Biomass performance and stability of 5-year outdoor microalgal cultivation for CO2 removal from cement flue gas

The study evaluated removal of industrial CO2 from cement flue gas using algal cultivation. Local polycultures were grown in an up-scaled outdoor photobioreactor over 5 years in northern Europe. Algal biomass was harvested 2–3 times per week and the closed panel system was re-filled with seawater amended with nutrients. Flue gas was fed to the photobioreactor circulatory system in one direction or re-circulated. Removal efficiency of CO2 averaged 9 % in non-recirculation and 17 % in re-circulation modes and reached 20–60 % under best cultivation conditions. Recovery of carbon into algal biomass reached up to 10 g m2d−1 in non-recirculation mode. Biomass performance was explained by circulation mode and shift of polyculture traits. Stability of biomass quality was shown over seasons, with higher relative content of protein in autumn. Toxic elements in biomass were below legal thresholds for upcycling. The study shows feasibility of algal solutions for conversion of waste, applied in temperate climate. © 2023 The Authors