Luminostat operation: A tool to maximize microalgae photosynthetic efficiency in photobioreactors during the daily light cycle?

The luminostat regime has been proposed as a way to maximize light absorption and thus to increase the microalgae photosynthetic efficiency within photobioreactors. In this study, simulated outdoor light conditions were applied to a lab-scale photobioreactor in order to evaluate the luminostat control under varying light conditions. The photon flux density leaving the reactor (PFDout) was varied from 4 to 20 mol photons m-2 s-1and the productivity and photosynthetic efficiency of Chlorella sorokiniana were assessed. Maximal volumetric productivity (1.22 g Kg-1 d-1) and biomass yield on PARphotons(400700 nm) absorbed (1.27 g mol-1) were found when PFDout was maintained between 4 and 6 mol photons m-2 s-1.The resultant photosynthetic efficiency was comparable to thatalready reported in a chemostat-controlled reactor.A strict luminostat regime could not be maintained under varying light conditions.Further modifications to the luminostat control arerequired before application under outdoor conditions.