Foam fractionation separates a solution containing a surface-active solute into two fractions: the foam fraction containing a high concentration of surface-active solute and a drain fraction depleted of the same solute. Foam formation also collects SS and oils and separates them from the wastewater being treated.
Figure 7.18.4 shows the basic concept of foam fractionation. Gas, usually air, is diffused into the bottom section of the fractionation unit while the feed flow enters above the gas inlet but below the liquid surface. Foam is generated and lifted upward by the gas in the unit. This process discharges the foam from the fractionation unit and collapses it by heating it or spraying it with previously collapsed foam. Heating to facilitate foam collapsing is preferred when SS are separated by this process. The effluent is discharged near the bottom of the fractionation unit.
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