• Journal of Korean Society of Water and Wastewater
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• v.20 no.4
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• pp.559-571
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• 2006

The overall objective of this research was to find out the interrelation of coagulant and organic matter during rapid mixing process and to identify the change of organic matter by mixing condition and to evaluate the effect of coagulation pH. During the coagulation, substantial changes in dissolved organics must be occurred by coagulation due to the simultaneous formation of microflocs and NOM precipitates. Increase in the organic removal efficiency should be mainly caused by the removal of microflocs formed during coagulant injection. That is, during the mixing period, substantial amount of dissolved organics were transformed into microflocs due to the simultaneous formation of microflocs and NOM precipitates. The results also showed that 40 to 80% of dissolved organic matter was converted into particulate material after rapid mixing process of coagulation. During the rapid mixing period, for purewater, formation of dissolved Al(III) (monomer and polymer) constant by rapid mixing condition, but for raw water, the species of Al hydrolysis showed different result. During the rapid mixing period, for high coagulant dose, Al-ferron reaction increases rapidly. At A/D(Adsorption and Destabilization) and sweep condition, both $Al(OH)_3(s)$ and dissolved Al(III) (monomer and polymer) exist, concurrent reactions by both mechanism appear to cause simultaneous precipitation.

• Bulletin of the Korean Chemical Society
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• v.34 no.8
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• pp.2358-2366
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• 2013

Iron oxide (ferrihydrite, hematite, and magnetite) coated silica gels were prepared using a low-cost, easily-scalable and straightforward method as the adsorbent material for arsenic removal application. Adsorption of the anionic form of arsenic oxyacids, arsenite ($AsO^{2-}$) and arsenate ($AsO{_4}^{3-}$), onto hematite coated silica gel was fitted against non-linear 3-parameter-model Sips isotherm and 2-parameter-model Langmuir and Freundlich isotherm. Adsorption kinetics of arsenic could be well described by pseudo-second-order kinetic model and value of adsorption energy derived from non-linear Dubinin-Radushkevich isotherm suggests chemical adsorption. Although arsenic adsorption process was not affected by the presence of sulfate, chloride, and nitrate anions, as expected, bicarbonate and silicate gave moderate negative effects while the presence of phosphate anions significantly inhibited adsorption process of both arsenite and arsenate. When the actual efficiency to remove arsenic was tested against 1 L of artificial arsenic-contaminated groundwater (0.6 mg/L) in the presence competing anions, the reasonable amount (20 g) of hematite coated silica gel could reduce arsenic concentration to below the WHO permissible safety limit of drinking water of $10{\mu}g/L$ without adjusting pH and temperature, which would be highly advantageous for practical field application.

• Journal of Korean Society on Water Environment
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• v.27 no.6
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• pp.754-759
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• 2011

A sequencing batch reactor (SBR) was operated under different pH conditions to better understand the influence of pH to granulation in enhanced biological phosphorus removal systems. Granules from the SBR were also investigated using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Considerable decreases in the amount of phosphorus released per substrate provided under anaerobic conditions and the content of biomass polyphosphate under aerobic conditions were observed when pH was changed from 7.5 to 7.0, followed by 6.5. Aerobic granulation was also observed at pH 7.0. A number of bacteria with the typical morphological traits of tetrad-forming organisms (TFOs) were observed at pH 7.0, including large members of cluster. Filamentous bacteria were also there in large numbers. The occurrence and growth of granules were further enhanced at pH 6.5. A SEM analysis showed that the aerobic granules had a compact microbial structure with shaperical shape and morphologically consisted of aggregates of small coccoid bacteria and filamentous bacteria encapsulated by extracellular polymeric substance. The main material ions identified by EDX moreover revealed that the structural materials for polyphosphate in the granules include phosphorus, potassium and calcium. Therefore, these results strongly suggested that PAOs are a dominant population in the microbial community of the aerobic granules.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.525-526
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• 2007

Over-polishing is required to completely remove the material of top surface across whole wafer, in spite of a local dishing problem. This paper introduces the two-step CMP process using protective layer and high selectivity slurry, to reduce dishing amount and variation. The 30nm thick protective oxide layer was deposited on the pattern, and then polished with low selectivity slurry to partially remove the projected area while suppressing the removal rate of the recessed area. After the first step CMP process, high selectivity slurry was used to minimize the dishing amount and variation in pattern structure. Experimental result shows that two-step CMP process can be successfully applicable to reduce the dishing defect generated in over-polishing.

