type below 0.66 L/s 15,000 GPD capacity or above
4.38 L/s 100,000 GPD capacity, for step aeration
type above 3.0 L/s 67,500 GPD capacity and all for
complete mixing type.
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Sludge and scum collection and transfer equipment shall include sludge
transfer pump(s), [mechanical sludge collection equipment [(if used)],]
scum collection and transfer system, and supernatant transfer. [Settling
tanks with hopper bottom and side walls having slope of not less than 1.05
rad 60 degrees with the horizontal need not be provided with mechanical
sludge collection equipment].
2.9.2
Sludge Transfer Pumps
Sludge transfer pump(s) shall be an air lift pump. Air lift type pump
shall include an air pipe, eductor, foot piece, tail pipe, air separator
and a vent pipe. The air pipe to the eductor shall be of zinc-coated steel
schedule 40 of adequate size to discharge the required amount of liquid
without excessive pressure drop. Sludge transfer pump(s), except separate
waste sludge pump, shall have a recirculation capacity ranging from zero
percent to not less than 100 percent of the design flow. An air control
valve shall be provided on the air pipe to provide accurate adjustment of
the air lift discharge rate. Air control valve shall be a needle valve,
globe valve, ball valve, or plug valve. Materials for globe, ball, and
plug valves shall be as specified in paragraph entitled "Piping." The tail
pipe below the foot piece, the eductor pipe, air separator, and vent from
it shall be of zinc-coated steel. All fittings shall be of zinc-coated
malleable iron or cast iron. Joints between elements shall be as specified
in paragraph "Piping." The eductor shall be provided with a clean-out
above the water level. Air lift pump shall be installed so as to permit
easy removal for maintenance.
2.9.3
Mechanical Sludge Collection Equipment
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NOTE: On the drawings, show:
1. Type of plant: (Extended aeration, Step
Aeration, or Complete Mixing).
2.
Design flow.
3.
5-day BOD loading.
4.
Suspended solids loading.
5. Whether a comminutor is needed for plants 1.09
L/s 25,000 GPD or less in size.
6.
Whether mechanical aerator should be allowed.
7. Whether plant should be concrete only, steel
only, or either concrete or steel at Contractor's
option.
8.
Whether piling is required for foundations.
9.
Whether hypochlorinator or whether chlorinator
SECTION 11375N
Page 42
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