Remy Stachowiak Highly Loaded Secondary Clarifier Field Tests

Remy Stachowiak

Highly Loaded Secondary Clarifier Field TestsBy: B. Davis, C. Applegate, W. Boyle and R. Gross

USFilter/Envirex

Industrial Solutions and ServicesYour Success is Our Goal

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


SAWEA 2005

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



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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


SAWEA 2005

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


SAWEA 2005

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


SAWEA 2005

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


SAWEA 2005

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


SAWEA 2005

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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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


SAWEA 2005

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


SAWEA 2005

Flow is Away from the Weirs


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Verification and Performance

Activated Sludge Final Clarifier

Sludge Removal & Blanket Control


SAWEA 2005

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


SAWEA 2005

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


SAWEA 2005

Field Verification Studies Provide Design Validation


SAWEA 2005

Plan View of Clarifier Floor-Header


SAWEA 2005

Field Verification Studies Provide Design Validation

Theoretical flow

distribution curve

through Unitube

sludge header


SAWEA 2005

Test ResultMatch Ideal Flow Curve

Actual field test

data plotted on

ideal flow curve

shows good fit and

confirms header will

perform as designed


SAWEA 2005

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


SAWEA 2005

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


SAWEA 2005

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

Documents

Remy Stachowiak Highly Loaded Secondary Clarifier Field Tests