1. Biogas Institute of Ministry of Agriculture, Chengdu 610041, China
2. Key Laboratory of Development and Application of Rural Renewable Energy, Ministry of Agriculture, Chengdu 610041, China
3. Institute of Ecological and Environmental Sciences, Sichuan Agricultural University, Chengdu, Sichuan 611130, China
4. Rural Environment Protection Engineering & Technology Center of Sichuan Province, Sichuan Agricultural University, Chengdu, Sichuan 611130, China
5. State Grid Sichuan Power Economic Research Institute, Chengdu, Sichuan 610041, China