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AERATION AND AIR STRIPPING 5.3

FIGURE 5.1 View of a typical cone aerator. (Courtesy ofOndeo Degremont.)

layers from one level to another. The exposure time of air to water can be increased by
increasing the number of steps, and the area-volume ratio can be improved by adding baf-
fles to produce turbulence. In cold climates, these aerators must be housed, and adequate
provisions must be made for ventilation. As with tray aerators, operating problems in-
clude corrosion and slime and algae buildup.

Cone Aerators. Cone aerators are similar to cascade aerators. They have several stacked
pans arranged so that water fills the top pan and cascades down to each succeeding pan.
A common type of commercial cone aerator is shown in Figure 5.1.

Packed Columns. Packed columns (also called packed towers or air strippers) are used
extensively in the chemical industry and have been used in the water industry primarily
for removal of volatile compounds such as VOCs from contaminated water. The extremely
large surface area provided by packing in a column, combined with forced air flowing
counter to the flow of water, provides considerably more liquid-gas transfer compared
with other air stripping methods. A packed column consists principally of a cylindrical
tower, packing material contained in the tower, and a centrifugal blower.
The quantity of air provided in relation to the quantity of water flowing through the
column is known as the air-to-water ratio. This ratio is important in designing for removal
of VOCs, as is the height of the packing material. A packed column installation is shown
in Figure 5.2.