Assessing the critical role of ecological goods and services in microalgal biofuel life cycles

Microalgal bioenergy systems are gaining attention as a commercial biotechnical platform for producing renewable transportation fuels. In recent years, process-based life cycle assessment (LCA) has been extensively applied to understand the life cycle environmental impacts of emerging microalgal biofuel systems. However, conventional process-based LCA fails to account for the role of ecological goods and services within fuel and product life cycles. Additionally, traditional life cycle energy analysis suffers from several limitations such as ignoring the difference in quality and substitutability of resources, and accounting for only the first law of thermodynamics. To address these shortcomings, a hybrid Ecologically based-LCA (EcoLCA) model is developed to quantify the contribution of ecological resources within the algae-to-fuel supply chain and to compare the resource intensity of producing microalgal derived renewable diesel (RD) to that of petroleum diesel (PD). Multiple thermodynamic return on investment (ROI) metrics and performance indicators are used to quantify the consumption of ecological goods and services, environmental impacts, and resource intensity of producing microalgal RD. Results indicate that the quality corrected thermodynamic return on investment and renewability index for microalgal RD ranges from 0.17 to 0.44 and 3.51% to 6.36% respectively, depending on the choice of coproduct options and processing technologies. This work reveals that algae-to-fuel systems are highly dependent on non-renewable ecological resources reflected in their low renewability index; have a low quality corrected thermodynamic ROI (< 1) and thus are not energetically viable; and are more ecologically resource intensive as compared to their petroleum equivalent-potentially negating their environmental benefits.