Evaluation of the life cycle of bioethanol produced from rice straws

This study evaluated the life cycle of bioethanol produced by enzymatic hydrolysis of rice straw. Net energy consumption, CO2 emission and production costs were estimated to determine whether environmentally preferable and economically viable bioethanol can be produced from rice straws. Two varieties of rice straw (Koshihikari and Leafstar), three energy scenarios (F-E-RH: Fuel-Electricity-Residues used for Heat; F-E-RE: Fuel-Electricity-Residues used to generate Electricity; F-RE: Fuel-Residues used to generate Electricity) and three types of primary energy (heavy oil; LNG: liquefied natural gas; agri-residues) were considered. The net energy consumption, CO2 emission and production costs were estimated to be 10.0–17.6 MJ/L, −0.5 to 1.6 kg/L and 84.9–144.3 ¥/L (1 US$ ≈ 100 ¥), respectively, depending on the feedstock and scenarios of this study. A shift in energy scenarios or in the type of primary energy (heavy oil to LNG or agri-residues) not only reduces emissions and production costs of bioethanol from rice straw, but may also reduce the fluctuation in production cost over time and risk on investment, which would encourage more investment in this sector.