Comparative evaluation of growth, CO2 capture, and biomass biochemical composition between Chlorococcum humicola and Chlorella vulgaris under varying CO2 concentrations and simulated cement flue gas

Abstract

This study presents a comparative evaluation of Chlorococcum humicola and Chlorella vulgaris cultivated under varying CO₂ concentrations (0.04 % to 20 %) and simulated cement flue gas. The highest biomass concentrations (869 mg/L for C. humicola and 1284 mg/L for C. vulgaris), together with the maximum CO₂ fixation rates (154 mg/L⋅d for C. humicola and 214 mg/L⋅d for C. vulgaris), were observed at 5 % CO₂. Both microalgae demonstrated tolerance to simulated cement flue gas (15.50 % CO₂, 220 ppm NO, and 1.3 ppm SO₂), achieving biomass concentrations and CO₂ fixation rates comparable to those observed under 10 % and 15 % CO₂ as well as ambient air. C. humicola yielded higher carotenoid contents than C. vulgaris across the tested CO₂ range. At 5 % CO₂, both microalgae exhibited the highest carotenoid contents, with neoxanthin and violaxanthin predominating in C. humicola while lutein predominated in C. vulgaris. Although C. humicola contained lower protein contents (32.55 % to 40.25 %) compared to C. vulgaris, it remains a promising alternative as live feed for aquacultures and as a source of bioactive compounds. Notably, unlike C. vulgaris, C. humicola formed large aggregates, which allowed simple biomass harvesting via filtration.