1. Hokkaido University, Graduate School of Engineering, Department of Environmental Engineering, Kita-13, Nishi-8, Kita-ku, Sapporo, 060-8628 Japan, (E-mail: malz31@hotmail.com)
2. Hokkaido University, Graduate School of Engineering, Department of Environmental Engineering, Kita-13, Nishi-8, Kita-ku, Sapporo, 060-8628 Japan, (E-mail: funamizu@eng.hokudai.ac.jp)