greenhouse effect intensively, there has been a growing interest in reducing $PFC_s$ emissions. Among various $CF_4$ decomposing techniques, a dielectric barrier discharge (DBD) is considered as one of a promising candidate because it has been successfully used for generating ozone ($O_3$) and decomposing nitrogen oxide (NO). Firstly, optimal concentration of oxygen for $CF_4$ decomposition was found to figure out how many primary and secondary reactions are associated with DBD process. Secondary, to find effective discharge method for $CF_4$ decomposition, a streamer and a glow mode in DBD are experimentally compared, which includes (i) coaxialcylinder DBD, (ii) DBD reactor packed with glass beads. and (iii) a glow mode operation with a helium gas. The test results showed that optimal concentration of oxygen was ranged 500 ppm~1% for treating 500 ppm of $CF_4$ and helium glow discharge was the most efficient one to decompose $CF_4$.

• Journal of Korean Society for Atmospheric Environment
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• v.22 no.E1
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• pp.19-26
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• 2006

The decomposition of gaseous $CH_3CHO$ was investigated by metal loaded $TiO_2$ (pure $TiO_2,\;Pt/TiO_2,\;Pd/TiO_2,\;Mn/TiO_2\;and\;Ag/TiO_2$) with $UV/TiO_2$ process and $UV/TiO_2/O_3$ process at room temperature and atmospheric pressure. Metal loaded $TiO_2$ was prepared by photodeposition. Decomposition of $CH_3CHO$ was carried out in a flow-type photochemical reaction system using three 10W black light lamps ($300{\sim}400nm$) as a light source. The experimental results showed that the degradation rate of $CH_3CHO$ was increased with Pt and Ag on $TiO_2$ compared to pure $TiO_2$, but decreased with depositing Pd and Mn on pure $TiO_2$. The considerable increase in the degradation efficiency of the $CH_3CHO$ was found by a combination of photocatalysis and ozonation as compared to only by ozonation or photocatalysis. Loading of Pt on $TiO_2$ promoted conversion of gaseous ozone. The degradation rate of gaseous $CH_3CHO$ decreased with an increase of water vapor in the feed stream for the both $UV/TiO_2\;and\;UV/TiO_2/O_3$ processes. The pure $TiO_2$ was more affected by the water vapor than Pt loaded $TiO_2$.

• Journal of Korean Society for Atmospheric Environment
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• v.30 no.6
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• pp.577-585
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• 2014

A series of experiments using atmospheric-pressure non-thermal plasma coupled with transition metal catalysts were performed to remove ethylene from agricultural storage facilities. The non-thermal plasma was created by dielectric barrier discharge, which was in direct contact with the catalyst pellets. The transition metals such as Ag and $V_2O_5$ were supported on ${\gamma}-Al_2O_3$. The effect of catalyst type, specific input energy (SIE) and oxygen content on the removal of ethylene was examined to understand the behavior of the hybrid plasma-catalytic reactor system. With the other parameters kept constant, the plasma-catalytic activity for the removal of ethylene was in order of $V_2O_5/{\gamma}-Al_2O_3$ > $Ag/{\gamma}-Al_2O_3$ > ${\gamma}-Al_2O_3$ from high to low. Interestingly, the rate of plasma-catalytic ozone generation was in order of $V_2O_5/{\gamma}-Al_2O_3$ > ${\gamma}-Al_2O_3$ > $Ag/{\gamma}-Al_2O_3$, implying that the catalyst activation mechanisms by plasma are different for different catalysts. The results obtained by varying the oxygen content indicated that nitrogen-derived reactive species dominated the removal of ethylene under oxygen-lean condition, while ozone and oxygen atoms were mainly involved in the removal under oxygen-rich condition. When the plasma was coupled with $V_2O_5/{\gamma}-Al_2O_3$, nearly complete removal of ethylene was achieved at oxygen contents higher than 5% by volume (inlet ethylene: 250 ppm; gas flow rate: $1.0Lmin^{-1}$; SIE: ${\sim}355JL^{-1}$).

• Journal of the Korean Chemical Society
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• v.35 no.2
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• pp.111-118
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• 1991

The kinetic of the gas phase reactions of ozone(0.5 torr) with sulfur dioxide was studied. The SO2 reaction was conducted in the 7∼22 torr range at 90∼155$^{\circ}$C. The reaction rate was faster than the reaction rate of O$_3$ in the presence of CO$_2$ alone. The reaction of O$_3$ with SO$_2$ follows the rate law: -d(O$_3)/dt=k_0(SO_2)(M)(O_3)+2k _1(SO_2)(O_3$). The first term of this rate law arises from a third order molecular reaction predominating in the lower temperature range and gave a rate constant k$_0$ = (9.35 $\pm$ 8.6) ${\times}$ 10$^9$e$^{-(11.05{\pm}2.04)kcal/RT}(M^{-2}s^{-1}$). The second term of the above rate law derived from a second order thermal decomposition reaction which was the major part of the reaction and gave a rate constant k$_0 =(9.35{\pm}8.6){\times}10^9e^{-(11.05{\pm}2.04)kcal/RT}(M^{-2}s^{-1}$). The overall reaction proceeds with kinetics of complex order composed mainly of second order and third order components.

