Application of Colloidal Gas Aphrons (CGAs) and their Bioprocess Separation Roles

Abstract

Colloidal gas aphrons (CGAs) are surfactant-based microbubbles. They are described as microfoams approximately 10–100 μm diameter with special structure which is different from that of conventional foam. Although the size of aphron exceeds that of colloid, which ranges from 1 nm to 1 μm, the term colloid is used firstly because of small size of the microfoams and secondly because the bubbles show some colloidal properties. They exhibit unique properties which distinguish them from conventional foams and are as follows: large interfacial area per unit volume which is beneficial for the adsorption of molecules, high stability compared with conventional foam, similar flow properties to those of water e.g. being easily pumped from one place to another, and their easy separation from the bulk liquid phase due to buoyancy. Because of these properties they have a wide spectrum of applications and a large body of research has been published on CGAs applications in various fields. Application of CGAs in biotechnology has been gaining importance in recent years. Some studies focused on the separating role of CGA systems in bioprocesses and discussed their usage in separation processes such as protein and enzyme recovery, carotenoids recovery, removal of organic dyes from wastewaters, removal of dispersed oil droplets from water, and cell harvesting. But other sector of literature deals with CGA systems used in mass transfer promoting areas in bioprocesses which include oxygen delivery in bioreactors and bioremediation; that is separation of hazardous contaminants from soil and water. The main purpose of this article is to review the usage of CGAs in the realm of biotechnology in recent years and to open up new fields.