1. Department of Chemical Engineering, Sogang University, C.P.O. Box 1142, Seoul, South Korea, Division of Environmental and Process Technology, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650, South Korea, and Department of Environmental and Civil Engineering, Kimpo College, San 14-1 Ponae-ri Wollgot-myun, Kimpo-si, Kyunggi-do, 415-870, South Korea