Design and parallelisation of a miniature photobioreactor platform for microalgal culture evaluation and optimisation

Miniature photobioreactors (mPBr) represent a potential platform technology for the high-throughput, phototrophic cultivation of microalgae. This work describes the development and characterisation of a novel orbitally shaken twin-well mPBr, and its scale-out to a 24-well microplate format, suitable for optimisation of microalgae culture conditions. Fluid hydrodynamics, oxygen mass transfer coefficient (k_La) and light intensity distribution in the mPBr were first investigated as a function of orbital shaking frequency. High speed video analysis of the shaken wells indicated rapid fluid flow and good mixing while measured k_La values varied between 20 and 80h^-1. Light intensity variation across the scaled-out platform was in the range ±20μmolm^-2s^-1. The use of the mPBr platform was demonstrated for optimisation of conditions for the batch cultivation of Chlorella sorokiniana. Using a modified tris-base phosphate (TBP) medium, the highest biomass concentration and productivity achieved were 9.2gL^-1 and 2.5±0.2gL^-1d^-1 respectively at 5% CO₂ with a light intensity of 380μmolm^-2s^-1. In general, cell growth rate and yield increased with increasing shaking frequency (up to 300rpm) while culture conditions had limited impact on pigment production. Overall, these results demonstrate the application of the mPBr for rapid optimisation of phototrophic culture conditions and establishment of high cell density cultures.