Civil Engineering Reference
In-Depth Information
TABLE 9-2. Typical Design Values for Packed Tower Aeration
Design Parameter
Value
Hydraulic loading rate
25 to 30 gpm / ft
2
(61 to 73 m / h)
Tower diameter
3 to 10 ft (0.9 to 3.0 m)
Tower height
15 to 30 ft (4.6 to 9.1 m)
Packing depth
10 to 20 ft
Air-to-water ratio
Typically 30:1 to 40:1, but may range up to 100:1
Gas pressure drop
0.25 to 0.5 in. H
2
O per foot of packing depth
(200 to 400 N / m
2
per meter of packing depth)
Source:
Reference 15. (Adapted from
Proceedings of 1995 AWWA Conference,
by permission. Copyright
1995, American Water Works Association.)
Figure 9-7 demonstrates the effect of the type of VOC on the packing depth and
air-to-water ratio. A ratio of about 10:1 is required to achieve 95 percent removal of
trichloroethylene (TCE) with 15 ft (4.6 m) of 1-in. (2.5-cm) packing medium. For 95
percent removal of 1,2-dichloroethane, a less volatile compound, an air-to-water ratio
of about 120:1 is required for the same column design.
Figure 9-8 illustrates the relationship between the air-to-water ratio and packing
depth to achieve various efficiencies for removal of VOCs (in this case TCE). As
illustrated, to achieve 80 percent removal of TCE with an air-to-water ratio of 20:1
would require a column roughly 6 ft (1.8 m) high when 1-in. (2.5-cm) packing medium
is used. By contrast, attaining 99 percent removal of TCE at the same air-to-water
ratio requires a roughly 20-ft high (6.1-m)-high column.
Removal Efficiency - 95%
Water Temperature - 55
90
°
F
80
Number in Parentheses
Indicates the Henry's Law
Constant at 55
°
F in atm.
70
Trichloroethylene
(320)
60
50
40
Chloroform
(95)
1, 2-Dichloroethane
(29)
30
20
10
0
80:1
100:1
120:1
140:1
0
20:1
40:1
60:1
Air:Water Ratio, ft
3
/ft
3
Fig. 9-7.
Effect of type of VOC on packed column design (Reprinted from
Occurrence and
Removal of Volatile Organic Chemicals from Drinking Water,
by permission. Copyright
1983,
American Water Works Association and the American Water Works Research Foundation.)
