1. College of Environmental Science and Engineering, Hunan University, Changsha 410082, P.R. China
2. Key Laboratory of Environmental Biology and Pollution Control, Ministry of Education, Hunan University, Changsha 410082, P.R. China
3. School of Hydraulic Engineering, Changsha University of Science and Technology, Changsha 410114, P.R. China
4. Department of Chemical Engineering and Technology, Imperial College London, Exhibition Road, London SW7 2AZ, United Kingdom