• Environmental Engineering Research
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• v.12 no.4
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• pp.148-154
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• 2007

The purpose of this research was to investigate the effects of low concentration of oxygen on reduction of perchlorate, especially low perchlorate influent concentrations in a biofilm reactor, as well as the effect of flow pattern in a biofilm reactor. Dissolved oxygen averaging 1 mg/L did not inhibit reduction of influent perchlorate from 23 to $426\;{\mu}g/L$ in the biofilm reactors when sufficient acetate was added, probably due to limitation of oxygen diffusion into the biofilm. Influent perchlorate ranging from 23 to $426\;{\mu}g/L$ was reduced to below detection level ($4\;{\mu}g/L$) in the presence of 1 mg/L dissolved oxygen (DO). Chloride was produced in a ratio of $0.37gCl^-/g{ClO_4}^-$ and $0.35gCl^-/g{ClO_4}^-$ in plug flow and recirculation biofilm reactor which is similar to stoichiometric amount ($0.36gCl^-/g{ClO_4}^-$) indicating complete perchlorate reduction at $426\;{\mu}g/L$ of ${ClO_4}^-$ feeding. At $23\;{\mu}g/L$L influent perchlorate, total biomass solids were 3.18 g and 2.81 g in the plug flow and recirculation biofilm reactors. The most probable number(MPN) analysis for perchlorate-reducing bacteria showed $10^4$ to $10^5\;cells/cm^2$ in both biofilm reactors throughout the experiments. The effluent perchlorate concentrations were not significantly different in the two different flow regimes, plug flow and recirculation biofilm reactors.

• Korean Chemical Engineering Research
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• v.59 no.1
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• pp.77-84
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• 2021

To control hot spot in a plug flow reactor (PFR) is important for the yield and purity of products and safety. In this paper, coolant temperature is set as a state variable, and radial distributions of heat and mass are considered to model the PFR more realistic than without considering radial distributions. The model consists of three state variables, reactant concentration, reactant temperature, and the coolant temperature. The flow rate of the isothermal coolant is a manipulated variable. This paper shows that the controller considering the radial distributions of heat and mass is more effective than the controller without them. Assuming that u3,0 is 0.7, the suggested control equation was robust when St is bigger than 1.3, and Ac/A is smaller than 2.0. Under this condition, the hot spot temperature changed within the relative error of one percent when the temperature of input altered within the range of five percent.

• New & Renewable Energy
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• v.18 no.4
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• pp.12-21
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• 2022

The pyrolysis characteristics of high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP) were analyzed numerically using a 1D plug flow reactor (PFR) model. A lumped kinetic model was selected to simplify the pyrolysis products as wax, oil, and gas. The simulation was performed in the 400-600℃ range, and the plastic pyrolysis and product generation characteristics with respect to time were compared at various temperatures. It was found that plastic pyrolysis accelerates rapidly as the temperature rises. The amounts of the pyrolysis products wax and oil increase and then decrease with time, whereas the amount of gas produced increases continuously. In LDPE pyrolysis, the pyrolysis time was longer than that observed for other plastics at a specified temperature, and the amount of wax generated was the greatest. The maximum mass fraction of oil was obtained in the order of HDPE, PP, and LDPE at a specified temperature, and it decreased with temperature. Although the 1D model adopted in this study has a limitation in that it does not include material transport and heat transfer phenomena, the qualitative results presented herein could provide base data regarding various types of plastic pyrolysis to predict the product characteristics. These results can in turn be used when designing pyrolysis reactors.

• Journal of Soil and Groundwater Environment
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• v.20 no.6
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• pp.85-94
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• 2015

RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) is the most important explosive contaminant, both in concentration and in frequency, at military shooting ranges in which green technologies such as phytoremediation or constructed wetlands are the best option for mitigation of explosive compounds discharge to the environment. A study was conducted with two identical lab-scale plug flow constructed wetlands planted with Amur silver grass to treat water artificially contaminated with 40 mg/L of toxic explosive compound, RDX. The reactor was inoculated with or without RDX degrading mixed culture to evaluate plant-microorganism interactions in RDX removal, transformation products distribution, and kinetic constants. RDX and its metabolites in water, plant, and sediment were analyzed by HPLC to determine mass balance and kinetic constants. After 30 days of operation, the reactor reached steady-state at which more than 99% of RDX was removed with or without the mixed culture inoculation. The major transformation product was TNX (Trinitroso-RDX) that comprised approximately 50% in the mass balance of both reactors. It was also the major compound in the plant root and shoot system. Acute toxicity analysis of the water samples showed more than 30% of toxicity reduction in the effluent than that of influent containing 40 mg/L of RDX. In the Amur silver grass mesocosm seeded with the mixed culture, the specific RDX removal rate, that is 1st order removal rate normalized to plant fresh weight, was estimated to be 0.84 kg⁻¹ day⁻¹ which is 16.7% higher than that in the planted only mesocosm. Therefore, the results of this study proved that Amur silver grass is an effective plant for RDX removal in constructed wetlands and the efficiency can be increased even more when applied with RDX degrading microbial consortia.

