Publisher Summary Foam, a dispersion of gas in liquid with bulk density approaching that of the gas, is an agglomeration of gas bubbles separated from each other by a thin liquid film. Foam formation is a common phenomenon in many industrial processes including chemical and fermentation processes. Its formation is a desirable property in some processes such as in the production of beer. However, foam in submerged fermentations poses a serious problem and results in the loss of material through the exhaust lines as well as the danger of contamination of the fermentation batch and the environment. The preferred method of foam control in fermentation is by the use of antifoam agents, although in a few instances, a mechanical foam breaker is used along with the chemical antifoam. In fermentations, the control of foam is a costly and nonproductive operation and therefore an effective foam control with reduced costs greatly influences the economics of the process.

Foam Control in Submerged Fermentation: State of the Art

(1972). Foam Separation Methods. Separation and Purification Methods: Vol. 1, No. 1, pp. 117-198.

Foam separation methods

There has been much recent activity in the theory and application of separation by flotation, both in the United. States and abroad. This review primarily addresses new developments in foam flotation, colloid flotation and precipitate flotation. The work in ore flotation represents a major effort and would itself require a lengthy article. Work from ore flotation which significantly impacts on the areas of interest listed above is included here, however. Foam separation of biological materials and the microflotation of bacteria are not routinely discussed in this review. A few recent review articles on these areas are included at the end of the Review Articles and Books Section to afford the interested reader a start on that literature. The development and use of flotation separation techniques for waste treatment and water reuse over the last few years are included in this article.

Separation by Flotation

The recovery of valuable proteins (like proteolytic enzymes) from nonconventional biological sources by using modern separation techniques is becoming increasingly important because of their high commercial potential. In the present investigation, isolation of proteins from human placental extract by using the continuous foam fractionation technique is studied. The effect of different physicochemical parameters on the separation of proteins and purification of proteolytic enzymes are reported. A method for finding a quasi-equilibrium relationship between the solute concentration in the foamate and in the effluent by using the same system is described. The quasi-equilibrium curve is also presented.

Effect of Physicochemical Parameters on the Separation of Proteins from Human Placental Extract by Using a Continuous Foam Fractionating Column

Role of bubble size for the performance of continuous foam fractionation in stripping mode

The foam separation process uses differences in surface activity to separate components of a solution. Stable foams can flow upward countercurrent to liquid to give countercurrent differential separations with stripping, enrichment, or scrubbing similar to solvent extraction.

Six- and 24-in. I.D. foam columns were operated with sodium dodecylbenzenesulfonate solutions to measure height of transfer unit (HTU) values and foam densities and to develop satisfactory gas spargers, liquid feed distributors, foam drainage conditions, and foam condensation equipment. The HTU values for stripping of Sr-89 were about 1 cm. for the best conditions of uniform foams, liquid flows of 100 gal./sq.ft.hr. or less, and uniform liquid feed distribution with low inlet velocities. Variations of countercurrent column lengths within 10 to 28 cm. caused little variation in HTU values. The foams were condensed, with four types of pneumatic or mechanical foam breakers used. A pilot plant was designed for decontamination of a low level radioactive waste.

H. F. Johnson

Papers

Foam columns for countercurrent surface—liquid extraction of surface-active solutes