(790g) Assessing the Critical Role of Natural Capital in Microalgal Biofuel Production

Current global trends in resource consumption and fossil fuel depletion have driven research in biomass-to-energy systems. In recent years, microalgal biofuel have gained increased attention as a sustainable liquid-fuel alternative. Microalgal derived fuels do not suffer from many of the major drawbacks associated with first or second generation biofuels, and have the potential to act as “drop in” replacements for traditional petroleum fuels. As an emerging field, holistic evaluation of algae-to-fuel systems that considers the resource consumption, emissions, and their impact across the entire life cycle is critical to ensure the long-term sustainability of emerging algae-based energy systems. Current interest in microalgal biofuels has led to several microalgae based life cycle assessments (LCA). Most of these studies have focused on quantifying the greenhouse gas emissions and the net energy balance for microalgal biofuel production without sufficient attention to the spatial variability in algal biomass growth rates, climatological conditions, and stresses on ecological goods and services. As ecosystem goods and services (natural capital) provide the foundation for manmade capital, incorporating the broader role of ecosystem goods and services is critical to any accurate measure of sustainability. Proper quantification of ecosystem goods and services is also critical to assess the vulnerability of emerging microalgal biofuels to the depletion of natural capital and the role that nature plays in making ecological resources available for biofuel supply chains.

This work focuses on a comprehensive life cycle evaluation of 48 microalgal biomass production pathways. We build upon our prior research and examine multiple cultivation locations, culture conditions, cultivation and harvesting options, and industrial symbiosis within microalgal biomass production for the continental United States. Process flows and life cycle inventories are constructed based on first principles, peer reviewed literature, LCA databases, and best available engineering knowledge. The role of natural capital for emerging algae-to-energy systems is accounted for via the use of EcoLCA model. EcoLCA is a recent environmentally extended input-output life cycle oriented approach capable of accounting for the role of natural capital such as ecosystem goods and services in LCA. EcoLCA model considers a wide array of goods and services derived from nature and a hierarchical, thermodynamic aggregation scheme to permit meaningful interpretation. We quantify and aggregate the contribution of ecosystem goods and services in terms of mass, energy, and exergy (available energy) for the algae-to-energy systems. A variety of hierarchical metrics such as quality corrected thermodynamic return on investment and renewability index for the algae-to-energy systems are also developed. Tradeoffs between life cycle environmental impacts are analyzed via a series of two-dimensional pareto optimal surfaces. Synthesis of these results provides insights regarding the vulnerability of the emerging algae-to-energy systems to the depletion of specific resources.