the rate of freezing must be very slow to meet this cri-
Table 2. Concentrations of TNT and RDX in residu-
terion. An alternative would be to conduct multi-stage
als.
freezing at a higher freezing rate. Calculations show
Freezing rate
Residual
Residual
that the TNT limit could be achieved in six freezing
(mm/hr)
TNT conc.
RDX conc.
cycles at 10 mm/hr. This approach may not be cost-
(mg/L)
(mg/L)
effective unless air conditioning can be produced as a
11.7
24.7
19.16
by-product.
9.4
33.0
18.65
6.7
34.7
26.34
5.4
41.4
21.76
LITERATURE CITED
3.8
46.1
38.74
2.1
52.2
27.11
EPA (1994) Nitroaromatics and nitramines by HPLC.
SW-846 Method 8330, Second update. Washington,
Instead of trying to meet the 1.0 mg/L discharge
DC: Environmental Protection Agency.
limit in one freezing step, it may be possible to use
EPRI (1987) Industrial applications of freeze concen-
several freezing steps at a high freezing rate until the
tration technology. EPRI EM-5232, Project 2662-1.
desired meltwater quality is achieved. This approach
Palo Alto, California: Electric Power Research Insti-
is similar to the multi-stage distillation process used
tute.
in desalination. In this case the number of freezing steps
Glen, J.W. (1974) The physics of ice. U.S. Army Cold
can be estimated from Figure 7, which is a plot of the
Regions Research and Engineering Laboratory,
entrapment coefficient versus the freezing rate. The
CRREL Monograph II-C2A.
entrapment coefficient (E) is defined as the adjusted
mean concentration of TNT or RDX entrapped in the
gressive freezing. Water Research, 14(6): 575580.
ice divided by the residual concentration. Based on the
Integrated-Ice Systems, Inc. (1999) Ice-X Benefits.
linear line of best fit to the TNT data, E is approxi-
Integrated-Ice Systems, Inc., Woodinville, Washing-
mately 0.6 for a freezing rate of 10 mm/hr. This means
ton (http://www.bio-radiant.com/IceBenefitsFR.html).
that using the same initial TNT concentration as be-
Leggett, D.C. (1985) Sorption of military explosive
fore (22.6 mg/L), it would take about six freezing steps
contaminants on bentonite drilling muds. U.S. Army
at 10 mm/hr to achieve 1.0 mg/L TNT in the meltwa-
Cold Regions Research and Engineering Laboratory,
ter.
CRREL Report 85-18.
Painter, D. (1996) Phytoremediation of TNT. The Mili-
CONCLUSION
tary Engineer, 88(580): 4546.
Taylor, S. (1989) Icewater partition coefficients for
The results of this study show that the freeze con-
RDX and TNT. U.S. Army Cold Regions Research and
centration process is capable of meeting a 1.0 mg/L
Engineering Laboratory, CRREL Report 898.
TNT discharge permit limit in the meltwater. However,
7
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