• Korean Journal of Metals and Materials
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• v.49 no.1
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• pp.9-16
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• 2011

To develop a 6061 aluminum alloy with low residual stress and high tensile strength, a cryogenic treatment process was investigated. Compared to the conventional heat treatment process for precipitation hardening with artificial aging, the cryogenic treatment process has two additional steps. The first step is cryogenic quenching of the sample into liquid nitrogen, the second step is up-hill quenching of the sample into boiling water. The residual stress for the sample was measured by the $sin^2{\psi}$ method with X-ray diffraction. The 6061 aluminum alloy sample showed 67% relief in stress at the cryogenic treatment process with artificial aging at $175^{\circ}C$. From this study, it was found that the optimum cryogenic treatment process for a sample with low residual stress and high tensile strength is relatively low cooling speed in the cryogenic quenching step and a very high heating speed in the up-hill quenching step.

• Korean Journal of Environmental Agriculture
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• v.23 no.1
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• pp.7-14
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• 2004

This study was conducted to investigate the effect on agricultural environment and crop productivity by different amount of applied fertilizer in consideration of irrigation water quality. N, P and K contents of irrigation water used in this experiment were 6.16, 0.26 and 9.37 mg/L, respectively. N, P and K Concentrations of runoff water were lower than those of inflow water during rice cultivation. N, P and K Concentrations of ponded and percolated water were changed according to the amount and time of applied fertilization. During rice cultivation in paddy soil, nitrogen balance was closed to 0 in SFT 50% (50% level of soil testing fertilization), 0.14 kg/ha, but it was 95.3 kg/ha in CF (conventional fertilization) treatment In SW 50% and STF (soil testing fertilization) treatment yield of perfect rice was not greatly different as compared with CF treatment due to the superiority of ripening rate, 1,000 grains weight and milling characteristics. Mechanical paratability of rice was excellent in NF (non fertilization) treatment, STF 50% treatment showed higher in nutrient availability and fertilizers use efficiency than other treatments.

• Environmental Engineering Research
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• v.16 no.4
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• pp.205-212
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• 2011

Reverse osmosis (RO) technology has developed over the past 40 years to control a 44% market share in the world desalting production capacity and an 80% share in the total number of desalination plants installed worldwide. The application of conventional and low-pressure membrane pretreatment processes to seawater RO (SWRO) desalination has undergone accelerated development over the past decade. Reliable pretreatment techniques are required for the successful operation of SWRO processes, since a major issue is membrane fouling associated with particulate matter/colloids, organic/inorganic compounds, and biological growth. While conventional pretreatment processes such as coagulation and granular media filtration have been widely used for SWRO, there has been an increased tendency toward the use of ultrafiltration/microfiltration (UF/MF) instead of conventional treatment techniques. The literature shows that both the conventional and the UF/MF membrane pretreatment processes have different advantages and disadvantages. This review suggests that, depending on the feed water quality conditions, the suitable integration of multiple pretreatment processes may be considered valid since this would utilize the benefits of each separate pretreatment.

• Magazine of the Korean Society of Agricultural Engineers
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• v.17 no.1
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• pp.3627-3641
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• 1975