• Korean Journal of Veterinary Service
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• v.47 no.2
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• pp.61-72
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• 2024

This study aimed to evaluate the feasibility of percutaneous endoscopic foraminotomy (PEF) for the treatment of intervertebral disc herniation of the thoracolumbar spine in large-breed dogs by comparing it with open hemilaminectomy (OH). Six large-breed canine cadavers were used in the present study. A barium and agarose mixture (BA-gel) simulating intervertebral disc herniation was injected into the spinal canal at two intervertebral spaces (T12-T13, L2-L3) of the thoracolumbar spine in each cadaver. PEF and OH were randomly allocated to the sites in each cadaver. Computed tomography was performed pre- and postoperatively. The incision length, vertebral window size, procedure time, and amount of simulated disc material removed were recorded to compare PEF and OH. Both procedures clearly exposed the simulated disc material and spinal cord. The size of the incision and vertebral window created after PEF was much smaller than those after OH. The surgical duration of PEF was longer than that of OH. However, no significant difference (P>0.05) was observed in the amount of BA-gel removed between PEF and OH. Thus, PEF could be used as an effective surgical option for intervertebral disc herniation of the thoracolumbar region in large-breed dogs in that it could lead to less tissue damage as well as sufficient removal of the simulated disc material.

• The Journal of Korean Academy of Prosthodontics
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• v.33 no.3
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• pp.569-583
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• 1995

Disinfection of dental impressions are necessary due to contamination with patient’s saliva and blood, which is a potential for cross-infection. The purpose of this study was to evaluate the effects of disinfection of four hydrophilic rubber impression materials with three disinfecting solutions, on the dimensional stability and surface hardness of improved stone casts. Three hydrophilic vinyl polysiloxane impression materials(Express, Reprosil, Exafine) and one polyether impression material(Impregum-F) were mixed according to the manufacturer’s directions and impressions were made on a ADA specification No. 19 stainless-steeldie. On removal of the impressions, each impression was immersed in one of the disinfectants(Banicide, Potadine, Clorox) for 10 minutes. After disinfection, type IV improved stone. casts were poured. On this cast, the linear dimension and surface hardness were measuredusing a Measurescope(Nikon, Japan) and a Barcol hardness tester(Barber, Colman Co U. S. A). The results were as follows : 1. The improved stone casts from disinfected Reprosil and Impregum-F impression material did not show dimensional changes(P>0.01). Those from disinfected Express and Exafine impression material showed dimensional changes(P<0.01). The amount of shrinkage was not clinically significant. 2. The improved stone casts from disinfected Express impression material did not exhibit changes in surface hardness(P>0.01), but those from disinfected Reprosil, Exafine, Imp regnum-F impression material showed changes in surface hardness(P<0.01). 3. The dimensinal stability and surface hardness of the improved stone casts were satisfactory using Banicide on Express, all disinfectants used in this study on Reprosil, Potadin and Clorox on Exafine, Banicide and Clorox on Impregum-F. According to these results, immersion disinfection of hydrophilic rubber impression mate rials did not adversely affect the resultant casts. Nevertheless compatibility tests of impression materials and disinfectants should be done when disinfecting impressions.

• Membrane and Water Treatment
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• v.13 no.3
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• pp.121-128
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• 2022

A tremendous amount of energy resources is being wasted in cleaning wastewater to save the environment across the globe. Several different procedures are commercially available to process wastewater. In this work, membrane filtration technique is used to treat the textile wastewater because of its cost effectiveness and low environmental impacts. Mixed Matrix Membrane (MMM) consist of Polyvinyl Alcohol (PVA) in which Graphene Oxide (GO) was added as a filler material. Five different membranes by varying the quantity of GO were prepared. The prepared membrane has been characterized by Scanning Electron Microscopy (SEM), X-Ray Diffractometry (XRD), Fourier Transformed Infrared Spectroscopy (FTIR) and Water Contact Angle (WCA). The prepared membranes have been utilized to treat textile wastewater. The synthesized membranes are used for the elimination of total dissolve solids (TDS), total suspended solids (TSS), Methylene blue (MB) dye and copper metallic ions from textile wastewater. It is concluded that amount of GO has direct correlation with the quality of wastewater treatment. The maximum removal of TDS, TSS, MB and copper ions are found to be 7.42, 23.73, 50.53 and 64.5% respectively and are achieved by 0.02 wt% PVA-GO membrane.

