• Journal of the Korean Electrochemical Society
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• v.15 no.4
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• pp.242-248
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• 2012

The measurement of residual chlorine as a disinfectant is very important to ensure the safety against the pathogenic microbes and to suppress injection. The portable free chlorine sensor was fabricated with a disposable strip format by a screen printing method. The strip sensors prepared with a carbon-Ag/AgCl(cathode-anode) combination exhibited less interfering responses towards combined chlorine species(especially $NHCl_2$) and oxygen than the sensors prepared with other metals(i.e., gold and platinum). Free chlorine was determined chronoamperometrically with carbon-based electrodes at an applied potential of -0.3 V(vs. Ag/AgCl). A channel was built on the strip-type electrode for easy sampling, and the resulting strip sensors were employed to determine the concentrations of residual free chlorine.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.4
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• pp.276-282
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• 2013

The reclaimed water has been highlighted as a representative alternative to solve the lacking water resources. This study examined the reduction of residual free chlorine by temperature (5, 15, $25^{\circ}C$) and initial injection concentration (1, 2, 4, 6 mg/L) in the reclaimed water and carried out propose on the calculating method of the optimal chlorine dosage. As the reclaimed water showed a very fast reaction with chlorine at the intial time comparing to that of drinking water, the existing general first-order decay model ($C_t=C_o(e^{-k_bt})$) was not suitable for use. Accordingly, the reduction of residual free chlorine could be estimated in a more accurate way as a result of applying the exponential first-order decay model ($C_t=a+b(e^{-k_bt})$). ($r^2$=0.872~0.988). As a result of calculating the bulk decay constant, it showed the highest result at 653 $day^{-1}$ under the condition of 1 mg/L, $25^{\circ}C$ for the initial injection whereas it showed the lowest result at 3.42 $day^{-1}$ under the condition of 6 mg/L, $5^{\circ}C$ for the initial injection. The bulk decay constant tends to increase as temperature increases, whereas the bulk decay constant tends to decrease as the initial injection concentration increases. More accurate calculation for optimal chlorine dosage could be done by using the experimental results for 30~5,040 min, after the entire response time is classified into 0~30 min and 30~5,040 min to calculate the optimal chlorine dosage. In addition, as a result of calculating the optimal chlorine dosage by temperature, the relationships of initial chlorine demand (y) by temperature (x) could be obtained such as y=1.409+0.450x to maintain 0.2 mg/L of residual free chlorine at the time after 4 hours from the chlorine injection.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.490-490
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• 2021

상수도 관망은 대표적인 사회기반시설로 수원으로부터 수용가에게 수질적으로 안전한 물을 안정하게 공급하는 것을 목표로 한다. 초기의 상수도 관망의 최적 설계는 비용만을 고려함으로써 미래의 불확실한 상황에 대한 대처가 매우 취약하고, 사용자의 다양한 요구를 충족시키지 못하였다. 또한, 유량과 안정적인 수질 공급을 고려하는 설계는 몇몇 비선형적 요소를 포함하고 있으며, 특히 사용자의 수요 패턴에 따른 잔류 염소 농도가 설계 기준에 부합하지 못하는 문제가 되는 경우 사용자의 심미적, 심리적 불편을 초래할 수 있다. 이는, 수질의 안전성과 직결되는 문제이다. 따라서 본 연구에서는 상수도 관망의 설계에 대하여 수질과 수리학적 특성을 고려한 상수도 관망 다목적 최적 설계를 수행하였다. 상수도 관망은 수질적인 측면을 고려하기 위해 수원에서 수용가까지 용수를 공급하는 과정에서 병원성 미생물을 소독하기 위하여 염소를 주입한다. 또한, 유리 잔류 염소의 평상시 기준을 (1.0-4.0mg/L) 유지하도록 규정하였다 (수도법 시행규칙 제22조의2). 하지만 사용자의 사용패턴, 체류 시간에 따라 잔류염소량이 달라진다. 따라서, 본 연구에서는 상수도 관망의 설계 비용과 염소 주입량을 동시에 설계 인자로서 고려하기 위해 Multi-objective Harmony Search를 적용하고, 그 결과를 분석하였다. 이러한 상수도 관망의 수질 인자와 설계 비용을 고려한 최적 설계안은 경제적 측면 뿐만 아니라 사용자의 수질 측면의 안전성을 충족하는 방안을 제시할 수 있다.