The Government is trying to increase total food grain yield to meet national self sufficiency by means of increasing unit yield as well as extending crop land, and this year he set the target of 321,000 hectare of forest to clear for cropping. This study was carried to investigate the most efficient method of clearing hillock by bulldozer, and successful method to develope yielding potential of newly cleared land in short term. Since the conventional land clearing method is just earth leveling and root removing neglecting top soil treatment, the growth of crop was poor and farmer tends not to care the land. The top-soil-furrowing method is applied through out this study, that is advantageous especially for the land having shallow top soil and low fertility like Korean forest. In this study, various operating method were tried to find out most efficient method separately in connection with the land slope less than 25 percent and over, and several fertilizing methods to develop yielding potential. The results are as follows; 1) For the natural land slope utilization method, applicable to the land having less than 25 percent slope, reverse operating was more efficient than using forward gear of bulldozer. The operating time was 3 hour 32 minutes and 36 seconds using forward gear was 2 hour 32 minutes and 30 seconds for reverse gear operation per 1,000 square meter. 2) Bulldozer having angle blade adjustment needed 7hr 15min. for constructing of terrace per 10a compaire with the one having angle & tilt adjustment needed 6hr 4min for same operations. Specially there is significant difference for operation time of first period (earth cutting) such as bulldozer having angle blade adjustment needed 3hr 56min compaired with the one having angle & tilt adjustment 3hr 59min. In construction of terrace, the bull-dozer having tilting and angle blade adjustment was most suitable and performed efficiently. 3) For the fertilizer application treatment, the grass (Ladino clover) yield in first year was almost same as ordinary field's in the plot applied(N.P.K+lime+manure) while none fertilizer plot showed one tenth of it, and (N.P.K.+lime) applied plot yielded on third. 4) The effect of different land clearing method to yield showed significant difference between each treatment especially in the first year, and the conventional method was the lowest. In the second year, still conventional terracing plot yielded only half of ordinary field while the other plots showed as same as ordinary field's. 5) The downward top soil treatment plot showed most rapid improvement in soil structure during one year physio chemically, it showed increase in pH rate and organic composition, and the soil changed gradually from loam to sand-loam and the moisture content increased against the pF rate, and it gives good condition to grow hay due to the increase of field water capacity with higher available water content. 6) Since the soil of tested area was granite, the rate of soil errosion was increased about 2 to 5 percent influencing in soil structure more sand reducing clay content, and an optimum contour farming method should be prepared as a counter measure of errosion.

• Journal of Korean Society of Water and Wastewater
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• v.25 no.2
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• pp.193-199
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• 2011

A method to improve internal corrosion control efficiency by adding lime and carbon dioxide, which, in turn increases the Langelier Index (LI) for filtered water at a conventional drinking water treatment plant (WTP) was investigated. The SJ WTP (Q=100,000 $m^{3}$/d) has been operating an internal corrosion control system since 2006. The system has achieved stable operation through technical development and trial and error over a period of several years. As a result of the operation, the LI of treated water has increased up to 29% by adjusting pH of filtered water to 7.8 with the addition of lime and carbon dioxide. Coupon tests in the distribution system indicated that the corrosion rate has been delayed by 24% when the internal corrosion method was implemented. The increase of LI by lime and carbon dioxide has been proven to be a practical method for controlling corrosion.

• Membrane and Water Treatment
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• v.3 no.4
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• pp.221-230
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• 2012

This study employed the modified fouling index (MFI) to determine the performance of a two-step recycling system - a membrane filtration integrated laminar flow water storage (LFWS) tank followed by an ion exchange process to reclaim ultrapure water (UPW) from the wastewater generated from semiconductor wafer backgrinding and sawing processes. The first step consisted of the utilization of either ultrafiltration (UF) or nanofiltration (NF) membranes to remove solids in the wastewater where the second step consisted of an ion exchanger to further purify the filtrate. The system was able to produce high purity water in a continuous operating mode. However, higher recycling cost could be incurred due to membrane fouling. The feed wastewater used for this study contained high concentration of fine particles with low organic and ionic contents, hence membrane fouling was mainly attributed to particulate deposition and cake formation. Based on the MFI results, a LFWS tank that was equipped with a turbulence reducer with a pair of auto-valves was developed and found effective in minimizing fouling by discharging concentrated wastewater prior to any membrane filtration. By comparing flux behaviors of the improved system with the conventional system, the former maintained a high flux than the latter at the end of the experiment.

• Journal of Preventive Medicine and Public Health
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• v.5 no.1
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• pp.43-48
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• 1972

5 bed sand filter, applying biological oxidation, was designed and studied on the treatment of water works. Never using any coagulant agent (drugs), which may cause water pollution in pre-treatment of head water, the auther attempt a high rate filtration by the microorganism (nitrofication bacteria) end plant which populate in multi layer sand beds. The result are as follows : In order to evaluate the oxygen effect on filtration, oxygen was injected in aeration tank attached to each filter tank while filtration, and $NH_3$ was tested as a representaiive ingredient. It was found out that the aeration method was more effective, with over 33% of $NH_3$ removal capacity, than the anerobic and this 5 bed filter showed double removal capacity of $NH_3$ by comparing with conventional sand bed (2 stage bed). According to the examination of two kind of head water, pre-treated with coagulant agent and activated carton, the filtration capacity was affected by the polluted condition of head water, resulting that lower value of pollution and slower velocity of filtration showed more efficiency of $NH_3$ removal. In this experiment $NH_3$ content tested in treated water had a fairly good correlation with others.

