• Journal of the Mineralogical Society of Korea
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• v.26 no.3
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• pp.151-160
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• 2013

A column experiment was carried out to study the reaction of Cr(VI) with organic carbon. Chemical analysis for the effluent collected at different times after the reaction of Cr(VI) with organic carbon in compost and SEM observation for the solid samples remaining after the reaction were conducted. Cr(VI) supplied to the column was not detected in the effluent from column at initial stage, but the concentration of Cr(VI) increased abruptly and maintained the initial supplied concentration (20 mg/kg), indicating that Cr(VI) was effectively removed from the solution at the first state. In general, the concentrations of cations and anions with the exception of $PO_4$ increased and decreased again. Considering that most of these ions were not detected or showed very low concentration, these ions are considered to originate from the organic carbon in the column. SEM observation showed that Cr was coprecipitated with Fe on the surface of organic carbon with small amount of other metals such as Mn, No, and Co. This indicated that on the reduction condition on the organic carbon, Cr(VI) was reduced to $Cr(OH)_3$ and coprecipitated with $Fe(OH)_3$, and that Fe is very important in the precipitation of Cr. After the soluble Fe and Mn are not dissolved any more, $Cr(OH)_3$ is not precipitated. Different from other ions, the concentrations of $PO_4$ decreased and increased, which was thought to be the result of the release of $PO_4$ from organic carbon and sorption on the precipitates. After the maximum sorption on the precipitates and no further release of Fe, the concentration of $PO_4$ returns to its original value measured for the ones released from the organic carbon.

• Korean Journal of Environmental Agriculture
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• v.22 no.2
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• pp.166-171
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• 2003

A total of 498 agricultural reservoirs ranging from $164{\times}10^3\;m^3$ to $253{\times}10^6\;m^3$ in storage volume were investigated from 1990 to 2001 with respect to Chl-${\alpha}$, COD concentration and pollutant loading of BOD, TN, and TP. The lakes and reservoirs could be classified to 4 types using the relationships between the ratio of storage volume per water surface area(ST/WS) and Chl-${\alpha}$ concentration. It is recommended that the improvement of polluted lakes should be performed in the order of integrated consolidation type ${\rightarrow}$ watershed consolidation type ${\rightarrow}$ in-lake consolidation type ${\rightarrow}$ Management type and reservoir should be constructed to be over $5{\sim}6\;m$ in depth(ST/WS ratio) for preventing the eutrophication of agricultural reservoirs. We propose that water quality criteria for agricultural water is changed from less than 8 mg/L to less than 6 mg/L for safety value, $6{\sim}10\;mg/L$ for concern value, and more than 10 mg/L for countermeasure value in COD concentration, respectively.

• Journal of fish pathology
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• v.4 no.1
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• pp.1-11
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• 1991

Histopathological changes and methemoglobinemia of the eels (Anguilla japonica) reared at six culture farms in the vicinity of Y$\check{o}$su city were investigated under the conditions of $22.0{\sim}29^{\circ}C$, 4.33~7.33ppm of D.O., pH 6.1~8.2 and 0.03~10.1ppm of nitrite from December, 1989 to June, 1990. All of the eels showed no any abnormal state in action, color and blood, but the eels reared in pH 6.0 had planty of mucus and stickiness on their body surface. Methemoglobin levels were 1.03~9.86% of total erythrocyes in Dec. and 5.05~25.69% in June, and poikilocyte levels were 5.8~30.17% in Dec. and 8.67~74.45% in June. These results indicate the fact that the water management of the culture farms was worse in summer than in winter, even though not good in winter. Hypertrophy was found in the gill, hepatic and kidney tissue of the eels in all the culture farms. In March and June, Fish of all culture farms appeared the detachment of gill lamella epithelium cells, pyknosis and sinusoids of nucleus in the hepatic tissue and hemosiderosis in the kidney tissue. The trend of increase in methemoglobin levels appeared in the fish of culture farms with high nitrite concentration, which didn't appear equally in all the culture farms. However, in the culture farms of pH 6.0, methemoglobin and poikilocyte levels were increased independently of concentration of nitrite, and degeneration in the tissue of the gill, liver and kidney was also appeared.

