Environmental Impacts of Cellulosic Biofuels Made in the South East: Implications of Impact Assessment Methods and Study Assumptions

National and state governments have responded to the potential threats of climate change by mandating the use of renewable fuels and energy sources. The Renewable Fuel Standard 2 (RFS2) legislation put into law in 2007 required the production of 36 billion gallons of renewable fuel by 2022 with specified GHG reductions as compared to gasoline (EISA 2007). The original legislation required petroleum producers to purchase 6 billion ethanol equivalent gallons of cellulosic biofuels in 2013, however, this mandate was recently adjusted to 810,184 ethanol equivalent gallons due to insufficient supply. The insufficient supply of cellulosic biofuels can be attributed to high delivered biomass cost, high conversion process capital requirements, and insufficient technology to profitably convert cellulosic biomass to biofuels.;In addition to technical difficulties, there is controversy surrounding the environmental impacts of biofuels and the methods used to calculate these environmental impacts. The environmental impacts of biofuels made from a range of cellulosic feedstocks using numerous emerging conversion technologies are difficult to compare due to inconsistent life cycle assessment (LCA) methods and data. Conversion pathways with the lowest environmental impacts can be identified through implementing the most robust LCA methods, using consistent study assumptions, and using consistent biomass LCA data. Increased consistency in biofuel LCA methodology will develop more evidence characterizing the environmental impacts of biofuels..;The goal of this dissertation work is to fill in some of the missing pieces mentioned above by providing focused research projects. This will be done using a series of associated studies. The first study determines the delivered cost and environmental impacts of cellulosic biomass grown in the South East with consistent assumptions and data. Results from this study enable more consistent technology comparisons as the environmental impacts and financial performance of each feedstock were determined using consistent data and assumptions. On a cradle-to-gate basis, forest based feedstocks were determined to have lowered delivered costs and lower environmental impacts due to no storage requirements, lower management intensity, and less frequent harvesting. Direct land use change (LUC) was shown to increase biomass GHG emissions when converting forest to agriculture lands and shown to reduce GHG emissions when converting agriculture lands to forest.;In the third and fourth study, the environmental impacts of cellulosic biofuels made with the thermochemical and biochemical conversion pathways. Global warming impacts (GWI) of forest based biofuels were lower than agriculture based feedstocks, however, all biofuel scenarios reduced GWI and energy use compared to gasoline. When examining additional impact categories, environmental tradeoffs were present when comparing biofuels to gasoline. A multivariate analysis determined the effects of weighting methods and study assumptions on the analysis conclusions. Single weighted score biofuel scenario ranking was different than the GWI scenario ranking as GWI contributed minimally to the single weighted score; carcinogens and non-carcinogens related to process chemical production dominated the single score result. Biofuel scenario ranking based on GWI was sensitive to LUC and co-product treatment methods, however, the single score ranking was not, except in one LUC scenario of converting natural forest to agricultural lands. Impact weighting methods did not to influence the biofuel scenario single score ranking.;The implications of GHG accounting method in the context of biofuel GWI was explored in the fifth study. Dynamic GHG accounting using consistent time horizons (TH) was compared to traditional global warming potential (GWP) method with a 100 year TH. Biofuel scenario ranking was sensitive to TH and the starting condition assumption of biomass planting or harvesting. Biofuel scenario GWI was more sensitive to these study assumptions when biomass types with longer growth cycles were used.