Off-flavors affecting the taste of tap water is considered as a major issue for drinking water supply. The bureau of Waterworks, Tokyo Metropolitan Government has taken its own approach to control 2-MIB, a substance that causes musty odor in tap water, at less than 3 ng/L. Recently, high concentration of 2-MIB has been detected in the upper stream of the Tama River where the water quality was considered as relatively good, and large amount of powdered activated carbon was used to remove 2-MIB. To improve the efficiency of removal of 2-MIB in conventional drinking water treatment plant, the application of fine powdered activated carbon is considered as a good option. However, remaining activated carbon in clarified water and release of 2-MIB from activated carbon by intermediate chlorination were concerned. Therefore, in order to ensure sufficient and effective removal by applying fine powdered activated carbon, the relationship between the residual amount of fine powdered activated carbon in the sedimentation water and the release of 2-MIB by intermediate chlorination was investigated. In addition, to enhance the removal of fine powdered activated carbon by coagulation sedimentation experiments were performed under the combined condition of PACl (poly-aluminum chloride) or high basicity PACl and polymer coagulant. As a result, we established the injection rate of fine powdered activated carbon and the conditions for coagulation and sedimentation treatment to suppress the release of 2-MIB, and to secure the target water quality.

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Trichloroacetic acid (TCAA) is a disinfection byproduct from the chlorination of natural organic matter. Because the Japanese drinking water quality standard of TCAA was revised to be 0.03 mg/L in 2015, the disinfection byproducts including TCAA were required to be controlled more severely in the water treatment process. The maximum concentration of TCAA in the tap water in Kyoto was 0.019 mg/L sampled on November in 2013, when the raphidophyte was observed in the raw water for the first time. The trend of TCAA concentration in the tap water showed the similar trend of the raphidophyte occurrence in the raw water. This study investigated the chlorination of the unialgal strain of the raphidophyte. As the result, TCAA formation was increased with increasing the cell number of the raphidophyte. In conclusion, the raphidophyte was found to be the main precursor of TCAA increased in the tap water in Kyoto on November in 2013. The pre-chlorination was stopped in the water treatment plants in Kyoto at the raphidophyte occurrence in the raw water.

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[in Japanese]

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