Influence of fractal-like aggregation on radiative properties of Chlamydomonas reinhardtii and H2 production rate in the plate photobioreactor

Chlamydomonas reinhardtii (C. reinhardtii) is regarded as one of the best candidates for photobiological H2 production. The radiative properties of its cells are pivotal in determining photosynthetic efficiency. The generalized multiparticle Mie-solution method is employed in this study to compute the radiative properties of fractal-like C. reinhardtii cells which aggregate in random orientations. The effects of fractal dimension, monomer radius, and the number of monomers of the aggregations on the radiative properties are investigated thoroughly. By comparing the radiative properties of the fractal clusters with those of volume-equivalent spheres, it is found that the difference in the extinction and scattering cross-sections of the aggregates and of the volume-equivalent spheres is significant for the cluster with a large fractal dimension and small monomers, whereas the variation in terms of the absorbing cross-section and the single-scattering albedo is slight. Similar conclusions can be obtained with respect to the differences between the radiative properties of the aggregates and those of the spheres with a corresponding radius of gyration. Finally, the light transfer and specific H2 production rate in the plate photobioreactor are investigated using the finite volume method and the Michaelis-Menten type equation. Results demonstrate that the effective H2 production region is large for photobioreactors that contain aggregates with a large fractal dimension and small monomers. However, the difference in the effective H2 production regions in terms of varying fractal dimensions and number of monomers in the aggregates decreases gradually with the increase in the size of the monomers in the aggregates. A similar conclusion can be drawn when the intensity of the incident irradiation on the photobioreactors changes.