Climate Implications of Next Generation Biofuels Produced from Algae

Abstract

Algae-based fuels are being widely investigated in an effort to develop renewable and carbon-neutral bioenergy feedstocks. Despite this, there is little evidence that largescale algae cultivation can achieve carbon reductions relative to conventional, petroleumderived liquid fuels. This work explores a variety of systems-level aspects of algae-toenergy processes in an effort to understand the real potential of algae fuels to achieve deep reductions in carbon emissions. This work is both challenging and important because the algae-to-energy industry is still in its nascent stage and few commercial scale facilities currently exist to model. Those that do exist are seeking guidance on how to produce low carbon fuels. To provide insights into this question, I made four specific contributions to the academic literature. The first contribution is the development of a meta-analysis of life cycle studies that modeled algae-to-energy systems. The literature is seemingly inconclusive about the anticipated impacts of algae-based biodiesel and this analysis was structured to reconcile these inconsistencies. The results indicate that algae biodiesel has environmental performance on par with that of traditional biofuels with room for improvement as the process is optimized. The second contribution of this work is the development of a comprehensive life cycle model of algae fuels produced via hydrothermal liquefaction. This model, which was developed in conjunction with an industry partner, is the first of its kind to use pilot-scale data. The model suggests that ii algae fuels can achieve significant reduction in GHG emissions compared with petroleum alternatives and will have viable energy return on investment when algae are cultivated at full scale. The third contribution from this work is the development of a method for characterizing land use effects of biofuel feedstock cultivation. The novel approach that I propose is based on the use of historical cropland data, rather than indirect or direct land use. This approach addresses several persistent issues in existing frameworks and the results of this analysis side step much of the uncertainty intrinsic to existing models and represent the first step toward developing a more integrated and equitable land use emissions framework. The fourth and final contribution from this work is to develop a nation-wide model of CO 2 industrial sources using newly available CO 2 emissions data collected by the US Environmental Protection Agency. This model suggests that there are significant portions of the country without access to commercially relevant volumes of CO 2 and this could impact pond location selection. The characteristics of the CO 2 sources are such that much of the CO 2 in the US is relatively 'dirty' coming from a source with a high carbon footprint of its own. This suggests that there are opportunities to optimize our CO 2 supply chain in an effort to achieve system-scale reductions and improve the sustainability of algae-to-energy processes.iii