Hybrid LCA: uncertainties on the sustainability assessment of first and second generation ethanol production

In this paper, a hybrid assessment integrating Life Cycle Assessment (LCA) and Input-Output Analysis (IOA) is used to assess the impacts of first and second generation ethanol production technologies in Brazil. This study will simulate three scenarios representing possible combinations of both agricultural and industrial technologies. Two scenarios will describe first generation ethanol production biorefineries: one is related to the average current technology in the country and the other represents the best current technology which enables the biorefinery to export electricity to the grid. A third scenario is built to represent an integrated first and second ethanol production technology considering solids loading, hydrolysis yield and other parameters achievable in a near future. The first scenario uses sugarcane with straw burning for manual harvesting; on the other hand, the second and the third scenarios use sugarcane without straw burning for mechanical harvesting. The model used to perform such simulations relies on data whose uncertainties are considered in this study. For instance, sugarcane yields, straw recovering costs, enzyme costs, ethanol yields and other inputs can be better described as distributions instead of point estimates. As a consequence, the outputs obtained will be related to probability density distributions instead of deterministic values. The main model outputs assessed in this paper are related to economic, environmental and socioeconomic impacts: the level of economic activity of sectors involved in ethanol production supply chain (measured in US$), greenhouse gas emissions (g CO_2-eq/MJ of ethanol), and job creation.