• Journal of Soil and Groundwater Environment
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• v.10 no.1
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• pp.1-5
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• 2005

Nitrate reduction with zero valent iron $(Fe^0)$ has been extensively studied, but the proper treatment for ammonium byproduct has not been reported yet. In groundwater, however, ammonium is regarded as contaminant species, and particularly, its acceptable level is regulated to 0.5 mg-N/L. for drinking water. This study is focused on developing new material to reduce nitrate and properly remove ammonium by-products. A new material, Fe-loaded zeolite, is derived from zeolite modified by Fe(II) chloride followed by reduction with sodium borohydride. Batch experiments were performed without buffer at two different pH to evaluate the removal efficiency of Fe-loaded zeolite. After 80 hr reaction time, Fe loaded zeolite showed about $60\%$ nitrate removal at initial pH of 3.3 and $40\%$ at pH of 6 with no ammonium release. Although iron filing showed higher removal efficiency than Fe-loaded zeolite at each pH, it released a considerable amount of ammonium stoichiometrically equivalent to that of reduced nitrate. In terms of nitrogen species including $NO_3-N$ and $NH_4^+-N$, Fe-loaded zeolite removed about $60\%\;and\;40\%$ of nitrogen in residual solution at initial pH of 3.3 and 6, respectively, while the removal efficiency of iron filing was negligible.

• Journal of Korea Foundry Society
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• v.31 no.2
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• pp.66-70
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• 2011

Hot dip aluminizing (HDA) is widely used in industry for improving corrosion resistance of material. The formation of intermetallic compound layers during the contact between dissimilar materials at high temperature is common phenomenon. Generally, intermetallic compound layers of $Fe_2Al_5$ and $FeAl_3$ are formed at the Al alloy and Fe substrate interface. In case of cast iron, high contact angle of graphite existed in the matrix inhibits the formation of intermetallic compound layer, which carry with it the disadvantage of a reduced reaction area and mechanical properties. In present work, the process for the removal of graphite existed on the surface of specimen has been investigated. And also HDA was proceeded at $800^{\circ}C$ for 3 minutes in aluminum alloy melt. The efficiency of graphite removal was increased with the reduction of particle size in sanding process. Graphite appears to be present both in the region of melting followed by re-solidification and in the intermetallic compound layer, which could be attributed to the fact that the surface of cast iron is melted down by the formation of low melting point phase with the diffusion of Al and Si to the cast iron. Intermetallic compound layer consisted of $Fe(Al,Si)_3$ and $Fe_2Al_5Si$, the layer formed at cast iron side contained lower amount of Si.

• Membrane Journal
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• v.24 no.1
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• pp.20-30
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• 2014

A membrane-coupled sequencing batch reactor (MSBR) was used for the advanced treatment of rural village sewage which is very low C/N ratio. The effect of powdered activated carbon, aeration rate, and external organic material loadings on the treatment efficiency and filtration performance were investigated in sequencing batch reactor, in which a flat-sheet type microfiltration membrane with a pore size of $0.4{\mu}m$ was submerged. At the initial operation (within 54 days) MLSS concentration, and the removal efficiencies of COD, T-N, and T-P were increased with the increase of C/N ratio. After 89 days the removal efficiencies of COD, T-N, and T-P were 97.1%, 75.0%, and 48.3%, respectively. Suspended solid-free effluent was obtained by membrane filtration. The T-P removal was relatively low because of depending on the amount of excess sludge wasting. During the operation of MSBR with powdered activated carbon, the particle size of the sludge reduced by the increase of collision frequency and mixing intensity. In comparison with MSBR without powdered activated carbon, TMP of MSBR with that was significantly elevated.