Foam Separation of Powdered Activated Carbon
PAUL L. BISHOP, Assistant Professor
Civil Engineering Department
University of New Hampshire
Durham, New Hampshire 03824
GREGORY D. BOARD MAN, Graduate Student
Civil Engineering Department
University of Maine
Orono, Maine 04473
INTRODUCTION
An important development in wastewater treatment recently has been an increased
interest in the use of activated carbon to remove organics. In addition to adsorbing soluble
and often refractory organics, granular carbon beds also serve as filters and provide a media
for biological degradation.
Knowledge of the applicability of activated carbon has been well established for nearly
a century; however, limitations have been placed on the use of powdered carbon forms due
to the difficulty encountered in separating them from solution and in regeneration.
Hence, granular forms have been principally used to adsorb organic and inorganic materials, color and toxic matter. Ironically, powdered carbon is less costly to manufacture,
offers more surface, and distributes more easily and uniformly in solutions, thereby providing greater removals and more rapid equilibrium.
In order for powdered activated carbon to become more universally acceptable, better
means for removal and regeneration will be necessary. This paper will consider foam
separation as one method for removal and recovery of the carbon.
Foam separation is a technique whereby bubble adsorption is used as a means of
separation. In general, there are two types of solute systems which lend themselves to foam
separation. The first is characterized by solutes which are inherently surface active.
Examples of these are proteins, dyes and detergents. The second class is comprised of those
materials which are not naturally surface active, but which may be rendered so through the
addition of a surfactant. Powdered activated carbon would be in this latter category.
Grieves, etal( 1,2, 3,4, 5) have investigated foam separation for clarification of water.
Foam separation was initiated by addition of a cationic surfactant (quarternary ammonium
salt) which adsorbed at the surfaces of the negatively charged, colloidal particles causing
turbidity in the water. The particles were then floated to the water surface by aeration and
attachment of the particles to diffused or precipitated air bubbles. With this procedure, the
turbidity could be reduced from about 250 Jackson Turbidity Units to about 4 JTU.
Approximately 2 percent of the feed water was lost with the foam.
Foam separation of domestic wastewater has also been investigated (6, 7, 8, 9).
Removals of ABS and COD were generally in the area of 50 percent. Little or no removal of
dissolved materials occurred.
Past efforts to separate activated carbon from water have been limited to batch runs
(10, 11, 12). These studies did show promise, however. They showed that at pH 7, carbon in
suspension could be reduced from as much as 800 mg/1 to 24 mg/1 in 10 minutes with the
addition of 0.37 mM EHDA-Br (ethylhexadecyldimethylammonium bromide), a cationic
surfactant.
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