treatment system be included upstream of the CLR to
remove grit and other larger particles to reduce the
likelihood of plugging the nozzles.
The aeration equipment covered in this specification
is listed below along with some general requirements
for their use. For further assistance in
determining the applicability of the CLR, refer to
TM 5-814-8 and for design criteria refer to TM
5-814-3.
a. Disc or Rotor (Brush) Aerators: This type of
aeration system creates surface agitation to provide
oxygen transfer and imparts a horizontal velocity by
the rotation of the unit. The channel may be
constructed with either sloped or vertical side
walls. Typically the channels are constructed 2.4 m
(8 feet) to 3.7 m (12 feet) deep. Channels greater
than 2.1 m (7 feet) deep may require a velocity
baffle downstream of the aeration unit to help
impart a downward velocity to the wastewater and
improve mixing along the channel bottom. The CLR
should not be constructed with a sidewater depth
greater than 4.3 m (14 feet) if disc or brush
aerators are specified. In addition, turning walls
are recommended at each bend to maintain channel
velocities around the corners.
b. Low Speed Surface Aerators: This type of
aeration system creates surface agitation to provide
oxygen transfer and imparts a velocity to the
wastewater by the swirling action created by the
impeller. The aerators must be placed at the turns
in the channel to achieve effective horizontal
velocity. At bends where aerators are not located,
turning walls are recommended to maintain channel
velocities around the corners. Floating aerators
should not be considered for use in a CLR
application due to the area required for the
pontoons. The channel may be constructed with
either sloped or vertical side walls. With this
equipment, vertical side walls are recommended at
the turns. Channel depths will vary from 1.8 to 4.9
m (6 to 16 feet). Draft tubes should be provided
when recommended by the manufacturer.
c. Submerged Turbine Aerators: Submerged turbine
aerators used in CLR's utilize a downward pumping
impeller to force an air and water mixture through a
draft tube that extends below the bottom of the
basin and through a barrier wall extending across
the basin. The barrier wall may be constructed of
concrete, compacted clay or reinforced earth. The
turbine's impeller should be located at a depth of
approximately 20 percent of the basin sidewater
depth. The air is discharged through a sparge ring
below the impeller and becomes entrained in the
downward flow of water through the draft tube. The
system requires an air blower, as well as the
SECTION 11391
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