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Imanaka S.,Water Examination Laboratory | Hayashi H.,Water Examination Laboratory
Water Science and Technology: Water Supply | Year: 2013

The analysis conditions for measuring trace concentration of Cr(VI) based on the ion chromatography-inductively coupled plasma-mass spectrometry (IC-ICP-MS) method was examined. By optimizing the analysis conditions, the measurement of 0.02 μg-Cr(VI)/L was achieved with a high degree of accuracy. The behavior of Cr(VI) through the water treatment process in Osaka city was investigated and it was determined that there was a tendency that the Cr(VI) concentration slightly fluctuated throughout the water treatment process with the highest concentration being observed in finished water. The Cr(VI) concentration at the outlet of Kunijima purification plant was less than 0.02-0.13 μg/L, while water taps where retention time from the plant was 4-15 h, were less than 0.02-0.10 μg/L. Also, it was found that Cr(III) was oxidized to Cr(VI) by sodium hypochlorite and ozone being used in the water treatment process. Based on this finding, the oxidation reaction of Cr (III) to Cr(VI) was examined. When sodium hypochlorite was added to granular activated carbon (GAC)-treated water and purified water containing Cr(III), the oxidation of Cr(III) to Cr(VI) proceeded and the Cr(VI) production in GAC-treated water was relatively higher. In addition, it was determined that the Cr(III) oxidation reaction rate depended on water temperature and it was faster when the water temperature was higher. Copyright © IWA Publishing 2013.

Fuchigami T.,Water Examination Laboratory | Takeda M.,Water Examination Laboratory | Terashima K.,Water Examination Laboratory
Water Science and Technology: Water Supply | Year: 2010

The behaviour of residual chlorine concentration in drinking water treated by the mid-chlorination or the advanced water treatment (AWT) was investigated. The AWT removes dissolved organic matter more than the mid-chlorination, thus the rate of residual chlorine reduction is decreased. The analysis of chlorine concentration data measured by automated continuous monitoring devices revealed that the introduction of AWT reduced the maximum and mean chlorine concentration by 0.33 mgL-1 and 0.21 mgL-1 compared to the mid-chlorination respectively, while the minimum concentration was maintained at around 0.3 mgL-1 in the whole city. The overall chlorine reduction rate coefficient in the AWT was reduced to approximately half of that in the mid-chlorination. Volatilization of chlorine from a water surface could be expressed by the zero-order rate of reaction from laboratory experiments. The rate of volatilization increases with increasing water temperature and shallower water depth. The residual chlorine prediction models were developed based on the results of data monitoring and laboratory experiments. The accuracy of simulated values is good and almost all of the predicted concentrations are in the range of ± 0.1 mgL-1 of measured concentrations. The models are very effective to control residual chlorine concentration at predetermined target value. © IWA Publishing 2010.

Fuchigami T.,Water Examination Laboratory | Terashima K.,Water Examination Laboratory | Bandow H.,Osaka Prefecture University
Water Science and Technology: Water Supply | Year: 2012

In real residual chlorine management practices, a simple criterion is required for evaluating chlorine consumption by inner wall surfaces of water distribution pipes. The amount of chlorine consumed by 1 m2 of the inner wall surface of a pipe per hour (J-value) can be used for this purpose. To estimate the J-value for a pipe, a zero-order rate equation was adopted for chlorine reduction caused by a pipe wall, based on laboratory experimental results. The J-value was closely related to characteristics of the pipe material. The J-value for old unlined metallic pipes was extremely large (J > 18 mg mr-2 hr-1), whereas that for plastic polymer pipes was very small (J < 0.08 mg mr-2 hr-1). The J-value for cement mortar lined pipes increased exponentially with increasing water temperature. This paper proposes an effective method on the basis of J-value for residual chlorine management practices. First, this method is used to identify those pipes which consume relatively more chlorine than other pipes. Maximum allowable residence time (MART), within which the required minimum chlorine concentration can be maintained, can also be estimated by this method. MART is useful to determine necessary and sufficient measures for shortening water residence time in identified pipes. © IWA Publishing 2012.

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