• Journal of Korean Society on Water Environment
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• v.21 no.2
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• pp.176-183
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• 2005

Chlorination of wastewater is recently practiced in Korea. While many researchers have studied the kinetics of aqueous chlorine(HOCl) with nitrogeneous compounds and other organic/inorganic contaminants in drinking water, the researches of wastewater chlorination are relatively few. The purpose of this study was to investigate the chlorine decay kinetics and parameters on wastewater chlorination. Chlorine decay rate increased with increasing initial chlorine concentration. The parameters affecting chlorine decay rate were different in each wastewater treatment plant. One of the most important parameters affecting chlorine decay was initial chlorine concentration, and other parameters such as $NH_3-N$, total coliform, $UV_{254}$ and Fe were also affected. The decay ratio of chlorine was decreased with increasing initial chlorine concentration, and the disinfection efficiency showed good correlation with the decay ratio.

• Journal of Environmental Health Sciences
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• v.27 no.1
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• pp.27-35
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• 2001

This aim of the work presented in this paper is to investigate the factors that affcet chlorine decay and to develop functional relationships that can be used to enhance the durability of network models. predictive relationships were established that correlated the rate of chlorine decay to the various water conditions such as DOC, N $H_3$-N, initial chlorine, contact time, temperature and pH values. Free chlorine residual decreased with increasing temperature, DOC, N $H_3$-N, reaction time and chlorine dose. At 2$0^{\circ}C$, pH 7, The initial chlorine demand per mg as DOC/L and mg as N $H_3$-N/L was about 0.43, 2.69 mg/$\ell$ respectively at 180 minutes contact time. The Reaction between chlorine and humic acids was lasted intil 48hr, but the reaction between chlorine and N $H_3$-N was almost completed in 180 min. When the temperature is raised by 1$0^{\circ}C$, chlorine is more consumed about 0.25 mg/$\ell$ in the absence of organic substances and it is more consumed about 3.4 mg/$\ell$ in the presence of humic acid (5 mg/$\ell$) in water at pH 7 for 180 min. Regression Analysis created the resulting prediction equation for the chlorine decay in a SPSS package of the computer system. The model is as follows; $C_{t}$=1.239+0.707(Co)-0.000529(Time)-0.0112(Temp)+0.02227(pH)-0.42(DOC)-2.132(N $H_3$-N).).

• Journal of Korean Society of Water and Wastewater
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• v.19 no.5
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• pp.625-631
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• 2005

Disinfection characteristics of mixed oxidants produced by mean of electro-chemical method were evaluated. Inactivation rate of B. subtilis spore on the mixed oxidants were similar with that of chlorine. Based on the experimental results, activation energy of mixed oxidants and chlorine with B. subtilis spore at pH 8.3 were calculated as 30.8, $34.7kJ{\cdot}mol^{-1}$ respectively. UV absorption spectrum of both chlorine and mixed oxidants present similar. Molar extinction coefficients of chlorine and mixed oxidants at 292nm, which is maximum absorption wavelength of $OCl^-$ were 357, $377M^{-1}cm^{-1}$, respectively. Disinfectant decay rate and formation rate of THM in the S WTP filtrate also shows insignificant difference for both mixed oxidants and chlorine. In consequent, it was confirmed that high portion of chlorine presents in the mixed oxidants.

• Journal of Korean Society of Water and Wastewater
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• v.12 no.2
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• pp.90-98
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• 1998

The optimal rechlorination in water distribution systems was investigated by incorporating optimization techniques into a numerical water quality model. For a hypothetical system that consists of 10 junctions including a storage tank and 12 links, the bulk ($k_b$) and pipe-wall ($k_w$) decay-rate constants of chlorine residual are assumed to be 2.0 1/day and 1.5 m/day, respectively. It was also assumed that the lower and upper limits of chlorine residual in the network are 0.2 mg/L and 0.6 mg/L. When the chlorine source is only the storage tank (without rechlorination), the high levels of chlorine residual appear near the storage tank to maintain the chlorine residuals above the lower limit over the junctions. On the other hand, the chlorine residuals in the network are distribute within the desirable range (0.2 - 0.6 mg/L) after the optimal rechlorination through five injection sites including the storage tank. In case of a real water distribution system that comprises 28 junctions including a clear well and 27 links, the bulk and pipe-wall decay-rate constants are 0.3 1/day and 0.2 m/day, respectively. Before rechlorination, the required chlorine residual at the clearwell is 5.1 mg/L to keep the chlorine residuals above the minimum level (0.6 mg/L) over the junctions. By the optimal rechlorination at five injection sites, the chlorine residuals are distributed within a desirable range of 0.6 mg/L through 2.0 mg/L, which can avoid the excess of chlorine residuals near the clear well. Consequently, total chlirine doses are decreased by 81% in the hypothetical distribution network and 69 % in the real distribution network for satisfying the minimum chlorine residuals.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.170-170
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• 2023

Providing safe and readily available water is vital to maintain public health. One of the most prevalent methods to prevent the spread of waterborne diseases is applying chlorine injection to the treated water before distribution. During the water transmission and distribution, the chlorine will experience a reduction, which can imply potential risks for human health if it falls below the minimum threshold. The ability to determine the appropriate initial intensity of chlorine at the source would be significant to prevent such problems. This study proposes two methods that integrate hydraulic and water quality modeling to determine the suitable intensity of chlorine to be injected into the source water to maintain the minimum chlorine concentration (e.g., 0.2 mg/l) at each demand node. The water quality modeling employs the first-order decay to estimate the rate of chlorine reduction in the water. The first method utilizes a backtracking algorithm to trace the path of water from the demand node to the source during each time step, which helps to accurately determine the travel time through each pipe and node and facilitate the computation of time-dependent chlorine decay in the water delivery process. However, as a backtracking algorithm is computationally intensive, this study also explores an alternative approach using a water age. This approach estimates the elapsed time of water delivery from the source to the demand node and calculate the time-dependent reduction of chlorine in the water. Finally, this study compares the outcomes of two approaches and determines the suitable and effective method for calculating the chlorine intensity at the source to maintain the minimum chlorine level at demand nodes.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.19 no.1
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• pp.17-27
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• 2013

