Study of photosynthetic mecanisms for light energy conversion by Chlorella vulgaris in solar photobioreactors ; Étude des mécanismes de conversion photosynthétique de l'énergie lumineuse par Chlorella vulgaris en photobioréacteur solaire

Large-scale production of microalgae is mainly carried out in solar cultures. Under these conditions, cells experience various light fluctuation dynamics that is mostly due to day/night cycles, weather conditions, cell displacement between the light surface and the near-dark bottom of the culture, or regular passage through the design dark fractions of the photobioreactor (PBR). In response to these light variations, microalgae developed response mechanisms. In the short term, they protect themselves from supersaturating light intensity for example by dissipating excess energy as heat. In the long term they change their pigment content to use light energy with the greatest efficiency. This study aims at understanding and optimizing the photosynthetic conversion of light energy by Chlorella vulgaris in solar PBR. For this purpose, experiments under controlled conditions were carried out at the laboratory scale. At the cell level, transient behaviours were observed, particularly in the presence of supersaturating light. Photoacclimation impacted photoprotection and photoinhibition mechanisms of the cells. At the reactor scale, characteristic times of photosynthetic responses were explored during increasing or decreasing light step transitions. Subsequently, an in vivo chlorophyll a fluorescence measurement sensor was implemented online on a PBR and its usefulness was studied for monitoring solar cultures, particularly for maintaining good culture conditions and estimating productivity. In addition, this probe supplemented by gas flux measurements also made it possible to measure the impact of PBR dark fractions on the photosynthetic response of C. vulgaris. ; La production à grande échelle de micro-algues est principalement réalisée en cultures solaires. Dans ces conditions, les cellules subissent de nombreuses variations de lumière à cause des cycles jour/nuit, de la météo, de leur déplacement entre la surface éclairée et le fond sombre de la culture ou de leur passage régulier dans des parties non éclairées du ...