• Journal of Korean Society of Water and Wastewater
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• v.30 no.5
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• pp.511-519
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• 2016

Shale gas has become increasingly important as a viable alternative to conventional gas resources. However, one of the critical issues in the development of shale gas is the generation of produced water, which contains high concentration of ionic compounds (> TDS of 100,000 mg/L). Accordingly, membrane distillation (MD) was considered to treat such produced water. Experiments were carried out using a laboratory-scale direct contact MD (DCMD). Synthetic produced water was prepared to examine its fouling propensity in MD process. Antiscalants and in-line filtration were applied to control fouling by scale formation. Fouling rates (-dJ/dt) were calculated for in-depth analysis of fouling behaviors. Results showed that severe fouling occurred during the treatment of high range produced water (TDS of 308 g/L). Application of antiscalant was not effective to retard scale formation. On the other hand, in-line filtration increased the induction time and reduced fouling.

• Journal of Environmental Health Sciences
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• v.29 no.1
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• pp.51-61
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• 2003

Pollution purification using titanium dioxide (TiO$_2$) photocatalyst has attracted a great deal of attention with increasing number of relent environmental problems. Currently, the application of TiO$_2$ photocatalyst has been focused on purification and treatment of waste water. However. the use of conventional TiO$_2$ powder photocatalyst results in disadvantage of stirring during the reaction and of separation after the reaction. And the usage of artificial UV lamp has made the cost of photocatalyst treatment system high. Consequently, we herein studied the pilot-scale design to aid in optimization of the energy-saving process for more through development and reactor design by solar light/UV lamp/ TiO$_2$system. In this study, we manufactured the TiO$_2$sol by sol-gel method. According to analysis by XRD, SEM and TEM, characterization of TiO$_2$ sol were nano-size (5-6 nm) and anatase type. Inorganic binder (SiO$_2$) was added to TiO$_2$ lot to be coated for support strongly, and support of ceramic bead was used to lower separation rate that of glass bead The influences were studied of various experimental parameters such as TiO$_2$ quantity, pH, flow rate. additives, pollutants concentration, climate condition and reflection plate by means of reaction time of the main chararteristics of the obtained materials. In water treatment system, variable realtor as solar light/ or UV lamp according to climate condition such as sunny and cloudy days treated the phenol and E-coli(Escherichia coli) effectively.

• Journal of Korean Society of Water and Wastewater
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• v.13 no.1
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• pp.61-71
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• 1999

For a high-rate fermentation and recovery of organic acid, we have developed a new organic acid fermentation reactor with membrane filter, which is the most important part in the new advanced wastewater treatment system. The recovered organic acid is to be reused as an organic carbon source at denitrification process. Some experiments were conducted to compare the performance of acid fermentation at different SRTs, such as 5, 10, and 20 days. The total organic acid concentration produced during the runs was in the range of 2,100-2,900 (mgC/L). The conversion efficiency from substrate to organic acid reached to from 43% to 59%. The recovery rate of organic acid from substrate based on TOC was from 26% to 53%. Regardless of operational conditions, it has been able to maintain the membrane flux constantly, in the range of 0.4-0.46 ($m^3/m^2/day$). The transmembrane pressure drop was 0.2-0.3 (kg/cm) for 100 day's operation. The result of simulation is as follows. Organic removal efficiency of the new advanced treatment system is 95%. 73% of Nitrogen is removed. The removal efficiency of Phosphorus is 93%. By coqulation, soluble phosphorus is able to remove from the water treatment lines, which is impossible at conventional activated sludge system. The unit construction cost is 65000 (yen/m3) and it was 1.4 times than that of the standard activated sludge system. The unit operation cast is 7.7 ($yen/m^3/day$) and it was 1.3 times than that of the standard activated sludge system.