Effects of CO₂ and pH on Stichococcus bacillaris in Laboratory Scale Photobioreactors

Abstract

The effects of both the CO2 concentration and the pH of the medium on biodiesel production by Stichococcus bacillaris (ACUF 158/11) were reported. Indoor cultures of S. bacillaris were carried out in both 0.6 L vertical bubble column photobioreactors and 1.7 L inclined bubble column photobioreactors. Batch, fed-batch and semi-continuous conditions were investigated as regards the biomass cultivation with Bold Basal Medium. pH was changed between 3 and 7. Tests were carried out at 23 °C, 200 µE/(m2 s). The CO2 concentration in the gas stream fed at the photobioreactors (0.5 vvm) was increased up to 15 %v to stimulate the growth process and to simulate the CO2 level in exhaust gas. Preliminary results showed that CO2 concentration higher than the air (0.035 %v) improved the process performances in terms of productivity and concentration of lipids. No strong differences were observed for the selected CO2 concentrations (5, and 15 %v). Tests at different pH carried out with 5 % CO2 supplemented air showed that pH of about 7 maximize the biomass productivity. Tests in inclined bubble columns resulted in a significant higher biomass and oil productivity (256 and 80 mg/L d) than those assessed in vertical bubble column (124 and 42 mg/L d).