Various designs and scales of vertical-column photobioreactors have been tested for cultivation of algae. Vertical-column photobioreactors are compact, low-cost, and easy to operate monoseptically . Furthermore, they are very promising for large-scale cultivation of algae. It was reported that bubble-column and airlift photobioreactors (up to 0.19 m in diameter) can attain a final biomass concentration and specific growth rate that are comparable to values typically reported for narrow tubular photobioreactors. Some bubble column photobioreactors are equipped with either draft tubes or constructed as split cylinders. In the case of draft tube photobioreactors, intermixing occurs between the riser and the downcomer zones of the photobioreactor through the walls of the draft tube.
High mass transfer, good mixing with low shear stress, low energy consumption, high potentials for scalability, easy to sterilize, readily tempered, good for immobilization of algae, reduced photoinhibition and photo-oxidation.
Small illumination surface area, their construction require sophisticated materials, shear stress to algal cultures, decrease of illumination surface area upon scale-up.
