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The California Low Carbon Fuel Standard (LCFS) regulations were recently re-adopted (2015) with numerous revisions to the 2009 LCFS. Many aspects of the California Air Resources Board's (CARB) approach to modeling indirect land use change (ILUC) emissions have changed, including significant updates to the Global Trade Analysis Project (GTAP) agro-economic model and use of a new emission factor (EF) database derived from the Agro-Economic Zone Emission Factor (AEZ-EF) model. These revisions have resulted in significantly reduced Carbon Intensity (CI) values for many biofuel pathways, making them more attractive to meet greenhouse gas (GHG) reduction targets. The objective of this work was to investigate the most significant changes made to CARB's approach of modeling ILUC, the reasons for these changes, and their impacts on calculated CI values of biofuels. In this effort, land use change (LUC) estimates from GTAP and the AEZ-EF emission factors (EF) were compared to previous values. A new subset of land type, referred to as "cropland-pasture" has been incorporated into the GTAP-BIO model, and now constitutes the bulk of LUC for corn ethanol, soy biodiesel and sugarcane ethanol. However, since EFs of cropland-pasture are not well established, the AEZ-EF model simply applies an EF that is equivalent to 50% of the EF for conversion of pasture to cropland for the same AEZ region. In addition, differences in carbon accounting between perennial crops and annual crops contribute significantly to large reductions in sugarcane CI. These influential assumptions require further investigation.

Expanding the domestic bioeconomy can help diversify the use of national resources and reduce emissions. Evaluating the sustainability of a growing bioeconomy, however, is inherently complex since it spans several sectors and supply chains. It requires a comprehensive, integrated analysis framework to assess the developments across the traditional sustainability dimensions. Further, the assessment of bioeconomy developments requires a robust baseline of historic data and trends. In this paper, we analyze the evolution of the biofuel portion of the US bioeconomy, focusing on two fuels that had an exponential growth in the last two decades: corn ethanol and soybean biodiesel. For this purpose, we created a novel time series of harmonized environmentally-extended input-output (EEIO) tables based on a publicly available model from the US Environmental Protection Agency and expanded its disaggregation to reflect the main supply chains of the biofuels sectors. The EEIO time series provides the historical evolution of these biofuels relative to the rest of the economy as well as on an energy-unit basis. We find that, except for energy use, the broader US economy declined in both resource intensity and most environmental impacts when normalized per one million dollars of gross domestic product. Deviating from this trend are freshwater ecotoxicity and human toxicity, mainly attributable to the expansion of commodity crops and the increase of domestic oil and gas extraction respectively. We also find that the biofuel industry's total socioeconomic, resource use and environmental impacts grew with their production increases over time. However, the industry's maturation and scale-up, combined with higher feedstock yields, contributed to a reduction of most impacts on an energy-unit basis over time.

Carbon dioxide (CO2) supply is an important consideration for algae production systems, and using high-purity CO2 eliminates the need for purification processes. This study assessed the challenges and opportunities inherent in using waste high-purity CO2 to produce algae in the United States. The United States’ upper Midwest region is rich in high-purity CO2 from corn ethanol production. However, its climate is not as favorable for algae production as that on the Gulf Coast. This study assessed the tradeoffs between these factors by comparing algae biofuel production with and without high-purity CO2 across these two regions. Monthly algae cultivation was modeled in open ponds co-located with high-purity CO2 sources in the Midwest and along the Gulf Coast, where many steam methane reforming and ammonia production facilities are located. This revealed that, by avoiding the energy-intensive carbon-capture process, an algae site that sources carbon from a high-purity CO2 source would achieve a 9–39% reduction in life-cycle greenhouse gas (GHG) emissions and a 9–37% reduction in life-cycle fossil energy use compared to a similar site using dilute CO2 for algae cultivation. The results also suggest that during warm months an algae pond in the Midwest would achieve results that are comparable to GHG emissions from a pond on the Gulf Coast. Furthermore, several Midwest algae ponds investigated in this study create less local water stress than those located along the Gulf Coast. The abundant high-purity CO2 from corn ethanol plants thus creates a potential opportunity for algae cultivation in the Midwest. This study illustrated the interplay between algae productivity, CO2 delivery, GHG emissions, and water stress in siting algae ponds.

