An air-lift bioreactor contains a draft tube that gives performance-improving internal circulation. In air-lift bioreactors, internal liquid circulation is achieved by sparging only a part of the reactor with gas. The sparged section contains a lower effective density than the bubble-free section, and the difference in fluid mechanics pressure between the 2 sectionsinduces the liquid to maneuver upward. That makes a draft that significantly improves circulation and atomic number 8 transfer whereas equalizing shear forces within the reactor. With no mechanical agitation, these bioreactors square measure low-shear vessels that allow high-efficiency mass transfer with glorious flow and compounding properties. However, they need many disadvantages, including significant back-mixing between gas and liquid phases, high drops, and bubble coalescency.