1. School of Environment, Tsinghua University, Beijing 100084, China
2. Department of Petroleum Engineering, Universiti Teknologi Petronas, 32610 Bandar Seri Iskandar, Perak, Malaysia
3. Department of Mechanical and Process Engineering, ETH Zürich, 8092 Zürich, Switzerland
4. Beijing Engineering Research Center of Biogas Centralized Utilization, Beijing 100084, China