Airlift reactors are submerged reactors in which the energy input is achieved by applying gas. Compressed air is often used as the gas.
During operation compressed air enters the airlift reactor at the bottom through the gas distributor. The added air mixes with the contents of the reactor and rises in the form of air bubbles. The rising air bubbles cause an upward flow. In doing so a portion of the oxygen in the air dissolves in the water. The area with the upward flow is called the riser. The remaining air bubbles leave the water at the top of the reactor. The gas-free liquid is fed back to the bottom section of the reactor in parallel to the riser. The area with the downward flow of an airlift reactor is called the downcomer. During operation the content of the reactor is recirculated through the riser and the downcomer. This recirculation is overlaid by perfusion in continuous operation. An additional tank with feed pump is provided for this purpose. The velocity of the circulation is set by the flow rate of the air.