Improvement of photoautotrophic algal biomass production after interrupted co₂ supply by urea and kh₂ po₄ injection

Microalgae-derived biomass is currently considered a sustainable feedstock for making biofuels, including biodiesel and direct combustion fuel. The photoautotrophic cultivation of microal-gae using flue gas from power plants has been continuously investigated to improve the economic feasibility of microalgae processes. The utilization of waste CO₂ from power plants is advantageous in reducing carbon footprints and the cost of carbon sources. Nonetheless, the sudden interruption of CO₂ supply during microalgal cultivation leads to a severe reduction in biomass productivity. Herein, chemical fertilizers including urea and KH₂ PO₄ were added to the culture medium when CO₂ supply was halted. Urea (5 mM) and KH₂ PO₄ (5 mM) were present in the culture medium in the form of CO₂ /NH₄⁺ and K⁺ /H₂ PO₄⁻, respectively, preventing cell growth inhibition. The culture with urea and KH₂ PO₄ supplementation exhibited 10.02-fold higher and 7.28-fold higher biomass and lipid productivity, respectively, compared to the culture with ambient CO₂ supply due to the maintenance of a stable pH and dissolved inorganic carbon in the medium. In the mass cultivation of microalgae using flue gas from coal-fired power plants, urea and KH₂ PO₄ were supplied while the flue gas supply was shut off. Consequently, the microalgae were grown successfully without cell death.