Investigation of environmental impacts of bioethanol production from wheat straw in Kermanshah, Iran

Renewable fuels have been gaining attention worldwide due to their promise of lower carbon footprint and energy security as well as their flexibility in converting a wide range of biomass resources including agricultural residues. This study investigates the potential environmental advantages that could be gained by local conversion of wheat straw, a residue of wheat grain – a major cereal crop, to bioethanol in Kermanshah, Iran. To identify and recommend strategies to address the environmental impacts hotspots of 1 MJ wheat straw-based ethanol production and consumption compared with gasoline, a cradle-to-grave (Well-to-Wheel) life cycle assessment using TRACI 2.1 method was conducted. Subsystems considered within the system boundary of this study included wheat straw production and collection, transportation of wheat straw to biorefinery, conversion of the straw to bioethanol and electricity as a byproduct, and distribution and combustion of bioethanol. Results demonstrated that straw production and collection subsystem was the main contributor to the life cycle environmental impacts of the bioethanol in all categories, mainly due to on-farm emissions and electricity consumption for irrigation. Compared with gasoline (93 g CO₂ eq/MJ), ethanol production and consumption avoided 55.7 g CO₂ eq/MJ. Carbon sequestration during wheat cultivation subsystem and surplus electricity credit generated at the ethanol biorefinery subsystem offset majority of the negative impacts from other parts of the life cycle. An uncertainty analysis was performed in order to evaluate the effect of inherent variation in LCA model inputs of straw production on the carbon footprint of the system. Results indicated that the mean value of GHG emissions from wheat cultivation step is 254 kg CO₂ eq/tonne wheat straw, confirming minimum uncertainty exists in our base case scenario.