Numerical Modelling of a Lab-scale Reactor for Microalgae Growth

In this paper we present the results of a numerical modelling work aimed at predicting the kinetics of microalgae production in a lab-scale photobioreactor. The experimental equipment is composed of a flat-plate bioreactor exposed to the light irradiation, and of a tank equipped with a hydraulic pump to secure the culture circulation. The numerical model addresses both the hydrodynamics of the experimental equipment and the kinetics of the relevant bio-chemical reactions. The hydrodynamics of the reactor was modelled as the one of a plug flow with a longitudinal dispersion, whereas the hydrodynamics of the tank was modelled as a cascade of continuous flow stirred tank reactors. The gaseous species transfer from the liquid free surface to the atmosphere was also considered. The relevant bio-chemical processes involved were modelled using common first-order rate expressions for the microalgae growth, and the effect of both thermal and photosynthetic phenomena, as well as the inhibition effects induced by substrate limitation and oxygen excess, have been taken into account. A calibration procedure has been conducted and showed that the model is able to reproduce with a satisfactorily degree of accuracy the experimental results, thus paving the way for its use as a production forecasting tool.