• Journal of the Korea Organic Resources Recycling Association
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• v.30 no.4
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• pp.5-13
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• 2022

The current environmental problem is that environmental pollution is accelerating due to the generation of large amounts of waste and indiscriminate consumption of energy. Fossil fuels, a representative energy production fuel, are burned in the process of producing energy, generating a large amount of greenhouse gases and eventually causing climate change. In addition, the amount of waste generated worldwide is continuously increasing, and environmental pollution is occurring in the process of waste treatment. One of the methods for simultaneously solving these problems is the energy recovery from and reduction of organic wastes. Sewage sludge generated in sewage treatment plants has been treated in various ways since ocean disposal was completely prohibited, but the amount generated has been continuously increasing. Since the sewage sludge contains a large amount of organic materials, it is desirable to recover energy from the sewage sludge and reduce the final discharged waste through anaerobic digestion. However, most of the excess sludge is a mass of microorganisms used in sewage treatment, and in order for the excess sludge to be anaerobically digested, the cell walls of the microorganisms must be destroyed first, but it takes a lot of time to destroy the cell walls, so high rates of biogas production and waste reduction cannot be achieved only by anaerobic digestion. Therefore, the pre-treatment process of solubilizing excess sludge is required, and the thermal solubilization process is verified to be the most efficient among various solubilization methods, and high rates of biogas production and waste reduction can be achieved by anaerobic digestion after destroying cell walls the thermal solubilization process. In this study, when pretreating TS 10% thickened excess sludge through a thermal solubilization system, a study was conducted on solubilization characteristics according to retention time and operating temperature variables. The experimental variables for the retention time of the thermal solubilization system were 30 minutes, 60 minutes, 90 minutes, and 120 minutes, respectively, while the operating temperature was fixed at 160℃. The soulbilization rates calculated through TCOD and SCOD derived from the experimental results increased in the order of 12.11%, 20.52%, 28.62%, and 31.40%, respectively. And the variables according to operating temperature were 120℃, 140℃, 160℃, 180℃, and 200℃, respectively, while the operating retention time was fixed at 60 minutes. And the solubilization rates increased in the order of 7.14%, 14.52%, 20.52%, 40.72%, and 57.85%, respectively. In addition, TS, VS, T-N, T-P, NH₄⁺-N, and VFAs were analyzed to evaluate thermal solubilization characteristics of thickened excess sludge. As a result, in order to obtain 30% or more solubilization rate through thermal solubilization of TS 10% thickened excess sludge, 120 minutes of retention time is required when the operating temperature is fixed to 160℃, and 170℃ or more of operating temperature is needed when the operating time is fixed to 60 minutes.

• Solar Energy
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• v.10 no.3
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• pp.3-12
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• 1990

This paper deals with experimental research to increase thermal storage efficiency of hot water stored in an actual storage tank for solar application. The effect of increased energy input rate due to stratification has been discussed and illustrated through experimental data, which was taken by changing dynamic and geometric parameters. Ranges of the parameters were defined for flow rate, the ratio of diameter to height of the tank and inlet-exit water temperature difference. During the heat storage, when the flow was lower, the temperature difference was larger and the ratio of diameter to height of the tank was higher, the momentum exchange decreased. As for this experiment, when the flow rate was 8 liter/min, the temperature difference was $30^{\circ}C$ and the ratio of diameter to height of the tank was 3, the momentum exchange was minimized resulting in a good thermocline and a stable stratification. In the case of using inlet ports, if the modified Richardson number was less than 0.004, full mixing occured and so unstable stratification occured, which mean that this could not be recommended as storage through thermal stratification. Using a distributor was better than using inlet ports to form a sharp thermocline and to enhance the stratification. It was possible to get storage efficiency of 95% by using the distributor, which was higher than a storage efficiency of 85% obtained by using inlet ports in same operation condition. Furthermore, if the distributor was manufactured so that the mainpipe decreases in diameter toward the dead end to maintain constant static pressure, it might be predicted that further stable stratification and higher storage efficiency are obtainable(ie:more than 95%).

