Chlorella vulgaris cultivation in airlift photobioreactor with transparent draft tube: effect of hydrodynamics, light and carbon dioxide on biochemical profile particularly ω-6/ω-3 fatty acid ratio

Abstract

Chlorella vulgaris is used for food and feed applications due to its nutraceutical, antioxidant and anticancer properties. An airlift photobioreactor comprising transparent draft tube was used for C. vulgaris cultivation. The effect of reactor parameters like hydrodynamics (0.3-1.5 vvm), light intensity (85-400 μmol m-2 s-1), photoperiod (12-24 h) and gas-phase carbon dioxide (CO 2) concentration (5-15% v/v) were evaluated on microalgae and associated bacterial growth, biochemical profile; with special emphasis on ω-3, ω-6 fatty acids, and vitamin B 12. The optimal growth of C. vulgaris without CO 2 supplementation was observed at 1.2 vvm, which was associated with higher algal productivity, chlorophyll, vitamin B 12 content, and bacterial load along with 72% of nitrate removal. The higher light intensity (400 μmol m-2 s-1) and photoperiod (24:0) increased biomass productivity and ω-3 fatty acid content (in lipid) up to 2-3 fold. The elevated levels of gas-phase CO 2 concentration (15% v/v) enhanced EPA content up to 7% and biomass productivity up to 171 mg L-1 day-1. However, the increase in CO 2 concentration lowered vitamin B 12 content (up to 30%) and bacterial load (2-3 log). Also, all the cultivation conditions favoured desirable ω-6/ω-3 ratio(in the range of 1-2).