• Journal of Life Science
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• v.16 no.4
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• pp.579-583
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• 2006

The influence of disinfectant on bacterial concentration and carbon usage patterns by Biolog GN plates were investigated for biofilm on carbon steel pipe. Heterotrophic bacterial concentrations were not different among non-, monochloramine- (1.0, 1.5 mg/l) and free chlorine- (0.5, 1.0 mg/l) treated samples (P = 0.56, ANOVA). However treatment of 1.5 mg/l free chlorine and 2.0 mg/l monochloraime showed significantly lower densities than control (P < 0.01, ANOVA). By the stepwise increasement of disinfectant concentration, the carbon usage activities of biofilm microflora were decreased after increase without the decrease of bacterial concentration, following reduction of cell density. Carbon usage patterns were qualitatively and quantitatively different with similar bacterial concentrations. Principal component analysis suggested that type and concentration of disinfectant were main factors on the usage of carbons. Our result suggest that the differences of bacterial communities were different among the samples and the need of monochloramine for the reduction of biofilm in drinking water.

• Journal of Korean Society of Water and Wastewater
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• v.19 no.3
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• pp.363-369
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• 2005

This paper presents the integrated technique of water quality analysis and Geographic Information System(GIS) for assessing the variation of free chlorine residuals by water temperature and supply distance in Sangri water supply system in Daegu. GIS was utilized for mapping projectmap, extraction of a pipeline route, and supply distance. Free chlorine residual is analyzed every month for appraising the seasonal variation. As a result, free chlorine residuals are affected both water temperature and water supply distance, and it becomes worse as water temperature and water supply distance is increased. To maintain 0.4mg/l of free chlorine residual, initial dose concentration should be over 1.85mg/l in summer.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.5
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• pp.720-725
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• 2012

Sodium hypochlorite is used worldwide as a water disinfectant and in bleaching agent. Sodium hypochlorite applied to water initially undergoes hydrolysis to form free chlorine consisting of hypochlorous acid(HOCl) and hypochlorite ion($OCl^-$). For free chlorine determination, an electrochemical method is simple due to the electroactivity of free chlorine; it measures current and is free of most reagents. Amperometric free chlorine sensor has been developed with gold (Au)-based electrode. The 3-electrode free chlorine sensor whose working and counter electrodes were Pt exhibited excellent response to HClO at +400mV vs. Ag/AgCl/sat. KCl. In addition, the use of a pH error correction algorithm provided a reliable measurement of residual free chlorine in water sample without any pretreatment in the normal pH range(pH 6~8) of municipal water supply. The free chlorine sensor installed in on-line monitoring system could be used to continually monitor the level of residual free chlorine in real samples.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.1
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• pp.115-119
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• 2005

As the regulations on DBPs are tightened, many water treatment plants (WTPs) in Korea have already introduced or will introduce enhanced coagulation, alternative disinfectants and advanced treatments such as ozonization and granular activated carbon to improve drinking water qualify. After a phenol leakage accident at the Nakdong-River in 1991, 26 WIPs in Korea introduced carbon dioxide generators, but there has been no accumulation of significant operating data. This research summarizes things that should be considered for the introduction of carbon dioxide disinfection process to WTPs based on one year operation data from A WTP that has had high concentration of DBP during a specific period in the summer. The removal efficiency of DBP was $30{\sim}40%$, but those of 2-MIB, Geosmin were less than 10%. The generation rate of $ClO_2$ by-products such as chlorite and chlorate were $70{\sim}100%$ of input dosage, but the ratios increased over time. At the same time, strong chlorine odors may be produced in the distribution system when $ClO_2$ was used with $Cl_2$ as a result of reaction between the chlorite and residual chlorine.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.10
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• pp.916-927
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• 2010

