Paper 3 · June 2017 · aeroponics and fermenter design
An air-lift fermenter has no mechanical stirrer. The culture is kept mixed because the
Aexhaust gas leaving the top draws the culture upwards behind it.
Bperforated pipes at the base release bubbles that rise and carry liquid with them.
Cvessel itself is rocked slowly so that the contents wash from side to side.
Dculture is pumped out at the base by an impeller and returned through the top of the vessel.
Explanation
Sterile air is forced through perforated pipes at the foot of the vessel. The column of liquid holding the rising bubbles is less dense than the liquid beside it, so it rises, spills over at the top and sinks again, and the whole culture circulates. Mixing and aeration are therefore done by the same air stream, and with no stirrer shaft there is no seal to leak and much less shear damage to the cells.
Derived from ZIMSEC Biology Paper 3, Jun 2017, Q11