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CHAPTER FIVE
5.24

It is critical for measurements of both waterflows and airflows to be accurate in order
to know the air-to-water ratio.
When one is using random packing in a column, the number of packing pieces per
unit volume is ordinarily less in the vicinity of column walls. This packing distribution
tends to produce a flow scheme in which water moves toward the walls and airflow is
directed more toward the center of the column--a phenomenon referred to as channel-
ing. Channeling is less pronounced when the diameter of the packing pieces dp is smaller
than one-eighth the column diameter dc. It is recommended that, if possible, the ratio
dp/dc = 1 : 15.

Testing Program and Evaluation of Results
A testing program for operating a pilot plant and evaluating results is usually necessary
before one begins to design full-scale treatment facilities. Decisions must be made on fac-
tors such as the number of operations to be made, loading rates, air-to-water ratio that
must be provided, and, in the case of packed columns, the type of packing to be used.
A critical part of operating a pilot plant is the sampling procedures. When samples are
collected for VOC analysis, they must be collected without allowing any entrapped air to
remain in the sample bottle. If even a very small bubble remains in the bottle, some of
the volatile chemicals may leave the water, causing incorrect results when the sample is
analyzed.
Other data that must be collected periodically during pilot plant operation are water
and air temperatures, as well as chlorine, iron, and total organic carbon levels.
Once samples have been analyzed, test results can be evaluated. From these data, op-
timum full-scale operational and design conditions can be established. In a diffused air
system, detention time, water depth, and air-to-water ratio are evaluated. In addition to
these conditions, with a packed column system, KLa is determined and the best packing
is chosen.

BIBLIOGRAPHY

Adams, J. Q., and R. M. Clark. "Evaluating the Costs of Packed Tower Aeration and GAC for Con-
trolling Selected Organics." Journal AWWA 83(1):49, 1991.
Air Stripping for Volatile Organic Contaminant Removal. Denver, Colo.: American Water Works
Association, 1989.
American Water Works Association. Water Quality and Treatment, 4th ed. New York: McGraw-
Hill, 1990.
Atoulikian, Richard G. "Proper Design of Radon Removal Facilities for Cost-Effective Treatment."
Journal NEWWA 111:4, December 1997.
Balla, John M. "MTBE Removal via Packed Column Air Stripping." 2001 AWWA Annual Confer-
ence Proceedings, Washington, June 2001.
Balla, John M. "Is Your Packed Column Air Stripper Ready for the 21 st Century?" 1999 AWWA En-
gineering and Construction Conference Proceedings, Orlando, Fla., March 1999.
Boyden, B. H., et al. "Using Inclined Cascade Aeration to Strip Chlorinated VOCs from Drinking
Water." Journal AWWA 84(5):62, 1992.
Controlling Radionuclides and Other Contaminants in Drinking Water Supplies: A Workbook for
Small Systems. Denver, Colo.: American Water Works Association, 1991.
Dixon, K. L., et al. "Evaluating Aeration Technology for Radon Removal." Journal A WWA 83(4): 141,
1991.