What this work is about, in plain words
Can a thick culture layer be compensated for by stronger mixing? The authors tested this on spirulina and showed that what matters most is how much light reaches the cells inside the layer.
When a photobioreactor is designed for a large volume, two parameters matter: the thickness of the suspension layer that light passes through and how intensively it is mixed. The thicker the layer, the less light reaches cells deep inside. The authors wanted to find out whether stronger vortex mixing can make up for this.
The object was a batch culture of the cyanobacterium Arthrospira (Spirulina) platensis. It was grown in vortex mode with working layers of different thickness and with mixing up to the critical intensity of the swirling flow.
According to the authors, even with mixing increased tenfold, making the layer three times thicker halved the productivity of the culture. Light inside the suspension turned out to be the main factor, with mixing acting together with it. The authors also showed conditions under which layers differing twofold in thickness give the same productivity.
The work is useful when choosing the layer thickness and mixing regime for vortex photobioreactors: it shows where mixing helps and where it runs up against a lack of light.
Limitations. The experiments were carried out on one culture under laboratory conditions. The authors note that the theory of mixing photosynthetic cultures is poorly developed and new models are needed for calculations. The results were obtained by the authors of the article and do not describe Laboratory 17 batches.