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

Abstract

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.

Use of Airfoils for Enhancement of Photosynthesis Rate of Microalgae in Raceway

“…Since it is important that the simulation and sampling properly capture the photosynthetic response of each particle, at least 50 position points of each particle have been recorded per second for a maximum of 50 seconds, which allows detecting frequencies between 0. 2 and 50 Hz (Fernández-Del Olmo et al 2017).…”

“…Currently, based on the use of Computational Fluid Dynamics (CFD), a more accurate analysis has been achieved by coupling Lagrangian particle tracking with the use of dynamic photosynthetic models, such as those proposed by Eilers andPeeters, 1988 or Rubio Camacho et al, 2003 where it is required to know the complete history of a large population of cells concerning time (Fernández-Del Olmo et al 2017) and its position, especially in vertical resolution. To increase the vertical mixing along culture channels, this article proposes the use of airfoils described in the patent of the University of Seville WO2020120818A1, which generates long stable vortices which can transport the cells between the illuminated and dark zone (Cheng et al 2015), thus generating improved conditions for the metabolism of photosynthesis.…”