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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
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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
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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
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West Boise WWTPWest Boise WWTP
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Secondary Clarifier Secondary Clarifier Secondary Clarifier Secondary Clarifier Performance TestingPerformance Testing
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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)
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Look at Current PerformanceLook at Current Performance
nUse Kemmerer samplers
nUse Wahlometer� Evaluate flocculation Evaluate flocculation potential
� Evaluate flocculation problems
� Determine problem areas
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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
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West Boise Background Test West Boise Background Test
16
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)
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Secondary ClarifierSecondary ClarifierSecondary ClarifierSecondary ClarifierPerformance ModelingPerformance Modeling
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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
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Model OutputModel Output
Conce: 0.01 0.05 0.24 1.21 6.00
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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
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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)
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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)
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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
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North Secondary Clarifier Capacity North Secondary Clarifier Capacity = 10 mgd= 10 mgd
90
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
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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)
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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
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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
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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)
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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
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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
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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
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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
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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)
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QUESTIONS?QUESTIONS?