• Journal of Korean Society of Water and Wastewater
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• v.25 no.5
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• pp.759-765
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• 2011

In this study, in order to investigate the effects of wall roughness on the hydraulic characteristics of chlorine contactor, CFD simulation and tracer tests were conducted for both of reactors whose walls are made of concrete and lined with PE(Poly Ethylene). In the case of walls contacted with water being lined with PE (relatively lower roughness), the flow within reactor is closer to plug flow than that in the case of concrete walls (relatively higher roughness). Especially, the longer tail of C-curve from the results of transient CFD simulation can tell that Morill index in the case concrete walls is much higher than that in the case of walls be lined with lower roughness material.

• Asian Journal of Atmospheric Environment
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• v.4 no.3
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• pp.177-188
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• 2010

The use of an activated carbon (AC) system alone has the limitation that the pollutants are not eliminated but only transferred to another phase with the consumed AC becoming hazardous waste itself. Therefore, the present study investigated the feasibility of using a combined system of granular AC (GAC) with S-doped visible-light-induced $TiO_2$ (GAC/S-doped $TiO_2$) to clean monocyclic aromatic hydrocarbons (MAHs) with concentrations at $\leq$ 3 mg $m^{-3}$, using a continuous air-flow reactor. This study conducted three different experiments: an adsorption test of pure GAC and GAC/S-doped $TiO_2$; a long-term adsorptional photocatalytic (AP) activity test of GAC/S-doped $TiO_2$; and an AP activity test of GAC/S-doped $TiO_2$ under different conditions. For the AP activity test, three parameters were evaluated: various weights of GAC/S-doped $TiO_2$ (0.9, 4.4, and 8.9 g); various flow rates (FRs) (0.5, 1 and 2 L $min^{-1}$); and various input concentrations (ICs) of the target MAHs (0.1, 1, 2 and 3 mg $m^{-3}$). The adsorption efficiencies were similar for the pure GAC and GAC/S-doped $TiO_2$ reactors, suggesting that S-doped $TiO_2$ particles on GAC surfaces do not significantly interfere with the adsorption capacity of GAC. Benzene exhibited a clear AP activity, whereas no other target MAHs did. In most cases, the AP efficiencies for the target MAHs did not significantly vary with an increase in weight, thereby suggesting that, under the weight range tested in this study, the weights or FRs are not important parameters for AP efficiency. However, ICs did influence the AP efficiencies.

• Journal of Korean Society of Water and Wastewater
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• v.27 no.1
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• pp.21-29
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• 2013

Present study was conducted to evaluate the performance of Anaerobic Hybrid Reactor (AHR) combined with two types of anaerobic attached growth reactors at mesophilic temperature ($37^{\circ}C$). The reactor was operated at the influent substrate condition of 19,400 mg/L soluble chemical oxygen demand (sCOD). The organic loading rate (OLR) and flow rate were varied in the range of $9.5{\sim}22.5kg/m^3$. day and 10.6 ~ 26.0 L/day respectively since start-up was done. The COD removal efficiency of 93 % was measured at the OLR of $14kg/m^3$. day in AHR. However a reduction in removal efficiency to as low as 85 % could have been related to a combined effect of high concentration suspended solids (SS) concentration over 3,800 mg/L. On the other hand the total COD removal efficiencies were measured to be 96.3 % and 96.2 % for AHR+APF and AHR+ADF respectively. The pH of the POME was adjusted to neutral range by using sodium bicarbonate at the initial stages of the reactor feed, later stages pH adjustment was not required as the pH was maintained in the desired neutral range due to self-buffering capacity of the reactor. The reactor proved to be economically acceptable and operationally stable. The biogas was measured to have $CH_4$ and $CO_2$ with a ratio of 35:65, and methane gas production rate was estimated to be $0.17{\sim}10.269L\;CH_4/g\;COD_{removed}$.

• Journal of Korean Society of Water and Wastewater
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• v.25 no.4
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• pp.497-502
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• 2011

In order to examine the effects of combination of plug flow reactors in series on hydraulic characteristics, comparative tracer tests were conducted for the cases of the existing clear well and clear wells combined in series. From the results of tests, $T_{10}$/T within existing clear well was 0.62~0.68 depending on inlet flowrate, and that in the case of combination in series was 0.69~0.78. While it would be minor improvement in contact efficiency, it would be appropriate to combine two clearwell with pipe in series for expansion.