The effects of chlorine dioxide gas ($ClO_2$) treatments between high-concentration-short-time and low-concentration-long-time on maintaining the quality of cherry tomatoes (Lycopersicon esculentum Mill. cv 'unicorn') were investigated. Tomatoes were treated with 5 ppm for 10 min and 10 ppm for 3 min as high-concentration-short-time $ClO_2$ gas treatment conditions and 1 ppm for once a day interval in terms of low-concentration-long-time $ClO_2$ gas treatment condition, respectively. After $ClO_2$ gas treatments, tomatoes were storage at 5 and $23^{\circ}C$ for 7 days. Weight loss, changes in tomato color, firmness, soluble solids content, pH, growth of total microorganism, and decay rate were evaluated. On day 7, tomatoes treated with chlorine dioxide gas showed low values of respiratory rate, total microbial growth, and decay rate compared to those of tomato without chlorine dioxide gas treatment. Additionally, tomatoes treated the chlorine dioxide were kept the values of firmness and soluble solids content during storage. However, chlorine dioxide gas treatment on tomatoes had no direct effect on weight loss, pH, and color. Results showed that both $ClO_2$ concentration and treatment time played the important roles for keeping the quality of tomatoes during storage. Tomatoes with chlorine dioxide gas treatment of low-concentration-long-time had more effective values of firmness, the total microbial growth, and decay rate than those with two chlorine dioxide gas treatments of high-concentration-short-time. Results suggest the potential use of chlorine dioxide gas treatment of low-concentration-long-time as an highly effective method for keeping the freshness of cherry tomato.

• Journal of Environmental Science International
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• v.11 no.4
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• pp.347-353
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• 2002

This study was conducted to investigate the characteristics of chloramination as a secondary disinfection in a drinking water distribution system. At the range from pH 6 to pH 8, monochloramine was predominant with a trace of dichloramine, and the free chlorine was detected after breakpoint. At $25^{\circ}C$, the breakpoints of pH 6, 7 and 8 appeared when the weight ratios of chlorine to ammonia nitrogen were 11:1, 9:1 and 10:1 respectively, and the peak points on the breakpoint curves at pH 6, 7 and 8 were in the Cl$_2$ / NH$_3$-N ratio of 9:1, 6:1 and 5:1 respectively. As pH increased from 6 to 8, maximum point of monochloramine on the breakpoint curve was moved from 7:1 to 5:1 in the weight ratio of chlorine to ammonia nitrogen. The maximum concentration of monochloramine was formed at the pH values of 7~8 and in the Cl$_2$ / NH$_3$-N ratio below 5:1. As the Cl$_2$/NH$_3$-N ratio increased and the pH lowered, chloramines decay proceeded at an increased rate, and residual chloramines lasted longer than the residual free chlorine. The monochloramine and the dichloramine were formed at pH 6, and then the dichloramine continued increasing with contact time.

• Journal of the Korean Society of Food Science and Nutrition
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• v.45 no.8
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• pp.1233-1238
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• 2016

Combined treatment of chlorine dioxide ($ClO_2$) gas, mild heat, and fumaric acid was performed to reduce microbial growth and maintain quality of Citrus unshiu during storage at $4^{\circ}C$. Citrus unshiu fruits were treated with $ClO_2$ gas (15 or 30 ppmv), mild heat (40, 50, or $60^{\circ}C$), and fumaric acid (0.1, 0.3, or 0.5%). Combined treatment of 15 or 30 ppmv $ClO_2$ gas, $50^{\circ}C$ mild heat, and 0.5% fumaric acid reduced populations of inoculated Listeria monocytogenes by 3.5~3.7 log CFU/g. In addition, combined treatment decreased populations of yeast and molds in Citrus unshiu by 2.54 log CFU/g after 30-day storage at $4^{\circ}C$. Combined treatment also reduced the decay rate by 48% after 30 days of storage compared with the control. Total solid content, titratable acidity, and color values were not significantly affected by the combined treatment. Therefore, combined treatment of $ClO_2$ gas, mild heat, and fumaric acid can be a useful hurdle technology to improve microbial safety and quality of Citrus unshiu during storage.

• Journal of the Korean Society of Food Science and Nutrition
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• v.45 no.4
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• pp.619-624
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• 2016

Chlorine dioxide ($ClO_2$) gas treatment (75 ppmv, 30 min) has been suggested to improve the microbial safety of postharvest paprika in a previous study. Based on these results, in this study, an additional combined treatment using low-concentration $ClO_2$ gas-generating sticks (3 ppmv) in paprika samples during storage was carried out at $8^{\circ}C$ and 90% relative humidity to further enhance the quality and reduce the decay rate of paprika for the purpose of lengthy storage. After the combined treatment, the initial populations of total aerobic bacteria as well as yeast and molds in the paprika samples decreased by 3.04 and 2.70 log CFU/g, respectively, compared with those of the control samples, and this microbial inactivation was maintained by the low-concentration $ClO_2$ gas-generating sticks during storage. In particular, the decay rate of samples with combined treatment was significantly lower than that of the control. Vitamin C content, hardness, and color quality parameters of paprika samples were not altered by treatment, while weight loss of the samples treated with the combined $ClO_2$ gas was lower than that of the control during storage. These results indicate that the combination of two different $ClO_2$ gas treatments is effective for retaining the quality of paprika during prolonged storage.