Civil Engineering Reference
In-Depth Information
VOC - Trichloroethylene
Removal Efficiency - 95%
40
30
40
°
F
20
55
°
F
10
75
°
F
0
40:1
50:1
60:1
70:1
0
10:1
20:1
30:1
Air:Water Ratio, ft
3
/ft
3
Fig. 9-9.
Effect of water temperature on packed column design (Reprinted from
Prediction of
GAC Performance Using Rapid Small-Scale Column Tests,
by permission. Copyright
1989,
American Water Works Association and the American Water Works Research Foundation.)
Operation and Maintenance
By and large, packed towers operate automatically,
with minimal maintenance. However, daily visits are necessary to verify that equipment
is running properly. Maintenance includes servicing of pumps and blower motors and
the replacement of air filters on the blowers. Even with rigorous cleaning, packed
material eventually needs replacement.
Operational difficulties that may be encountered include biological fouling and the
precipitation of iron and calcium carbonate compounds on the packing material. These
problems can be minimized by pretreatment of the influent or by use of a cleaning
package. The frequency of cleaning depends on the influent water quality. A poly-
phosphate agent may be added to the tower influent to minimize deposition on the
packing material.
Multiple-Tray Aeration
General Description
Multiple-tray aerators consist of a series of trays with slatted,
perforated, or wire-mesh bottoms. The water is distributed evenly over the top, flows
from tray to tray, and is collected in a basin at the bottom. Coarse media can be placed
in the trays to increase gas transfer effectiveness. Applications for multiple-tray aera-
tion include removal of CO
2
, hydrogen sulfide, and (to a lesser extent) taste and odor,
as well as the addition of oxygen for iron and manganese oxidation. Figure 9-10
shows a diagram of a typical multiple-tray aeration system.
