Remy Stachowiak
Highly Loaded Secondary Clarifier Field TestsBy: B. Davis, C. Applegate, W. Boyle and R. Gross
USFilter/Envirex
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SAWEA 2005
Typical “Activated-Sludge”Flow Diagram
WAS• Flotation
Primary/WAS• Gravity
Primary/WAS• GBT
WAS• Centrifuge
WAS
Thickening
GritGrit
PrimaryScreenings
S PrimaryClarifier
AerationTanks
Final
Final
Stabilization
• Anaerobic• Aerobic
Dewatering
ML
Scum
Activated SludgeRAS
ML
Scum
Digestion
Effluent
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PERIPHERAL FEED/PERIPHERAL OUTLET (PF/PO) SECONDARY CLARIFIER
Integration of 2 technologies to optimize secondary clarifier operation:
Peripheral feed, peripheral outlet channels that fold flow
Process capability to 2.5 m/hr peak and 1.5 m/hr average
Multi-point sludge collection for uniform sludge withdrawal
Solids loading capability to 10 kg/m2/hr peak
Independent testing and extensive references verified high rate performance
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PF/PO for Uniform Flow and Solids Distribution
Channel varies in width: -Maintain constant velocity-Uniform flow distribution-Low inlet velocity/reduced short circuiting
Equal flow and load
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PF/PO for Uniform Flow and Solids Distribution
Flow folded to maximize use of tank volume
No dead zones/ increased clarifier efficiency
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SECONDARY CLARIFIER FIELD TESTS -Proof / Verification of PF/PO Design
Clarifier Dye Studies to Show Internal Flow Patterns
Clarifier Dye Plume Studies to Show Surface Movement
Clarifier Drogue Studies to Show Flow Velocities
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EPA commissioned Robert Crosby in the early 1980’s to study final clarifier hydraulics and how to improve existing units
“Hydraulic Characteristics of Activated Sludge Secondary Clarifiers” by Bob Crosby was generated
Study is an extensive collection of dye studies and suspended solids contours.
Able to see how mixed liquor moves in a clarifier.
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Dye Dispersion on a 43 m diameter x 4.3 m SWD PF/PO secondary clarifier at Oakland, California, East Bay MUD
EPA commissioned Robert Crosby in the early 1980’s to study final clarifier hydraulics and how to improve existing units
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EPA commissioned Robert Crosby in the early 1980’s to study final clarifier hydraulics and how to improve existing units
Crosby confirmed the “Wall Effect” due to density currents in Center Feed basins
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Additional Field Dye Studies by Independent Consultant on PF/PO Secondary Clarifiers
Several plants with PF/PO clarifiers were tested by independent consultant in 1999, 2001 and 2002
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CPE Study - Raleigh, North Carolina WWTP
Raleigh, North Carolina Results on 49 m Diameter PF/PO Clarifier Nov. 30 Dec. 1 Dec. 2 Dec. 3 Hydraulic operating conditions Normal high high normal Inlet concentration g/l 4.18 2.99 3.03 3.03 RAS Concentration g/l 7.59 8.39 7.6 6.26 Effluent TSS mg/l 8 13 16 9 Stirred SVI - 75 95 75 75 Q, Effluent Flow Rate m3/day 60945 96906 98799 42775 R, RAS Rate m3/day 39745 51103 51103 51103 Q+R, Influent Flow Rate m3/day 100690 148009 149902 93878 Surface Overflow Rate m/hr 1.4 2.2 2.2 1.0 Mass Loading kg/m2/hr 9.4 10.0 10.2 6.3
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CPE Study - Dye AnalysisRaleigh North Carolina
Dye Dispersion on 49 m diameter x 4.3 m SWD PF/PO clarifier at Raleigh, North Carolina Neuse River WWTP
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CPE Study - Kenosha, Wisconsin WWTP
Kenosha, Wisconsin Results on 43 m Diameter PF/PO Clarifier Aug. 7 Aug. 8 Aug. 9 Aug. 10 Hydraulic operating conditions High high normal normal Inlet concentration g/l 1.88 2.09 2.33 2.32 RAS Concentration g/l 6.50 7.71 9.20 8.20 Effluent TSS mg/l 19 17 10 12 Stirred SVI - 83 72 Q, Effluent Flow Rate m3/day 64352 64352 45425 45425 R, RAS Rate m3/day 23848 19684 10978 10978 Q+R, Influent Flow Rate m3/day 88200 84036 56403 56403 Surface Overflow Rate m/hr 1.9 1.9 1.3 1.3 Mass Loading kg/m2/hr 5.3 5.3 3.7 3.7
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Toledo, Ohio WWTP PF/PO Test Study
Toledo, Ohio 35 m Diameter PF/PO Clarifier
Ave. MLSS 2100 mg/lRAS SS 11 000 mg/lETSS 10 mg/lStirred SVI30 63
Q. Flow Rate 68 MLDR, RAS Rate 23 MLDQ + R 91 MLDSurface O’flow Rate 2.95m/hSolids Loading 9.8 kg/m2/hr
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Preparing the Dye to Add to Influent ChannelToledo, Ohio WWTP PF/PO Clarifier
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Dye plume –Toledo, Ohio WWTP PF/PO Clarifier
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Dye plume –Toledo, Ohio WWTP PF/PO Clarifier
