Aeration in Biotechnology

The supply of oxygen to a growing organism, aeration, in bioreactors is a critical requirement in biotechnology because of the limited solubility of oxygen in water. Aeration involves transfer of oxygen from the air into the fluid surrounding the organism, from where it is transferred to the organism itself. During the course of a batch bioreaction, oxygen demand often passes through a marked maximum when the species is most biologically active. The basic principles that underlie aeration are exactly the same as those that determine the rate of transfer of any sparingly soluble gas (oxygen) from the gas stream (air) to the unsaturated liquid (broth). In each case, energy is dissipated to increase the rate of transfer beyond simple diffusion, and the mode of energy input defines the two‐phase fluid dynamics. Though there are many different types of bioreactor, there are basically four ways of imparting the energy required: rotating agitators (stirred tanks), gas compression (bubble columns/loop fermenters), liquid circulating (jet loop reactors), and shaking (shake flasks, microtiter plates), the last one being common at the screening stage of process development and in clone selection. In addition, the transfer rate depends on the area of contact between the phases, the driving force available (ie, the difference in concentration of oxygen in the two phases), the chemical composition of the liquid, and its temperature. Aeration is used in bacterial, aerobic yeast, polysaccharide, and mycelial fermentations, animal, stem, and plant cell culture, single‐cell protein production, and biological aerobic wastewater treatment.