1. School of Environmental Science and Engineering/Tianjin Engineering Research Center of Bio Gas/Oil Technology, Tianjin University, Tianjin 300072, P. R. China
2. School of Ecology and Environment, Tibet University/Key Laboratory of Plateau Environmental Engineering and Pollution Control, Lhasa 850000, P. R. China
3. School of Civil Engineering and Architecture, East China Jiaotong University, Nanchang 330013, P. R. China
4. Department of Chemical Engineering, Tianjin University, Tianjin 300350, P. R. China
5. Metener Ltd., Nokia 37150, Finland
6. School of Mechanical Engineering, Tianjin University of Commerce, Tianjin 300134, P. R. China