The pneumatic bioreactor (bubble co

The pneumatic bioreactor (bubble column and air-lift) consists of a cylindrical vessel in which compressed air or gas mixture is introduced at the bottom of the vessel through a sparger for aeration and mixing. The features of low capital and operational cost, no moving mechanical parts and sealing elements, and ease of scale-up are advantageous for large scale plant cell cultures. The low shear stress in pneumatic bioreactors is desirable for shear-sensitive plant cells (Eibl and Eibl, 2008). Bubble columns are often used for organogenic micropropagations, however, they are unable to provide homogenous mixing and are less applicable to high biomass cultures due to the lower gas-liquid interfacial area resulting from bubble coalescence in the viscous cultures and lack of mechanical break-up of bubbles. The performance of a bubble column can be improved by installing multiple spargers in different segments for delivering oxygen into the zones of high cell density hairy root cultures in the column (Mishra and Ranjan, 2008).