Exploring a Bicarbonate-based Carbon Capture Approach Applicability to Industrially Relevant Marine Microalgae

Microalgae represent the primary producers of valuable molecules in the marine ecosystems, such as essential fatty acids and antioxidants, that can be exploited as nutritive supplements in animal feeds and human food, as well as in nutraceuticals. However, their industrial massive production is currently limited by high cultivation costs. CO2 insufflation and management as well as mixing and cooling operations require an important energetic investment, decreasing the overall profitability of the process. The recently theorized BICCAPSO (Bicarbonate-based Induced Carbon Capture and Algae Production System on Ocean) approach aims at addressing these limitations by coupling the exploitation of alternative inorganic carbon sources, such as sodium bicarbonate, with the use of cheaper sea-powered floating photobioreactors. Although the promising potential, some challenges must be faced when applying such a cultivation rationale. The use of bicarbonate as sole carbon source, for instance, leads to a progressive pH increase in the cultivation environment, affecting both microalgae growth and carbon availability. For this reason, most of the literature regarding bicarbonate-based cultivation is limited to alkaliphilic microalgae species, eventually excluding industrially-relevant strains. In this work both alkaliphilic and mesophilic microalgae were cultivated in batch mode applying the BICCAPSO approach. Results suggest that this strategy can be extended also to mesophilic strains when carbon concentration is well-balanced, reaching a maximum biomass productivity of 0.35 g L-1 d-1 with the model diatom Phaeodactylum tricornutum. Moreover, we focused also on pH management, by trying diverse strategies to stabilize this operative variable with the aim of further increasing biomass productivity without affecting process economics.