Objectives : The objectives of this study are to assess the degree of uniformity of the flow rate flowing into four grit chamber for actual waste water treatment and to to improve hydraulic structure of the existing distribution channel.Methods : Mobile ultrasonic flow meter was used to measure each flow rate flowing into four grit chambers, and the CFD technique was used to suggest several hydraulic structure improvements for enhancing flow rate evenness.Results and Discussion : From the results of the actual measurement using ultrasonic flowmeter and CFD simulation, The flow rates distributed to four grit chamber through the existing complicated open channels (four outlets) showed a severe unevenness. It was revealed that the flow rate passing through the outlets 1 and 4 at both right anf left ends showed a difference of more than 20% compared to those through outlets 2 and 3 installed in the center.Conclusion : As a result of examining the data of the water level, flow rate, and distribution percentages passing through the 4 distribution channels using the CFD simulation, it was found that case 4 (the case to install the orifice walls on both sides) had the most even flow rate distribution effect. However, as a result of comparing the water levels in case 4 and case 6, the case installing both orifice walls make relatively higher head loss.
Objectives : A water treatment system, combining aeration and reverse osmosis (RO) processes, was introduced to improve water supply facilities in a small village where additional water treatment was required due to high concentrations of natural radioactive substances, nitrate nitrogen, and fluoride. In this study, CCRO(Closed-circuit reverse osmosis) was first introduced for commercial use in Korea. With this system, we evaluated its water treatment efficiency and effectiveness of blending the aerated water and RO permeate for improved waterworks in rural areas.Methods : The removal rate of major pollutants and other ionic substances was evaluated by analyzing the water quality of raw water and unit processes. In addition, the operational efficiency of a small-scale water supply facility was verified and optimized by evaluating a change in operational characteristics depending on the blending ratio of the treated waters by aeration and CCRO processes.Results and Discussion : Up to 86% of the radon contained in raw water was removed by the aeration process within 2 hours, and 98.9% of uranium, 85.5% of nitrate nitrogen, and 82.8% of fluoride were removed by the RO process. In the case of other ionic substances, more than 80% was removed on average by the RO process. The higher blending ratio of RO permeate up to 75% resulted in the better quality of the final treated water. However, since requiring the high flux and pressure (at 1.8 m<sup>3</sup>/hr and 7.6 bar, respectively), CCRO operation resulted in a relatively high specific power consumption at 0.27 kWh/m<sup>3</sup>.Conclusion : In this study, we found that the major contaminants (natural radioactive substances, nitrate nitrogen, and fluoride) were effectively removed by the water treatment system wherein the aeration and CCRO processes were combined. In particular, it was confirmed for the first time in Korea that the stable operation and water treatment efficiency of the CCRO process was satisfactory for commercial purposes. It could produce high-quality tap water through the blending of waters treated by aeration and CCRO, expecting that meeting drinking-water quality standards would be attainable even when raw water contains high-concentration pollutants.
Objectives : In this study, membrane autopsy was performed for a parallel arrayed low-pressure membrane (microfiltration) filtration process that is actually applied to water treatment, to check out whether there are differences in the degree of membrane fouling due to the uneven flow rate into each module. Also, membrane foulants were evaluated quantitatively.Methods : In this study, autopsy was performed for over 10 year old membranes used for drinking water purification. In this way, the outer casings of membrane modules at different positions were disassembled and visually observed. In addition, In addition, the size of the pores and the porosity were investigated by taking a SEM (Scanning Electron Microscope) photograph for the new and the used membrane module fiber samples in different positions from the header pipe. The used membrane foulants were classified into organic and inorganic matters and quantitatively analyzed.Results and Discussion : As a result of visually observing inside the membrane module that has produced drinking water for over 10 years, the inside of the No. 1 membrane module close to the inlet was contaminated with black foulants. On the other hand, in the case of No. 10 membrane module located farthest from the header pipe inlet, no foulants were observed with the naked eye. Also, it was observed from SEM photograph results that there were large differences in the surfaces among No. 1, 4, 6, 8 and 10 MF module fibers.Conclusion : Even after periodic physical and chemical cleaning, it was concluded that the fouling levels were different each other in the parallel arrayed low-pressure membrane modules. In addition, the pore size distribution and porosities of the membrane modules may vary depending on the position.
Objectives : The purpose of this study is to suggest operating conditions that can minimize the disinfection by-products of sodium hypochlorite produced in on-site sodium hypochlorite generators.Methods : The characteristics of disinfection by-products were investigated by operating conditions (dissolved water type, brine concentration, temperature of electrolytic cell inflow water, pH of electrolytic cell inflow water and electrolyzer current density) using a on-site sodium hypochlorite generator(5 kg/day).Results and Discussion : The concentration of disinfection by-products (chlorate, bromate) according to the type of dissolved water was found to be high in the order of softened water > tap water > RO treated water. As the brine concentration increased, chlorate decreased and bromate increased. The optimal saline concentration was found to be 3% or more. As temperature of electrolytic cell inflow water increases,, chlorate decreases and bromate increases. The difference in the concentration of disinfection by-products(chlorate, bromate) according to the pH of electrolytic cell inflow water is not large, and the appropriate pH is determined to be about 7 when the free available chlorine and disinfection by-products are taken into account. Also, as the current density increases, the chlorate increases and bromate showed a decreasing trend.Conclusion : It has been shown that the concentration of disinfection by-products can be minimized when operating within the operating range suggested by the on-site sodium hypochlorite generator manufacturer, and some operating conditions are thought to have been suggested by the manufacturer to protect the electrolyzer cells. As the market for on-site sodium hypochorite generator gradually expands, it is expected that improved facilities will be continuously released in consideration of the stricter standards for disinfection by-products.
Objectives : This study was conducted to suggest field operating conditions that can minimize disinfection by-products for three types of sodium hypochlorite.Methods : In this study, changes in free available chlorine, chlorate and bromate were analyzed according to storage temperature, storage time and presence or absence of sunlight for three types of sodium hypochlorite(two types of bleach and one type of sodium hypochlorite made on-site hypochlorite generator).Results and Discussion : In the case of bleach with 12% free available chlorine, when operating with a target of 10% of more of free available chlorine, the storage time for each storage temperature was 3 days at 40℃, 13 days at 30℃, 27 days at 20℃, 85 days at 10℃, and 200 days at 5℃. In the case of bleach with 5% free available chlorine, when operating with a target of 4% of more of free available chlorine, the storage time for each storage temperature was 37 days at 35℃, 255 days at 20℃, 1,343 days at 10℃, and 4,821 days at 4℃. In the case of sodium hypochlorite with 0.8% free available chlorine made on-site hypochlorite generator, when operating with a target of 0.7% of more of free available chlorine, the storage time for each storage temperature was 10 days at 3 5℃, 42 days at 20℃, 470 days at 10℃, and 1,770 days at 4°C. As a result of evaluating the quality change according to the presence or absence of UV protection, the free available chlorine decreased rapidly when exposed to sunlight, whereas the free available chlorine decreased slowly in the case of indoor storage.Conclusion : Bleach with 12% free available chlorine can be stored for about 60 days at 15℃, and bleach with 5% free available chlorine can be used within about 6 months at 15℃. And sodium hypochlorite with 0.8% free available chlorine can be used within 10 days at room temperature. In addition, when storing sodium hypochlorite, it is suggested that it be stored indoors protected from sunlight.
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