Sustainability assessment of bioethanol and petroleum fuel production in Japan based on emergy analysis

To promote the reduction of greenhouse gas emissions, research and development of bioethanol technologies are encouraged in Japan and a plan to utilize untilled fields to develop rice for bioethanol production as a substitute for petroleum fuel is being devised. This study applies emergy methods to compare the sustainability of petroleum fuel production and two Japanese rice‐to‐ethanol production scenarios: (a) ethanol from rice grain, while straw and chaff are burned as energy and (b) ethanol from rice+straw+chaff. The major emergy indices, Emergy Yield Ratio (EYR), Environmental Loading Ratio (ELR), Emergy Investment Ratio (EIR), Emergy Sustainability Index (ESI), Environmental Impacts Ratio (EVR) and system transformity (Tr), are analyzed to assess the production processes. The results show that (1) petroleum fuel production presents higher ELR, EIR, EVR and lower EYR, ESI, Tr than rice‐to‐ethanol production, indicating rice‐to‐ethanol production makes sense for reduction of greenhouse gases (GHG); (2) scenario (a) performs similarly on major indicators (EYR, ESI, ELR, EIR and EVR) to scenario (b), yet the system efficiency indicator (Tr) of scenario (a, 7.572×10⁵ semj/J) is much higher than (b, 4.573×10⁵ semj/J), and therefore (b) is a better alternative for policy decisions; (3) both petroleum fuel production and rice‐to‐ethanol processes are mainly driven by purchased resources and are unsustainable and nonrenewable in the long run.