Cultivation of cyanobacteria for extraction of lipids

Cyanobacteria were cultivated in laboratory to determine CO2 fixation rates and for extraction of lipids. The experiments were carried out in 4 phases, namely: flask cultivation of Synechocystis aquatilis TISTR8612 (S. aquatilis) to determine their optimal growth conditions; batch experiments in airlift photo-bioreactor (PBR) for estimation of CO2 fixation rates; continuous experiments in airlift PBR to evaluate biomass production and CO2 fixation rates; and development of appropriate method for lipid extraction from S. aquatilis. Investigations revealed that the optimum conditions for cultivating S. aquatilis were: pH 8, temperature of 30 °C, and illuminance of 4 klx. Batch experiments conducted at 5% inlet CO2 yielded maximum CO2 fixation rate at space velocity of 14 min−1. On the other hand, continuous experiments in airlift PBR revealed optimum dilution rate of 0.012 d−1 with maximum biomass production rate of 932 mg L−1 d−1. Inlet CO2 concentration of 8% was found to be most suitable to yield CO2 fixation rate of 5.3 g L−1 d−1. Lipid extraction procedure comprising of sonication and solvent extraction (chloroform:methanol as 1:1 by volume) resulted in highest lipid yield of 18.58%. The extracted fatty acids were mostly composed of polyunsaturated fatty acids such as linoleic and α-linolenic acid. ► Synechocystis aquatilis was cultivated in laboratory for extraction of lipids. ► Optimum growth conditions for S. aquatilis were found as pH 8, 30 °C, and 4 klx. ► Continuous experiments were carried out in airlift photo bioreactor. ► Maximum biomass production rate of 932 mg L−1 d−1 was obtained. ► Extracted lipids contained saturated and polyunsaturated fatty acids.