Cultivation of Chlorella vulgaris in tubular photobioreactors: A lipid source for biodiesel production

• Chlorella vulgaris is investigated as a biodiesel source.
• Different bicarbonate concentrations are tested in shake flasks.
• Horizontal and tubular photobioreactors are compared at the best bicarbonate level.
• Lipid quality of biomass cultured in both reactors proves suited for biodiesel.

Chlorella vulgaris was cultivated in two different 2.0 L-helicoidal and horizontal photobioreactors at 5 klux using the bicarbonate contained in the medium and ambient air as the main CO2 sources. The influence of bicarbonate concentration on biomass growth as well as lipid content and profile was first investigated in shake flasks, where the stationary phase was achieved in about one half the time required by the control. The best NaHCO3 concentration (0.2 g L−1) was then used in both photobioreactors. While the fed-batch run performed in the helicoidal photobioreactor provided the best result in terms of biomass productivity, which was (84.8 mg L−1 d−1) about 2.5-fold that of the batch run, the horizontal configuration ensured the highest lipid productivity (10.3 mg L−1 d−1) because of a higher lipid content of biomass (22.8%). These preliminary results suggest that the photobioreactor configuration is a key factor either for the growth or the composition of this microalga. The lipid quality of C. vulgaris biomass grown in both photobioreactors is expected to meet the standards for biodiesel, especially in the case of the helicoidal configuration, provided that further efforts will be made to optimize the conditions for its production as a biodiesel source.