• Applied Biological Chemistry
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• v.45 no.2
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• pp.84-91
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• 2002

If contaminated river water is sprayed over the floodplain, organic matter and nitrogen would be removed by microbial processes in the rhizosphere of vegetation during the filtration through soil. In this study we tested the organic matter and nitrogen removal from contaminated river water by the floodplain filtration. Model system of floodplain was constructed using a PVC pipe (15 cm i.d. ${\times}$ 150 cm L) which was packed with a loamy sand soil collected from a floodplain in Nakdong river. The model system was instrumented with soil solution samplers and gas samplers. A river water collected from Omogcheon in Kyongsan was sprayed from top of the model system at three different rates. The concentration of organic matter, DO, $NO_3^-$, $NO_2^-$, $NH_4^+$, $N_2$ and $N_2O$, and redox potential were measured as a function of soil depth for 24 days after the system reached a steady state. When river water was sprayed at the rates of 40.8 and 68.0 $l/m^2/day$, a significant reductive condition for denitrification was developed at below 5-cm depth of the soil. When the water reached at 90-cm depth of the soil, COD and concentration of inorganic nitrogen were lowered, on an average, from 18.7 to 5 mg/l and from 2.7 to 0.4 mg/l, respectively. $N_2$ comprised most of the N gas evolved from denitrification and $N_2O$ concentrations emitted at the surface of soil were less than 1 {\mu}l/l. The effective removal of organic matter and nitrogen by the filtration in the model system of floodplain demonstrates that the native floodplains, which include rhizosphere of vegetation at the top soil, could be more effective in the treatment of contaminated river waters and other industrial waste waters containing high concentration of organic matter and nitrogen.

• Applied Chemistry for Engineering
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• v.7 no.3
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• pp.554-564
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• 1996

Oxygen reduction in an alkaline fuel cell was studied by using perovskite of $La_{0.6}Sr_{0.4}Co_{1-x}Fe_xO_3$(x=0.00, 0.01, 0.10, 0.20, 0.35, and 0.50) as an oxygen electrode catalyst. The changes in the catalytic properties as a function of Fe content were investigated by XRD, TG, and TPR. XRD patterns gave different lattice parameters of the catalysts. TG study revealed that Fe was so stabilized in the perovskite structure as to be hardly reduced even up to $900^{\circ}C$, and the amount of oxygen which was eliminated at high temperature increased with the fraction of Fe because Fe induced the increase of Co-O binding energy. From TPR study, ${\alpha}$-(low temperature peak) and ${\beta}$-(high temperature peak)states were observed. The bond strength of the ${\beta}$-species which was associated strongly with Co of the perovskite increased proportionally with the fraction of Fe. The ${\alpha}$-species, reversible oxygen, was the active species in the oxygen reduction. The ${\alpha}$-peak temperature which reflected the binding energy between Co and ${\alpha}$-state oxygen moved to lower temperature with the increase of lattice parameter of the catalytst due to the increase of Fe content. The decrease in the binding energy increased the activity in the oxygen reduction, but the decrease of ${\alpha}$-species with the increase of Fe content decreased the activity. The increase in the surface area with Fe content had little effect on the activity.

• Journal of Dental Rehabilitation and Applied Science
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• v.28 no.2
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• pp.119-126
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• 2012

