TM 5-852-5/AFR 88-19, Volume 5
(3) Direct-fired boiler. These systems use oil,
gas or coal furnaces to maintain the contained water
The basic requirement, criteria and procedures for
at just below boiling temperature. This is then
water treatment systems for military facilities are
blended with the cold water source or used in a heat
covered in TM 5-813-1/AFM 88-10, Vol. 1. This
chapter will discuss only those aspects unique to the
Arctic and Subarctic. There are three major process
4-3. Low temperature treatment.
concerns: the low temperature of the raw water,
removal of glacial silt from surface sources and
Almost all of the physical, chemical, and biological
removal of dissolved minerals and organics from
processes used in water treatment are sensitive to
temperature either through viscosity effects or as an
influence on reaction rates. Figure 9-1 illustrates the
4-2. Temperature effects.
influence of viscosity, and the multiplier shown must
be used to adjust the design of a water treatment
The temperature of surface water sources during
process component for temperature.
winter will be at or very near 32 degrees F, while
a. Mixing. Mixing is strongly dependent on tem-
ground-water sources in permafrost regions may be
perature because of viscosity changes in the water.
a few degrees warmer and maintain that level year-
The power input for mechanical flocculation is
round. The water must be preheated to at least 40 to
directly dependent on fluid viscosity as defined by:
50 degrees F or the unit processes must be designed
for low temperature operation. The effect of low
P = G2VF
temperatures on equipment operations must also be
evaluated during facility design.
= power input
a. Preheating. A number of methods have been
= velocity gradient
successfuly used to heat water in arctic systems.
= tank volume
= absolute fluid viscosity.
(and cross connections) during the heating process
and the corrosion induced if dissolved oxygen is
To maintain the same velocity gradient in the tank
released from solution. Very cold surface waters
as the liquid temperature decreases, it is necessary
may be at or near saturation with respect to dis-
to adjust the 68 degree F power requirement by the
solved oxygen. Oxygen is then released as a gas as
multiplier from figure 9-1. This relationship will be
the water is warmed and can cause severe corrosion
valid for any kind of mechanical mixing. Detention
in iron and steel pipes, pumps, and tanks. Use of
time for mixing is determined separately. Detention
non-ferrous metals in the heating stage and control-
times for flocculation range from 15 to 30 minutes
ling the release point for this oxygen will reduce
and tend to be arbitrarily based on successful
performance. The multiplier from figure 9-1 must be
(1) Liquid-liquid heat exchangers. Hot water is
used for this adjustment. Multiple basins are
the preferred source of heat for these devices to
recommended when surface water is the source and
eliminate problems from tube leakage and contam-
warmer temperatures are expected in the summer.
ination. The source of hot water might be a central
In this way some of the units can be taken out of
heating system or cooling water from an engine.
service when not needed.
Double wall, or double liquid to liquid exchangers
b. Sedimentation. Settling of discrete particulate
are necessary to prevent any possibility of contami-
material is retarded by the increased viscosity in
nation of potable water.
cold waters. As shown in figure 9-2 the effect of
(2) Blending. In some cases a source of clean
low temperature decreases as the solids
hot water may be available and can be blended
concentration increases. Plain gravity sedimentation
directly with the cold water to achieve the desired
of individual particles would be subject to full
temperatures. Condenser water from a steam system
viscosity effects and the detention time must be
was successfully used in this way in Fairbanks,
adjusted with the multipliers from figure 9-1.