Model based analysis of the growth kinetics of microalgal species residing in a waste stabilization pond

BACKGROUND: In this study the growth kinetics of Chlorella and Scenedesmus, isolated from a Waste Stabilization Pond were investigated under different conditions of light intensity and temperature. Experimental data were collected by means of a combined respirometric and titrimetric set-up and used to extend a mathematical model. RESULTS: The experimental results illustrated the interdependent relationship of light intensity and temperature, which had a significant influence on the microalgal growth. Consequently, a previously developed model was extended with a mathematical function that describes this relationship. The maximum specific growth rate and oxygen mass transfer coefficient were considered for model calibration. The optimized parameter values for Chlorella were μ_max = 0.56 ± 0.0008 d⁻¹ and K_La = 10.02 ± 0.02 d⁻¹. For Scenedesmus, the optimized parameter values were μ_max = 0.19 ± 0.0004 and K_L a = 7.71 ± 0.004 d⁻¹. The model with optimized parameter settings described the dissolved oxygen production (derived from the respirometric data) and the related proton consumption (derived from the titrimetric data) reasonably well for both microalgal species. The threshold value for Theil's Inequality Coefficient of 0.3 was never exceeded. In addition, model validation for both species was performed indicating good correspondence between model prediction and experimental values. CONCLUSIONS: Based on the experimental observations, a previously developed mathematical model was extended with a function that describes the interaction between light intensity and temperature. After model calibration a difference in maximum specific growth rate between the two microalgal species was observed. This might be explained by differences in cell metabolism.