Small Systems Water Treatment Plant Operator Program Manual

SMALL
SYSTEMS
SEWA
EWAGE
LAGOON
OPERATION
& MAINTENANCEM
10.6.9 FREE FALL DISCHARGES
& M
10
Continuous overflow lagoons are now rarely designed with free fall discharges, but
they have been used in the past. The principal reason for not using them is that during
periods of low flow in the pipe, the air moving up the discharge pipe can cause glaciertype
water freezing which could eventually cause freeze-up of the pipe. In addition, the
cold air temperature around the discharge pipe can cause freezing inside.
Some existing lagoons do have free fall discharges. This was more common in the
past but still may be done due to the topography of the site. In these cases, the operator
must be aware of the following locations of possible problems:
The support structure holding the pipe;
1. The foundation of the support structure;
2. The insulation of the discharge pipe;
3. In heat tracing tape (if you have it);
4. Potential for ice build-up; and
5. Potential for ice damage.
The build-up of ice and its movement during spring break-up are among the most
serious problems. Winds can drive large ice masses onto the shore and damage
unprotected support structures.
A metallic support structure should also be inspected for corrosion and related
problems, which may weaken the structure. If necessary, attaching a sacrificial anode
to a metal support is one step to reduce the maintenance required due to corrosion.
The next step is inspection, repair or replacement of heating cable systems. These have
be checked regularly to ensure proper operation.
10.6.10SUBMERGED GRAVITY
When the inlet flow enters the lagoon below the surface (either through the side or
bottom), routine maintenance requirements are minimal. The concern is limited to the
need to clean the pipe line periodically to prevent increased head loss due to sludge and
deposits build-up.
10.6.11SUBMERGED PRESSURE
In many locations, the topography of the lagoon site will require the use of a forcemain
and pumping station to deliver the wastewater to the lagoon, including the use of
submerged pressure discharge to the first cell, the short-detention lagoon. In this case,
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