Reportedly, the yield of photobioreactors (PBR) system ranges from 0.02 to 3.22 g/L per day and are used to cultivate algae in closed environment under manageable conditions. Efficiency of this system can be appreciated by considering the fact that it does not permit the algae to be exposed to the external environment. There are various configurations of the PBR systems like:

1. Vertical tank

2. Polybag

3. Helical tube

4. Horizontal tube

5. Inclined tube

6. Flat-plate

7. Vertical-column photobioreactor

13.3.2.1 Tubular PBR

A tubular PBR is constructed by arranging linear tubes made up of plastic or glass. This configuration can be easily manipulated to form arrangements like helical tubes and fence-like PBR. The ability of this configuration to expose the culture to maximum sunlight makes it suitable to use during outdoor cultivation. A slight glitch in tubular PBR is the settling of algae at the bottom of the tubes. Sedimentation can, however, be avoided by utilizing an airlift propeller to maintain an exceedingly turbulent flow. Tubular PBR are the largest in terms of size with areas reaching up to 750 m3.