1. School of Chemical Engineering, Seoul National University, Seoul 151-742, Korea, and Division of Architectural, Civil, and Environmental Engineering, Taegu University, Kyungsan, Kyungpook 712-714, Korea, and School of Environmental Engineering, Pohang University of Science and Technology, Pohang 790-784, Korea, and Department of Chemical and Environmental Engineering, Soongsil University, Seoul 156-743, Korea