Foam Separation by Dispersed Air Flotation Cell

Many contaminants in wastewater today, such as dissolved dyestuffs, lignins, detergents, proteins, fatty acids, tannins, and so on, possess surface-active properties that decrease surface tension and oxygen transfer rate, but increase the demand for dissolved oxygen. Particularly, the sharp reduction in surface tension of water by these pollutants seems to be a basic cause of increasing the susceptibility of aquatic life to the surfactant poison. 

Foam separation process involves the selective adsorption of the surface-active pollutants at the gas-liquid interfaces of fine air bubbles in a foam separation column. The surface-active pollutants, which are adsorbed on the surfaces of the rising bubbles, can be carried upward to the top of the foam separation column and thus removed from the aqueous system as condensed foam. Foam separation can be used for both waste treatment and water purification. This section presents the data on the feasibility of removing various organics and inorganics by the foam separation processes. A general survey of foam separation process and its fundamental principles are also presented. 

The basic principle for solid/liquid and solute/liquid separation by the adsorptive bubble separation processes has been introduced previously. This section further presents fundamental principles on foam phenomena and foam separation cell s operation. 

For foam separation processes, adsorption takes place in solution, the essential basis exists for solute separation by foaming. Foam consists of gas bubbles separated by thin liquid films. The liquid films are often formed by the mutual approach of two already existing liquid surfaces (e.g., two bubbles below the surface). Foam structures may vary between two extreme situations. The first is wet foam, which consists of nearly spherical bubbles separated by rather thick liquid films. The second is dry foam, which may develop from the first type as a result of drainage (i.e., foam drainage). 

The second cause of coalescence is the film rupture between bubbles. This can easily be very significant. Physically, the film rupture stems from a depletion of surfactant at the film surface when the surface is stretched. The film stability is commonly ascribed in large measure to the so-called Marangoni effect and Gibbs effect. The Marangoni effect involves the inability of surfactant molecules to diffuse instantaneously to any locally stretched area in the film surface. The resulting lag permits the stretched surface to be momentarily depleted of surfactant. The Gibbs effect involves 

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Foam Separation by Dispersed Air Flotation Cell Chemical Reagents for Adsorptive Bubble Separation Laboratory Foam Separation Tests Engineering Applications... 

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