• Journal of Korean Society of Environmental Engineers
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• v.28 no.11
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• pp.1186-1191
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• 2006

Removal efficiency of As(III) through oxidation and adsorption in column reactors was investigated at different ratios of manganese-coated sand(MCS) and iron-coated sand(ICS) : MCS-alone, ICS-alone and both of ICS and MCS. The breakthrough of arsenic immediately occurred from a column reactor with MCS-alone. However, most of the arsenic present in the effluent was identified as As(V) due to the oxidation of As(III) by MCS. While five-times delayed breakthrough of arsenic was observed from a column reactor with ICS-alone. At a complete breakthrough of arsenic, the removed As(III) was 36.1 mg with 1 kg ICS. To find an optimum ratio of ICS and MCS in the column packed with both ICS and MCS, the removal efficiency of As(III) was investigated at three different ratios of ICS/MCS with a fixed amount of ICS. The breakthrough time of arsenic was quite similar in the different ratios ICS/MCS. However, much slower breakthrough of arsenic was observed as the ratio of ICS/MCS decreased. As the ratio of ICS/MCS decreased the concentration of As(III) in the effluent decreased and then showed below 50 ppb at an equal amount of ICS and MCS, suggesting more efficient oxidation of As(III) by greater amount of MCS. When a complete breakthrough of arsenic occurred, the removed total arsenic with an equal amount of ICS and MCS was 68.5 mg with 1 kg of filter material.

• Journal of Korean Society of Water and Wastewater
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• v.22 no.4
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• pp.429-436
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• 2008

Membrane system has been increasingly considered as a safe and cost-effective water treatment process especially in case of small scale water works. This research is a basis of membrane application in water works through a long period test with obtaining operation skills and evaluation of water quality and cost competitiveness. For the research, the UF membrane system was installed in small water treatment plant that uses river-bed water as raw water. The system was consisted of 2 stage membrane and operated in constant flow mode (Flux: 1.5, 1.0, 0.9, 0.6). In each different flux condition, TMP trends were showed better results at lower flux condition. And through the high flux condition test, it is certified that membrane system could deal with breakdown of one stage. Water quality of permeate was satisfied the water quality standards especially turbidity. To know what mainly causes fouling on membrane, the test by membrane with several cleaning agents and EDX analysis have done in lab. Through the tests, ferrous concentration in raw water, backwashing water and membrane surface etc. was high and it causes fouling inside and outside of membrane. So acid cleaning using organic acid such as oxalic acid is necessary in Chemical in Place (CIP). At the economical aspect the electrical cost of membrane system is higher than that of slow sand filtration but labor cost can be reduced by automation. However, the use of labor should be determined considering effectiveness and stability of operation. Because during the operation, there are several breakdown such as electrical shock by lightning, water drop in summer, etc.

• Journal of Korean Society of Water and Wastewater
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• v.12 no.1
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• pp.102-107
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• 1998

This study was conducted to investigate how the pore sizes of MF and UF membranes affected the removal efficiencies. The experimental results were compared with those obtained from the existing sand filter to select the optimum membrane. Turbidity of the raw water was adjusted to 10, 30, 50, 100, and 200NTU. The removal efficiencies of the turbidity and SS were nearly 100% for all membranes applied. Not membrane differences in the removal efficiencies of dissolved organics were also found. Thus, MF membrane with pore size $0.1{\mu}m$ was selected to obtain satisfactory removal efficiencies of turbidity and bacteria. Permeable flux was also considered. The $0.1{\mu}m$ MF membrane system was operated in the treatment plant to compare the results with those obtained from the existing sand filter. Turbidity, SS, $KMnO_4$ consumption, and number of coliform were chosen to be compared. Because there were not much differencies in the quality of the treated water, the existing coagulation-sedimentation-filtration process might be replaced and upgraded by simpler membrane process.

• Journal of Korean Society for Atmospheric Environment
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• v.15 no.2
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• pp.79-87
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• 1999

$^{239+240}Pu$ concentrations in precipitation were determined for the period of May 1994 to August 1996 in oder to describe current $^{239+240}Pu$ deposition at the mid-western coat of Korea (Ansan, 37$^{\circ}$17'N, $126^{\circ}$50'E). $^{239+240}Pu$ concentration in daily precipitation varied from 0.05 to 131$\mu$Bq $kg^{-1}$ with a geometric mean of $1.26\mu$Bq $kg^{-1}$. The concentration was high in the period of Yellow Sand Storm in spring and low in wet summer monsoon. The specific $^{239+240}Pu$ concentration in daily precipitation appears to be controlled by the $^{239+240}Pu$ input to the atmosphere in spring and washout effects by precipitation in the wet summer monsoon. Wet depositional flux of $^{239+240}Pu$ varied from 4 to 123$\mu$Bq $m^{-2}d^{-1}$ with a geometric mean of $33.8\mu$Bq $m^{-2}d^{-1}$ and with a maximum in the period of Yellow Sand Storm and a minimum in the period of wet summer monsoon. $^{238}Pu$/$^{239+240}Pu$ activity raios(0.04~0.31) in precipitation for March-June period suggested that one of the major sources of Pu isotopes falling in Ansan area is the arid region of the Chinese continent.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.8
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• pp.714-721
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• 2005

