• Journal of Korean Society of Water and Wastewater
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• v.20 no.4
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• pp.617-626
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• 2006

Compared with the sludge from gravity sedimentation, it is difficult for operations to settle the sludge occurred from dissolved-air-flotation (DAF). Even though there are some problems in treating DAF sludge with conventional gravity thickeners, those has been used until now. In this study, Solid Flux theory for gravity thickening was applied to the Solid Flux of DAF sludge through flotation in order to develop new methodology for treatment of DAF sludge. Also, characteristics of DAF sludge were investigated. From the experiment results, it was revealed that the higher the polymer dosage, at fixed the solid concentration, the greater the rising velocity becomes. When we applied solid flux theory, the relationship, which is similar to that of gravity thickening, has been achieved. Also, we could find the proper polymer dosage from the rising velocity is about 50 mg/L. Consequently, the limiting solid flux can be derived from the relationship between the total solid flux and the withdrawal velocity of DAF sludge. Furthermore, the factors, such as solid concentrations, bubble volume, pH, zeta potential, and temperature, have effects on the flotation and sedimentation for DAF sludge treatment.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.8
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• pp.855-860
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• 2011

We numerically simulated a dissolved air flotation (DAF) tank to predict the performance of the pilot facility. The flow was assumed to be two-dimensional and two-phase. The velocity distributions in the separation zones of differently shaped DAFs were compared to find the effect of the shape on the performance. The results showed that the typical flow pattern that appeared in a well-designed DAF-tank was generated in the separation zone of the base model. This flow pattern could be maintained while the baffle height was sufficiently tall regardless of the other geometric parameters. However, the baffle height and angle, the contact zone width, and the perforated plate affected the uniformity of the downward flow in the separation zone. Except for the baffle height, the base model used in this study showed a better uniformity of downward flow than did other models with different geometric parameters.

• Journal of Korean Society on Water Environment
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• v.28 no.1
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• pp.129-136
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• 2012

In this century, scientists realized that carbon dioxide gas in the atmosphere cause a greenhouse effect which affects the planet's temperature. Therefore lots of attempts have carried out to decrease the discharge of carbon dioxide gas in the field. The dissolved carbon dioxide flotation (DCF) process was developed as an alternative of DAF process to decrease the discharge and reuse of carbon dioxide as well as to save energy consumption. To investigate the particle separation characteristics and the flotation efficiency of carbon dioxide, SCC model was employed in the DCF process which has been applied extensively for the evaluation and simulation in the DAF process. The simulation results by the SCC model revealed the predicted curve of flotation efficiency became decreased gradually over the optimal pressure range of saturator about 1.6 atm in accordance with the experiment results of the DCF pilot plant and the size distribution and the bubble volume concentration of $CO_{2}$ bubbles depending on the operation pressure of saturator. The findings through the simulation results led to the conclusion that there was no significant difference between $CO_{2}$ bubbles and air bubbles, affecting on the practical flotation efficiency, in terms of the initial collision and attachment efficiency.

• Journal of Environmental Science International
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• v.16 no.9
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• pp.1085-1090
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• 2007

The performance of EF (electroflotation) on the thickening of activated sludge were investigated using laboratory scale batch flotation reactor. In this paper, the effects of parameters such as electrode material, NaCl dosage, initial sludge concentration and electrode distance were examined. The results showed that the performance for sludge thickening of the five electrodes lay in: Pt/Ti > Ru/Ti > Ir/Ti > Ti mesh > Ti plate. The more NaCl dosage was high, the more sludge was thickened and the shorter thickening time was obtained. However, considering the final thickening time and sludge concentration, optimum NaCl dosage was 0.5 g/L. Thickening time and sludge concentration was not affected by electrode distance. In DAF (dissolved air flotation) system, optimum recycle ratio was 40% and thickening performance was lower than that of the EF.

• Journal of Korean Society on Water Environment
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• v.20 no.6
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• pp.676-684
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• 2004

Many researchers have been carrying on study to figure out the exact collision efficiency between bubble and floc. Collision efficiency can has generally been quantified by using trajectory analysis which uses the hydrodynamic, the electrostatic and van der waals forces. Two types of method are considered to induce the hydrodynamic force in the trajectory analysis. One is to use stream function and the other is to use mobility function. There was some difference between stream and mobility function depending upon modelling factors and conditions in trajectory analysis.

• Resources Recycling
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• v.27 no.1
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• pp.45-54
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• 2018

This study aimed to investigate the effects of mechanical factors such as agitation speed and air rate in fly ash flotation. Specifically, we used thermal power plant fly ash with unburned carbon content of 3.4 to 3.7%. The effect of pH, agitation speed, collector dosage, and frother dosage - the key factors of froth flotation - showed unburned carbon recovery and unburned carbon content of 63% and 34%, respectively, when the dosage of safflower oil used as collector was 800 g/ton, pH was 7, agitation speed was 1,200 rpm, and frother dosage was 400 g/ton. The SEM/EDS analysis of fly ash in that case indicated that the spherical fly ash particles lowered the unburned carbon content as they floated with the air bubbles without being dissolved in the unburned carbon or settled in the ore solution. The other experiment of changing the mechanical factors such as agitation speed and air rate resulted in unburned carbon recovery and unburned carbon content of 74% and 67%, respectively, at air rate of 8 L/min and agitation speed of 900 rpm. The recovery and unburned carbon content increased as the low agitation speed and additional air injection decreased the strength of the eddy current in the ore solution and consequently prevented the floating of fine fly ash particles with unburned carbon. In addition, the recovery rate and unburned carbon increased further to 80% and 70%, respectively, showing the best performance when the agitation speed and air rate were lowered to 800 rpm and 6 L/min, respectively.

