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 (PFD(out)) was varied from 4 to 20 μmol photons m(-2)s(-1)and the productivity and photosynthetic efficiency of Chlorella sorokiniana were assessed. Maximal volumetric productivity (1.22g kg(-1)d(-1)) and biomass yield on PAR photons (400-700 nm) absorbed (1.27 g mol(-1)) were found when PFD(out) was maintained between 4 and 6 μmol photons m(-2)s(-1). The resultant photosynthetic efficiency was comparable to that already reported in a chemostat-controlled reactor. A strict luminostat regime could not be maintained under varying light conditions. Further modifications to the luminostat control are required before application under outdoor conditions.