Kinetic parameters of <i>Scenedesmus obliquus</i> (Chlorophyceae) growth and yield under different cultivation conditions <i>in vitro</i>

The aim of the present study is to assess the kinetic growth and yield of microalgae belonging to the species <i>Scenedesmus obliquus</i> (Kützing, 1833) grown under different macronutrient concentrations (N:P:K), pH and temperature. A three-level three-variable Box-Behnken factorial design was developed to test the influence of environmental factors on the growth parameters applied to a microalgal crop, namely: maximum cell density (N_max), specific growth rate (µ, d^-1), doubling time (T₂) and maximum yield (P_max). A classical logistic growth model was applied to estimate the kinetic behavior of a <i>S. obliquus</i> culture in comparison to other studies in the literature. Maximum cell density (N_max) significantly changed between 32.3 ± 0.84 and 101.5 ± 12.5 × 105 cells mL^-1 (<i>p</i> = 0.004). Specific growth rates (µ) and P_max showed significant mean variations between 0.28 ± 0.10 day^-1 and 6.21 ± 4.57 cells mL^-1 d^-1, respectively. All growth curves were adjusted to the proposed logistic model and range variation was (0.65 ≤ r² ≤ 0.99, <i>p</i> = 0.01). Maximum microalgae cell density per crop was found at temperature of 24 °C (N_max = 49.0 × 105 cells mL^-1) (<i>p</i> = 0.01), in 20 mL Nitrogen, Phosphorus, and Potassium (NPK) dilution (N_max = 46.5 × 105 cells mL^-1) (<i>p</i> = 0.02). Despite the significant variation in pH values (5.0 ≤ pH ≤ 9.0, <i>p</i> = 0.05), it did not have strong influence on plant growth responses. In conclusion, the kinetic study applied to <i>S. obliquus</i> growth and yield parameters emerged as reference for this species' kinetic behavior and bioprospecting under controlled and experimentally standardized conditions, and as support for pilot projects on bioreactors.