Abstract :
[en] ValoAlgue project aims at cultivating fixed biomass (encapsulated microalgae) to product high added value metabolites. Microalgae harvest (separation from their culture medium), which is a high energy consuming step, can be avoided thanks to encapsulation. However, the industrial feasibility of this innovative production technology is not yet assessed due to the lack of large scale experiments involving encapsulated microalgae.
The project, funded by the FEDER, involves three Belgian Universities. The purpose of the Chemical Engineering department of the University of Liège is to design and optimize an integrated pilot photobioreactor (5 liters) to cultivate encapsulated microalgae.
In traditional photobioreactors, light is most often considered as the main scale up parameter as it influences growth rate and cannot be easily controlled [1]. In encapsulated microalgae culture, the aim is not any more the cell growth (it is even undesirable because of cell leakage from beads due to growth) but the metabolite productivity. Mixing might have a key role as it controls light access and transport processes which can be limiting factors for encapsulated microalgae. Light and mixing hence need to be characterized at the pilot scale.
The studied photobioreactor is a plan (rectangular) reactor involving a fluidized bed of encapsulated microalgae in the form of beads. To characterize the fluid flow, Particle Image Velocimetry (PIV) monophasic measurements (with liquid only) and then diphasic PIV (considering liquid flow in presence of beads), will be performed. The reactor hydrodynamics will be modelled using Computational Fluid Dynamics (CFD) and the resulting model will be validated by comparison with PIV results. A CFD-based compartment model, which predicts mixing accurately and reduces calculation time, will be adapted [2].
Light distribution in the photobioreactor will also be measured in the photosynthetically active radiation range. The aim is to model the light absorption and scattering by the beads, as well as their circulation in the photobioreactor, and to integrate this information in the reactor model.
[1] Legrand, Advances in Chemical Engineering, Vol. 48, Photobioreaction Engineering, 2016
[2] Delafosse et al, Chemical Engineering Science, 106, 76-85, 2014
