A dense Spirulina culture was split in half and used to start two identical photobioreactors. After one day of growth, both reactors were harvested (approx half the biomass removed). After two days of growth, one reactor has flocculated (left-hand sample in the photograph) and the other has not (right-hand sample in the photograph). What factor or combination of factors do you think could have caused this auto-flocculation?
The two reactors were identical in size and shape and both cultures had the same nutrient medium and agitation. The only differences we can think of were: the culture that flocculated had slightly higher light intensity, slightly higher temperature and part of the culture was passed through a pump.
very interesting. I never saw this type of flocculation with good agitation, but you say both photobioreactors had the same agitation. The only thing I can imagine for your situation is maybe the flocculated photobioreactor stayed for a long time unagitated, which led to strong flocculation that couldn't disappear with your agitation rate. You must increase the agitation rate and probably it will be fixed.
Hello there,
have you checked the pH of the photobioreactor? pH is a critical factor for the flocculation of microalgae, and considering that spirulina is a biomass that usually grow with sodium bicarbonate, maybe something went wrong during medium preparation.
During the pumping, maybe the cells were "disrupted" somehow?
Over-exposure to light can lead to the floculation of spirulina. Be careful with that, as when it happens there is no much time before bleaching begins !
Agitation default and iron depletion can lead to floculation too (for iron depletion, it is due to the increased lenght of spirulina filaments).
Iron depletion seems unlikely as the replica is good, but is not impossible : a higher pH can lead to a partial precipitation of iron, which will be no longer available.
A faster growth in the "floculated" PBR could have led to both higher pH and faster iron consumption.
Did you take a look under a microscope ? It will help a lot : If the cells are broken and/or pale -> over-exposure or pumping stress. If the filaments are longer than usual -> iron depletion
This answers helped me a lot, thanks! Can you recommend any articles on this subject?
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