State of problem: Cement-retained implant-supported prostheses are routinely used in dentistry. The use of high strength cements has become more popular with the increasing confidence in the stability of the implant-abutment screw connection and the high survival rates of osseointegrated implants. No clinical data on retention of metal copings using CAD/CAM. To evaluate retention of metal copings using CAD/CAM system bonded to short titanium abutment with four different cements and compare retentive strength of metal copings with sandblasting or without sandblasting before cementation. Forty titanium abutment blocks were fabricated and divided into 4 groups of 10 samples each. Forty metal copings with occlusal hole to allow for retention testing were fabricated using CAD/CAM technology. The four cements were Fujicem(Fuji, Japan), Maxcem Elite(Kerr, USA), Panavia F2.0(Kurarary, Japan) and Superbond C&B(Sunmedical, Japan). The copings were cemented on the titanium abutment according to manufacture's recommendation. All samples were stored for 24h at 37oC in 100% humidity and tested for retention using universal testing machine(Instron) at a crosshead speed of 1.0mm/min. Force at retentive failure was recorded in Newton. The mode of failure was also recorded. Means and standard deviations of loads at failure were analyzed using ANOVA and Paired t-test. Statistical significance was set at P<0.05. Panavia F2.0 provided significantly higher retentive strength than Fujicem, Maxcem Elite(P<0.05). Sandblasting significantly increased bond strength(P<0.05). The mode of failure was cement remaining principally on metal copings. Within the limitation of this study, Panavia F2.0 showed significantly stronger retentive strength than Fujicem, Maxcem Elite(p<0.05). The Ranking order of the cements to retain the copings was Panavia F2.0, Fujicem = Maxcem Elite. Sandblasting significantly increased bond strength(P<0.05). The retentive strength of metal copings on implant abutment were influenced by surface roughness and type of cements.

• Korean Journal of Agricultural Science
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• v.12 no.1
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• pp.75-85
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• 1985

This study is intended to find out the influence of Lignosulfonic Acid Type Admixture on compressive, tensile, flexural strength and dispersing action of mortar, and fixation of by-product of pulp industry. 1. The more Pozzolith-84 is added, the larger flow value is. The admixture of lignosulfonic acid type adhere to cement particles and the surface potential of particles is generated. On account of the repulsion among the cement particles, they are dispersed and the mortar get workable, so the production cost of precast product is curtailed and the amount of cement is reduced in a certain workability of mortar. 2. The strength of mortar is greater than plain mortar when P/C added is 0.2 and 0.4%. As time passed the potential energy is reduced and the distance of particles which lignosulfonic acid adhered to get near according as the amount of adhesion is increased. The setting and hardening reaction of morter is occurred in close state, so the strength of mortar is increased a little. The strength of mortar is less than plain mortar when amount P/C added is 0.8%. Pozzolith-84 is mainly composed of lignosulfonic acid and lignin does not influence the hardening of mortar, therefore the remained $SO_3$, $SO_3H$ are the reason of decrease of strength. 3. There is high significance between specific gravity and compressive strength. The larger specific gravity is, the more compressive strength is increased. There is high significance between 7 day's strength and 28 day's strength. The larger compressive strength is, the more tensile and flexural strength are increased. 4. Since Pozzolith-84 is a by-product of pulp industry, by using the Pozzolith-84 admixture the concreate quality is improved. The water pollusion is reduced according to fix by-products in concrete structure.

• Korean Journal of Materials Research
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• v.8 no.12
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• pp.1158-1164
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• 1998

Aluminium sulfate solution was prepared by sulfuric acid treatment from gibbsite. Aluminium sulfate hydrate [$Al_2(SO_4)_3$ · $nH_2O$] was precipitated from aluminium sulfate solution by adding it into ethylalcohol. From XRD analysis as-prepared $Al_2(SO_4)_3$ · $nH_2O$ was confirmed to have mixed-crystalization water(n=18, 16, 12, 6). The average water of crystalization calculated from thermogravimetry(TG) was 14.7. Aluminium sulfate hydrate [$Al_2(SO_4)_3$ · $nH_2O$] was thermally decomposed and converted to $Al_2(SO_4)_3$ at $800^{\circ}C$, $\gamma-Al_2O_3$ at $900-1000^{\circ}C$, and $\alpha-Al_2O_3$ at $1200^{\circ}C$. Ni-doped $\gamma-Al_2O_3$, was synthesized from the slurry of as-prepared $\gamma-Al_2O_3$, with the ratio of [Ni]/[Al]=0.5. The reaction conditions of synthesis were determined as initial pH 9.0 and temperature $80^{\circ}C$ The basicity(pH) of slurry was controlled by using urea and $NH_4OH$ solution. Urea was also used for deposition-precipitation. For determining termination of reaction, the data acquisition was performed by oxidation reduction potential(ORP), conductivity and pH value in the process of reaction. Termination of the reaction was decided by observing the reaction steps and rapid decrease in conductivity. On the other hand, BET(Brunauer, Emmett and Teller) and thermal diffusity of Ni- doped $\gamma-Al_2O_3$, with various content of Ni were measured and compared. Thermal stability of Ni- doped $\gamma-Al_2O_3$ at $1250^{\circ}C$ was confirmed from BET and XRD analysis. The surface state of Ni-doped $\gamma-Al_2O_3$ was investigated by X-ray photoelectron spectroscopy(XPS). The binding energy at $Ni2P_{3/2}$ increased with increasing the formation of $NiAl_2O_4$ phase.

