Synergistic impact of elevated CO2 and photo-bioreactor illumination surface area on marine microalgal biomass and bio-chemicals production

This study investigates the synergistic effects of enriched CO₂ and illumination surface area of a photo-bioreactor (PBR) on the growth, biochemicals and pigment production of marine microalgae. Accordingly, marine Chlorella sp. and D. salina were cultivated under various conditions, including ambient CO₂ (AC: 0.04 %, v/v) and high CO₂ (HC: 15 %, v/v), with two illumination surface area-to-volume (IS/V) ratios: low (0.22 cm⁻¹) and high (0.44 cm⁻¹). The results demonstrated that both marine strains showed significant changes in biochemical yields under different cultivation conditions, with the highest biomass yield of 2.01–2.07 g L⁻¹ observed when HC and high IS/V ratio were combined. These biomass yields are 107–132 % higher compared to AC and low IS/V conditions. Chlorella sp. and D. salina cultured under the combined HC with high IS/V conditions significantly improved the production of lutein and lipid by 163–417 % and 12–36 %, respectively. However, the maximum protein (178–188 mg g⁻¹) and carbohydrate (182–284 mg g⁻¹) yields in both strains were achieved under AC with high IS/V and low IS/V conditions, respectively. CO₂ sequestration of 0.40–0.51 g L⁻¹ d⁻¹ exhibited by these strains are comparatively higher than most of the marine microalgae reported in the literature. The novelty of this study lies in the demonstration of the synergistic effects of elevated CO₂ levels (15 %, v/v), equivalent to coal-fired flue gas, and PBR's illumination surface area on marine microalgal cultivation in a seawater-supplemented medium, leading to optimized CO₂ fixation, biomass yield, and bio-chemicals production.