Evaluating the West Boise Evaluating the West Boise Secondary Clarifiers: CFD Secondary Clarifiers: CFD Modeling and Field Verification of Modeling and Field Verification of PerformancePerformance

PNCWA 2009 PNCWA 2009 –– Boise, IDBoise, ID

PerformancePerformance

Rick Kelly, Henryk Melcer, Dean Smith, Robert Kresge

Why Look at Secondary Clarifier Why Look at Secondary Clarifier Performance?Performance?

n Comply with increasingly stringent regulatory requirements� Determine if clarifier upgrades will improve performance

n Get a “true” picture of clarifier capacity� Develop timeline for expansion to facility

n Lack of funding to construct new facilities� Re-rate clarifier and possibly plant treatment capacity

How Do We Evaluate Secondary How Do We Evaluate Secondary Clarifiers?Clarifiers?

n Surface Overflow Rate and Solids Loading Rate (Manual of Practice)� Assumes all clarifiers are equal� Assumes all sludges are equal

n State Point Analysis (1-D, steady state)

60

70

80

90

Solid

s Flux (lb/ft2d

)

state)� Assumes all clarifiers are equal � Accounts for sludge settleability and clarifier

operation

n Computational Fluid Dynamic (CFD) modeling (2-D, dynamic)� Accounts for tank geometry � Accounts for sludge settleability and

flocculation

0

10

20

30

40

50

0 5 10 15

Solids Concentration (g/L)

Solid

s Flux (lb/ft2d

)

Conce: 0.01 0.05 0.24 1.21 6.00

West Boise WWTPWest Boise WWTP

Secondary Clarifier Secondary Clarifier Secondary Clarifier Secondary Clarifier Performance TestingPerformance Testing

What’s First? What’s First? –– Look at the sludge!Look at the sludge!

n Sludge Settling Characteristics (Batch Settling Tests)

n Sludge Flocculation Characteristics (Jar Tests)

Look at Current PerformanceLook at Current Performance

nUse Kemmerer samplers

nUse Wahlometer� Evaluate flocculation Evaluate flocculation potential

� Evaluate flocculation problems

� Determine problem areas

Evaluate Clarifier OperationEvaluate Clarifier Operation

nRun background tests� Observe normal performance

� Calibrate CFD model � Calibrate CFD model

nRun stress test� Observe stressed performance

� Verify CFD model� Validate capacity

West Boise Background Test West Boise Background Test

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20

24

Flow (MGD)

8

10

12

TSS (mg/L) an

d B

lanke

t Dep

th (ft)

Total Flow

Influent Flow (no RAS)

Compact Blanket

Dispersed Blanket

Effluent TSS

0

4

8

12

6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00

Time

Flow (MGD)

0

2

4

6

TSS (mg/L) an

d B

lanke

t Dep

th (ft)

Secondary ClarifierSecondary ClarifierSecondary ClarifierSecondary ClarifierPerformance ModelingPerformance Modeling

CFD Modeling Using UNO 2DcCFD Modeling Using UNO 2Dc

nDeveloped at University of New Orleans under Professor Alex McCorquodale

nModel accounts for:nModel accounts for:Clarifier Geometry Sludge Settling & CompactionHydrodynamics Flocculation and BreakupSludge Rheology Temperature*TIME*

nModel outputsEffluent TSS RAS Concentration Sludge Blanket Depth

Model OutputModel Output

Conce: 0.01 0.05 0.24 1.21 6.00

Model OutputModel Output

Conce: 0.01 0.05 0.24 1.21 6.00

Arrows indicate flow pattern and velocity

Center well

TSS profile indicated by color gradient (g/L in legend)

Horizontal (Stamford) baffle

Scum baffle and effluent

Center well

Clarifier inlet

Calibration Calibration –– Ensuring Accurate Ensuring Accurate Results (Do We Trust the Model)Results (Do We Trust the Model)

8

12

Effluen

t TSS (mg/L) an

d B

lanke

t Dep

th (ft)

Compact Blanket

Effluent TSS

Model Blanket

Model TSS

Calibrate with Background TestCalibrate with Background Test

0

4

6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00

Time

Effluen

t TSS (mg/L) an

d B

lanke

t Dep

th (ft)

9

12

Blanke

t Dep

th (ft)

18

24

TSS (mg/L)

Compact BlanketModel BlanketEffluent TSSModel ESS

Validate with Stress TestValidate with Stress Test

Calibration Calibration –– Ensuring Accurate Ensuring Accurate Results (Do We Trust the Model)Results (Do We Trust the Model)

0

3

6

6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00

Time

Blanke

t Dep

th (ft)

