Post on 17-Apr-2020
Mill Creek WWTP Secondary Clarifiers Assessment
2017 OWEA Technical Conference & Expo
Pete McKee, MSDGCChad Cecrle, Black & Veatch
Agenda
• Secondary Upgrades Project Background• Project goals and improvements
• Secondary Clarifier Field Testing• Field testing goals and results
• Secondary Clarifier CFD Analysis• CFD analysis goals and results
• Secondary Clarifier Follow-up Field Testing• Follow up field testing goals and results
• Final Recommendations• Recommended enhancements for achieving up to 300 mgd
wet weather treatment2MSDGC
Black & Veatch
Secondary Upgrades Project Goals
• Increase secondary treatment capacity to 240 MGD• More reliable wet weather treatment
• Improve control of RAS withdrawal from clarifiers• Add dedicated RAS pumps
• Evenly distribute RAS to aeration tanks• Add RAS flow control
• Add option for step feed operation• Add new influent gates into 3rd pass of aeration tanks
Ensure reliable operation during wet weather (240+ mgd) 44MSDGC
Black & Veatch
Conceptual Design Evaluation• Rectangular with three
rotating manifolds• $35M cost estimate• 3-4 year construction
• Rectangular with chain and flight scrapers
• $45M cost estimate• 4 year construction
• Circular with rotating scraper
• $45M cost estimate• 4 year construction
Option 2
Option 3
Option 1
5MSDGCBlack & Veatch
Mill Creek Secondary Treatment
6
Aeration Tanks
Clarifiers
1WS2WS
3WS1WM
2WM
3WM
1WN
2WN
3WN
1,2,3 E S,M,N
6MSDGCBlack & Veatch
Mill Creek Secondary Treatment
RAS evenly distributed to head of aeration tanks7
Aeration Tanks
Sludge Withdrawal
RAS PumpsRAS Distribution
MSDGCBlack & Veatch
7
Mill Creek Secondary Treatment
Step feed allows 240+mgd treatment during wet weather flows8
Primary Effluent RAS3rd Pass 1st pass
Reduced Solids Loading
2W
1W
3W
MSDGCBlack & Veatch
8
Mill Creek Secondary Treatment
Unsightly scum can be removed via sprays and skimmings troughs9
Scum Removal2W
1W
3W
MSDGCBlack & Veatch
9
Clarifier Field Testing Goals
• Confirm secondary treatment capacity of 240+ mgd• Stress test clarifier trains 1W and 2W up to 40 mgd
• Measure hydraulic efficiency• Dye testing at 20 mgd and 40 mgd
• Measure hydraulic profile• Drogue testing at 20 mgd and 40 mgd
• Prepare field data for CFD model• Calibration data for CFD
Testing performed in Fall 2011
11MSDGCBlack & Veatch
11
Secondary Clarifier Influent
• Influent baffle wall
• Sludge withdrawal arm
• Reaction baffle
• Corner fillets
1
2
3
4
MSDGCBlack & Veatch
12
Dye Testing at 20 mgd and 40 mgd
Introduce dye at clarifier influent
Measure concentration at effluent
MSDGCBlack & Veatch
13
Dye Testing Reveals Short Circuiting
Rapid rise to peak indicates high velocity current
0
20
40
60
80
100
120
140
0 50 100 150 200 250
Dye
Conc
entr
atio
n
Time (minutes)
Theoretical D.T. = 115 minutesClarifier 1W D.T. = 51 minutesClarifier 2W D.T. = 52 minutes
0
20
40
60
80
100
120
140
0 50 100 150 200 250
Dye
Conc
entr
atio
n
Time (minutes)
Theoretical D.T. = 230 minutesClarifier 1W D.T. = 75 minutesClarifier 2W D.T. = 81 minutes
( )
Clarifier 1W Clarifier 2W
Dye Curve @ 20 mgd Dye Curve @ 40 mgd
MSDGCBlack & Veatch
14
Velocity profile
High velocity currents along inlet side of clarifier
25W 25E7WClarifier 1W Drogue Station: South Flow Rate: 40 mgd
-2’
-6’
-10’
O
O
O O
O
+7 +14
+3
To effluentTo influent
O
fpm
Dept
h
MSDGCBlack & Veatch
16
CFD Model Goals
• Is there benefit in having the reaction baffle (2W)?• 20 mgd & 40 mgd simulated flows through 1W & 2W
• Is there benefit in adding full corner fillets?• Simulated flows with and without full depth fillets
• Can flow be better distributed across clarifier with an influent baffle?• Simulated flows with and without influent baffle
CFD model calibrated using field test data18MSDGC
Black & Veatch 18
Secondary Clarifier ModelEffluent (North)
Reaction baffle (2W only)
Effluent Launder
RAS Withdrawal
Inlet (South)MSDGCBlack & Veatch
19
Simulated Flow with Reaction Baffle
High velocities along inlet side present in both scenarios
40 MGD Clarifier 1W (no reaction baffle)
Clarifier 2W (reaction baffle)
MSDGCBlack & Veatch
20
Velocity Profile
More uniform streamlines. Improved flow distribution.
reamlines biased to wnstream side of annel. Poor distribution th higher velocities on ht side of clarifier.
Simulated Flow with Influent Baffle
Baffle in inlet channel improves flow distribution21
40 MGD 40 MGD
Inlet Baffle
No Influent Baffle
MSDGCBlack & Veatch
21
Simulated Flow with Influent Baffle
Predicted 500 mg/L solids elevation 2 ft lower with baffle
40 MGD
Influent BaffleMSDGCBlack & Veatch
22
Simulated Flows with Full Corner Fillets
Flow distribution improves during dry weather, worsens during wet weather flows
20 MGD
40 MGD
MSDGCBlack & Veatch
23
Field Testing and CFD Modeling Recommendations
• Is there benefit in having the reaction baffle?• No appreciable benefit. Not recommended for remaining tanks.
• Is there benefit in adding full corner fillets?• Not recommended due to cost and adverse flow distribution
impacts during wet weather flows• Recommend regular operation of skimmings troughs
• Can flow be better distributed across clarifier with an influent baffle?• Yes. Recommend further development of influent baffle design
to implement for trial.
MSDGC implemented recommendations including trial influent baffle
24MSDGCBlack & Veatch
24
Influent and Intermediate Baffles Addition
Recommended baffle additions for follow up field testing26
3E
Influent Baffles
2E1E
Intermediate Baffle
MSDGCBlack & Veatch
26
Influent and Intermediate Baffles Addition
Influent baffles – recommended from CFD modelIntermediate baffles– recommended by CPE
27
Intermediate Baffle in Clarifier 3EInfluent Baffle in Clarifiers 2E & 3E
MSDGCBlack & Veatch
27
Follow Up Field Testing Results
Recommend installing L shaped influent baffle on other four clarifiers 1W, 2W, 3W, & 1E
28MSDGCBlack & Veatch
28