the settling tank. The aeration tank influent distribution channel shall
be located on the inside face of the outer tank or outside face of the
inner tank and not less than one-half the length of the periphery. The
effluent launder shall be located completely around the inner face of the
settling tank wall. The inner side of the effluent launder shall be higher
than the outer (weir) side to act as a scum baffle. The influent and
effluent launders shall be constructed of steel [, except that for
concrete-wall settling tank, launders may be of concrete in lieu of steel.]
Weir loadings shall not exceed 0.44 L/s per 300 mm 10,000 GPD per linear
foot. Weir and scum baffles shall be as specified under paragraph entitled
"Appurtenances and Accessories."
2.8
AERATION EQUIPMENT
2.8.1
General
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NOTE: Delete reference to mechanical aerator when
step aeration type or complete mixing type is
specified, or when not allowed for extended aeration
type. Mechanical aerator may not be suitable for
use in areas having prolonged periods of
sub-freezing temperatures when spray may form
accumulation of ice. Consideration should be given
to temperature and detention time of the liquid and
freeboard in the tank in determining temperatures
that may be tolerated. Mechanical aerator is not
suitable for extended aeration type where eventual
conversion to step aeration is contemplated.
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The aeration system shall be of the diffused air type [or fixed mechanical
aeration type] capable of transferring not less than 0.45 kg 1.0 lb of
oxygen to the mixed liquor per pound of 5-day BOD aeration tank loading and
maintaining complete suspension of all sludge solids throughout the entire
aeration tank. The aeration equipment shall completely mix the contents of
the aeration tank so that the velocity in any part of the tank shall be not
less than 0.18 m/s 0.6 fps. The aerator shall have sufficient mixing
capacity to thoroughly mix the wastewater throughout the tank depth, to
maintain essentially equal D.O. concentration within the basin, and to
maintain the biological floc in suspension in concentrations of up to 4,000
mg/l. Minimum acceptable velocity throughout the basin is 0.18 m/s 0.6 fps.
2.8.2
Diffused Air Aeration Equipment
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NOTE: Delete reference to coarse bubble type when
not allowed for the plant. For plants of 2.19 L/s
50,000 GPD capacity and below, fine bubble diffusers
or coarse bubble diffusers should be allowed as
Contractor's option. For plants of more than 2.19 L/s
50,000 GPD, fine bubble diffusers only should be
used.
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Aeration equipment shall include diffusers, diffuser holder assembly, air
blower assembly, piping and accessory items as specified hereinafter.
Diffusers shall be of the fine bubble type [or the coarse bubble type]. The
oxygen transfer capacity of the diffuser system shall be capable of
SECTION 11375N
Page 34
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