MIL-HDBK-1138
condensate freezing in the lines.
Using a desiccant on the air
supply is recommended.
7.2.4
Other Preliminary Treatment Processes. Sometimes
septage trucks discharge material to the headworks of the plant.
To ensure that the discharge hoses do not freeze, drain them
completely and hang them up so that water does not collect
inside. On fixed lines, heat tracing will prevent the liquid
from freezing. However, fixed lines should be installed with a
slope to drain. Septic trucks should be kept in heated garages
because they have many parts in which water may freeze, including
the pumps, valves, piping, and tank. Tankers should be
completely empty if they are left out in the freezing weather.
Automatic samplers should be housed in a heated and
insulated compartment. Sampler suction lines should be heat
traced or enclosed in a heated space. A light bulb in the
sampler "shed" can supply enough heat to prevent the sampler from
freezing. A small shelter the size of a doghouse may be suitable
for this purpose, if it is insulated. Operate screw pumps
routinely to prevent the shaft from freezing to the walls of the
chute. Rotate the screw pumps a few turns every half hour to
ensure that they do not freeze. The rotation can be performed
with a simple timer.
7.3
Clarifiers. Clarifiers are affected in several
ways by the decrease in seasonal temperatures. The density of
water changes with temperature, and this change affects the
settling characteristics of the solids. Materials at the surface
of these quiescent basins will tend to freeze. Weirs and
launders may also freeze, depending upon the ambient and
wastewater temperature. Table 8 summarizes some potential
problems and solutions associated with clarifier freezing.
Surface Freezing Conditions. The most serious
7.3.1
problem associated with clarifiers is freezing on the surface,
surface scum, and ice buildup on the scum beach plate. These
problems damage skimming mechanisms and may even cause the
clarifier rake mechanism to fail. Check torque limits on the
rake mechanism routinely and adjust them if necessary to ensure
that they will work if ice affects the collector. Removing the
skimming arm in winter may prevent this problem; however, the
problems of scum freezing and removal remain. Hot water sprays,
heat tape, and enclosed lamps may be valuable in addressing these
problems. Many times, ice must be carefully chopped off the
surface of the tanks and removed to the launders.
60
Previous Page
