Airlift Internal Circulation Bioreactor

Sterile air is injected at high velocity through the sparger into the bottom of the draft tube. The gas-liquid mixture inside the tube has high gas holdup and significantly lower density than the liquid outside the tube. Driven by density difference and gas flow kinetic energy, the mixture rises rapidly through the draft tube. At the top gas-liquid separation zone, part of the gas is released and degassed liquid flows from the draft tube upper rim into the annular downcomer zone, returning to the bottom by gravity to re-enter the circulation loop. This continuous internal circulation achieves efficient mixing and oxygen mass transfer without mechanical agitation.

The absence of impellers results in very low shear stress, making this fermenter ideal for animal cells, plant cells, and filamentous fungi. Energy consumption is typically 30%–50% lower than mechanically agitated vessels. The simple construction with minimal sealing points reduces contamination risk. CIP/SIP operations are more straightforward with fewer dead zones.

Mixing and mass transfer efficiency decrease in high-viscosity systems. The height-to-diameter ratio requirements may limit applicability in some facility configurations.

In biopharmaceutical production, the internal circulation airlift fermenter is used for animal cell culture (antibodies, vaccines) and plant cell culture (secondary metabolites). In food and enzyme production, it serves for vitamin C, yeast, single-cell protein, and enzyme fermentation. Environmental and energy applications include aerobic treatment of high-concentration organic wastewater and algae cultivation for biodiesel production.