Assessment and Selection of Cyanobacterial Strains for CO2 Mineral Sequestration: Implications for Carbonation Mechanism

CO2 mineral carbonation induced by microalgae is an emerging approach to carbon capture, utilization, and storage (CCUS). Freshwater cyanobacteria are common microalgae in nature that can raise the pH of eutrophic waters and drive the precipitation of carbonate. Still, limited studies have been conducted to evaluate and select appropriate cyanobacteria strains for CCUS. Here we present experimental investigations to compare the capacity of different freshwater cyanobacterial strains in converting CO2 to carbonates. We compare five cyanobacterial strains by monitoring their growth curves. We examine three metrics, the maximum pH of the solution, hydroxide production capacity, and extracellular polymeric substances (EPS) secretion capacity, to assess the capacity for carbon sequestration. Our results indicate that among the five strains, Microcystis aeruginosa shows the highest pH and EPS content per unit cell number, marking the most significant capacity for CO2 carbonation. We observe carbonate precipitates as hydromagnesite and dypingite. We suggest the negatively charged, hydrophilic EPS can effectively promote the precipitation of magnesium carbonate and inhibit the precipitation of calcium carbonate. Overall, our approach provides a framework for assessing and selecting cyanobacterial strains for CO2 carbonation, advancing the understanding of the mechanism of microalgae-induced CO2 Mg-carbonation from the perspective of EPS surface properties.