Papers by Author: Jung Hun Lee

Abstract: Recently, increasing of impervious surface as concrete or asphalt pavement with urban development brought increasing of air temperature in city. So many researchers have explored ways to reduce the urban heat island effect and water-retentive or water absorbing pavements have been found to be very effective. In this study, to evaluate the reduction effects of urban heat reduction of water-retentive pavement, surface temperature of pavement, air temperature, wind speed and albedo were measured for 3 years (2008~2010, summer period). And the intensity of sensible heat flux was calculated to estimate a influence on air temperature. Experimental results indicated that water-retentive was effective to reduction of air temperature by decreasing of surface temperature of pavement compare to other pavements. This is showed that water-retentive pavement can be contributed to mitigation of urban heat island.

Abstract: Urban areas consume huge amounts of water and produce much wastewater, which deteriorate the aquatic environment and exhaust the country’s freshwater resources. Water reuse from sewage and wastewater is recognized as a good option for securing water. There are several kinds of processes for improving the water quality. Nutrient removal is very important for water reuse, especially in water supply for outdoor use, to prevent water quality deterioration via eutrophication. Moreover, low cost and easy maintenance should be considered for nutrient removal. In this study, red mud and Bauxsol^TM, a mixed mineral powder made of physicochemically modified red mud residue generated by the Bayer process for alumina refineries, was used for the removal of nitrate and heavy metals in artificial solution, and of phosphate in final effluent, from a sewage treatment plant in Dae-gu, Republic of Korea. Nitrate removal by red mud showed little efficiency while heavy metal removal showed high efficiency. The concentrations of the total phosphate in the effluent and treated water were 1.51 and 0.14 mg/L, respectively, which represent about 90.7% removal. Before and after the treatment, the pH was maintained at a neutral range of 6.5-7.2. Bauxsol^TM also showed a high heavy metal removal capacity. Therefore, Bauxsol^TM in powder and pellet form can be applied individually or mixed with soil to improve water quality for water reuse.

Abstract: Pollutants in rainwater often cause problems such as non-point source pollutant and deterioration of collected water quality in rainwater harvesting systems. Fiber filter media have been developed to resolve these problems by removing pollutants in rainwater by filtration and ion-exchange mechanisms. They have been also successfully applied for the treatment of first-flush rainwater. However, little information is available on the long-term efficiency and the lifetime of the fiber filter media. In this study, new and used fiber filter media were compared in terms of their filterability and ion-exchange capability. The used filter media samples were taken from a first flush filter in a rainwater harvesting system located in an elementary school in Kyonggi-Do. They were used from 2005 to 2010 without any replacement or cleaning. Water quality parameters of an inflow and outflow in the first flush filter were analyzed to quantify the on-site treatment efficiency of the used media. It was shown that the turbidity was removed by approximately 60% and COD was partly removed. The removal efficiency of particles by the used media was similar to that by the new media. Nevertheless, the removal efficiencies of nitrogen and phosphorous by the used media were substantially reduced when compared with the new media. This suggests that the fiber filter media should be periodically replaced to maintain high removals of nutrients. On the other hand, they can be used for more than 6 years if their primary purpose is to removal particles.

Abstract: First-flush rainwater is of great interest in the research on urban environmental protection and rainwater harvesting. It deteriorates the chemical, physical, and microbiological quality of the collected/stored water as well as the water body in an urban area. Accordingly, effective and economic treatment of first-flush rainwater is highly required. This study aimed to develop a technology for the treatment of first-flush rainwater using new filters made of wood fiber mat, dental cotton, and feldspar. The removal of pollutants in first-flush rainwater with each filter material was evaluated. Experiments were carried out using an artificial rainwater solution made of road dust particles (less than 200 um small) and D.I. water that contained ionic species. The SS concentration of the solution was set between 30 and 150 mg/L. Prior to the experiments, the fiber materials were pretreated with NaOH, FeCl₃, and Al₂O₃. The batch test results indicated that the phosphate removal efficiency of the wood fiber mat was 8.6%; of the dental cotton, 34.7%; and of the feldspar, 1.7%. On the other hand, the heavy metal removal efficiency of the wood fiber mat was 91%; of the dental cotton, 26%; and of the feldspar, 0%. The highest cation exchange capacity of the wood fiber mat that was pretreated with NaOH was attributed to the existence of carboxyl and hydroxyl functional groups in the wooden polymers. Combinations of filter materials were found to have been effective in removing particles in the rainwater. The combination of the wood fiber mat with polyethylene beads resulted in 97-98% particle removal. Other combinations such as DP (dental cotton and polyethylene beads), MF (wood fiber mat and feldspar), and DF (dental cotton and feldspar) showed particle removal rates of 90-95%, 84-96%, and 87-94%, respectively. After 30 minutes, all the combinations had a particle removal rate of over 90%.

Abstract: The creation of large impervious surface in urban and urbanizing areas have led to significant impacts on local climate, which is commonly known as urban heat island (UHI). In this study, porous pavements made of recycled sludge were examined as a way to control UHI by lowering the surface temperature. A novel image analysis technique was applied to quantify cooling effect of porous pavement materials without and with water. Although the porous pavement itself has smaller heat capacity than the natural soil, supplying water to the pavement decreased its surface temperature. At its highest point, the difference in surface temperatures without and with water was more than 10 oC. The water was supplied either from the top of the pavement or from the bottom of the pavement using the capillary effects. In both cases, pavement temperature was effectively lowered. The cooling effect of pavement by surface coating using epoxy-based polymers was negligible because surface pores were blocked. Field tests also confirmed the cooling potential of porous pavements.

Abstract: Carbon and boron were mainly considered to strengthen grain boundaries formed during single crystal casting of complex shaped components. However, those elements cause segregation forming the phase with low melting temperature or with brittle nature. To determine the optimum amount of these elements, the effect of boron on solidification behavior was investigated in the C doped single crystal RR 2072 alloy. The solid/liquid interface morphologies and the solidification microstructures were studied at various solidification rates and with B addition by directional solidification.

Abstract: The embrittlement fracture mechanism caused by microstructural evolution of 17-4 PH stainless steel at long term aging was studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The solution treated specimen consists largely of lath martensite with a small fraction of elongated δ-ferrite. The spherical particles existed a little in the martensite matrix, while no precipitates were present in the δ-ferrite at the solution treated specimen as non-aging. The precipitation of Fe-Cu in the δ-ferrite causes the aged hardening after long term aging accormpanied by decreases in elongation and charpy V-notch energy absorption. The increased fraction of brittle fracture on the fractured surface by impact and tensile test reveals that the embrittlement of the 17-4 PH alloys during long term aging is mainly caused by the precipitation hardening in the δ-ferrite matrix.

Abstract: Rainwater utilization has great potentials for recovering hydrological cycles, for buffering extreme run-off situations in the watercourses, and for reducing the costs for water supply in urban area. However, little information is available on the water qualities and runoff properties of collected rainwater, which is critical for efficient design and maintenance strategies of rainwater harvesting facilities. In this study, characteristics of rainwater collected in a rainwater harvesting system were examined in terms of pollutant concentrations. Based on these results, TiO2 photocatalysts were applied on the roof surface as a novel coating material to improve the quality of collected rainwater. The analysis of rainwater samples shows that the contamination by turbidity, conductivity, and color occurs during the catchment process, which may result in troubles for further use. The roof coating technique developed in this study appeared to be effective in increasing the wash-off of pollutants and improving the water quality in roof runoff because of its increased hydrophililicy as well as photocatalytic reactivity. Further research is required on trace pollutants such as endocrine disruptors to estimate and minimize health risk in rainwater harvesting.