Light distribution in a novel photobioreactor - modelling for optimization

The paper reports a novel photobioreactor developed to achieve homogeneous and flexible illumination inside the reactor. This is to overcome the probl em of studying kinetics in standard photobioreactors, which are characteriz ed by strong light gradients and light fluxes that cannot be controlled. Th e reactor is used for the study of microalgal kinetics for modelling purpos es. The new reactor combines the advantages of a stirred reactor (homogenei ty) and a plate reactor (short path length). The light input system consist s of an external light source, a fibre-optical ring-light and a light emitt ing tube. Light is generated in a light source arranged externally and dire cted into the reactor using optical fibres. The fibres are spread in a ring -light to provide a uniform illumination in the concentrically arranged cyl inder. Any focusable light source can be applied; by using a shutter module , light fluctuations can be generated in a wide range of frequencies. In or der to change the light quality, spectral filters are placed between the la mp and the optical fibre. A model based approach was used to optimize the i llumination: light distribution was calculated employing a Monte-Carlo simu lation. Light emission characteristics, reflection, refraction, scattering in the suspension and on rough surfaces were studied numerically. Propositi ons were derived how to optimize the reactor, e.g. now to achieve higher li ght intensities and a more uniform illumination. Finally, mean photon flux densities of 100 +/- 15 mu mol m(-2) s(-1) were achieved at the illuminated surface. The simulation results revealed that the light distribution at co nstant biomass concentration is mainly determined by the geometrical parame ters of the lightening device mentioned above and that any simplifications lead to serious misinterpretations.