Modeling of biomass productivity in dense microalgal culture using computational fluid dynamics

Biomass productivity is the variable to optimize in microalgal processes and is strongly related to light availability inside the photobioreactor. The so-called “light regime” in dense microalgal cultures is the result of the movement of microalgal cells inside the irradiance field caused by the stirring of the culture. Proper mixing increases productivity and helps microalgal cells to move frequently between dark and light zones but it is not trivial to ascertain the adequate level of mixing for a particular microalgal strain and culture system. Computational Fluid Dynamics (CFD) allows a precise description of the irradiance field inside a microalgal culture and makes it possible to calculate the movement of a population of single cells as a function of geometry and mixing intensity. Thus, realistic light-time patterns can be obtained and their effects on the photosynthetic response of microalgae can be analysed. In this work, we present the analysis of an actual horizontal tubular photobioreactor whose mixing patterns are obtained by CFD and are coupled with a dynamic model of photosynthesis for Nannochloropsis gaditana to determine biomass productivity. This data is compared to the experimental data of biomass productivity obtained in the same photobioreactor to show that the model developed agrees with the experimental results within a 20% error margin.