Efficiency and sustainability analysis of biogas and electricity production from a large-scale biogas project in China: an emergy evaluation based on LCA

摘要

Biogas, which plays an important role in energy production and environmental protection, is developing at a large-scale in China to accommodate the modernization and fast pace that the Chinese agricultural sector has experienced over the last decade due to the rapid development of large-scale farms and stockbreeding in recent years. This study introduced life cycle assessment (LCA) into emergy evaluation to analyze each production step of a large-scale biogas project in China and to compare the economic and ecological performance of the biogas production system (BPS) and biogas plus electricity production system (BEPS) of a project. Our findings indicated that the energy return rate of biogas production system was lower than that of traditional energy production system currently. Emergy efficiency of the large-scale biogas project was 77.9-95.6% higher than that of the small-scale biogas project. The emission mitigation intensity was also 125.7-172.7 times higher for the large-scale plant than for the small-scale plant. The sustainability of the large-scale biogas project was 1.16-11.87 times higher than that of other renewable energy production systems, but 66.0-74.4% lower than that of the small-scale biogas project due to an insufficient amount of raw material inputs and the higher cost of equipment investment in anaerobic fermentation and electricity generation steps. Moreover, the economic and ecological performance of BEPS was worse than that of BPS. We suggested that the sustainability of the large-scale biogas project would be improved by measures: first, providing a suitable quantity and ratio of raw materials; second, reducing the equipment investment of fermentation and the generator; third, using the electricity from the biogas system.