Optimization of thin-layer photobioreactors for the production of microalgae by integrating fluid-dynamic and photosynthesis rate aspects

The optimal configuration of Thin-Layer Photobioreactors (TLP) for the production of microalgae is analyzed. For that, a TLP of 40 m long, 1.5 m wide, and a slope of 1% was used, with both Computational Fluid Dynamics (CFD) and experimental measurements being used as data sources. First, the influence of culture inlet flows on the thickness of the fluid sheet and liquid velocity was studied, and a laminar flow was observed. Next, the light gradients at which the cells are exposed inside the cultures were calculated by considering both the light attenuation and movement of the cells along the reactor. A low frequency of light exposure was found. Combining the light regime to which the cells are exposed and different photosynthesis models the expected oxygen production rate was calculated. Although dynamic models are more precise, the use of static models is also suitable because of the low frequency of light exposition. The overall model of the reactor integrating fluid-dynamic and photosynthesis rates allows the optimization of the operation conditions on the photobioreactor. Results show that the optimal biomass concentration is 4 g L −1 , at which the frequency of L/D cycles, oxygen production, and dissolved oxygen saturation is maintained at adequate values. Whatever the operating conditions the desorption of oxygen in the bubble column has been identified as essential for optimal operation. In conclusion, major phenomena taking place in this type of photobioreactors are determined by the thickness of the culture depth which is a function of the culture flow rate provided to the channel, otherwise, the liquid flow determines the energy consumption on the reactor. Thus, the optimization of the overall configuration of this type of photobioreactor still is a challenge for its further industrial development.