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Plant brochure designed by Charles L.
Woodruff 1999 and revised in June 2004.
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Centre Feed Clarifiers
The 2 WesTech, 1 HiTech and 2 Envirex secondary clarifiers serve two
purposes, to remove the solids from the wastewater and to concentrate the
bacteria before returning it to biological treatment or removal to bio
solids treatment. Heavy metals are also removed with the solids in this
phase.
In the Centre Feed
clarifiers, the influent enters through the centre column.
These clarifiers also feature a Ducking Skimmer for surface sludge removal.
Studies have demonstrated that excessive velocities in the centre column and
its outlets can cause floc degradation. The centre column size and outlets
are designed to control floc shear and provide a limited energy input into
the energy dissipating inlet (EDI). It is the first step of the critical
staged reduction of energy into the clarifier.
The EDI (Energy
Dissipating Inlet) is an integral part of the optimum introduction of
influent into the clarification zone. In conjunction with the flocculating
feed well (FFW), the EDI receives the jetting flow from the centre column
outlets, stills the
currents, and re-orients the flow through outlets that discharge the flow
horizontally and tangentially at a reduced, but directed, energy level into
the upper zone of the FFW. The EDI eliminates the need to use deep
flocculating feed wells by controlling the jetting discharge from the centre
column outlets, which can cause sludge blanket upsets and limit floc growth
in the FFW.
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Centre Feed Clarifier |
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Centre Feed Clarifier Illustrations |
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Ducking Skimmers
Ducking Skimmers were developed and
applied by Walker Process Equipment over twenty (20) years ago. Ducking
Skimmers provide an alternative to conventional skimming equipment, and many
successful installations prove its viability. They can be applied to any
type of circular collector mechanism and where existing conventional
skimming devices are deficient, Ducking Skimmers can be applied as a
retro-fit to existing equipment.
Advantages of this device include total coverage of the clarifier surface,
as well as automatic and adjustable control of scum pipe dipping interval
and volume.
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3 Views of The Ducking Skimmer |
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The Ducking Skimmer was developed
many years ago, but popularised in the early 80's, a ducking skimmer is a
form of full-radius skimmer made up of a radial pipe skimmer, usually
motorized and automated, and a full-radius skimming blade supported above
the collector arms. Its name comes from the fact that the skimming blade
must "duck" upon its approach to the scum pipe, to move past the pipe and
continue for another 360 degree skimming run.
The scum pipe is supported from beneath the access bridge, and the motorized
operator is mounted on the bridge. As the segmented skimming blade
approaches the scum pipe, it engages and adjustable limit switch which
actuates the operator, causing the pipe crest to dip below the liquid
surface, thereby accepting liquid, and scum to enter and flow out of the
basin. The blades, mounted on pivots from the rake arm, engage a ramp to
guide them below the scum pipe, and back upward on the far side, restoring
them to their original, upright position on the far side. The rest
position is restored when an adjustable timer in the control panel causes
the operator return the skimming pipe to its upright position. The
electrical circuitry also has a lockout feature, which permits the tipping
of the scum pipe to occur only every "n"th time, useful when scum loads vary
by the clock or calendar.
Modern practices of high solids loadings in the aeration basins can cause
nitrification to occur, causing sludge bulking and extreme evidence of
surface flotsam, making the "ducking" skimmer to be a popular choice of
skimmer design in these instances. |
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