Effects of photobioreactors design and operating conditions on Stichococcus bacillaris biomass and biodiesel production

Indoor cultures of Stichococcus bacillaris were carried out to investigate the effect of pH, CO2, and hydrodynamics on biomass and biodiesel productivity in a 0.6 L vertical bubble column (VBC) and a 1.7 L inclined bubble column (IBC) photobioreactor. The temperature and the irradiance level were set at 23 °C and 300 μE/(m2 s), respectively. The pH of the liquid culture was in the range 3.0–8.5. The CO2 concentration in the gas phase was increased up to 15%, typical of exhaust gas from power plants. The increased CO2 concentration in the gas phase stimulated the microalgal growth. Tests carried out at different pH and spreading a 5% CO2 gas stream showed that the biomass productivity was maximum at a pH of about 7.0. Acid and alkaline conditions can also be adopted with an approximate 25% decrease in biomass productivity. The comparison between a IBC and a VBC reactor operated under the same conditions pointed out that the performances of IBC were higher than those of VBC: 0.26 gbiomass/(L d) and 0.032 gFAME/(L d) for IBC, and 0.124 gbiomass/(L d) and 0.010 gFAME/(L d) for VBC. IBC was characterized by an intensive liquid circulation that promotes a continuous renewal of microalgal cells in the photic zone.

► Autotrophic cultures of Stichococcus bacillaris were carried to produce biodiesel.
► Two photobioreactor configurations were investigated.
► Effects of pH, CO2 concentration and hydrodynamics were investigated.
► Biomass and FAME productivity were optimized: 0.26 g/(L d) and 0.032 g/(L d).