Table C.1

Aeration Technologies Used for Removing Radon from Water

Common Name

Other Name

Packed tower aeration (PTA)

Diffused bubble aeration

Spray aeration

Tray aeration

Slat-tray aeration

Jet aeration

Venturi or ejector aeration

Shallow-tray aeration

Sieve tray aeration

Cross-current packed-tower aeration

Cascade aeration

Pressure aeration

Aeration in hydrophor degasification

although more difficult and expensive to produce, provide a greater surface area per unit volume over which mass transfer can occur. In the most common systems, the water passes through a series of tanks (0.5–6 m deep), simulating a plug-flow reactor. The radon-contaminated air leaves the water when the bubbles reach the surface and is vented out of the unit. Diffused aeration systems cannot match the surface area available for radon transfer from water to air in PTA, but they can be easily retrofitted into basins and made as compact package units to treat small to medium flows. Shallow-tray (20–30 cm deep) aeration is a variant of this technology in which a thin layer of water passes across a series of plates perforated with holes. Air coming up through the holes causes the water to froth, and mass transfer occurs.

Spray Aeration

In spray aeration, water is formed into droplets (with a high ratio of surface area to volume) when it is forced through a nozzle. The droplets are sprayed upward, downward, or at an inclined angle into a large volume of air that is often flowing in a countercurrent direction. The simplicity of spray-aeration systems means that they can easily be retrofitted onto the inlet of an existing atmospheric storage tank to enhance radon removal from water. Their radon-removal efficiency is mainly a function of the size of the water droplets and the ratio of air to water (A:W ratio).

Tray Aeration

Tray-aeration systems are similar to countercurrent PTA except that the tower contains a series of slats (for example, made of redwood) or trays with perforated bottoms (for example, made of wire mesh). In some cases, a solid medium (such as, stone, ceramic spheres) is placed in the trays to promote transfer of radon to the air (Drago 1998). Water entering the top of the aerator is



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