furnishing an adequate supply of oxygen in the aeration tank to meet
treatment requirements at the design sewage load. Air flow shall be from
0.00071 to 0.0014 cubic meter per second 1 1/2 to 3 cubic feet per minute
(CFM) at 150 mm 6 inch spacing from each diffuser, giving a minimum air
velocity of 12.2 meters per second 40 feet per second through 13 mm 1/2 inch
diameter orifice or 0.0008 cubic meter per second 1 3/4 CFM which will
give a minimum air velocity of 18.3 meters per second 60 feet per second
through 6 mm 1/4 inch diameter diffuser orifice.
2.8.2.1
Air Diffusers
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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.
**************************************************************************
The diffuser layout shall have sufficient mixing capacity to thoroughly mix
the waste water throughout the tank depth and to maintain the biological
floc in suspension in concentrations of up to 4,000 mg/1. Diffusers shall
be [fine bubble] [coarse bubble] type.
a.
Fine Bubble Diffusion: Oxygen absorption rating of diffuser tubes
shall be not less than 53.0 ppm per hour. Permeability rating of
the diffuser tubes furnished under this contract shall be within
the following limits:
Mean
Permeability
Minimum
Maximum
Porous Ceramic
Tube Diffusers
26
23.4
28.8
Porous Plastic
Tube Diffusers
40
36.0
44.0
Fine bubble diffusers shall be porous ceramic tube type or porous
plastic tube type.
(1) Porous Ceramic Tube Diffuser: The tube shall be free from
any ingredients or processes of manufacture which will cause
leaching, clogging, or disintegration when the tube is
continuously immersed in, and supplying compressed air to, sewage
or sludge. Tube shall be of crystalline aluminum oxide grains,
bonded with high alumina glass. Tube shall be kiln-burned at a
high temperature. Tube shall withstand sudden changes in
temperature which may be experienced during installation and
normal operation without cracking or spalling. The individual
grains shall be thoroughly bonded together to form a strong,
uniformly porous, and homogeneous structure; the tube shall be
free of loose or unbonded material. The bond material shall have
a coefficient of thermal expansion similar to the grain
coefficient so that the structure will remain thoroughly united in
cooling. Grain size shall be uniform. Each diffuser tube
assembly shall have one connector assembly with 19 mm 3/4 inch
SECTION 11375N
Page 35
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