The aim of this study was to conduct the first comprehensive life cycle assessment and economic analysis on ethanol produced from agave. Compositional and field data from a field experiment in Queensland, Australia was used. Our study shows that ethanol yields from agave (7414 L/ha/year) are comparable to Brazilian sugarcane (9900/L/ha/year) and higher than US corn ethanol (3800/L/ha/year). Furthermore, agave outperforms current first generation biofuel crops in water-related impacts, including Freshwater Eutrophication (96% lower than corn and 88% lower than sugarcane), Marine Ecotoxicity (59% lower than corn and 53% lower than sugarcane) and Water Consumption (46% lower than corn and 69% lower than sugarcane). The life cycle fossil energy use (Fossil Resource Scarcity) for agave is 58% lower than corn and 6% higher than sugarcane. The Global Warming impact for agave is also 62% and 30% lower than that of corn and sugarcane, respectively. Although its Land Use impact, measured by land occupied per unit ethanol output, is 98% higher than corn and 2% higher than sugarcane, agave can be grown on arid land that is not suitable for food crops. The economic analysis suggests that first generation ethanol production from agave is not commercially viable without government support. Overall, the results show that agave is promising for biofuel production in the water-energy-food-environment context.

European and United States' (U.S.) regulatory schemes mandate the use of biofuels based on estimates of life cycle GHG emissions that indicate their environmental superiority compared with conventional fuels. This paper analyzes the quality of the activity data used in calculating these estimates for Brazilian sugarcane and U.S. corn ethanol, in terms of completeness, reliability, and transparency. The findings demonstrate that it is impossible to determine the completeness of the data because the regulation's texts and related documents, and their sources fail to provide information on the representativeness or origins of the data. Moreover, there is no transparency about the sample from which data is extracted. To obtain this information it is necessary to review the literary sources referenced in the regulation's documents. Among the 37 sources of data examined in this analysis, 23 are no longer available, and only 3 sources contain information allowing for the characterization of the adequacy of the sample. In addition, none of the data items analyzed were subject to a verification process. These findings highlight the urgent need to modify biofuel regulation to set minimum standards for data quality and the reporting of data sources, paying particular attention to default activity data.

The existing methods of process-based life cycle assessment (LCA) fail to account for the role of ecosystem goods and services derived from natural capital. This study presents an in-depth analysis of resource consumption and atmospheric emissions across a wood-derived bioethanol supply chain. The analysis is based on energy consumption, Industrial Cumulative Exergy Consumption (ICEC), and Ecological Cumulative Exergy Consumption (ECEC) of resources used in the production of one ton of ethanol from woodchips using the near-neutral hemicellulose extraction technology. We found that when compared with fossil-based fuels and corn ethanol, wood-based cellulosic ethanol derived under the near-neutral hemicellulose extraction process demonstrated superior environmental performance. Renewable resources - mostly sunlight and detrital matters-are the dominant contributors to ICEC analysis, whereas non-renewable resources such as crushed stone, crude oil, ores and minerals contribute more to total ECEC. Lime manufacturing, inorganic chemicals production for green liquor preparation, and anthraquinone production have the highest resource consumption. The woodchip washing process and transportation stages consume relatively fewer resources. A performance metric analysis suggests that even though cellulosic ethanol uses a renewable feedstock, its environmental sustainability performance is reduced due to the large consumption of non-renewable resources during the ethanol production stage.

This study reviews corn–ethanol life cycle assessment studies and modeling tools to identify key discrepancies between studies, and shortcomings in analysis of greenhouse gas emissions. The primary conclusions are that direct land use change modeling, soil N 2 O emissions modeling, and co-product crediting were either poorly treated or treated inconsistently across most or all studies. Despite the existence of improved methods and tools proposed by institutional bodies and the broader research community, the state of the practice tends towards over-simplified and highly generalized methods that increase potential uncertainty in greenhouse gas estimates and prevents differentiation among producers of corn ethanol.