• Environmental Engineering Research
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• 제20권2호
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• pp.175-180
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• 2015

This research focused on the solid and nitrate removal efficiency in a solid digestion-denitrification column. The 20 L up-flow column consisted of 18 L acrylic column with 2 L down-comer inlet tube located in the middle. In the first part, the wastewater with high suspended solids from the Tilapia fish tank was applied into the sedimentation unit at 5 variable flow rates i.e., 11.25, 25.71, 60, 105.88 and 360 L/h. The results indicated that the flow rate of 11.25 L/h (0.57 m/h) gave the highest solid removal efficiency of $72.72%{\pm}8.24%$. However, the total suspended solids removal was highest at 360 L/h (18.13 m/h). In the second part, methanol was added as an external organic carbon source for denitrification process in a hybrid column containing settled solids. The COD:N ratios of 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1 and 6:1 were investigated and compared with control without methanol addition. This experiment was operated at the HRT of 1 h with 450 L wastewater from recirculating aquaculture pond containing 100 mg-N/L sodium nitrate. The results indicated that the COD:N ratio of 3:1 gave the highest nitrate removal efficiency of $33.32%{\pm}21.18%$ with the denitrification rate of 5,102.88 mg-N/day.

• 대한기계학회논문집B
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• 제41권7호
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• pp.435-443
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• 2017

본 연구는 고 레이놀즈 영역에서 상류측에 작은 정방형주(Square prism)를 가진 정방형주의 유동장 특성을 양 항력측정 실험과 PIV를 이용한 가시화 실험으로 파악한 것이다. 실험변수는 정방형주 한변의 길이에 대한 작은 정방형주의 폭비(H/B=0.2~0.6) 및 정방형주 전면에서부터 작은 정방형주의 후면 까지의 거리(G/B=0~3)로 했다. 작은 정방형주의 폭비를 고정시킨 경우 정방형주의 항력감소율은 간격비가 증가할수록 증가하다 감소하는 특성을 보였다. 또한 같은 간격비에서는 작은 정방형주의 폭비가 클수록 정방형주의 항력감소율이 컸다. 또한 같은 간격비에서는 작은 정방형주의 폭비가 클수록 정방형주의 항력감소율이 증가했으며, 폭비 H/B=0.6, 간격비 G/B=1.0일 때 최대 98.0%의 항력감소율을 보였다. 정방형주의 양력감소율은 작은 정방형주의 폭비 및 간격비에 거의 영향을 받지 않았으며, 양력감소율의 전체 평균치는 66.5% 정도였다. 작은 정방형주를 설치한 경우 정방형주 상류측과 하류측에 정체영역이 나타났다.

• Wind and Structures
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• 제20권1호
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• pp.37-58
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• 2015

As wind flows around a sharp-edged body, the resulting separated flow becomes complicated, with multiple separations and reattachments as well as vortex recirculation. This widespread and unpredictable phenomenon has long been studied academically as well as in engineering applications. In this study, the flow characteristics around rectangular prisms with five different aspect ratios were determined through wind tunnel experiments and a detached eddy simulation, that placed the objects in a simulated deep turbulent boundary layer at $Re=4.6{\times}10^4$. A series of rectangular prisms with the same height (h = 80 mm), different longitudinal lengths (l = 0.5h, h, and 2h), or different transverse widths (w = 0.5h, h, and 2h) were employed to observe the effects of the aspect ratio. Furthermore, five wind directions ($0^{\circ}$, $10^{\circ}$, $20^{\circ}$, $30^{\circ}$, and $45^{\circ}$) were selected to observe the effects of the wind direction. The simulated results of the surface pressure were compared to the wind tunnel experiment results and the existing results of previous papers. The vortex and spectrum were also analyzed to determine the detailed flow structure around the body. The paper also highlights the pressure distribution around the rectangular prisms with respect to the different aspect ratios. With an increasing transverse width, the surface suction pressure on the top and side surfaces becomes stronger. In addition, depending on the wind direction, the pressure coefficient experiences a large variation and can even change from a negative to a positive value on the side surface of the cube model.

• 한국수산과학회지
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• 제52권3호
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• pp.256-267
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• 2019

Styrofoam beads, which are relatively inexpensive and can provide a large specific surface area, were tested as filter media. Styrofoam beads with a diameter of $3{\pm}0.5mm$ were used; the specific surface area of the beads was $1,034m^2{\cdot}m^{-3}$. Five independent recirculating culture systems were used in the experiment. Each system consisted of one culture tank and three trickling bio-filters. Using the systems, nitrification efficiency was evaluated with respect to hydraulic loading rate (HLR) and carbon/nitrogen (C/N) ratio. The lowest ammonia and nitrogen concentrations were $0.84mg{\cdot}L^{-1}$ and $1.30mg{\cdot}L^{-1}$, respectively, observed at an HLR of $50.9m^3{\cdot}m^{-2}{\cdot}h^{-1}$. Nitrification efficiency in the culture tank was highest at a C/N ratio of 0, with ammonia and nitrite nitrogen concentrations of $0.32mg{\cdot}L^{-1}$ and $0.90mg{\cdot}L^{-1}$, respectively. Ammonia and nitrite nitrogen concentrations in the culture tank abruptly changed at C/N ratios ${\geq}3$.

