Aeration is a bottleneck in many processes in minerals refinement and biotechnology .
Aeration is the pumping or sparging of bubbles into liquid, often with mechanical stirring to break up and distribute the bubbles. Aeration typically supplies the gas needed for a chemical reaction in a liquid, or the oxygen demanded by organisms in bio-engineering. Bubbles are also widely used in chemical and metallurgical engineering to drive recirculating and mixing flows in reactors. In some cases, mechanical stirring is too harsh for delicate crystals or biological cells, so bubbles do the job. Often, a small bubble size is ideal to maximize mass transfer, while a large bubble size is needed to maximize recirculation and mixing.