Effects of carbon dioxide feeding rate and light intensity on the fed-batch pulse-feeding cultivation of Spirulina platensis in helical photobioreactor

The behavior of S. platensis was investigated in this study through fed-batch pulse-feeding cultures performed at different carbon dioxide feeding rates (F = 0.44–1.03 g L−1 d−1) and photosynthetic photon flux density (PPFD = 80–250 μmol photons m−2 s−1) in a bench-scale helical photobioreactor. To achieve this purpose, an inorganic medium lacking the carbon source was enriched by gaseous carbon dioxide from a cylinder. The maximum cell concentration achieved was 12.8 g L−1 at PPFD = 166 μmol photons m−2 s−1 and F = 0.44 g L−1 d−1 of CO2. At PPFD = 80 and 125 μmol photons m−2 s−1, the carbon utilization efficiency (CUE) reached maximum values of 50 and 69%, respectively, after about 20 days, and then it decreased, thus highlighting a photolimitation effect. At PPFD = 166 μmol photons m−2 s−1, CUE was ≥90% between 20 and 50 days. The photosynthetic efficiency reached its maximum value (9.4%) at PPFD = 125 μmol photons m−2 s−1. The photoinhibition threshold appeared to strongly depend on the feeding rate: at high PPFD, an increase in the amount of fed CO2 delayed the inhibitory effect on biomass growth, whereas at low PPFD, excess CO2 addition caused the microalga to stop growing.