Biogas has been earmarked as an efficient way to promote economic development and mitigate environ- mental emissions, and it requires a better accounting framework to evaluate its performance. In this study, we aim to develop an emergy-based accounting framework to assess and report the sustainability performance of biogas projects. First, the existing financial accounting and environmental accounting methodologies are combined to measure and report the economic events and environmental character- istics of a biogas project. Then, using the new metric of Emdollar value, the cost and revenue flows within the system boundary are unified and quantified by multiplying specific emergy transformity to reflect their embodiment and hierarchical characteristics. An integrated accounting framework covering economic aspects (economic profitability, economic efficiency, operation risk), environmental aspects (environmental resource utilization, load, emissions) and environmental-economic composited charac- teristics (emissions reduction efficiency, Emdollar intensity of emission reduction, emission intensity of profit) is set up accordingly. Results show that the biogas project has a positive net present value of 1.64E+04 Emdollars. The total cost can be returned after 5 years. The renewability ratio, environmental load ratio (ELR), and composite sustainability indicator (CSI) reflecting environmental load are 9%, 10.1, and 0.76, respectively. The proposed sustainability accounting framework may unveil the real environmental support and assess the ecological economic performance of a biogas project.
