Production of Chlorella vulgaris as a source of essential fatty acids in a tubular photobioreactor continuously fed with air enriched with CO2 at different concentrations

To reduce CO2 emissions and simultaneously produce biomass rich in essential fatty acids, Chlorella vulgaris CCAP 211 was continuously grown in a tubular photobioreactor using air alone or air enriched with CO2 as the sole carbon source. If from the one hand nitrogen-limited conditions strongly affected biomass growth, on the other hand they almost doubled its lipid fraction. Under these conditions using air enriched with 0, 2, 4, 8 and 16% (v/v) CO2, the maximum biomass concentration was 1.4, 5.8, 6.6, 6.8, 6.4 gDB L-1 on a dry basis, the CO2 consumption rate 62, 380, 391, 433, 430 mgCO2 L-1 day-1, and the lipid productivity 3.7, 23.7, 24.8, 29.5, 24.4 mg L-1 day-1, respectively. C. vulgaris was able to grow effectively using CO2-enriched air, but its chlorophyll a (3.0-3.5 g 100gDB-1), chlorophyll b (2.6-3.0 g 100gDB-1) and lipid contents (10.7-12.0 g 100gDB-1) were not significantly influenced by the presence of CO2 in the air. Most of the fatty acids in C. vulgaris biomass were of the saturated series, mainly myristic, palmitic and stearic acids, but a portion of no less than 45% was constituted by unsaturated fatty acids and about 80% of these were high added-value essential fatty acids belonging to the ω3 and ω6 series. These results highlight that C. vulgaris biomass could be of great importance for human health when used as food additive or for functional food production.