Abstract

The supply of oxygen to a growing biological species, aeration, in aerobic bioreactors is one of the most critical requirements in biotechnology. Aeration is usually accomplished by transferring oxygen from the air into the fluid surrounding the biological species, from where it is in turn transferred to the biological species itself. During the course of a batch bioreaction, oxygen demand often passes through a marked maximum when the species is most biologically active. The main reason for the importance of aeration lies in the limited solubility of oxygen in water. The basic principles that underlie oxygenation (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). The rate at which this transfer takes place is dependent on the area of contact between the gas and the liquid, the driving force available (ie, the difference in concentration of oxygen in the two phases), the two-phase fluid dynamics, and the chemical composition of the liquid. A huge variety of bioreactors have been developed; a useful subdivision has been made into three generic types. These are bioreactors driven by rotating agitators (stirred tanks) that are by far the most common, bioreactors driven by gas compression (bubble columns/loop fermenters), and bioreactors driven by circulating liquid (jet loop reactors). Aeration is used in bacterial, aerobic yeast, polysaccharide and mycelial fermentations, mammalian and plant cell culture, single-cell protein production, and biological aerobic wastewater treatment.