• Journal of the Korean GEO-environmental Society
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• v.11 no.8
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• pp.33-40
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• 2010

In this study, evaluation of basic unit of non-point pollutant, which is fundamental evaluation of non-point loading, was conducted using both road point and angle of intersection point in Maesong area, West coast highway by utilizing Event Mean Concentrations(EMC). Concentration of pollutants except heavy metals at these two points rapidly decreased in 30 minutes after start of runoff. According to the results of EMC, for both sampling points, it was determined that the concentrations of TSS(Total Suspended Solid), $BOD_5$(Biological Oxygen Demand), and DOC(Dissolved Organic Carbon) were higher than those of wastewater effluent standard in Korea, however, the concentrations of T-N(Total Nitrogen) and T-P(Total Phosphorus) were lower than those of the standard. In terms of heavy metals, Fe, Pb, and Zn showed higher concentrations than others. When compared with the units established by the Ministry of Environment in Korea, the basic units of $BOD_5$ and T-N in this study were lower. On the other hand, when compared with foreign units, Cu, Pb, and Zn showed approximately 10 times higher concentrations. It was estimated that a long term monitoring should be conducted for obtaining additional data and more reliable basic units for the non-point pollutnats based on the results from this study.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.7
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• pp.779-785
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• 2015

Cathodic protection is recognized as the most cost-effective and technically appropriate corrosion prevention method for the submerged zone of offshore structures, ships, and deep-sea facilities. When cathodic protection is applied, the cathodic currents cause dissolved oxygen reduction, generating hydroxyl ions near the polarized surface that increase the interfacial pH and result in enhanced carbonate ion concentration and precipitation of an inorganic layer whose principal component is calcium carbonate. Depending on the potential, magnesium hydroxide can also precipitate. This mixed deposit is generally called "calcareous deposit." This layer functions as a barrier against the corrosive environment, leading to a decrease in current demand. Hence, the importance of calcareous deposits for the effective, efficient operation of marine cathodic protection systems is recognized by engineers and scientists concerned with cathodic protection in submerged marine environments. Calcareous deposit formation on a marine structure depends on the potential, current, pH, temperature, pressure, sea-water chemistry, flow, and time; deposit quality is significantly influenced by these factors. This study determines how calcareous deposits form in sea water, and assesses the interrelationship of formation conditions (such as the sea water temperature and surface condition of steel), deposited structure, and properties and the effectiveness of the cathodic protection.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.17 no.2
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• pp.83-91
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• 1984

The formation and structure of tidal front in the eastern part of the Yellow Sea were studied based on the oceanographic data compiled during the periods of $1982{\sim}1983$ and $1966{\sim}1970$. Well-defined fronts occurring in the Yellow Sea in summer mark the boundary between the stratified and vertically mixed regimes. The occurrence of vertically mixed regimes may be interpreted in terms of available turbulent kinematic energy of tidal currents. The tidal frontal regions were determined by horizontal gradients of temperature, salinity and dissolved oxygen, and were verified by water colour and transparency. In summer the tidal fronts were found at depths of $15{\sim}25m$ at about 20 miles from the shore. Potential energy of vortical stratification in the tidal frontal region was 10 $Joule/m^3$. The stratification parameter in the frontal region computed from the numerical tidal model was $S_p=1.0.$ Tidal front is formed in regions with $S_p=1-1.5,$ if surface heat flux are constant. Waters in the stratified region have the layer structures of wind-mixed surface layer, thermocline and tidal-mixed bottom layer. In the vertically mixed region, however, sea water is nearly homogeneous. in winter no distinctive tidal front was seen.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.33 no.3
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• pp.262-271
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• 2000

This study was carried out to clarify the spatial and temporal patterns of benthic environments and macrobenthos on the subtidal soft-bottom in Chonsu Bay. Seasonal surface water temperature was similar to the bottom layer, but freshwater discharges into the outlets dereased the surface salinity around the dyke in summer. Bottom dissolved oxygen was decreased deeply around the dyke and created the de-oxygenated layer during summer. Sediment grain size was consisted of finer at the neighboring of the dyke than the mouth of the bay. Organic matters including the sediment were decreased at the mouth of the bay. A total of 311 species ($769\;ind./m^2$) were identified. Polychaetes were the most abundant faunal group in the number of species and densities. The number of species revealed the spatial patterns that it was higher in the mouth of the bay, and their densities showed seasonal changes by mass recruitment occurred at the most of the area in summer, At this time, opportunistic species, Lumbrineris iongifolia and Theora fragilis, were also recruited massively. Chonsu Bay were classified into five station groups by the cluster analysis. The dominant species around the dyke were composed to opportunistic species, those in middle area were Sternaspis scutata, Paraplionospio pinnata, and those in the mouth of the bay were Mediomastus californiensis, Nephtys polybranchia. Seasonal fluctuations and spatial difference of environments seem to have influenced to the species compositions and affected to the stability of benthic ecosystems spatial-temporally In Chonsu nay.

