Papers by Author: Sang Ho Lee

Abstract: Membrane distillation (MD) is a special evaporation process to produce fresh water from seawater or contaminated water using membranes. MD has advantages over other evaporation technologies such as multi-stage flash vaporization (MSF) and multi-effect distillation (MED) due to its relatively low energy requirements, allowing the use of solar energy as its heat source. Nevertheless, lack of membrane materials for MD process hinders its practical implementation for desalination and water treatment. In this study, membranes made of carbon nanotube (CNT) are presented for MD. Flat sheet hydrophobic membranes made of polyvinylidene fluoride (PVDF) were selected as supports for bucky-paper membranes, allowing formation of CNT bucky-paper without chemical reactions. Laboratory-scale systems were used to evaluate their potential and performance in direct contact MD. Water permeability and salt rejection were analyzed for each case. D.I water and synthetic feed water were used for the lab-scale tests. It was demonstrated that the physical immobilization of CNT on a hydrophobic membrane changed led to an increase in vapor permeability while improving salt rejection.

Abstract: Low pressure membranes such as microfiltration (MF) and ultrafiltration (UF) have been widely used for water and wastewater treatment. However, most MF and UF membranes are made of polymeric materials, leading to limited resistance to external streeses. Ceramic membranes are also used but they are more expensive than the polymeric membranes. In this study, novel inorganic membranes were developed for water treatment applications. Colloidal silica and kaolin were used to form dynamic membranes. Stainless steel filter was used as supports for the dynamic membranes. Laboratory-scale systems were used to evaluate their potential and performance. Water permeability and turbidity removal were monitored to confirm their initial efficiency and long-term stability.

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: Rainwater collection and use is usually considered for runoff from building roofs. Runoff from impervious layers such as roads and pavements, however, has hardly been used as water supply due to its high pollutant concentration. If runoff from roads will be treated and used properly, though, it can be a good water resource and will contribute minimally to a non-point source. In this study, a multistage soil filter system (MSFS) composed of a gravel layer, a functional-media layer with zeolite, a sand layer, and a lawn layer, was developed to treat the runoff from roads and green areas. To evaluate the performance of MSFS, its removal rate of total suspended solids (TSS) was investigated based on the rainfall intensity and the thickness of each layer. The experiment results were compared with the predicted values using the Minitab^TM program. The TSS removal rates ranged from 82 to 96%, with various combinations of experiment conditions. The predicted removal rates well fitted with the removal rates obtained from the experiment. An equation was formulated for predicting the TSS removal rate based on the rainfall intensity and the thickness of each layer. The optimum design factors for MSFS considering its TSS removal rate could be derived based on such equation. Based on the study results, it is expected that MSFS can contribute to securing water resources and to controlling non-point sources.

Abstract: Trace organic micropollutants have adverse effects on human health and ecosystem at low concentrations. In this study, feasibility of new catalysts for oxidation of organic micropollutants was investigated. Iron tetrasulfophthalocyanine (FeTsPc) has been immobilized on the surface of functionalized MCF (mesocellular silica form)-NH₂ and MCM-41 mesoporous silicas by means of chemical bonding to ammosilane groups. MCF, prepared by precipitation from a micellar solution, consisted of unit cells which had internal void (~20 nm) and pores (~11 nm). NH₂-functional groups were added to the surface of MCF and MCM-41 using (3-aminopropyl)triethoxysilane (APTES). 1-ethyl-3-(3’dimethylaminopropyl)carbodiimide (WSC) was used as a coupling agent. N-hydroxysuccinimide (NHS) was added during the reaction to improve the efficiency of amination. The prepared materials, FeTsPc/NH2-MCF and FeTsPc/NH2-MCM-41, were characterized by UV-DRS (diffuse reflectance UV-vis spectroscopy) and FT-IR. Bisphenol-A (BPA) was chosen as a model micropollutant. The catalytic activities of the supported Fe-TsPc were examined by the oxidation of BPA in the presence of hydroperoxide. The amount of immobilized FeTsPc and the specific reactivity were also analyzed to provide quantitative evaluation of the catalysts. The results indicated that the FeTsPc/NH2-MCM-41 showed higher activity and durability in the liquid-phase oxidation of BPA under mild condition compared with the FeTsPc/NH2-MCF and unsupported catalyst.

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: Membrane distillation (MD) integrates membrane technology with evaporation process to produce fresh water from seawater or contaminated water. In this study, we investigated the effect of membrane materials on the efficiency of membrane distillation process. Flat sheet hydrophobic membranes (PVDF, PTFE) with different characterizes were chosen as well as hollow fiber membranes (PE). Laboratory-scale systems were developed for initial screening of various membranes. The performance of the membrane was analyzed in terms of water permeability and salt rejection. Synthetic seawater (TDS = 35,000 mg/L) was used for the lab-scale tests. A simple model to analyze the transport of water through MD membranes was developed to interpret experimental results. In addition, long-term performances of the membranes were compared to examine the stability of membrane materials and fouling tendency using real seawater. Based on the lab-scale experiments, techniques to improve the performance of the membranes were examined by applying physical and chemical modification.