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Dye plume –Toledo, Ohio WWTP PF/PO Clarifier
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Dye plume –Toledo, Ohio WWTP PF/PO Clarifier
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Dye plume –Toledo, Ohio WWTP PF/PO Clarifier
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Dye plume –Toledo, Ohio WWTP PF/PO Clarifier
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Dye plume –Toledo, Ohio WWTP PF/PO Clarifier
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Dye plume –Toledo, Ohio WWTP PF/PO Clarifier
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Dye plume –Toledo, Ohio WWTP PF/PO Clarifier
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WhatDye Studies
Show
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INOUT
Center Feed ClarifierCLCL
OUT
IN
CLCLPF/PO Clarifier
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INOUT
CL Center Feed Clarifier
PF/PO
Clarifier
CL
OUT
IN
Dead Zone
CLCL
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DROGUE TEST
A DROGUE is a physical way to show
currents in a clarifier
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Drogue Studies by CPE at Raleigh, North Carolina WWTP PF/PO Clarifier
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Flow patterns
MLSS enters
v
1 2 3INLET
Center Feed
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Center Feed
v
1 2 3INLET
Sludge separates and moves out
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Center Feed
And Out
1 2 3INLET
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Center Feed
And Sludge hits wall and goes UP the WALL
1 2 3INLET
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Flow Patterns for: Peripheral Feed
OR MLSS enters
v
1 2 3INLET
NO WALL
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Peripheral Feed
Moves out
v
1 2 3INLET
NO WALL
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Peripheral Feed
And out
v
1 2 3INLET
NO WALL
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Peripheral Feed
v
And Sludge hits Sludge
1 2INLETHydraulic
Wall
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Flow is Away from the Weirs
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Verification and Performance
Activated Sludge Final Clarifier
Sludge Removal & Blanket Control
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Rectangular-shaped, tapered arm tilted 45° to trap sludge
Decreasing cross-section and increasing orifice size for uniform sludge withdrawal velocity and complete hydraulic balance
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Activated Sludge Removal Process -Unitube Header and RAS System
Rapid sludge removal - > Reduced sludge septicity
Maximum solids concentration - > Reduced pumping
Minimum sludge agitation - > Reduced sludge dilution
Balanced hydraulic design - > Uniform sludge loading and blanket
Flat floor design - > Lower installation costs
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Field Verification Studies Provide Design Validation
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Plan View of Clarifier Floor-Header
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Field Verification Studies Provide Design Validation
Theoretical flow
distribution curve
through Unitube
sludge header
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Test ResultMatch Ideal Flow Curve
Actual field test
data plotted on
ideal flow curve
shows good fit and
confirms header will
perform as designed
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Conclusions on Sludge Removal
The uniform pickup of sludge from the clarifier floor allows for complete blanket control. This can be a zero blanket to a high blanket depth.
By having a level sludge blanket, the clarifier floor can be flat – saves significant construction costs.
Solid loadings of 10 kg/m2/h and higher can be achieved with the Unitube multi-point sludge withdrawal header
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Results of Field Tests on Peripheral Feed/Peripheral Outlet Clarifier
Independent Studies Verified:PF/PO clarifier acts as an upflow system and needs
little or no modifications to its design
Mixed liquor flow is away from the effluent weir
Possible to maintain an overflow rate of up to 2.5 m/hwith a solids loading of up to 10kg/m2/h
High Overflow and Solids Loading of PF/PO Clarifier Leads to:
Lower total installed cost due to smaller tank diameter/reduced number of secondary clarifiers
Reduced footprint/site space savings
Flexible operation to handle stormflow/peak loadingevents
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Where Can I Find This Clarifier?
Developed by USFilter/Envirex in the 1950s to improve on the performance of conventional center feed secondary clarifiers
We call it the “Rim-Flo/Tow-Bro” Clarifier
Over 650 references globally – significant experience
System has undergone extensive independent testing to verify its high rate performance