• Asian-Australasian Journal of Animal Sciences
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• v.28 no.6
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• pp.896-902
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• 2015

Milking center wastewater (MCW) has a relatively low ratio of carbon to nitrogen (C/N ratio), which should be separately managed from livestock manure due to the negative impacts of manure nutrients and harmful effects on down-stream in the livestock manure process with respect to the microbial growth. Simultaneous nitrification and denitrification (SND) is linked to inhibition of the second nitrification and reduces around 40% of the carbonaceous energy available for denitrification. Thus, this study was conducted to find the optimal operational conditions for the treatment of MCW using an attached-growth biofilm reactor; i.e., nitrogen loading rate (NLR) of 0.14, 0.28, 0.43, and $0.58kg\;m^{-3}\;d^{-1}$ and aeration rate of 0.06, 0.12, and $0.24\;m^3\;h^{-1}$ were evaluated and the comparison of air-diffuser position between one-third and bottom of the reactor was conducted. Four sand packed-bed reactors with the effective volume of 2.5 L were prepared and initially an air-diffuser was placed at one third from the bottom of the reactor. After the adaptation period of 2 weeks, SND was observed at all four reactors and the optimal NLR of $0.45kg\;m^{-3}\;d^{-1}$ was found as a threshold value to obtain higher nitrogen removal efficiency. Dissolved oxygen (DO) as one of key operational conditions was measured during the experiment and the reactor with an aeration rate of $0.12\;m^3\;h^{-1}$ showed the best performance of $NH_4-N$ removal and the higher total nitrogen removal efficiency through SND with appropriate DO level of ${\sim}0.5\;mg\;DO\;L^{-1}$. The air-diffuser position at one third from the bottom of the reactor resulted in better nitrogen removal than at the bottom position. Consequently, nitrogen in MCW with a low C/N ratio of 2.15 was successfully removed without the addition of external carbon sources.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.3
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• pp.230-237
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• 2017

In this study, electrochemical methods were used to determine the optimum protection potential of S355ML steel for the cathodic protection of offshore wind-turbine-tower substructures. The results of potentiodynamic polarization experiments indicated that the anodic polarization curve did not represent a passivation behavior, while under the cathodic polarization concentration, polarization was observed due to the reduction of dissolved oxygen, followed by activation polarization by hydrogen evolution as the potential shifted towards the active direction. The concentration polarization region was found to be located between approximately -0.72 V and -1.0 V, and this potential range is considered to be the potential range for cathodic protection using the impressed current cathodic protection method. The results of the potentiostatic experiments at various potentials revealed that varying current density tended to become stable with time. Surface characterization after the potentiostatic experiment for 1200 s, by using a scanning electron microscope and a 3D analysis microscope confirmed that corrosion damage occurred as a result of anodic dissolution under an anodic polarization potential range of 0 to -0.50 V, which corresponds to anodic polarization. Under potentials corresponding to cathodic polarization, however, a relatively intact surface was observed with the formation of calcareous deposits. As a result, the potential range between -0.8 V and -1.0 V, which corresponds to the concentration polarization region, was determined to be the optimum potential region for impressed current cathodic protection of S355ML steel.

• Journal of Wetlands Research
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• v.19 no.1
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• pp.69-79
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• 2017

Protected area of water for supply source is located mostly of rural area in Korea. Normally, sewage treatment system is poor to manage in rural, because low population and density. Rural area need sewage treatment system to supervise supply source of water. In this study, analysis on operation result of 4 RCSTP and MWTP is located at the rural area. Higher concentration of pollutant were inflows to MWTP than RCSTP, and effluent quality standard is satisfaction. However, RCSTP effluent pollutant concentrations was researched higher than MWTP. The organic matter(BOD, COD) were about 5% of a high treatment efficiency to a median. The nutrient(T-N, T-P) were detected Up to high 30%. Also, we analyzed to effect reactor operational parameters on the pollutant treatment efficiency like mixed liquer suspended solid(MLSS), dissolved oxygen(DO) and sludge retention time(SRT). As a result, pollutant treatment efficiency showed fluctuation in accordance with operating condition. Thus, it is necessary to manage the reactor operation condition for management of rural area sewage treatment.

