Biodiesel production from Stichococcus strains on laboratory scale

The paper reports the results of an experimental campaign of autotrophic cultures of Stichococcus strains aiming at selecting the most promising strain for biofuel production. The strain selected - S. bacillaris 158/11 - was cultivated in 1 L lab-scale bubble column photobioreactors under fed-batch and semi-continuous conditions. A Bold basal medium supplemented with NaNO3 as nitrogen source was adopted. Tests were carried out at 23 °C, 140 microE/(m2s), and air flow rate ranging between 0.4 and 4 vvm. Cultures were characterized in terms of pH, concentration of total nitrogen, total organic carbon, total inorganic carbon, biomass, lipid fraction and methyl-ester distribution of transesterified lipids. S. bacillaris 158/11 proved to be the best strain to produce biodiesel. Methyl-ester distribution was characterized by a large fraction of methyl palmitate, methyl linolenate, methyl linoleate, and methyl oleate along with phytol. The process photosynthetic efficiency – fraction of available light stored as chemical energy - was about 1.5%. Specific biomass productivity was ~60 mgDM/(L•day) under the semi-continuous conditions tested. Total lipid productivity was 14 mg/(L•day) at a dilution rate of 0.050 1/day. S. bacillaris 158/11 is a potential strain for massive microalgae cultures for biofuel production. Higher biomass/total-lipid productivity could be obtained at sunlight.