Potential of Microalgal Biomass Production in Coastal Deserts for Carbon Dioxide Removal.

High photosynthetic yields and the ability to grow without fresh water make microalgae interesting mechanisms for carbon dioxide removal (CDR). We characterize two CDR systems which grow microalgae in seawater in coastal deserts─microalgal bioenergy with carbon capture and storage and microalgal biomass burial─and evaluate their potential when using carbon sourced from the atmosphere or ocean to meet CDR objectives via a comparison with direct air carbon capture and storage (DACCS). By deriving and validating a theoretical model of chemically enhanced carbon dioxide mass transfer, we identify the importance of gas-liquid mass transfer into raceway ponds as limiting microalgal productivities and determining technoeconomic viability. Our analysis shows that, while microalgal CDR cannot compete with DACCS in the areal productivity of removals, net removal costs with marine carbon supply are only slightly higher than DACCS with prospects for parity. Though such outcomes may not yet support the use of microalgal biomass for CDR, the carbon supply apparatuses outlined and the theoretical models accompanying them can inform ongoing research into microalgal cultivation without carbon addition for diverse applications.