Biological CO2 sequestration from industrial flue gases using coccolithophores: lab-scale studies and preliminary photobioreactor design

Climate change and increasing atmospheric CO2 concentrations require the development of sustainable carbon capture and sequestration strategies. Among biological solutions, coccolithophores represent a particularly interesting group of microalgae, as they combine organic carbon fixation with inorganic CaCO3 precipitation into structured shells (coccoliths). This thesis investigated the species Chrysotila carterae through laboratory-scale studies, with the aim of evaluating its growth under different cultivation conditions, stimulating coccolith production, and assessing its potential for application in CO2 bio-sequestration systems. Environmental and nutritional parameters influencing productivity (light intensity, nutrient concentration, agitation systems) were analysed, measuring biomass, ratio between inorganic and organic carbon fractions, carbon dioxide fixation, and photosynthetic yield. The results highlighted the optimal conditions for maximizing both biomass accumulation and coccolith formation, confirming the species' dual contribution to carbon sequestration. In parallel, a preliminary design of a large-scale photobioreactor was developed, including mass and energy balances, water and energy consumption assessments, and emissions analyses, to verify its technical and environmental feasibility. The comparative evaluation of outdoor (natural light) and indoor (artificial light) configurations highlighted that natural light systems, although requiring larger surface areas, are more sustainable in terms of energy demand and emissions, while artificial light systems offer compactness and higher controllability at the cost of high energy consumption. Overall, the work contributes to defining the potential of coccolithophores as model organisms for biological CO2 sequestration and lays the foundation for future developments at pilot and industrial scale.