Photocatalytic reactions are considered as a promising path in mitigating ecological impacts. In the case of heterogeneous reactions where the photoactive material is dispersed in the liquid phase (slurry), it is essential to identify and control the factors influencing efficiency, with a view to possible scale-up. These factors include the transmission of light in the system, the hydrodynamics of the reactor, the specific chemical reactions involved and, above all, the coupling of all these elements. In this PhD subject, the versatility of the Taylor-Couette flow will be exploited, which allows the flow to go from a plug flow to high turbulence in the same apparatus, while allowing high illumination thanks to a maximised surface/volume ratio, making it possible to study these different phenomena and their coupling. The study will rely on Monte Carlo and DNS (Direct Numerical Simulation) modeling to respectively describe the behavior of light and multiphase flow in the reactor. This will help identify and study influential parameters such as flow structure, spatial distribution of particles, photon transport, and photon-matter interactions within the reactor, not to mention the role of the gas phase. These models will be compared to experimental results obtained on a dedicated optical test rig and will contribute to a deeper understanding of the important processes at play in these photo(bio)reactors. The thesis is located in Marcoule CEA research center, near Avignon, in a multidisciplinary team with a strong focus on processes for green transition. The applicant we are looking for is an engineer and/or master 2 having a generalist profile and interested in playing an active role in this field. At the end of this Ph.D., the candidate will have a first experience in the present issues of low carbon energies in circular economy. Such a type of versatile profile will undoubtedly be an asset for a future career in academia as well as in industry.