Abstract
This chapter provides an overview of the economic and environmental performance of biogas-linked agricultural system (BLAS) in China based on emergy. A set of emergy indices are incorporated to describe the energy and materials transformation within the system, and an emergy-based CO2 emission indicator (EmCO2) is proposed to achieve low-carbon optimization of the whole system. Emergy synthesis and emergetic ternary diagram are then utilized to evaluate the BLAS and its subsystems, with scenario analysis performed to identify a more sustainable development pathway for the BLAS. Finally, a framework is developed to track dynamical behaviors of the whole system (Level I), transforming process (Level II), and resource component (Level III) simultaneously, and two new indicators, emergy contribution rate (ECR) and emergy supply efficiency (ESE) are proposed to address the contribution and efficiency of resource components within each process. The results showed that BLAS made a favorable contribution to carbon mitigation and was more environment-friendly than the traditional agricultural systems. Scenario analysis demonstrated that continual biogas construction and effective technological revolution were preferable routes to further improve the whole system’s performance. It can be concluded that breeding and biogas subsystems were economic input-dependent. Electricity and diesels were the most efficient components in supplying all the processes in BLAS. The relatively high transformities and the constant descent of sustainability within all processes are the key problem that hinders the promotion of BLAS.