Total environmental impacts of biofuels from corn stover using a hybrid life cycle assessment model combining process life cycle assessment and economic input–output life cycle assessment
Authors: Liu Changqi , Huang Yaji , Wang Xinye , Tai Yang , Liu Lingqin , Liu Hao 
Published: August 2017

Abstract

Studies on the environmental analysis of biofuels by fast pyrolysis and hydroprocessing (BFPH) have so far focused only on the environmental impacts from direct emissions and have included few indirect emissions. The influence of ignoring some indirect emissions on the environmental performance of BFPH has not been well investigated and hence is not really understood. In addition, in order to avoid shifting environmental problems from one medium to another, a comprehensive assessment of environmental impacts caused by the processes must quantify the environmental emissions to all media (air, water, and land) in relation to each life cycle stage. A well-to-wheels assessment of the total environmental impacts resulting from direct emissions and indirect emissions of a BFPH system with corn stover is conducted using a hybrid life cycle assessment (LCA) model combining the economic input–output LCA and the process LCA. The Tool for the Reduction and Assessment of Chemical and other environmental Impacts (TRACI) has been used to estimate the environmental impacts in terms of acidification, eutrophication, global climate change, ozone depletion, human health criteria, photochemical smog formation, ecotoxicity, human health cancer, and human health noncancer caused by 1 MJ biofuel production. Taking account of all the indirect greenhouse gas (GHG) emissions, the net GHG emissions (81.8 g CO2 eq/MJ) of the biofuels are still less than those of petroleum-based fuels (94 g CO2 eq/MJ). Maize production and pyrolysis and hydroprocessing make major contributions to all impact categories except the human health criteria. All impact categories resulting from indirect emissions except eutrophication and smog air make more than 24% contribution to the total environmental impacts. Therefore, the indirect emissions are important and cannot be ignored. Sensitivity analysis has shown that corn stover yield and bio-oil yield affect the total environmental impacts of the biofuels more significantly than the biomass transportation distance and biofuel transportation distance. Integr Environ Assess Manag 2018;14:139–149. © 2017 SETAC

Key Points
Indirect environmental impacts and direct environmental impacts of biofuel production systems are evaluated by a hybrid LCA model combining process-analysis–type life cycle assessment (PLCA) and economic input–output LCA (EIO-LCA). Net GHG emissions (81.8 g CO2  eq/MJ) of the biofuels produced by BFPH of corn stover, including direct and indirect emissions, are found to be lower than the overall emissions of petroleum-based fuels (94 g CO2 eq/MJ). The indirect emissions are found to be significant and cannot be ignored for the impact categories of global warming, acidification, ozone depletion, human health criteria, ecotoxicity, human health cancer and noncancer, especially for the stages of maize production and pyrolysis, and hydroprocessing. More attention and action should be applied to improving corn stover yield and bio-oil yield in order to reduce the impacts on the environment.