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Plant brochure designed by Charles L.
Woodruff 1999 and revised in June 2004.
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Rim Feed Clarifiers
Rim Feed Clarifiers, the peripheral feed,
peripheral takeoff clarifiers have a proven record of performance in
wastewater plants worldwide. Used as secondary activated sludge clarifiers
in sewage treatment plants, they offer greater capacity, higher overflow
rates, optimum hydraulic stability, full surface and feed channel skimming,
maximum design versatility and lower construction costs. Because of its
greater hydraulic efficiency (50 to 80% more than centre feed clarifiers) a
Rim Feed Clarifier can be smaller than a centre feed unit.
COMPARISONS WITH CENTRE FEED CLARIFIERS
A number of cost studies have been made comparing Rim Feed Clarifiers with
centre feed clarifiers. These studies demonstrate that there is little, if
any, cost difference between the two types where tank dimensions are
identical and all costs are included. The requirement for cantilevered
effluent troughs and energy dissipating feed wells in the centre feed design
makes the Rim-Flow Clarifier very cost-effective.
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Empty Rim Feed Feed Clarifier |
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Influent is introduced into a channel
surrounding the periphery of the tank.
The channel has a varied cross section that helps maintain a constant
velocity in the channel so as to prevent settling out of solids. The
confined influent provides a uniform distribution around the periphery.
Orifices in the feed channel floor are computer sized and spaced to provide
a controlled head loss that assures an equalized flow distribution into the
tank around the entire periphery. Orifice spacing also helps prevent
deposition of solids on the channel floor.
As the controlled flow enters the tank through the orifices it is deflected
by a baffle on the underside of the feed channel.
This baffle, and the orifice length (never greater than the channel floor
thickness), eliminates “jetting” action into the basin. The flow is diffused
rapidly and completely in the large area between the tank wall and the
influent skirt baffle. The skirt baffle defines a clear liquid zone and its
cross sectional area is such that the inlet velocities are controlled at not
greater than 5-feet per minute at maximum flow.
Flow enters the tank near the bottom below the skirt baffle uniformly and at
low velocities. The flow moves outwards, up and back to the peripheral
effluent channel in a gentle circular motion. Full tank volume is utilized.
Eddies that cause short circuiting are eliminated. Solids uniformly drop out
of suspension.
Rim Feed Clarifier design, with both influent and effluent channels located
on the tank periphery, permits effective skimming of the entire tank surface
as well as the influent raceway.
In the Rim Feed Clarifier, collected surface scum is prevented from entering
the effluent channel by a scum baffle attached to the effluent launder. A
hinged wiper assembly and blade assures constant contact between blade, scum
baffle and beach as the blade travels up the beach.
Influent channel skimming is provided by a blade mounted on an extension of
the skimmer arm that directs scum in the channel to a weir gate for removal.
This skimmer design prevents scum from bridging in the channel.
The weir gate is an economical standard design. Collected scum is directed
by the flow and skimmer arm to the scum box area. The gate is lowered when
the scum is to be removed from the channel.
Type and volume of floatable material dictates the operating time cycle. |
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Illustration Top View |
Illustration Inlet Flow |
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1. INFLUENT CHANNEL
(varying width to suit flow requirements). Varied cross section controls
flow and prevents solids drop out in channel. Can be provided in
unidirectional or split-flow styles.
2. INLET ORIFICE
Computer sized and spaced to provide controlled head loss for equal flow
distribution into tank around entire periphery. Eliminates “jetting” action
into basin and spiral flow vectors. Spacing also prevents solids drop out.
3. EFFLUENT CHANNEL
Hydraulically designed for wide range of flows. Effluent at the periphery
reduces short circuiting.
Helps make cleaning of weirs and channel easier.
4. EFFLUENT WEIR AND SCUM BAFFLE
Adjustable V-notched weir. Scum baffle, attached to effluent launder,
effectively prevents scum from entering the effluent channel.
5. FULL SURFACE SKIMMING
Surface skimmer with attached inlet channel skimmer mounted on vertical arms
attached to truss.
6. SCUM REMOVAL
Raceway scum is concentrated in a small area easily accessible from outside
the basin. Weir gate skimmer provides complete, effective removal.
7. COMMON CHANNEL WALL
Assures substantial savings in construction costs.
8. DEFLECTOR BAFFLE
Located under orifice. Eliminates “jetting” and spiral flow vectors. Assures
rapid, complete flow dispersion.
9. INFLUENT SKIRT BAFFLE
Extends five feet below water surface. Helps direct flow into distribution
zone. Defines inlet completely around the periphery for uniform flow
distribution and acts as a flocculation zone. Controls velocity to not more
than 5 FPM at maximum flow. Steel plate (3/16”) will not be damaged during
construction or wash down.
10. LARGE INLET AREA
Assures low entrance velocities and aids flocculation.
11. SLUDGE REMOVER
For most effective removal of activated sludge.
12. TANK DRAIN |
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