Light Transfer in a Bubble Sparged Photobioreactor for Simultaneous Hydrogen Production and CO2 Mitigation

This paper presents a parametric study of light transfer simulations in a rectangular photobioreactor containing gas bubbles and cyanobacteria Anabaena variabilis suspended in water. To the best of our knowledge, this paper presents for the first time a model for such system (i) using a consistent set of radiative properties of the medium derived from experimental data and from Mie theory, (ii) accounting for anisotropic scattering by two types of scatterers namely the bubbles and filamentous microorganisms, and (iii) considering the spectral dependency of radiation characteristics in the spectral range from 400 to 700 nm using a box model. The steady-state one-dimensional radiation transfer equation is solved using the modified method of characteristics. Parameters studied include the bacteria concentration, the bubble radius and void fraction, as well as the scattering phase function. It was established that the strongly forward scattering by the bubbles must be accounted for and the truncated phase function is recommended. In the absence of bubbles ignoring forward scattering by the bacteria leads to errors as high as 20%.