• 한국환경보건학회:학술대회논문집
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• 한국환경보건학회 2004년도 International Conference Global Environmental Problems and their Health Consequences
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• pp.207-209
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• 2004

This study was performed to estimate the effects of salinity and washing of food wastes on temperature, pH, and salinity in aerobic composting of food wastes. Weight ratios of food wastes to water in washing were 1:0(Control), 1:1(W-1), 1:2(W-2), 1:3(W-3) and 1:4(W-4), respectively. Ratios of food wastes to wood chips in reactor of Control, W-1, W-2, W-3 and W-4 were 5kg:5L, respectively. Reactors were operated for 24 days with 1 hour stirring by 1 rpm and 2 hours aeration per day. The increase in the ratio of food wastes to water used in washing resulted in the decrease of the highest reaction temperature and the elongation of the high temperature reaction period. The lowering of the ratio of food wastes to water used in washing resulted in faster pH increase The final salinities of Control, W-1, W-2, W-3 and W-4 were 0.95%, 0.73%, 0.65%, 0.57% and 0.41%, respectively.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2003년도 추계학술발표회
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• pp.192-195
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• 2003

The hight density sludge process (HDS) is a process that has been developed to achieve greatly increased sludge densities compared to those resulting from conventional pH modification systems. This study was carried out to apprehend variation of sludge properties and removal of metals during recycling of the sludge. The principal neutralization and settlement took place in neutralization beaker and mass cylinder. Sludge was recycled, as a volumetric ratios of 20%, 40% and 60%. The pH was controlled in neutralization tanks near 9.5. The average lime consumption rate was about 10g per L of AMD. The increment of sludge density was correlated with the volumetric ratios of recycled sludge.

• Bulletin of the Korean Chemical Society
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• 제29권4호
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• pp.758-760
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• 2008

Nanoporous AAO (Anodic Aluminum Oxide) membranes have many advantages as a template for variety of magnetic materials. Materials can be embedded into the pores by electrodeposition, sputtering or magnetic-field-assisted infiltration of magnetic nanoparticles. This work focuses on the fabrication of the magnetic structures in the AAO templates by electrodeposition. Our method allows the controlled growth of Co nanostructures within the porous alumina membrane in the form of dots, rods and long wires. The shape of Co nanostructures has been investigated by field emission scanning electron microscope (FESEM). The magnetic hysteresis loops of Co nanostructures were measured using SQUID at 5 K and 300 K. The magnetic properties of the Co nanostructures are proportional to their aspect ratios and can be controlled by changing the aspect ratios.

• 한국조리학회지
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• 제14권1호
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• pp.152-160
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• 2008

The purpose of this study was to investigate the sensory characteristics of brown sauce made with different ratios of Jubak. In the brown sauce made from Jubak, the followings showed changes according to the amount of Jubak. The content of crude lipid increased, that of crude protein and moisture decreased, and that of crude ash and reduced sugar increased. Brown sauce made from Jubak contained more reduced sugar than general brown sauce, and the content of reduced sugar increased. pH increased from initial pH 4.32 to 5.42 respectively, and viscosity increased. The "L" value expressing brightness of samples had a tendency to increase with Jubak added. "a" value had a tendency to increase in case of no Jubak added, and "b" value had a tendency to decrease according to the amount of Jubak. In the sensory evaluation, color and flavor decreased and viscosity increased with the amount of Jubak. Overall, it was the highest in 0% Jubak. From the above results, an addition of 25% Jubak to brown sauce is recommended for commercial use.

• 한국결정성장학회지
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• 제28권2호
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• pp.63-68
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• 2018

Natural convection of a two dimensional laminar steady-state incompressible fluid flow in a rectangular enclosure has been investigated numerically for low aspect ratios with the physical vapor transport crystal growth. Results show that for aspect ratio (Ar = L/H) range of $0.1{\leq}Ar{\leq}1.5$, with the increase in Grashof number by one order of magnitude, the total mass flux is much augmented, and is exponentially decayed with the aspect ratio. Velocity and temperature profiles are presented at the mid-width of the rectangular enclosure. It is found that the effect of Grashof number on mass transfer is less significant when the enclosure is shallow (Ar = 0.1) and the influence of aspect ratio is stranger when the enclosure is tall and the Grashof number is high. Therefore, the convective phenomena are greatly affected by the variation of aspect ratios.

• 한국물환경학회지
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• 제34권3호
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• pp.316-327
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• 2018

Liquid fertilizers made from livestock manure contain high concentrations of nitrogen and phosphorus and thus are used as a fertilizer. However, excessive use of liquid fertilizer causes eutrophication of agricultural land and nonpoint source pollution. In this study, as a means of lowering the nutrient concentrations, struvite ($MgNH_4PO_4{\cdot}6H_2O$) production from the liquid fertilizer was investigated. When liquid fertilizers produced in Gyeonggido were analyzed, its characteristics differed by region and season, but the phosphorus concentration was commonly lower than that of nitrogen. When $K_2HPO_4$ and $MgCl_2$ were added to the liquid fertilizers, the optimal pH for struvite formation was pH 9.5. For environmentally friendly sources of magnesium and phosphate, ferronickel slag (FNS) and sewage sludge ash (SSA) were suspended in deionized water and extracted by sulfuric acid with various mass ratios. The optimum conditions for extracting FNS and SSA were 4.0 M sulfuric acid and 0.35 mass ratio of sulfuric acid to sewage sludge ash, respectively. For forming struvite, 0.233 L of SSA leachate (SSAL) was added into 0.3 L of liquid fertilizer containing 2,586 mg/L of ammonia and 110 mg/L of phosphate, pH was then adjusted to pH 9.5 using 10 M of NaOH. Afterwards 0.333 L of FNS leachate (FNSL) was added to this mixed solution. After a reaction for 1 hr at room temperature, the remaining concentrations of magnesium, ammonium, and phosphate were less than 50 mg/L, 500 mg/L and 150 mg/L, respectively, and 30 g of precipitates were obtained, most of which were struvite.