MIL-HDBK-1138
Table 9 (Continued)
Problem
Solution
Impeller icing causing ponding
Remove shroud. Ice will still
on fixed shroud
build up, but aerator will not
be damaged.
Ice buildup on supporting
Shorten detention times; run
columns causing rotating
aerators on timers.
shroud to pond on columns
Cooling of mixed liquor
Install timers on aerators.
Use diffused air instead of
surface aeration.
Remove some aerator blades.
Icing in idle tank damaging
Fill tank 1 foot above baffle.
structure
Install small sump pump to keep
surface free of ice.
Exercise units regularly during
sunny days. Care must be taken
not to damage units.
Use inner tubes to absorb ice
expansion.
Bubble air to prevent freezing.
Ice buildup on splash guard,
Use good snow and ice removal
electrical conduit, and
procedures, salt.
walkways
Plant policy requires operators
to keep one hand free to hold
railing.
Decreased removal efficiencies
Increase MCRT, decrease F/M.
Source: Taken in part from U.S. Army CRREL Special Report 85-11.
7.4.1
Activated Sludge Systems. Cold weather does not
affect conventional activated sludge systems with a detention
time of 4 to 6 hours as significantly as systems with longer
detention times. Extended aeration systems having detention
times of 10 to 24 hours will experience a temperature decrease
that will affect the biological process. Systems that use
diffused air for oxygen transfer will actually be adding heat to
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