• Journal of Environmental Science International
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• v.21 no.12
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• pp.1455-1462
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• 2012

The vertical distributions of nitrifying bacteria in aerobic fixed biofilm were investigated to evaluate the relationship between nitrification performance and microbial community at different HRT. Fluorescent in situ hybridization (FISH) and portable ion selective microelectrode system were adopted to analyze microbial communities and ions profiles according to the biofilm depth. Cilia media packed MLE (Modified Ludzack-Ettinger) like reactor composed of anoxic, aerobic I/II was operated with synthetic wastewater having COD 200 mg/L and $NH_4{^+}$-N mg/L at HRT of 6 hrs and 4 hrs. Total biofilm thickness of aerobic I, II reactor at 4 hrs condition was over two times than that of 6 hrs condition due to the sufficient substrate supply at 4 hrs condition (6 hrs; aerobic I 380 ${\mu}m$ and II 400 ${\mu}m$, 4 hrs; aerobic I 830 ${\mu}m$ and II 1040 ${\mu}m$). As deepen the biofilm detection point, the ratio of ammonia oxidizing bacteria (AOB) was decreased while the ratio of nitrite oxidizing bacteria (NOB) was maintained similar distribution at both HRT condition. The ratio of AOB was higher at 4 hrs than 6 hrs condition and $NH_4{^+}$-N removal efficiency was also higher at 4 hrs with 89.2% than 65.4% of 6 hrs. However, the ratio of NOB was decreased when HRT was reduced from 6 hrs to 4 hrs and $NO_2{^-}$-N accumulation was observed at 4 hrs condition. Therefore, it is considered that insufficient HRT condition could supply sufficient substrate and enrichment of AOB in all depth of fixed biofilm but cause decrease of NOB and nitrite accumulation.

• Environmental Engineering Research
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• v.20 no.2
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• pp.181-189
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• 2015

A composite material was tested to eliminate phenol in aqueous solution combining adsorption on activated carbon and photocatalysis with $TiO_2$ in two different ways. A first implementation involved a sequential process with a loop reactor. The aim was to reuse this material as adsorbent several times with in situ photocatalytic regeneration. This process alternated a step of adsorption in the dark and a step of photocatalytic oxidation under UV irradiation with or without $H_2O_2$. Without $H_2O_2$, the composite material was poorly regenerated due to the accumulation of phenol and intermediates in the solution and on $TiO_2$ particles. In presence of $H_2O_2$, the regeneration of the composite material was clearly enhanced. After five consecutive adsorption runs, the amount of eliminated phenol was twice the maximum adsorption capacity. The phenol degradation could be described by a pseudo first-order kinetic model where constants were much higher with $H_2O_2$ (about tenfold) due to additional ${\bullet}OH$ radicals. The second implementation was in a continuous process as with a fixed bed reactor where adsorption and photocatalysis occurred simultaneously. The results were promising as a steady state was reached indicating stabilized behavior for both adsorption and photocatalysis.

• Journal of the Korean Chemical Society
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• v.57 no.6
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• pp.769-777
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• 2013

The effect of operating conditions (temperature and the partial pressures of H2 and CO) on the reaction rate of Fischer-Tropsch synthesis (FTS) were investigated by carrying out experiments according to a Box-Behnken design (BBD), and were mathematically modeled by using response surface methodology (RSM). The catalyst used was a nano-structured cobalt/manganese oxide catalyst, which was prepared by thermal decomposition. The rate of synthesis was measured in a fixed-bed micro reactor with $H_2/CO$ molar feed ratio of 0.32-3.11 and reactor pressure in the range of 3-9.33 bar at space velocity of $3600h^{-1}$ and a temperature range of 463.15-503.15 K, under differential conditions (CO conversion below 2%). The results indicated that in the present experimental setup, the temperature and the partial pressure of CO were the most significant variables affecting reaction rate. Based on statistical analysis the quadratic model of reaction rate of FTS was highly significant as p-value 0.0002.

• Applied Chemistry for Engineering
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• v.17 no.1
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• pp.100-105
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• 2006

The photocatalytic activity of phenol degradation was investigated with the variation of operating parameters in $UV/TiO_2$ honeycomb reactor. In the comparison of phenol degradation rates among various $TiO_2$, Ishihara (STS-02)-coated honeycomb exhibited a slightly higher photocatalytic activity than Degussa P25-coated honeycomb. On the other hand, honeycomb coated by alcohol-mixed $TiO_2$ (N Co.) did not exhibit any photocatalytic activity on phenol degradation. With the increase of Degussa P25 coating amounts, the honeycomb reactor exhibited the gradual increase of phenol degradation rates. The degradation rate of phenol over $UV/TiO_2$ (Degussa P25) honeycomb reactor was asymptotically increased up to 500 mL/min, subsequently followed by a slight decrease as the recirculation rate (100~700 mL/min) was increased. UV absorption at 269 nm was high due to partial degradation of phenol at initial reaction time because the honeycomb surface was pre-adsorbed by phenol prior to UV irradiation.

