• Journal of Korean Society of Water and Wastewater
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• v.26 no.1
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• pp.149-157
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• 2012

Experiments for As(V) removal using synthesized $Ca{\cdot}Al$-monosulfate was performed from the water contaminated with arsenate. Monosulfate is known as LDHs (Layered Double Hydroxides) which is one of the anionic clay minerals. Monosulfate was synthesized mixing $C_3A$ (tricalcium aluminate), gypsum (calcium sulfate), and water with an intercalation method. The product form the synthesis was characterized by FE-SEM, WDXRF, PXRD, and FT-IR. Experiments with different doses of monosulfate were carried out for kinetic. As a result of experiment, the concentration of As(V) was reduced from 0.67 mM to 0.19 mM (0.67mM of monosulfate) and 0.178 mM (1.34 mM of monosulfate). The concentration of sulfate was increased with As(V) decrease. The result of PXRD showed that the d-spacing of inter layer ($d_{003}$ peak) was shifted from 8.927 ${\AA}$ to 8.095 ${\AA}$ because the sulfate in the inter layer of monosulfate was exchanged arsenate with water molecules bonded. From the FT-IR results, a new single band (800 cm-1) was observed after the reaction of monosulfate and As(V). The arsenic removal can be regarded as anion exchange mechanism that is one of the characteristics of LDHs from the results of PXRD and FT-IR analysis.

• Restorative Dentistry and Endodontics
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• v.46 no.1
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• pp.11.1-11.11
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• 2021

Objectives: The aim of this study was to compare smear layer removal by conventional application (CA), passive ultrasonic irrigation (PUI), EasyClean (EC), and XP-Endo Finisher (XPF), using 17% ethylenediaminetetraacetic acid (EDTA) after chemomechanical preparation, as evaluated with scanning electron microscopy (SEM). Materials and Methods: Forty-five single-rooted human mandibular premolars were selected for this study. After chemomechanical preparation, the teeth were randomly divided into 5 groups according to the protocol for smear layer removal, as follows: G1 (control): CA of distilled water; G2 (CA): CA of 17% EDTA; G3 (PUI): 17% EDTA activated by PUI; G4 (EC): 17% EDTA activated by EC; and G5 (XPF): 17% EDTA activated by XPF. SEM images (×1,000) were obtained from each root third and scored by 3 examiners. Data were evaluated using the Kruskal-Wallis and Dunn tests (p < 0.05). Results: In the apical third, there were no statistically significant differences among the groups (p > 0.05). In the cervical and middle thirds, the experimental groups performed better than the control group (p < 0.05); however, G2 presented better results than G3, G4, and G5 (p < 0.05), which showed no differences among one another (p > 0.05). Conclusions: No irrigation method was able to completely remove the smear layer, especially in the apical third. Using CA for the chelating solution performed better than any form of activation.

• Journal of Korean Society of Water and Wastewater
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• v.18 no.1
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• pp.73-80
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• 2004

This study investigated the phenomena of membrane fouling by NOM and the effect of the fouling on removal of micro-pollutants. NOM has a great effect on decline of permeate flux. Permeate flow rate was reduced by 88% in RO and 34.8% in NF for 323hr operation period. Removal rate of $UV_{254}$, is 87.4% in RO and 78.5% in NF and removal rate of DOC is 42.7% in RO and 32.9% in NF for 2mg/l humic acid. Removal efficiency of the micro-pollutants by the RO and NF membranes fouled by humic acid was mostly lower than that by the new membrane. The concentration polarization which affects the flux and the rejection was thought to occur in the active layer of the membrane, as the membrane was getting fouled.

• Journal of Environmental Science International
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• v.5 no.4
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• pp.513-524
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• 1996

Laboratory investigation was conducted to evaluat the mixing effects on organic removal efficiency to treat low-strength synthetic wastewater using modified anaerobic - filter reactor combining anaerobic filter and upflow anaerobic sludge blanket. Using the modified process the low-strength wastewater like municipal sewage could be treated with 85% T-COD removal efficiency at hydraulic retention time of 6 hours. At the constant organic loading of 0.5 kg COD/m 3-day, the organic removal efficiency and effluent COD concentration are increased as influent COD concentration increased from 125 mg/l to 500 mg/l. Mixing effects on organic removal efficiency are evident and optimum mixing speed is found as 50RPM. Placing the granular sludge and media on which slime layer was pre-formed into the reactor seemed to be very effective In achieving short start-up period. Therefore, the steady state was achived after 4 weeks and 1 week based on T-COD and S-COD, respectively.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.8
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• pp.754-760
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• 2010

Geosmin removal by biodegradation was investigated in lab-scale slow sand filtration column with different empty bed contact times (EBCTs) and water temperature. Schmutzdecke layer was built up after 30 days operation and biomass and activity were $4.5{\times}10^6\;CFU/g$ and $3.42\;mg{\cdot}C/m^3{\cdot}hr$, respectively. The attached bio-film microorganisms in schmutzdecke layer were isolated and identified. The dominant species was Pseudomonas sp. that had occupied 56%. Removal efficiencies of dissolved organic carbon (DOC) and geosmin were 27% and 95% after 30 days operation. In lab-scale slow sand filtration column, geosmin and DOC removal efficiencies were 62% and 10% at $5^{\circ}C$, respectively. And increasing water temperature ($15^{\circ}C$ and $25^{\circ}C$) increased the geosmin and DOC removal efficiencies (88~100% and 25~42%) in lab-scale slow sand filtration column. Geosmin and DOC biodegradation rates (k) in the schmutzdecke layer (in the upper 5 cm filter bed) were $1.842{\sim}15.965\;hr^{-1}$1 and $0.253{\sim}1.123\;hr^{-1}$, respectively. It were about 18~32 times and 20~51 times of the rates in the deeper filter bed (5~60 cm).

