1. Mikawashima Sewage Treatment Plant, Sewage Bureau, Tokyo metropolitan Government, 8-5-1, Arakawa, Arakawa-ku, Tokyo, 116-0002, Japan (E-mail: takahome0511@dream.com)
2. Water Environment Research Group, Public Works Research Institute, 1-6, Minamihara, Tsukuba city, Ibaraki, 305-8016 Japan (E-mail: tamamoto@pwri.go.jp; htanaka@pwri.go.jp)
3. Chemical and Environmental Technology Laboratory, Kobe Steel, Ltd., 1-5-5, Takatukadai, Nisi-ku, Kobe city, Hyogo, 651-2271 Japan
4. EAC Corporation, Ltd., 456, Johoji, Onishi-machi, Gunma, 370-0014 Japan