<![CDATA[This study studied the optimum nitrogen (N) and phosphorus (P) concentrations for biomass and astaxanthin production in Spirogyra sp. Spirogyra sp. was cultivated in Blue Green (BG) medium with N/P concentrations adjusted to 1.1/0.01; 1.1/0.03; 1.1/06; 1.1/0.09; 2.2/0.01; 2.2/0.03; 2.2/0.06; 2.2/0.09; 4.4/0.01; 4.4/0.03; 4.4/0.06; 4.4/0.09, 6.6/0.01; 6.6/0.03; 6.6/0.06 and 6.6/0.09 mM. The results showed an increase in biomass accumulation for lower concen‐ trations of N and N:P ratio with the highest accumulation at N/P 1.1/0.03 mM, i.e. 485 mgdryweight and a growth rate of 0.22 d‐1. Astaxanthin accumulation was also found to increase, with the highest at N/P 1.1/0.01 mM, i.e. 0.269 mg/gdryweight, on the 12th day of cultivation. Based on biomass and astaxanthin accumulation, the highest astaxanthin productivity was 0.07 μg/cm2/d at N/P concentration 1.1/0.09 mM. Kinetic models were developed using the Haldane and Luedeking–Piret equations. The growth and astaxanthin production parameters obtained were μmax 0.18±0.02 d‐1, kN 68.2 ± 24.2 mg/L, ki 301.8 ± 78.5 mg/L, YN 0.93 ± 0.68 gbiomass/nitrate, α 0.36 ± 0.69, β ‐0.01 ± 0.02, and kA 0.04 ± 0.03, thus indicating that a lower N concentration is suitable for the cultivation of Spirogyra sp. In conclusion, Spirogyra sp. should be cultivated under nitrogen deficiency for continuous astaxanthin production.]]>
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