• Restorative Dentistry and Endodontics
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• v.31 no.3
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• pp.169-178
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• 2006

This study was to verify that the combined application of NaOCl and EDTA was more effective in removal of smear layer than the application of NaOCl alone. furthermore it was aimed to find out the optimal time for the application of EDTA. Thirty five single rooted teeth were cleaned and shaped. NaOCl solution was used as an irrigant during instrumentation. After instrumentation, root canals of the control group were irrigated with 5 ml of NaOCl for 2 minutes. 30 sec, 1 min, and 2 min group were irrigated with 5 ml of 17% EDTA for 30 sec, 1 min, and 2 min respectively. Then the roots were examined with scanning electron microscopy for evaluating removal of smear layer and erosion of dentinal tubule. The results were as follows; 1. The control group: The smear layer was not removed at all. 2. The other groups: 1) $Middle\frac{1}{3}$: All groups showed almost no smear layer. And the erosion occurred more frequently as increasing irrigation time. 2) $Apical\frac{1}{3}$: The cleaning effect of 2 min group was better than the others. The results suggest that 2 min application of 17% EDTA should be adequate to remove smear layer on both $apical\frac{1}{3}\;and\;middle\frac{1}{3}$.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.71-76
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• 2001

In general, it is known that the wear rate of the abrasive and the removal rate of the metal bond of the grinding wheel should be balanced to maintain the depth of the insulating surface layer to an appropriate level. In order to accomplish, the high quality ELID grinding, therefore, it is necessary to measure the depth of the insulating layer in real-time and then to control the electrolytic conditions to keep the depth to a certain level. In this study, an in-process measurement system of the insulated layer using two gap sensors - a capacitor type and an eddy current type - developed and the change of the status of the insulated layer during ELID grinding is detected. And from the experimental data, we have chosen the best mathematical model to predict the depth of the insulating layer.

• Journal of Korean Society on Water Environment
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• v.27 no.4
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• pp.461-466
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• 2011

The feasibility of utilizing food waste leachate as an external carbon source was tested to enhance biological nutrient removal from an industrial wastewater with an average flow rate of $164,800m^3/d$ and a low carbon/nitrogen ratio of 2.8. A considerable improvement in the removal of nitrogen and phosphorus was observed when a certain amount of the leachate, ranging from 70 to $142m^3/d$, was supplemented to the biological industrial wastewater treatment process. The addition of the leachate led to an increase in the BOD/N ratio (4.5) and the removal efficiency of nutritents from 29.7% to 71.7% for nitrogen and from 34.8% to 65.6% for phosphorus. However, an excessive dose of the leachate that significantly exceeded $120m^3/d$ caused serious operational problems, like oil-layer formation in the grit chamber and scum layer in the primary clarifier. Thus, an supplement of food waste leachate at a dose acceptable to an existing facilities can be a practical and effective means to enhance the nutrient removal from industrial wastewater and to dispose of the food waste leachate.

• Journal of Korea Soil Environment Society
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• v.3 no.1
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• pp.31-44
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• 1998

The geochemical experiments were carried out to investigate a removal effect of heavy metals in abdndoned metallic mine wastes, and to conceive a treatment techniques of them. In order to prevent contamination, experiment appature was made of acrylic acid resin and polyethylene which resist to acid and alkali. Experiment models are devided into four groups based on the system environments, distribution patterns and a kind of filling materials. The first group is background model(model I ) which is filled with waste only and opened to air. The second one is four layer group which is subdivided into two models, opened and closed systems, and the third mix group which is subdivided into three models based on mixing ratio of filling materials and system environment like a layered group. The forth is composed of two layer model, lower one composed of waste and upper one limestone chips. Solution drained from Model Ishows a high contents of heavy metals on the all terms of experiments. Among the models, however, the closed mix model V and Ⅶ show the most effective removal of heavy metals liberated from wastes. Models having different mixing ratios of filling materials on closed systems does not affect in heavy metal removal effect. But, the distribution patterns of filling materials affect very much on removal effect of heavy metals. The closed models with same constitution ratios and distribution patterns of filling materials show more and less effective removal to the open models.

• Journal of Advanced Marine Engineering and Technology
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• v.21 no.5
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• pp.522-526
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• 1997

잔류 응력이 존재하는 부품의 가공 시에는 잔류 응력 상태가 새로운 평형 상태를 이루기 위해 재 분포되며 이는 가공 자체에 따른 변형 이와의 부가적 변형을 초래한다. 고도의 정밀도를 요하는 가공에는 이러한 잔류 응력에 의한 부가적 변형을 고려하여야 하며, 가공 후의 잔류 응력의 재 분포 상태는 가공 후 부품의 물질적 성능을 결정하는데 중요한 요소이므로 이를 예측할 수 있어야 한다. 본 연구에서는 잔류 응력에 의한 부가적 치수 변화를 고려한 가공 후의 부품의 내경 및 두께와 잔류 응력의 재 분포를 예측할 수 있는 이론적 수식을 제시하고 유한요소법에 의한 시뮬레이션의 결과와 비교하였다. 초기 잔류 응력의 분포는 autofrettage process에 의해 유도되었다.