Experimental Study and Numerical Modeling of CO2 Bio-Fixation in a Continues Photobioreactor

A dynamic numerical model was developed to predict the biomass concentration, pH, and carbon dioxide fixation rate in the continuous culture of cyanobacteria in a photobioreactor. The model is based on the growth rate equation of microalgae combined with mass transfer equations for gas and liquid phases in the photobioreactor as well as thermodynamic equilibrium of inorganic carbon ions in the culture media. The model was validated by comparing its predictions with experimental results obtained from turbidostat cultivation of Synechocystis in a flat-plate photobioreactor. Optical density, pH, and CO2 concentration in outlet gas were measured continuously in this photobioreactor. The model was used to simulate this system at the same conditions that the experiments were performed at two light intensities of 75 mE/m2/s and 150 mE/m2/s. Although the growth rate and outlet gas CO2 concentration were quite different at these two light intensities, the model predicted the system behavior accurately. The average error in the prediction of biomass concentration, pH, and outlet gas CO2 concentration was 0.40%, 0.61%, and 0.34%, respectively.