The water jet impingement cooling with boiling is one of the techniques to remove heat from high heat flux equipments. The configuration of surface roughness is one obvious condition of affecting the performance on heat transfer in nucleate boiling, The present study investigates the water jet impinging single-phase convection and nucleate boiling heat transfer for the effect of surface roughness to enhance the heat transfer in free surface and submerged jet. The distributions of the averaged wall temperature as well as the boiling curves are discussed. Jet velocities are varied from 0.65 to 1.7 m/s. Surface roughness by sand blast and sand paper varies from 0.3 to 2.51 ${\mu}m$ and cavity shapes on surface are semi-circle and v-shape, respectively The results showed that higher velocity of the jet caused the boiling incipience to be delayed more. The incipient boiling and heat transfer increase with increasing surface roughness due to a large number of cavities of uniform size.

• Journal of The Geomorphological Association of Korea
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• v.26 no.3
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• pp.1-17
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• 2019

Naeseongcheon is Korea's representative sand stream, and it is one of the regions where the dynamic changes of various river topography developed in the sand bed can be observed. Most of drainage area near of the river channel are formed with Daebo granite, and the granite weathering zone is developed at the surface of hill. Due to the massive input of sediment flux, braided channel reaches are found some of the area. However, the results of the study shows that the alluvial layer is very thin in some reaches. In addition, bedrock or weathered materials, including the Tors are exposed at the channel beds. On the other hand, during the flood, a considerable amount of sediment was introduced, causing the massive sediment to be close to 1m thick. In addition, despite the short distance, large changes in the particle size and sorting of the sediment were observed. Vegetation, on the other hand, has been shown to have a significant effect on the development of the overall channel bed topography, as reported in previous studies. In small floods or low water levels, vegetation's protection role of the surface is predominates, but in large flood conditions, herbaceous loss at the surface of the point bars, accelerating the erosion of surface.

• Journal of Korean Society of Environmental Engineers
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• v.39 no.3
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• pp.155-163
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• 2017

Membrane filtration has become more popular in drinking water treatment recently, since the filtration can control not only particulate matters but also pathogenic microorganisms such as giardia and cryptosporidium very effectively. Pilot-scale ($120m^3/d$ of treatment capacity) and test-bed ($25,000m^3/d$ of treatment capacity) microfiltration experiments were conducted to find optimum operating mode and the critical flux. Optimum operating mode of pilot-test was assessed as inflow 1.0 min, filtration 36.5 min, air backwash 0.9 min, backwash 1.0 min and outflow 1.0 min with 50 LMH ($L/min{\cdot}m3^$) of critical flux. Critical Flux was calculated to be $50L/m^2-h$ (within TMP 0.5 bar) based on the increase formula of the transmembrane pressure difference according to the change of time at Flux 20, 40, 56 and 62 LMH in pilot operation. Chemical cleaning was first acid washed twice, and alkali washing was performed secondarily, and a recovery rate of 95% was obtained in the test-bed plant. The results of operating under these appropriate conditions are as follows. Turbidity of treated water were 0.028, 0.024, 0.026 and 0.028 NTU in spring, summer, autumn and winter time, respectively. Microfiltration has superior treatment capability and performance characteristics in removing suspended solids and colloidal materials, which are the main cause of turbidity and important carrier of metal elements, and it has shown great potential in being an economically substitute to traditional processes (sand filtration).

