Other Considerations
Settling basins should be designed
and constructed to minimize erosion of
the earthwork. Inflow should enter at the
surface on one side and exit at the surface
on the other side. Baffles can be installed
in settling ponds to avoid flow passing
straight from inlet structure to outlet
structure.
Settling basins must not be aerated,
for turbulence reduces the settling velocity
of particles. If effluent must be aerated
before discharge, a separate aeration basin
should be installed.
The average depth of settling ponds
should be measured at regular intervals to
confirm that the minimum design HRT
is achieved. When settling basins are
cleaned out, sediment should be disposed
of in a responsible manner.
Settling basins designed as described
above will function primarily to remove
coarse mineral solids – suspended soil
particles. If space is available to provide
an HRT of a day or more, smaller soil
particles can settle, and phosphate will be
absorbed by sediment in the pond bot
-
tom. Some ammonia nitrogen will be
nitrified, and some will diffuse into the
atmosphere. Denitrification will occur in
anaerobic zones of the sediment, and
water will be naturally reaerated. Thus,
there are considerable benefits to building
settling basins as large as practical