FREEZE CONCENTRATION OF PINKWATER
C. JAMES MARTEL, SUSAN TAYLOR, AND STEPHEN W. MALONEY
The freeze concentration process has the potential
INTRODUCTION
to overcome these difficulties. This method is used in
the food industry for concentrating milk, fruit juices,
Background
beer, wine, and other food products (EPRI 1987). It
Army industrial operations, such as munitions pro-
has long been the technology of choice in the food in-
duction and demilitarization, generate large volumes
dustry because it uses less energy than evaporation and
of hazardous wastes. A single Army Ammunition Plant
it produces a purer product. Freeze concentration may
(AAP) can discharge as much as 500,000 gallons of
also provide a method of treating redwater and ammo-
wastewater per day. Untreated discharges and solid
nium perchlorate. Present methods, such as the use of
wastes have contaminated billions of tons of soil as
granular activated carbon, are unable to treat these
well as the underlying groundwater. Currently, 20 Army
wastes.
Ammunition Plants have TNT-contaminated soil or
Once most of the water is removed, the cost of dis-
groundwater, and 10 are on the National Priority List
posal is significantly reduced. For example, plasma arc
(NPL) (Painter 1996). Also of concern at Operations
vitrification has been proposed as a treatment for many
Support Command (OSC) facilities are new water qual-
wastes. By removing most of the water by freeze con-
ity standards and revised permit limits. Most of these
centration, most of the plasma energy would be used
treatment facilities are 3050 years old. If industrial
to oxidize organic matter and vitrify metals rather than
wastes continue to be discharged to these plants, they
evaporate water. Removing water has the secondary
may not be able to meet these standards. New pretreat-
effect of reducing off-gases, whether plasma arc or con-
ment technologies will be required at many of these
ventional incineration is used. Another treatment op-
installations to facilitate compliance.
tion would be to discharge the concentrate to drying
According to information posted on the U.S. Army
lagoons as is done with demilitarization wastewaters.
Environmental Requirements Technology Assessment
Removing most of the water by freeze concentration
(AERTA) Web site (http://aec.army.mil/prod/usaec/et/
would reduce the land area required for the lagoons.
aerta.htm), the cost of Army projects related to treat-
A bonus benefit of the freeze concentration process
ment of wastewater from munitions in FY 97 was over
is central air conditioning of facilities. The ice can be
M. The total cost of treatment, monitoring, and
stored and used in conjunction with a heat pump to
control of Army wastewater, including plating wastes,
produce cooling energy. Savings range from 30% to
is over 3 M.
70% over conventional air conditioning depending on
One way to reduce disposal costs is to reduce the
location and use of off-peak power (Integrated-Ice
amount of wastes generated by removing some of the
Systems, Inc. 1999). This benefit would be a boon to
water. Conventional methods of separation, such as
most Army Ammunition Plants located in warm cli-
sedimentation and filtration, are only partially success-
mates.
ful because the munitions compounds are mostly dis-
The mechanism of freeze concentration is a physi-
solved in water and thus cannot settle out or be filtered
cal process whereby water is separated from impuri-
out. Evaporation is not attractive for munitions pro-
ties during the formation of ice crystals. As explained
duction and demilitarization wastes because they are
by Glen (1974), ice is a solid that consists of a crystal-
explosive and flammable.
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