Air bubbling results in carbon loss during microalgal cultivation in bicarbonate-enriched media: experimental data and process modeling

Turbulence is a major variable controlling growth of microalgae. When turbulence is provided by means of air bubbling, mass transfer phenomena take place between the culture medium and the air bubbles. A mathematical model has been developed to evaluate the effects of air bubbling in bicarbonate-enriched media for microalgae cultivation, and in cultures of the halotolerant alga Dunaliella viridis. Simulations have been made using a four order Runger-Kutta method combined with Marquardt's algorithm to establish the parameters of the system. The model permits: (i) simulation of the experimental behavior of organic (cellular) and inorganic (CO2 + H2CO3 + HCO3− + CO32−) carbon in the cultures; (ii) performance of a sensitive analysis of the effects of varied operative conditions and (iii) development of strategies for optimizing the use of culture media and subsidiary energy. Simulation of the model demonstrated that in air-bubbled HCO3− enriched media there is a loss of CO2 from the medium to the air bubbles, which escapes from the culture vessel, and no transference of CO2 from the air bubbles to the water occurred. Validation of the model has been carried out by comparison of experimental and predicted values under different conditions.