0

6

12

TSS (mg/L)

Determine Capacity with 2DcDetermine Capacity with 2Dc

Need to define capacity constraintsn Maximum Sludge Blanket Depth

� Percentage of clarifier sidewater depth� Distance from effluent launder� Height of centerwell� Height of centerwell� Comfort level of plant staff

n Maximum Effluent Suspended Solids concentration� Permit concentration or mass limit� Comfort level of plant staff

North Secondary Clarifier Capacity North Secondary Clarifier Capacity = 10 mgd= 10 mgd

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100

110

120

130

140

150Effluen

t Susp

ended

Solid

s (m

g/L)

8 mgd9 mgd10 mgd11 mgd

0

10

20

30

40

50

60

70

80

0 200 400 600 800 1000 1200 1400 1600

Time (minutes)

Effluen

t Susp

ended

Solid

s (m

g/L)

Weekly Permit Limit

Modeling Shows Extra CapacityModeling Shows Extra Capacity

n2Dc shows capacity of 10 mgd peak daily flow/clarifier� Confirmed with field testing

nDesign rated capacity is 9.1 mgd/ clarifier

nCapacity increase of 10 percent = 0.9 mgd/clarifier, 1.8 mgd total extra flow (2 North Clarifiers)

Getting More From Your SystemGetting More From Your System

n Build new clarifiers ($$$$)

n Optimize existing

Enlarged CenterwellEnergy Dissipating Inlet (EDI) Enlarged CenterwellEnergy Dissipating Inlet (EDI)

n Optimize existing clarifiers ($$)� Flocculator centerwell� Baffling� Inboard launders� Sludge collection

Benefit of Centerwell ModificationsBenefit of Centerwell Modifications

Conce: 0.01 0.05 0.24 1.21 6.00 Current Centerwell:Current Centerwell:

5.5’ deep, 30’ diameter 5.5’ deep, 30’ diameter

10 mgd10 mgd

Modified Centerwell:Modified Centerwell:

9.5’ deep, 42’ diameter 9.5’ deep, 42’ diameter

11 mgd11 mgd

Conce: 0.01 0.05 0.24 1.21 6.00

75

90

105

120Effluen

t TSS (mg/L)

5.5 ft depth, 9.8 mgd

7.5 ft depth, 10 mgd

8.5 ft depth, 10 mgd

9.5 ft depth, 10 mgd

Benefit of Centerwell ModificationsBenefit of Centerwell Modifications

0

15

30

45

60

120 240 360 480 600 720 840 960 1080 1200 1320 1440

Time (minutes)

Effluen

t TSS (mg/L)

Benefit of Peripheral (Stamford) Benefit of Peripheral (Stamford) BaffleBaffle

Current baffle location:Current baffle location:

12 mgd = Failure12 mgd = Failure

Conce: 0.01 0.05 0.24 1.21 6.00

Raise Baffle by 1.5’:Raise Baffle by 1.5’:

12 mgd = OK12 mgd = OK

Conce: 0.01 0.05 0.24 1.21 6.00

Improvements to Internals Can Improvements to Internals Can Increase North Capacity FurtherIncrease North Capacity Further

Existing Capacity: 9.1 mgd per clarifier

Model Capacity: 10 mgd per clarifier+ 1 mgd (centerwell dimensions)+ 1 mgd (centerwell dimensions)+ 1 mgd (move Stamford baffle)

Improved Capacity: 12 mgd per clarifier

~30% increase in clarifier capacity

Mix Liquor Settleability Affects Mix Liquor Settleability Affects CapacityCapacity

Conce: 0.01 0.05 0.24 1.21 6.00Current SVI and capacity:Current SVI and capacity:

134 mL/g134 mL/g

4 mgd4 mgd

Conce: 0.01 0.05 0.24 1.21 6.00

Modified SVI and capacity:Modified SVI and capacity:

94 mL/g94 mL/g

6.5 mgd6.5 mgd

Improved Settling Can Drastically Improved Settling Can Drastically Improve South CapacityImprove South Capacity

Existing Capacity: 4 mgd per clarifier+ 2.5 mgd (settling improvement)

Improved capacity: 6.5 mgd per clarifier

63% increase in overall clarifier capacity

ConclusionsConclusions

nNorth Clarifiers are Underrated (9.1 mgd vs. 10 mgd)

nModifications to Clarifier Internals Could Increase North CapacityCould Increase North Capacity� Centerwell Modifications = 11 mgd� Baffle Location = 12 mgd

n Improved Mixed Liquor Settleability Could Improve South Capacity up to 63% (4 mgd vs. 6.5 mgd)

QUESTIONS?QUESTIONS?