• Journal of Korea Water Resources Association
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• v.41 no.12
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• pp.1219-1230
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• 2008

Stream inflows induced by flood runoffs have a higher density than the ambient reservoir water because of a lower water temperature and elevated suspended sediment(SS) concentration. As the propagation of density currents that formed by density difference between inflow and ambient water affects reservoir water quality and ecosystem, an understanding of reservoir density current is essential for an optimization of filed monitoring, analysis and forecast of SS and nutrient transport, and their proper management and control. This study was aimed to quantify the characteristics of inflow density current including plunge depth($d_p$) and distance($X_p$), separation depth($d_s$), interflow thickness($h_i$), arrival time to dam($t_a$), reduction ratio(${\beta}$) of SS contained stream inflow for different flood magnitude in Daecheong Reservoir with a validated two-dimensional(2D) numerical model. 10 different flood scenarios corresponding to inflow densimetric Froude number($Fr_i$) range from 0.920 to 9.205 were set up based on the hydrograph obtained from June 13 to July 3, 2004. A fully developed stratification condition was assumed as an initial water temperature profile. Higher $Fr_i$(inertia-to-buoyancy ratio) resulted in a greater $d_p,\;X_p,\;d_s,\;h_i$, and faster propagation of interflow, while the effect of reservoir geometry on these characteristics was significant. The Hebbert equation that estimates $d_p$ assuming steady-state flow condition with triangular cross section substantially over-estimated the $d_p$ because it does not consider the spatial variation of reservoir geometry and water surface changes during flood events. The ${\beta}$ values between inflow and dam sites were decreased as $Fr_i$ increased, but reversed after $Fr_i$>9.0 because of turbulent mixing effect. The results provides a practical and effective prediction measures for reservoir operators to first capture the behavior of turbidity inflow.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.16 no.2
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• pp.59-67
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• 1983

An experiment on the rearing of tilapia stocked in closed recirculating tanks eliminating biological filter beds was carried out at the Fish Culture Experiment Station of the National Fisheries University of Pusan, from May 18 through October 21, 1982, and the growth rates, feed conversion, water quality, spawning prevention and space utilization efficiency were discussed. Finally discussed is the feasibility on the establishment of commercial production units. On the water quality, the water temperature ranged from $22.8^{\circ}C\;to\;29.1^{\circ}C$, and total ammonia arround 10 ppm or slightly up. Maintaining phytoplankton bloom was not successful probably because of the active consumption by the heavily stocked tilapia. Several attempts were made by changing the culture water with green water from a nearby earthen pond with results of fading-away in a couple of days. Feed conversions were relatively high ranging from 0.9 to 1.2 except for experiment 1 when the fish were not fully recovered from weakened wintering state. The feed used was partly laboratory prepared $25\%$ protein diet and mostly commercially available $39\%$ protein carp feed. Spawning was completely controlled during the experiment, resulting from density effect, which ranged from 10kg to 40.7kg per square meter with water depth of 0.5 to 0.6m. Space utilization efficiency was very high. Daily net production from the experiment division 3, which showed the highest result, was 6.206 kg per tank, which is calculated 3,235 metric tons per hectare per year, This time, water temperature ranged from 27.8 to $29.1^{circ}C$, average being $28.4^{circ}C$, and total ammonia arround 10 ppm. An estimation for the commercial set-up of the production system based on the results of experiment divisions which had initial stocking rate $15\;kg/m^2$ or up, is made. If the total facility, 8 tanks comprising $56\;m^2$ in surface area, is used for the present study, the yield would become 5,639 kg from 200 day rearing, which would be possible under double sheets vinyl house without additional heating, and it is thought feasible in the economic view point, when 10 or more units are operated.