1. Department of Chemical Engineering, Korea University, 1, 5-Ka, Anam-dong, Sungbuk-gu, Seoul 136-701, Korea, KOPEC Ltd., 449-713, Mabuk-li, Gusung-myun, Yongin, Kyonggi-do 449-713, Korea, and Department of Environmental Engineering, Kyonggi University, San 94-6, Yiui-dong, Paldal-gu, Suwon, Kyonggi-do 442-760, Korea