• Korean Chemical Engineering Research
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• v.40 no.6
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• pp.746-751
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• 2002

Fluidized bed combustion is a coal combustion technology that can reduce both SOx and NOx emission; SOx is removed by limestone that is fed into the combustion chamber and the NOx is reduced by low temperature combustion in a fluidized bed combustor and air stepping, but $N_2O$ generation is quite high. $N_2O$ is not only a greenhouse gas but also an agent of ozone destruction in the stratosphere. The calcium oxide(CaO) is known to be a catalyst of $N_2O$ decomposition. This study of $N_2O$ decomposition reaction in fixed bed reactor packed over CaO bed has been conducted. Effects of parameters such as concentration of inlet $N_2O$ gas, reaction temperature, CaO bed height and effect of $CO_2$, NO, $O_2$ gas on the decomposition reaction have been investigated. As a result of the experiment, it has been shown that $N_2O$ decomposition reaction increased with the increasing fixed bed temperature. While conversion of the reaction was decreased with increasing $CO_2$ concentration. Also, under the present of NO, the conversion of $N_2O$ decomposition is decreased. From the result of kinetic study gained the heterogeneous reaction rate on $N_2O$ decomposition. In the case of $N_2O$ decomposition over CaO, heterogeneous reaction rate is. $\frac{d[N_2O]}{dt}=\frac{3.86{\times}10^9{\exp}(-15841/R)K_{N_2O}[N_2O]}{(1+K_{N_2O}[N_2O]+K_{CO_2}[CO_2])}$. In this study, it is found that the calcium oxide is a good catalyst of $N_2O$ decomposition.

• Applied Chemistry for Engineering
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• v.26 no.3
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• pp.311-318
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• 2015

This work investigated the plasma treatment of aqueous bisphenol A (BPA) solution and mineralization pathways. For the effective contact between plasmatic gas and aqueous BPA solution, the plasma was created inside a porous ceramic tube, which was uniformly dispersed into the aqueous solution through micro-pores of the ceramic tube. Effects of the gas flow rate, applied voltage and treatment time on the decomposition of BPA were examined, and analyses using ultraviolet (UV) spectroscopy, ion chromatography and gas chromatography-mass spectrometry were also performed to elucidate mineralization mechanisms. The appropriate gas flow rate was around $1.0L\;min^{-1}$; when the gas flow rate was too high or too low, the BPA decomposition performance at a given electric power decreased. The increase in the voltage improves the BPA decomposition due to the increased electric power, but the energy required to remove BPA was similar, regardless of the voltage. Under the condition of $1.0L\;min^{-1}$ and 20.8 kV, BPA at an initial concentration of $10L\;min^{-1}$ (volume : 1 L) was successfully treated within 30 min. The intermediates produced by the attack of ozone and hydroxyl radicals on BPA were further oxidized to stable compounds such as acetate, formate and oxalate.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.2
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• pp.215-223
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• 2005

Non-thermal plasma decomposition of gas-phase styrene was investigated in this study using three different types of plasma reactors; dielectric-barrier discharge (DBD) reactor, surface discharge (SD) reactor and plasma-driven catalyst (PDC) reactor packed with 2.0 wt% $Ag/TiO_2$ catalysts. The main parameters used for the comparative assessment of the plasma reactors include the decomposition efficiency, carbon balance, byproduct distribution, COx ($CO+CO_2$) selectivity and COx yield. The SD and the DBD reactors showed better conversion efficiency of styrene than that of the PDC reactor due to their larger capability in ozone formation. On the other hand, the PDC reactor showed better carbon balance, the yield and the selectivity of COx. The required specific input energies to achieve 100% carbon balance from the decomposition of 100 ppmv styrene using the plasma alone reactors and the PDC reactor were 420 J/L and 110 J/L, respectively. The major decomposition products in gas-phase were CO, $CO_2$ and HCOOH regardless of the types of plasma reactors. In the case of SD and DBD reactors, the $CO_2$ selectivity ranged in $39.5{\sim}60%$. The $CO_2$ selectivity in the PDC reactor was in range of $68.5{\sim}75.5%$.