In general water treatment process, the disinfection process by chlorine is used to prevent water borne disease and microbial regrowth in water distribution system. Because chlorines were reacted with organic matter, carcinogens such as disinfection by-products (DBPs) were produced in drinking water. Therefore, a suitable injection of chlorine is need to decrease DBPs. Rechlorination in water pipelines or reservoirs are recently increased to secure the residual chlorine in the end of water pipelines. EPANET 2.0 developed by the U.S. Environmental Protection Agency (EPA) is used to compute the optimal chlorine injection in water treatment plant and to predict the dosage of rechlorination into water distribution system. The bulk decay constant ($k_{bulk}$) was drawn by bottle test and the wall decay constant ($k_{wall}$) was derived from using systermatic analysis method for water quality modeling in target region. In order to predict water quality based on hydraulic analysis model, residual chlorine concentration was forecasted in water distribution system. The formation of DBPs such as trihalomethanes (THMs) was verified with chlorine dosage in lab-scale test. The bulk decay constant ($k_{bulk}$) was rapidly decreased with increasing temperature in the early time. In the case of 25 degrees celsius, the bulk decay constant ($k_{bulk}$) decreased over half after 25 hours later. In this study, there were able to calculate about optimal rechlorine dosage and select on profitable sites in the network map.

• Journal of Industrial Technology
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• v.21 no.B
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• pp.11-20
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• 2001

This laboratory study examined the impact of free chlorine residual and pipe material on the formation of biofilm in drinking water distribution pipe surfaces. Result of heterotrophic plate counts(HPC) of the biofilm in the tap water-supplied reactor averaged $2.17{\times}10^5CFU/cm^2$ on PVC and $2.43{\times}10^5CFU/cm^2$ on STS 316, respectively. HPCs on the surface exposed to the tap water containing 0.2mg/L of free chlorinne residual averaged $4.24{\times}10^4CFU/cm^2$ on PVC and $6.54{\times}10^4CFU/cm^2$ on STS 316, respectively. Average of HPC/Total direct counts in the tap water-supplied reactor ranged from 1.08%(PVC) to 1.26%(STS 316) and from 0.38%(PVC) to 0.65%(STS 316) in the reactor supplemented with disinfectant, respectively. No correlation was observed between disinfectant addition and biofilm density. With regard to the biofilm formation, little difference existed between PVC and STS 316. Yellow and red pigmented bacteria were the dominant expressions in bulk fluid, whereas non-pigmented bacteria were found dominant in the biofilm. Pink/red pigmented bacteria were found to be facultative anaerobic, while yellow pigmented bacteria and non-pigmented bacteria were found to be obligate aerobic.

• Proceedings of the Korea Society of Environmental Toocicology Conference
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• 2002.10a
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• pp.153-153
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• 2002

수돗물의 염소소독 과정에서 부식질의 초기 분해생성물인 MX(Mutagen X)는 수돗물의 전체 돌연변이유발성의 최고 60%까지 차지하는 것으로 알려져 있다. 그러나 존재하는 농도는 수 ng/L로 정량분석을 위해서는 resin을 사용하여 10 ~ 20L의 물을 농축하여야 한다. 이 연구에서 MX의 농축에 사용된 resin은 XAD-4와 XAD-7HP의 1:1 mixture이었으며, 사용 전에 Soxhlet extractor를 사용하여 ethyl acetate와 methanol로 각각 12시간씩 세척하였다. 15L의 물 시료는 37%의 염산으로 pH 2에 맞춘 후 직경 2cm의 유리관에 15cm의 높이로 채워진 resin을 40mL/min의 유속으로 통과시켰다. 유리관에 잔류하는 물은 질소가스로 대부분 불어 제거한 후 ethyl acetate 200mL를 가해 1mL/min의 유속으로 흘려주어 MX를 용출시킨 후 회전증발기로 5mL의 부피까지 농축시키고 10% H$_2$SO$_4$ in MeOH 0.1mL를 가하여 6$0^{\circ}C$에서 methyl ester화하였다. 과포화된 $Na_2$SO$_4$ 수용액 0.3ml를 가한 후 MTBE 0.3mL로 추출하고 GC/ECD로 분석하였다. MX의 회수율은 60% 이상이었으며 일부수돗물 시료에 대해 분석하였다.