• Ocean and Polar Research
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• v.30 no.4
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• pp.519-536
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• 2008

The relatively tranquil area within the Gogunsan Archipelago was for the first time investigated preliminarily with respect to modern sedimentological processes in association with the emplacement of the Saemangeum Dyke. Basic sedimentological observations, bathymetry and surface sediments were performed twice during 2006-2008 to compare the results and elaborate changes during that period of time. In addition, sediment dynamical observations were carried out with latest measuring equipment along two transects crossing the entrances of the archipelago, including 12-hour onboard measurements of current, suspended sediments, temperature, and salinity. This dataset was used to reveal hydrodynamic characteristics for spring season April-May and to estimate the direction and relative magnitude of the net flux of suspended sediments. There occurred three depositional areas (A to C) within the archipelago, where sediment texture was also changed. In area A, around Yami Island and the dyke, and area B, in the center of the archipelago, surface sediments became coarsened over the two-year period; sand content increased 5% at the expense of silt content in the former, whereas silt content increased 3% at the expense of clay content in the latter. By comparison, area C in the western entrance of the archipelago shows a textural trend of fining with more silt and clay (combined increase of 5%) at the expense of sand content. The accumulation of sediments in areas A and B is attributable to the sand and silt resuspended from the seabed sediments off sector 4 of the dyke during the winter. The origin of the fine materials depositing on area C is uncertain at present, although suspended sediments moving offshore around the archipelago may be one of the most likely candidates for the source. The temperature of seawater increased rapidly from $9-10^{\circ}C$ in April to $14-16^{\circ}C$ in May, whereas salinity remained more or less constant at 31-32%o during the two months. Both of these parameters showed little variations with depth through a tidal cycle, suggesting good mixing of seawater without any help of significant waves. The consistency of salinity during a tidal cycle also indicates no insignificant effects of freshwater from the rivers Mangyung and Donjin emitting through the opening gap near Sinsi Island. The suspended sediment concentrations were higher at the entrance between Sunyu and Sinsi islands than at the entrance between Hoenggyong and Sinsi islands, ranging from 20 and 30 mg/l and from 5 and 15 mg/l, respectively at the sea surface. Although tidal currents were variable across a transect between Sunyu and Sinsi islands, the currents across the entrance between Hoenggyong and Sinsi islands flowed consistently in the same direction all over the transect during a tidal cycle. The estimation of net flux of suspended sediments indicates that suspended sediments are transferred to the Gogunsan Archipelago mainly through a relatively deep trough adjacent to Sinsi Island toward the shallow area around Yami Island and the dyke.

• Journal of Korea Water Resources Association
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• v.52 no.11
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• pp.917-929
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• 2019

Denitrification in streams is of great importance because it is essential for amelioration of water quality and accurate estimation of $N_2O$ budgets. Denitrification is a major biological source or sink of $N_2O$, an important greenhouse gas, which is a multi-step respiratory process that converts nitrate ($NO_3{^-}$) to gaseous forms of nitrogen ($N_2$ or $N_2O$). In aquatic ecosystems, the complex interactions of water flooding condition, substrate supply, hydrodynamic and biogeochemical properties modulate the extent of multi-step reactions required for $N_2O$ flux. Although water flow in streambed and residence time affect reaction output, effects of a complex interaction of hydrodynamic, geomorphology and biogeochemical controls on the magnitude of denitrification in streams are still illusive. In this work, we built a two-dimensional water flow channel and measured $N_2O$ flux from channel sediment with different bed geomorphology by using static closed chambers. Two independent experiments were conducted with identical flume and geomorphology but sediment with differences in dissolved organic carbon (DOC). The experiment flume was a circulation channel through which the effluent flows back, and the size of it was $37m{\times}1.2m{\times}1m$. Five days before the experiment began, urea fertilizer (46% N) was added to sediment with the rate of $0.5kg\;N/m^2$. A sand dune (1 m length and 0.15 m height) was made at the middle of channel to simulate variations in microtopography. In high- DOC experiment, $N_2O$ flux increases in the direction of flow, while the highest flux ($14.6{\pm}8.40{\mu}g\;N_2O-N/m^2\;hr$) was measured in the slope on the back side of the sand dune. followed by decreases afterward. In contrast, low DOC sediment did not show the geomorphological variations. We found that even though topographic variation influenced $N_2O$ flux and chemical properties, this effect is highly constrained by carbon availability.

• Nuclear Engineering and Technology
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• v.32 no.3
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• pp.274-282
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• 2000

The simulation of water balance was conducted for suggested four alternative multi-layer cover design of near-surface radioactive waste disposal facility under domestic climate condition. The analysis was also conducted for the most favorable one out of four alternative cover design under conservative scenarios. Until 100 years after closure of disposal vault, the infiltration flux for the most favorable cover design was negligible even under doubling of the ambient precipitation condition. When the degradation of asphalt and geomembrane after 100 years of closure was considered, the infiltration flux significantly increased almost to the design criteria of cover system in I' Aube disposal facility. And it was found that the hydraulic conductivity of bentonite/sand as a bottom barrier should be no greater than 1$\times$10$^{-7}$ cm/sec recommended by U.S. EPA.