Static supply of different simulated flue gases for native microalgae cultivation in diluted cow manure digestate

The application of microalgae to sequester CO₂ from flue gases can be an interesting process since it can contribute to mitigate CO₂ emission into the atmosphere. One obstacle of such application is the high CO₂ concentration in the flue gases, which can lead to low pH in the cultivation medium and hence process failure. This study aims to investigate static CO₂ gas supply for microalgae cultivation as a potential alternative that might allow applying different flue gases with different compositions and higher CO₂ concentrations. Two sets of experiments were performed. First, the effect of increasing the amount of supplied carbon was tested. In the second experiment, the applicability of such system for different flue gases regarding their oxygen and carbon content was tested. In all experiments, 50 times diluted cow manure digestate was used as a culture medium. By increasing CO₂ concentration up to 10% in the supplied air, microalgae growth productivity of 48.7 mg/L/d was achieved. A further improvement of microalgae growth was shown with increasing the gas/culture volume ratio. Microalgae productivity rate increased form 48.7 mg/L/d to 73.5 mg/L/d when the volume of gas increased from 47% to 81% of total volume. Applying CO₂ in air (O₂ content around 20%) or in N₂ (O₂ content less than 2%) didn't show any difference regarding inorganic carbon dissolution, pH, ammonium nitrogen removal, CO₂ fixation or biomass productivity. Generally, it can be concluded that static gas supply for microalgae cultivation can allow the application of different flue gases from different industries with low or high O₂ content and with CO₂ concentration as high as 20%. According to our results, a microalgae cultivation system with continuous static gas supply was proposed.