PNNL

Abstract

Building on our previous “2022 Algae Harmonization Update” work establishing harmonized models for investigating economics, greenhouse gas emissions, and resource availability for microalgae cultivation and conversion at a national scale, this study incorporates assessments of the water scarcity footprint, emissions from land use change, and the marginal cost of greenhouse gas (GHG) avoidance under varying levels of electricity decarbonization. Our findings demonstrate that electricity and nutrient consumption are the primary drivers of GHG emissions, while biomass yield is the key factor for the minimum selling price. Using the existing electricity grid, saline microalgal biorefineries can only achieve acceptable costs when high-value bio-coproducts, such as whey protein concentrate, are substituted, contingent on the protein coproduct's selling price, supply-demand conditions, and other market drivers. However, saline microalgae can achieve 61-83% of GHG emission reductions with carbon-neutral electricity at very small economic costs, resulting in marginal costs of GHG avoidance below the reference threshold. Additionally, saline microalgal biorefineries show great potential in addressing water stress, as the electricity requirements for desalinating brackish and saline water are relatively low compared to the overall system electricity demand.