There is considerable interest in minimizing the chlorine residual in Japan's tap water because of increasing consumer complaints about the chlorinous odor of drinking water. However, minimization of the chlorine residual requires stricter control of biodegradable organics in finished water to ensure biological stability during water distribution. In this context, we investigated the improvement of biological stability of drinking water by nanofiltration (NF). The removal of assimilable organic carbon (AOC) was 52% on average, but showed large seasonal variation. It was found to be difficult to maintain the acceptable AOC level for biologically stable water by NF. In addition, significant bacterial regrowth in NF permeates was still observed without chlorination, although 52% AOC was removed. Then, the chlorine concentration required to prevent bacterial regrowth during distribution of nanofiltrated water was determined using continuous-flow reactor systems. The heterotrophic plate counts (HPC) densities in biofilm were monitored at different chlorine conditions. The results indicated that the NF process could significantly reduce the chlorine requirement of the finished water. The relationship between free chlorine residual and HPC in biofilm formed from 1 μgC AOC showed that a trace level of chlorine residual, <0.1 mg/L, could inactivate heterotrophic bacteria and prevent biofilm formation.
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Research Article|
November 23 2013
Chlorine requirement for biologically stable drinking water after nanofiltration
Y. Ohkouchi;
1School of Life and Environmental Science, Azabu University, 1-17–71 Fuchinobe, Chuo-ku, Sagamihara-shi, Kanagawa 252-5201, Japan
E-mail: okochi@azabu-u.ac.jp
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Y. Yata;
Y. Yata
2Engineering Headquarters, Hitachi Zosen Corporation, 7-89, Nanko-kita 1-chome, Suminoe-ku, Osaka 559-8559, Japan
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R. Bun;
R. Bun
3Kure Research Laboratory, Babcock-Hitachi K.K., 3300 Kazahaya, Akitsu-cho, Higashihiroshima-shi, Hiroshima 739-2403, Japan
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S. Itoh
S. Itoh
4Graduate School of Engineering, Kyoto University, Kyoto Daigaku Katsura C-cluster Building I, Nishikyo-ku, Kyoto 615-8540, Japan
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Water Supply (2014) 14 (3): 405–413.
Article history
Received:
August 13 2013
Accepted:
November 11 2013
Citation
Y. Ohkouchi, Y. Yata, R. Bun, S. Itoh; Chlorine requirement for biologically stable drinking water after nanofiltration. Water Supply 1 June 2014; 14 (3): 405–413. doi: https://doi.org/10.2166/ws.2013.214
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Y. Ohkouchi, Y. Yata, R. Bun, S. Itoh; Chlorine requirement for biologically stable drinking water after nanofiltration. Water Supply 1 June 2014; 14 (3): 405–413. doi: https://doi.org/10.2166/ws.2013.214
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