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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
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
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)
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
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
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?