Cultivating oleaginous microalgae in specific culturing devices such as raceways is seen
as a future way to produce biofuel. The complexity of this process coupling non linear
biological activity to hydrodynamics makes the optimization problem very delicate. The
large amount of parameters to be taken into account paves the way for a useful
mathematical modeling. Due to the heterogeneity of raceways along the depth dimension
regarding temperature, light intensity or nutrients availability, we adopt a multilayer
approach for hydrodynamics and biology. For free surface hydrodynamics, we use a
multilayer Saint–Venant model that allows mass exchanges, forced by a simplified
representation of the paddlewheel. Then, starting from an improved Droop model that
includes light effect on algae growth, we derive a similar multilayer system for the
biological part. A kinetic interpretation of the whole system results in an efficient
numerical scheme. We show through numerical simulations in two dimensions that our
approach is capable of discriminating between situations of mixed water or calm and
heterogeneous pond. Moreover, we exhibit that a posteriori treatment of
our velocity fields can provide lagrangian trajectories which are of great interest to
assess the actual light pattern perceived by the algal cells and therefore understand its
impact on the photosynthesis process.