Influence of ammonium sulphate feeding time on fed-batch Arthrospira (Spirulina) platensis cultivation and biomass composition with and without pH control

Previous work demonstrated that a mixture of NH₄Cl and KNO₃ as nitrogen source was beneficial to fed-batch Arthrospira (Spirulina) platensis cultivation, in terms of either lower costs or higher cell concentration. On the basis of those results, this study focused on the use of a cheaper nitrogen source mixture, namely (NH₄)₂SO₄ plus NaNO₃, varying the ammonium feeding time (T = 7-15 days), either controlling the pH by CO₂ addition or not. A. platensis was cultivated in mini-tanks at 30 °C, 156 μmol photons m⁻² s⁻¹, and starting cell concentration of 400 mg L⁻¹, on a modified Schlösser medium. T = 13 days under pH control were selected as optimum conditions, ensuring the best results in terms of biomass production (maximum cell concentration of 2911 mg L⁻¹, cell productivity of 179 mg L⁻¹ d⁻¹ and specific growth rate of 0.77 d⁻¹) and satisfactory protein and lipid contents (around 30% each).