A Methodology for the Determination of the Light Distribution Profile of a Micro-Algal Photobioreactor

The following work presents an in depth analysis of the distribution of the light absorbance profile. The proper identification of conditions that maximize the growth efficiency of photosynthetic algae is necessary to optimize the productivity as a whole of the photobioreactor. In an effort to understand light as it interacts with an absorbing species such as algae, various tests were completed to extrapolate extinction coefficient ε or a calibration curves based on Beer-Lamberts Law. To characterize the absorbance conditions in a photobioreactor, a light distribution model was developed. From the basis of an external radiated light system, a single-source system was developed. Mathematical expressions for the local light intensity and the average light intensity were derived for a cylindrical photobioreactor with external sources, single internal sources, and multiple internal sources. The proposed model was used to predict the light absorbance values inside an externally and internally radiated photobioreactor using Nannochloropsis Oculata. The effects of cell density and light path length were interpreted through experimental and model simulation studies. The predicted light intensity values were found to be within +/− 7% to those obtained experimentally. This level of accuracy could be better improved with more testing and more precise instrumentation. Due to the simplicity and flexibility of the proposed model, it was also possible to predict the light conditions in other complex multiple light source photobioreactors.