Photobioreactors (PBRs) come in all shapes & sizes, but fundamentally they are open or closed containers for growing microalgae.
Closed PBRs have controlled growing conditions, water loss in minimised and contamination is reduced. Open PBRs (ponds & raceway types) are more economical but suffer from high evaporation, invasive species & animals!
Open
Closed
Examples of current commercial photobioreactors