Novel photo-microrespirometric method for the rapid determination of photosynthesis-irradiance (PI) curves in microalgal-bacterial systems

Abstract Photoreactors are now largely used in a span of applications but are complex systems that would still benefit from a better constraint of their kinetic behaviour. Among others, the determination of the Photosynthetic-Irradiance (PI) curve in photoreactors, which describes the correlation between light irradiance and activity of the algal or algal-bacterial culture, is of utmost importance for modelling, optimization, and control purposes. Habitually, PI curves in photoreactors are determined through incubation done under a range of irradiance, and even if many remarkable advances have been achieved in the methods applied, there is still a need for a simple, robust, polyvalent and fast method. We present here a method based on a modified respirometer, commercially available, that allows to measure the dissolved oxygen production/uptake, simultaneously in 24 replicates under a controlled irradiance. This so-called photo-microrespirometric method, was applied successfully to the determination of PI curves of a microalgal-bacterial culture obtained from a pilot-scale pond treating the liquid fraction of an anaerobic digestate. The PI curves obtained, in a few hours of experimental work, were well fitted by the Bernard-Remond's kinetic model. In addition to PI curves, the method allowed for the quantification of the inhibitory effect of dissolved oxygen as well as the response time of the photoactivation and photoinhibition.