• Resources Recycling
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• v.15 no.1 s.69
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• pp.66-73
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• 2006

The effects of operation conditions, such as bed temperature, temperature rising rate, particle size, moisture content and so on, on thermo-chemical conversion of waste wood have been determined in a micro fixed bed gasifier. The samples were waste wood-chips such as pine, oak, acacia and ginkgo. The thinning timbers used as reactants in the experiments had $35wt\%$ moisture content, $0.5wt\%$ ash content and 4,550 kcal/kg heating value on a dry basis. A typical product distribution was a $40wt\%$ liquid, $20wt\%$ solid, and $40wt\%$ dry syngas. The syngas concentration was affected by operation conditions and average syngas concentration was $H_2:40vol\%,\;CO:30vol\%,\;CH_4:10vol\%$.

• Journal of Korean Society on Water Environment
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• v.18 no.4
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• pp.379-386
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• 2002

In this study, estimation model for iron compound originated from upflow, anaerobic fixed bed reactor, which treats sewage domestic wastewater, was developed. The estimation model was formulated by a mathematical expression which was based on the mass balance. Below the HRT of 60 minute, sulfide concentration combining with iron $FeS_2$ is the highest because the maximum sulfate consumption rate $V_{maxS}$ and half-saturation constant of sulfate $K_{mS}$ exert an important effect on the estimation model as temperature was increased. But increment of $FeS_2$ concentration is weakened above the HRT of 60 minutes and represent the lowest value at the HRT of 108 minutes. It implies that liquid phase distribution ratio of sulfide ${\alpha}r$ becomes lower as temperature was increased. While phosphorus concentration combining with iron $Fe_3(PO_4)_3$ is increased as HRT and temperature are increased, which is affected by phosphorus removal rate constant $k_p$. As the result of estimating the iron concentrations of corrosion by the model, the concentration of iron corrosion is higher than any other at the HRT of 108 minute and $20^{\circ}C$. The predicted values were compared with measured ones at different HRT(13.5, 27, 54, 108 min) and temperature(20, 25, $30^{\circ}C$). The experimental data could be fitted with the simulated curves. Therefore, the mathematical expression could be applicable to design full-scale wastewater treatment plants.

• Clean Technology
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• v.2 no.1
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• pp.60-68
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• 1996

The oxidation of carbon monoxide of low concentration on the natural manganese dioxide (NMD) has been investigated in a fixed bed reactor. The experimental variables were concentration of oxygen (500ppm~99.8%) and carbon monoxide (500ppm~10000ppm) and catalyst temperature ($50{\sim}750^{\circ}C$). The NMD(Natural Manganese Dioxide) has been characterized by temperature - program reduction(TPR) using 2.4% $CO/H_2$ as a reducing agent, thermogravimetric analysis (TGA), and reduction of NMD by 2.4% $CO/H_2$. It was found that the NMD catalyst activity on the unit area was greater than the $MnO_2$ catalyst for oxidation of CO at the same temperature. The thermal stability of oxidation activity was considered to be maintained when the NMD was heated to $750^{\circ}C$. The TGA, reduction by CO, and TPR of the NMD showed that the NMD had active lattice oxygen which was easily liberated on heating in the absence and low concentration of oxygen. The reaction order in CO is 0.701 between 500~3500ppm and almost zero between 3500~10000ppm of CO.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.658-663
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• 2010

With petroleum reserves dwindling, interest has been increasing worldwide in Fischer-Tropsch synthesis (FT) as a method of producing synthetic liquid fuels and chemicals from coal, natural gas or biomass. In general, FT synthesis is operated through the gas phase fixed-bed reaction system. Recently, there are lots of study in supercritical fluid due to unique characteristics such as the quick diffusion of reactant gas, effective removal of reaction heat, and the in-situ extraction of high molecular weight hydrocarbon, such as wax. In this study, our major aim is to obtain a deeper insight into the effect of the type of support on the reaction performance over a supported cobalt catalyst in a fixed bed reactor.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.3
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• pp.15-21
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• 2011

With petroleum reserves dwindling, interest has been increasing worldwide in Fischer-Tropsch synthesis (FT) as a method of producing synthetic liquid fuels and chemicals from coal, natural gas or biomass. In general, FT synthesis is operated through the gas phase fixed-bed reaction system. Recently, there are lots of study in supercritical fluid due to unique characteristics such as the quick diffusion of reactant gas, effective removal of reaction heat, and the in-situ extraction of high molecular weight hydrocarbon, such as wax. In this study, our major aim is to obtain a deeper insight into the effect of the type of support on the reaction performance over a supported cobalt catalyst in a fixed bed reactor.

• Korean Chemical Engineering Research
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• v.50 no.5
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• pp.908-912
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• 2012

Lauan sawdust was gasified by steam reforming for hydrogen production from biomass waste. The fixed bed gasification reactor with 1m height and 10.2 cm diameter was utilized for the analysis of temperature and catalysts effect. Steam was injected to the gasification reactor for the steam reforming effect. Lauan sawdust was mixed with potassium carbonate, sodium carbonate, calcium carbonate, sodium carbonate + potassium carbonate and magnesium carbonate + calcium carbonate catalysts of constant mass fraction of 8:2 which was injected to the fixed gasification equipment. The compositions of production gas of gasification reaction were analyzed at the temperature range from $400^{\circ}C$ to $700^{\circ}C$. Fractions of hydrogen, methane and carbon monoxide gas in the production gas increased when catalysts were used. Fractions of hydrogen, methane and carbon monoxide gas were increased with increasing temperature. The highest hydrogen yield was obtained with sodium carbonate catalyst.