• Journal of the Korea Organic Resources Recycling Association
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• v.16 no.2
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• pp.29-37
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• 2008

In this work, it was investigated that various aspects of process, application situation, merits and short-coming results of the thermophilic methane fermentation with highly concentrated organic waste substances such as sewage sludges, food wastes and excretions. The merits of this methane fermentation were that it had a very fast reaction rate and was possible to proceed in high loads. It was also high in mortality for pathogenic microorganism and the digested sludge was more hygienic. However, the short-comings were that more energy was required for heating in the fermentation facility, no surplus energy could be gained from low concentration of organic waste, the fermentation treatment dropped level of water quality, thus burdens discharging process of water. Especially, the high concentration of methane fermentation could possibly lack nutritious salt and could face the disturbance by ${NH_4}^+-N$, a proper alternative was required. In general, thermophilic methane fermentation was considered as a better mean in disposing of cow excretion and food waste which were highly concentrated organic wastes. On the other hand, under the condition where the concentration of waste material was low and the high concentrate waste material became higher than 3,000 mg/L in ${NH_4}^+-N$, thermophilic methane fermentation resulted less desirable outcome.

• Journal of the Korean Society for Marine Environment & Energy
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• v.19 no.1
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• pp.7-17
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• 2016

The present study experimentally considers dynamic performance of large floating wave-offshore hybrid power generation platform in extreme conditions. In order to evaluate the motion performance of the large floating hybrid power generation platform, 1/50 scaled model was manufactured. A mooring line was also manufactured, and free-decay and static pull-out tests were carried out to check the mooring model. A mooring line table was introduced to satisfy the water depth, and environmental conditions were checked. Motion responses in regular waves were measured and complicated environmental conditions including wave, wind, and current were applied to see the dynamic performance in extreme/survival conditions. Maximum motion and acceleration were judged following the design criteria, and maximum offset and mooring tension were also checked based on the rule. The characteristics of hybrid power generation platform are discussed based on these data.

• Journal of the Korean earth science society
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• v.27 no.2
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• pp.221-235
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• 2006

In order to understand the transport mechanism of tidal beach sediments in Deukryang Bay, south coast of Korea, beach profiles, surface sediments, sedimentation rates and hydrodynamic conditions have been investigated. The beach is composed of a steep beach face and gentle low-tide terrace, showing general morphologic characteristics of tide dominated beach. Central beach face of an indented coast becomes flattened in summer, but ridge and runnel system developed in other seasons makes the beach profile rather irregular. These seasonal variations of beach profiles and sedimentation rate indicate that beach sedimentation is mainly controlled by both tide and wave processes. Erosion is prevalent in winter when strong wind wave is dominant, while deposition is dominant in other seasons. However, central beach showed an apparent erosional phase in summer. This is caused by strong waves induced by southerly strong winds occurring ephemerally during the summer. On the other hand, sedimentation rates are -89.2 mm/yr on the central beach and 60.5 mm/yr and 38.2 mm/yr on the sides. This result suggests that sediments are eroded on the central beach and subsequently transported to the both sides. Therefore, the central part of Sumun beach, used as a beach bathing site, will be continuously eroded, if nearby dyke continues to prevent the sediment supply from sources.

• Journal of Korea Foresty Energy
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• v.25 no.1
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• pp.18-23
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• 2006

pH dependent K/S values, Hue, Value, and Chroma change of the hot-water and alkali extract of Boehmeria tricuspis have investigated as a part of the studies on natural dye resources. Maximum optical absorption of the dyed cotton, Korean paper, and silk with the extract were observed at 400 nm. According to the result of pH dependent K/S values change, it tended to increase as pH decreased except for the silk and there was no change near pH 7. For Hue, the materials dyed with hot-water and alkali extract indicated YR and R color, respectively. The change in Value of the dyed materials tended to increase, whereas Chroma of them decreased as the pH moved to alkali conditions although there were no significant changes near pH 7. As a result, it is considered that the optimum pH would be 7 when the mentioned materials are dyed with Boehmeria tricuspis extract.

