The challenge of scaling up photobioreactors: Modeling and approaches in small scale

Abstract

Commercial large‐scale application of photobiotechnology calls for acceptable rates and high cell densities. The latter results in self‐shading and a temporally declining growth rate, making the process inefficient. Upscaling phototrophic processes requires knowledge of the reaction kinetics with special attention on the μ ‐ I relation. Model‐based calculations for studying the effect of self‐shading on growth were performed for three μ ( I ) concepts. The nonrealistic μ ( I 0 ) concept results in exponential growth without limit, the widely used concept exhibits a growth behavior that significantly deviates from real processes, but the sophisticated concept describes real processes best. A Respiration Activity Monitoring System (RAMOS) with CultiLux unit was tested regarding its applicability for exploring the μ ‐ I dependency of Arthrospira platensis . The results were not satisfactory because of self‐shading due to a high cell density (which was essential for yielding detectable oxygen‐evolution signals). An innovative cultivation system in which self‐shading does not interfere with phototrophic growth was required. A flat‐panel system was constructed (designed by CFD, short light path of 1 cm, uniform planar light supply by LED and OLED units), allowing continuous cultivation of phototrophic microbes at varied light intensities.