Repeated fed-batch cultivation of Thermosynechococcus elongatus BP-1 in flat-panel airlift photobioreactors with static mixers for improved light utilization: Influence of nitrate, carbon supply and photobioreactor design

Microalgae mass cultivation is limited by light availability due to effects of absorption and reflection. These effects can only partially be coped with by increasing the photon-flux density. Further inhibitive effects, especially during outdoor cultivations, are described by photoinhibition and photosaturation. Therefore, moving the cells towards the light source and away from it in a distinct mode by convective mass transfer is the method of choice to cope with these inhibitive effects. Hereby, the utilization of culture-flow directing installations, e.g. static mixers, within photobioreactors can be of great benefit. The thermophilic model organism Thermosynechococcus elongatus BP-1 was cultivated in flat-panel airlift photobioreactors with and without static mixers in order to show their positive influence on growth kinetics. Optimal nitrate and carbon concentrations were 2000 mg L− 1 NO3−, 0.04 g L− 1 Na2CO3 combined with 6.3% v/v CO2. It was shown that photobioreactors with static mixers increase volumetric productivity by a factor of 3.4 and final biomass concentration by a factor of 2.0. A maximum productivity of 2.9 gDW L− 1 d− 1 was demonstrated, to the knowledge of the authors the highest to be reported for the cyanobacterium T. elongatus BP-1.