• Journal of the Korean Society for Marine Environment & Energy
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• v.8 no.1
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• pp.17-22
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• 2005

The movement of drifting ships on the sea is closely related to marine environmental forces such as waves, currents, winds, etc. To develop a prediction model for trajectories oi drifting ships, an experiment on the movement of drifting ships was carried out in the Southeastern Sea of Korea. Five types of ships including a lire raft and tour ships with G/T 10tons, G/T 2o tons, G/T 50 tons, and G/T 80 tons, were considered in the experiment. The G/T 50 ton class ship was used as a base ship for obtaining the currents, winds and heading angles of ship following the trajectory. The trajectory of each ship was measured by DGPS(Differential Global Positioning System) and collected using APRS(Automatic Position Reporting System) installed on the base ship. The error range in position fix of DGPS are approximately ±1 m. The drift speed of ship in the experiment was between 3％ to 5％ of wind speed and drift direction of ship was deflected by ±90° from wind direction. Also, the heading of drifting ship was normal to wind direction.

• Journal of the Korean Society for Marine Environment & Energy
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• v.8 no.3
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• pp.140-147
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• 2005

We investigated the interactions between coastal waters of the Yeongil Bay, Korea, and oceanic waters of the Eastern Sea, as wet 1 as the development mechanism of vertical circulation currents in the bay. The oceanic waters of the bay have an average water temperature of $12.2{\sim}18.4^{\circ}C$ and salinity of $33.32{\sim}34.43$ PSU. Results of spectral analysis have shown that the period of revolution between oceanic and coastal waters is about 0.84-0.91 years in the surface waters and 1.84 years in the bottom layer. The wind direction in the bay shifts between SW and NE, with the main wind direction being SW during the winter period, and water mass movement is influenced by such seasonal variations in wind direction. Vertical circulation currents in the bay are structured by two phenomena: the surface riverine outflow layer from the Hyeong-san River into the open sea and the bottom oceanic inflow layer with high-temperature and salinity into the bay. These phenomena start the spring when the water mass is stable and become stronger in the summer when the surface cold water develops over a 10-day period. Consequently, tidal currents have little influence in the bay; rather, these vertical and horizontal circulation currents play an important role in the transport of the pollutant load from the inner bay to the open sea.

• Journal of the Korean Society for Marine Environment & Energy
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• v.15 no.2
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• pp.101-110
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• 2012

In order to understand temperature and salinity variations, and the characteristics of the seawater exchange through two channels of Gamak Bay, we conducted measurements of water temperature, salinity and current for fifteen days in the summer and winter. Based on the observational data, the current seemed to have a close relation with wind. In addition, a correlation analysis result proved that water temperature is likely to be more influenced by air temperature rather than tide. Moreover, water temperatures at the south channel varied more sensitively with the season rather than at the east channel because of its shallow depth. Seawater exchange rates were estimated to be 0.5~29.9% (mean: 11.6%) at the east channel but 1.3~62.6% (mean: 18.6%) at the south channel in summer. On the contrary, they were estimated to be 0.3~28.5% (mean: 8.9%) at the east channel but 0.1~97.9% (mean: 31.2%) at the south channel in winter. Thus, the rates of seawater exchange in Gamak Bay turned out that the south mouth is approximately three times higher than the east mouth, and it also suggested that seasonal winds affect the rates of seawater exchange in Gamak Bay.

• Journal of Korea Foresty Energy
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• v.25 no.2
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• pp.22-27
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• 2006

K/S values, Hue, Value, and Chroma changes of the hot-water and alkali extract of Boehmeria tricuspis have investigated to obtain an optimum dyeing conditions. Maximum optical absorption of the cotton, Hanji, and silk dyed with the extract were observed at 400 nm. The K/S value of the dyed silk was higher than those of other materials in the treatments with the temperature and time condition and there was not much changes in the treatments near $80\;^{\circ}C$ and 40 minutes. Also, the K/S value of the dyed silk was drastically increased as the concentration of the dye was increased. In the treatments with temperature and time condition, Hue of the materials dyed with alkali extracts resulted in YR color, whereas materials dyed with hot-water extracts provided R color. In the time and temperature condition of treatment, there were no significant changes in the samples treated near $80\;^{\circ}C$ and 40 minutes. The Value and Chroma of the dyed materials were not significantly changed. As a result, it is suggested that the optimum temperature, time, and concentration of dye would be $80\;^{\circ}C$, 40 minutes, and 100%, respectively, when cotton, Hanji, and silk are dyed with Boehmeria tricuspis extract.