• Journal of Surface Science and Engineering
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• v.51 no.2
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• pp.95-103
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• 2018

Recently, many types of constructional steels have been often exposed to under severe corrosive environments due to acid rain with increasing environmental contamination. In order to inhibit their corrosion in severe corrosive environments, a painting method has been widely applied to numerous constructional steels of land as well as marine. Therefore, development of paint having a good quality of corrosion resistance is considered to be very important. In this study, four types of anti-corrosive paints (AP: Phenol epoxy, AC: Ceramic epoxy, AT: Coal tar epoxy, AH: High solid epoxy) were coated to the specimens, and then, were immerged in various salt solutions (0.1, 0.3, 3, 6, 9 and 15% NaCl solutions) for 11 days. And, the corrosion resistance of these samples by effect of osmotic pressure with salt concentration was investigated with electrochemical methods such as measurement of corrosion potential, impedance and corrosion current density. The corrosion current densities of all samples (AC, AT and AH) submerged in 3% NaCl solution exhibited the smallest values compared to other salt solutions. However, in the case of lower values of salt solutions than 3% NaCl solution, the corrosion current density increased again because it makes easier for water, dissolved oxygen and chloride ion etc. to invade toward inner side of coating film due to increasing of the osmotic pressure than 3% NaCl solution, but in the case of higher values of salt solutions than 3% NaCl solution, the coating film is easily deteriorated due to high concentration of chloride ion rather than the osmotic pressure, which resulted in increasing the corrosion current density. In particular, the AC sample indicated the best corrosion resistance in 6% NaCl solution compared to other samples. Consequently, it is considered that the corrosion mechanism of the coated steel plate is completely different from bare steel plate, and the corrosion resistance of coating film by osmotic pressure and chloride ion depend on various types of epoxy of paint in NaCl solution.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.2
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• pp.120-131
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• 2011

A pilot-scale experiment of floodplain filtration with a filtration depth of 3.6m was performed employing flood/rest type raw-water supply system in an effort to find ways to improve river water quality by additional treatments of discharged effluent from sewage treatment plant. Soil samples were taken from 3 sites including Gumi, Daegu and Gimhae along the Nakdong river. Reductions of infiltration rates following increases in operating time was investigated in each soil sample, along with the analysis of removal efficiencies of various pollutants according to different depths and infiltration rates. The results show incremental development of clogging on the soil surface with increases in operation time, and illustrate exponential decrease in the infiltration rate. The time required for the removal of the clog from the soil surface was longer than 2 weeks for all soil samples analyzed. The stable infiltration rates for soils were 5 m/day for Gumi and for Daegu and Gimhae was 1 m/day. In unsaturated soils dissolved oxygen levels increased following the increase of filtration depth, suggesting that alternating application of flood and rest for raw-water supply effectively keeps the soil environment aerobic. For all soils, the nature of pollutant removal depending on the depth of filtration remained the same regardless of the infiltration rate. Most of the BOD and turbidity were removed within 1.2 m, about 30% of COD was removed within 3.6m and was expected to be removed further with increases in filtration depth. Nitrification occurred near the surface of all soils; however there was no significant removal of nitrogen in the filtration depths tested in this study. Although removal rate of phosphorus was low for Gumi's soil, it was high enough for other soils, suggesting that the method developed in this study could significantly improve river water quality.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.4
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• pp.184-192
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• 2016

A profiling monitoring system has been developed to monitor the water quality variations according to each water depth and applied for a test-bed. The key parameters were derived to disclose the aquatic ecology and environment of river systems, and the real-time monitoring techniques to profile the variations of each parameter were verified. Monitoring parameters were configured to include water quality, hydrodynamic, and weather conditions. Considering the water depth of the 4 major rivers in Korea, a profiling monitoring system with 1.0 m water depth interval for each monitoring has been established. To understand the real-time variation properties in the Han river, the monitoring system has been installed and operated at the YangHwa-Dock as a test-bed. Based on the results of the detailed analyses on the spring season, as the characteristic diurnal and water-depth-related variations for water temperature, pH, dissolved oxygen (DO), and chlorophyll-a were observed, it could be concluded that the real-time water-depth profiling monitoring system is a very effective tool for the proper management of river environment.