• Journal of the Korean GEO-environmental Society
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• v.11 no.10
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• pp.49-55
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• 2010

The oil spill occurred frequently due to probably the increased consumption of oil as the energy source and the raw materials of various chemicals. For the treatment of oil contaminated groundwater, DAF(Dissolved Air Flotation) is being used but the removal efficiency is low. Therefore it is necessary to reduce the free phase oil, oil-in water type or water-in oil type emulsified oil, and soluble oil which are the main sources of contaminated groundwater. In this study, treatment of contaminated groundwater was performed using the Fenton oxidation process. The optimum conditions for the removal of THP(Total Petroleum Hydrocarbon) were 3 of pH, 25mM of $H_2O_2$ concentration and 25mM of $Fe^{2+}$ concentration. THP and COD(Chemical Oxygen Demand) concentrations decreased less than 1.5mg/L and 40.0mg/L in 7 minutes using DAF and Fenton oxidation process. However it is necessary to install the settling basin as the sludge concentration increased approximately 5 times.

• Journal of Korean Society of Water and Wastewater
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• v.18 no.2
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• pp.201-207
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• 2004

Dissolved air flotation (DAF) is a solid-liquid separation process that uses fine rising bubbles to remove particles in water. Most of particle-bubble collision occurs in the DAF contact zone. This initial contact considered by the researchers to play a important role for DAF performance. It is hard to make up conceptual model through simple mass balance for estimating collision efficiency in the contact zone because coupled behavior of the solid-liquid-gas phase in DAF system is 90 complicate. In this study, 2-phase(gas-liquid) flow equations for the conservation of mass, momentum and turbulence quantities were solved using an Eulerian-Eulerian approach based on the assumption that very small particle is applied in the DAF system. For the modeling of turbulent 2-phase flow in the reactor, the standard $k-{\varepsilon}$ mode I(liquid phase) and zero-equation(gas phase) were used in CFD code because it is widely accepted and the coefficients for the model are well established. Particle-bubble collision efficiency was calculated using predicted turbulent energy dissipation rate and gas volume fraction. As the result of this study, the authors concluded that bubble size and recycle ratio play important role for flow pattern change in the reactor. Predicted collision efficiency using CFD showed good agreement with measured removal efficiency in the contact zone. Also, simulation results indicated that collision efficiency at 15% recycle ratio is higher than that of 10% and showed increasing tendency of the collision efficiency according to the decrease of the bubble size.

• Journal of Korean Society of Water and Wastewater
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• v.32 no.6
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• pp.479-485
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• 2018

Large amounts of oily wastewater discharged from various industrial operations (petroleum refining, machinery industries and chemical industries) cause serious pollution in the aquatic environment. Although dissolved air flotation (DAF) separating oil pollutants using microbubbles represents current practice, bubble size cannot be selectively controlled, and lots of power is required to generate microbubbles. Therefore, to investigate performance of the DAF process, this study examined the distribution of different sizes of microbubbles resulting from changes in physical shear force via modifying shapes of a slit-nozzle without an additional power supply. Three types of slit-nozzles (different angle, shape and length of the slit-nozzle) were used to analyze the distribution of bubble size. At a slit angle of $60^{\circ}$, shear force was 4.29 times higher than a conventional slit, and particle size distribution (PSD) in the range between 2 and $20{\mu}m$ more than doubled. Treatment efficiency of synthetic oily wastewater through the coagulation-DAF process achieved 90% removal of COD by injecting $FeCl_3$ and PACl of 250 mg/L and 100 mg/L, respectively, and the same performance resulted using $FeCl_3$ of 200 mg/L and PACl of 80 mg/L employing a slit-nozzle angle of $60^{\circ}$. This study shows that a coagulation-DAF process using a modified slit-nozzle can improve the pre-treatment of oily wastewater.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.474-474
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• 2022

미세플라스틱이 물 환경으로 배출되는 주요 경로로는 하수처리장 방류수와 강우유출수가 있다. 하수처리장 및 유역에서 배출된 미세플라스틱은 하천과 하구역을 거쳐 해양과 같은 대규모 수역으로 이동하는데, 이 과정에서 해양뿐만 아니라 담수호, 저수지 등과 같은 공공수역에도 미세플라스틱이 지속적으로 축적되고 있다. 특히 강우유출수에 포함된 미세플라스틱은 적절한 처리 과정 없이 하천으로 유입되는 경우가 많아 공공수역 내 미세플라스틱 저감 기술의 필요성이 증가하고 있다. 그러나 미세플라스틱 관련 기존 연구는 미세플라스틱의 분포 등 현황에 대한 모니터링 및 환경위해성과 관련한 것이 대부분이며, 미세플라스틱 저감기술 관련 연구 또한 일부 정수처리 및 하수처리 공정을 대상으로 하는 초기 단계의 연구가 진행되고 있을 뿐 공공수역에서의 미세플라스틱 저감기술 개발 관련 연구는 전무한 실정이다. 따라서, 본 연구에서는 기존의 물리·화학적 수처리 공정인 용존공기부상법(Dissolved Air Flotation, DAF)에 물의 전기분해 시발생하는 브라운가스를 활용하여 응집된 물질을 빠르게 부상시켜 수체 내 오염물질을 제거할 수 있는 기술을 통해 수체 내 미세플라스틱 저감효과를 분석하였다. 또한, 해당 기술을 공공수역인 저수지에 적용하여 오염물질과 함께 미세플라스틱을 제거할 수 있는지 검토하였다.