Evaluation of the life cycle of bioethanol produced from soft carbohydrate-rich and common rice straw in Japan with land-use change

This study evaluates the life cycle of ethanol produced from soft carbohydrate (SC)-rich rice straw (cv. Leafstar) and common rice straw (cv. Koshihikari) while considering land-use change to estimate CO2 emissions, energy balance (expressed as Net Energy Ratio, NER), and production costs. Three different pretreatment methods were considered: the DiSC (direct saccharification of culms), RT-CaCCO (room temperature-CaCCO) and CaCCO (calcium capturing by carbonation) processes. Although the reduction in CO2 emission was found to be 59%, 42% and −3.5% for the DiSC, RT-CaCCO and CaCCO processes, respectively, the CO2 emission reduction decreased significantly when land-use change was considered. This result clearly shows that the biomass (rice straw) should be obtained from paddy fields without land-use change. The NER values for the bioethanol produced by the DiSC, RT-CaCCO and CaCCO processes were estimated to be 2.7, 2.1 and 1.0, respectively, and the total costs were estimated to be 102, 134 and 151 Yen/L ethanol, respectively (US $1 = 100 Yen). The use of the SC-rich rice straw contributes to a reduction of the environmental load and costs for the pretreatment, enzyme production, and enzymatic hydrolysis processes. Therefore, the use of SC-rich rice straw for bioethanol production reduces the total cost of production, reduces CO2 emissions, and improves the NER. Our results suggest that the DiSC and RT-CaCCO pretreatment processes are promising pretreatment techniques and that SC-rich rice straw is a promising resource for bioethanol production.