• Journal of Korean Society on Water Environment
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• v.18 no.2
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• pp.201-212
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• 2002

The objective of this study was to investigate the treatment efficiency, kinetics, and morphological characteristics of biofilm in upflow $Biobead^{(R)}$ process, a kind of biological aerated filter(BAF). The $Biobead^{(R)}$ system showed high removal rates of $COD_{Mn}$(76~83%), $BOD_5$(67~88%) and SS(71~91%) for food wastewater with high salt concentration ($>4,000mg/{\ell}$) under short reaction times(2~3hrs). Even at aerobic condition, the system had high treatment efficiency for both T-N (51~63%) and T-P(62~81%). The removal kinetics of $COD_{Mn}$, $BOD_5$, T-N, T-P, and $Cl^-$ in the $Biobead^{(R)}$ system showed a plug-flow pattern with reaction rate constants($hr^{-1}$) of 0.58, 0.63, 0,30, 0.48, and 0.38 respectively. A backwashing process to remove excess biomass and filtered solids was needed at least once during 22-hour operation at $0.5kg\;BOD\;m^{-3}{\cdot}d^{-1}$ loading. At the higher loading($1.0kg\;BOD\;m^{-3}{\cdot}d^{-1}$) the backwashing interval was shorten by 8 hours. The COD, BOD, T-N, and T-P were removed from 43 to 66% only by aerobic biodegradation. The SS was removed over 70% by the filtering of $Biobead^{(R)}$ media in the treatment system. The first one of three serial Biobead reactors showed the highest removal values for $COD_{\alpha}$(52.3%), $COD_{Mn}$(38.8%), BOD(62.5%), and T-N(40.0%). The SS and T-P had the highest removal values(47.5% and 29.2%) at the second one of the serial reactors. The biofilm had non-homogeneous spatial distribution and the colonies were embedded in the sunk area of the Biobead. The thickness of the biofilm was very thin ($5.0{\sim}29.4{\mu}m$) compared to the biofilm thickness($200{\sim}300{\mu}m$) used in other BAF systems.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.589-593
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• 2007

재생 가능한 자원인 동식물성 기름을 원료로 제조되는 수송용 연료 바이오디젤은 낮은 대기오염물질 배출과 $CO_2$ Neutral 특성으로 환경친화적인 연료로 인정을 받으며 전세계적으로 그 생산량이 급격히 증가하고 있다. 대부분의 상용화 공정은 염기촉매를 이용한 전이에스테르화 반응에 근거하고 있으며 높은 생산성을 위해 연속 공정을 채택하고 있다. 원료유 중의 유리지방산(free fatty acid, FFA)은 염기 촉매와 반응하여 지방산염(Soap)과 수분을 생성하며 반응촉매의 투입양을 증가시카고 반응 후에 글리세롤과 지방산 메틸에스테르와의 분리를 어렵게 만든다. 높은 수율과 후속공정의 부하를 줄이기 위해서는 식물성 원료유 중의 FFA는 고체 산촉매 하에서 메탄올과 에스테르화 반응시켜 전환 제거되어야 한다. 본 연구에서는 고체산 촉매인 Amberlyst-15을 충전한 4단 PBR(Packed Bed Reactor, 충전율 60%(v/v))에서 반응시간과 반응온도에 따른 대두원유의 전처리 효율을 조사하였으며 최적 전처리 조건을 도출하였다. 최적 전처리 조건에서 대두원유는 초기 산가 1.6에서 0.4-0.6으로 연속 전처리할 수 있었다. 본 연구에서는 연속 흐름 반응기인 PFR(Plug Flow Reactor)와 4단 CSTR(Continuous Stirred Tank Reactor)에서 균질계 촉매인 KOH 존재하에 대두유와 메탄올과의 전이에스테르화 반응 특성을 조사하였으며 각 연속 반응시스템에서 최적 운전 조건을 도출하였다. PFR 반응기에서 반응온도, 반응시간, 반응물 흐름방향, static mixer(SM) 개수에 따른 반응특성을 조사한 결과, PFR에서의 최적 반응조건은 하향류 흐름 방향과 3개의 SM를 설치한 조건에서 반응시간 5.8분, 반응온도 90$^{\cdot}C$, 메탄올:오일 몰비 9:1, KOH 농도 0.8%로 도출되었다. CSTR 반응기에서는 반응온도와 체류시간에 따른 반응특성을 조사하였으며 최적반응 조건으로 반응온도 80$^{\cdot}C$, 메탄올/오일 몰비 9:1, KOH 농도 0.8%, 체류시간 18.4분, 교반속도 250rpm로 조사되었다.