1. College of Environmental Science and Engineering and Key Laboratory of Environmental Biology and Pollution Control (Ministry of Education), Hunan University, Changsha 410082, P R China
2. Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Kowloon 999077 Hong Kong SAR, P. R. China
3. Department of Applied Science, School of Science and Technology, Hong Kong Metropolitan University, Ho Man Tin, Kowloon 999077 Hong Kong SAR, China