제주지역 수돗물의 잔류염소 균등화를 위한 관망모델적용

Abstract

To supply clean tap water from a purification plant to a faucet at home, water quantity and quality in distribution pipes should be stable and drinking-water distribution system should be optimally managed. Three filtration plants in Jeju island whose source water has different features from that of mainland of Korea are selected for this study. They are Eoseungsaeng, Namwon and Gangjeong purification plants. To find out the reduction properties of residual chlorine by features of source water, the lab test is carried out. Eoseungsaeng purification plant uses surface water, Namwon uses underground water and Gangjeong uses springwater as source. The experiment to determine the decay constant in the each source water indicates that Eoseungsaeng water shows a sharp decrease of the decay constant in the early stage of chlorine injection. It declines gradually 20 hours later. As the temperature of water goes up, the decrement of residual chlorine increases. The experiment shows clear distinctions in the decay constant by water quality. At 5℃, the decay constants are -0.003hr-1, –0.002hr-1 and –0.001hr-1 for Eoseungsaeng, Gangjeong and Namwon respectively. The decay constant of Eoseungsaeng is three times higher than that of Namwon, and 1.5 times higher than that of Gangjeong. The surface water at Eoseungsaeng contains more organic matters than other source water. It is verified that there are clear distinctions in the decrement of organic matters by properties of source water. To predict the concentration of residual chlorine by water supply channels, the supply area of the Eoseungsaeng purification plant is chosen as the study area. The hydraulic analysis for the lines is first carried out. Based on the result, the worst-case simulation experiment is done. It shows that water of four spots is below the water quality standard. They are E5(0.03mg/L) and E6(0.02mg/L) spots in the eastern lines and W21(0.02mg/L) and W25(0.03mg/L) spots in the western lines. If chlorine is injected at water purification plants to maintain adequate amount of residual chlorine, at least 1.9mg/L of chlorine is needed. So rechlorination can be a good tool in controlling adequate residual chlorine in a large distribution system. The effect of rechlorination is analyzed through research into changes in residual chlorine. For introducing rechlorination system at the study area, the appropriate spots are before the main water pipes which diverge into E5 and E6 in the east and before the main water pipes which diverge into E21 in the west. Under the present condition, the adequate injection concentrations of rechlorination are 0.42mg/L for the east and 0.27mg/L for the west. The simulation experiment indicates that the chlorine injection concentration can be reduced to 0.4mg/L at purification plants by introducing rechlorination system. And spots with excessive residual chlorine can have stable water quality. After the rechlorination, the concentration of residual chlorine at the first point of junction is lowered by 0.27mg/L from 0.63mg/L to 0.36mg/L. The concentration of spots of 0.5mg/L or over is lowered to below 0.4mg/L. And the concentration of spots of under the standard increases up to 0.1mg/L or over. To conclude, rechlorination can maintain even concentration of residual chlorine and stable water quality from purification plants to end-pipes.