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Primary Clarifier RehabilitationCase Study
MWEA Annual Conference
TJ Bates – Donohue & Associates, Inc.June 25, 2019
33
Outline
What’s so Complicated?
Holland WRF Background
Clarifier Condition Assessment
Alternative Evaluation
Construction Update
Lessons Learned
My Advice
44
What’s so Complicated?
Primary
Effluent
Primary Clarifier
Sludge
RW
W
SCUM
55
What’s so Complicated?
Circular
66
What’s so Complicated?
Squircles
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What’s so Complicated?
Rectangular
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What’s so Complicated?
Covered
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What’s so Complicated?
Not all Primary Clarifiers are created equal
Primary clarifier repair shouldn’t be a standard detail
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Holland WRF Background
Average day flow: 9 MGD
Design capacity: 12 MGD
Four covered primary clarifiers:
Two 7-ft deep, constructed in 1960
Two 14-ft deep, constructed in 1980
Odor control covers added in 1995
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Centralized influent distributed to all four clarifiers
Holland WRF Background
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2
3
4
Splitter
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Weir modifications to better control distribution
Holland WRF Background
1
2
3
4
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Effluent conditions vary
Holland WRF Background
1
2
3
4
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Holland WRF Background
Covers and odor control to address complaints
Corrosive gassed trapped below cover
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Holland WRF Background
Bridge creates air dam, making uniform air flow difficult
Concrete and steel are exposed and unprotected
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Clarifier Condition Assessment
Significant corrosion to steel components above the water line
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Clarifier Condition Assessment
Corrosion on the steel walking surface
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Clarifier Condition Assessment
Conditions even worse than expected once portion of the cover was removed
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Clarifier Condition Assessment
Iron oxide buildup
Holes in steel members
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Clarifier Condition Assessment
Concrete deterioration
Most notable on outside face of the launder
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Clarifier Condition Assessment
Exposed aggregate
“Soft” areas
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Alternative Analysis
Design a repair that fits the existing conditions
Corrosion and concrete protection only where required
Corrosion and concrete deterioration require oxygen
Can existing conditions be made better
Remove corrosive gasses below cover
Improve odor control efficiency
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Corrosion Protection – Only Where Required
Clarifier Mechanism
SS components were corrosion potential is high
Coated components where corrosion potential is low
Alternative Analysis
PC Mechanism Prices Based on Varying Materials
Construction Material Total Cost Cost Increase
Coated Steel $ 456,000 --
Partial Coated Steel,
Partial 304 SS$ 527,000 71,500
304 SS $ 612,000 156,000
316 SS $ 736,000 280,000
Prices from Nov 2017
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Alternative Analysis
Corrosion Protection – Only Where Required
Concrete Repair
Epoxy coating
Applied only where necessary
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Alternative Analysis
Remove gasses from below the cover
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Alternative Evaluation
Odor Control Efficiency
Majority of odors are generated as the water falls over the weir
Capture odors at the source
Minimize volume the odor control system protects
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Alternative Evaluation
Image Source: NEFCO
Launder Covers
Cover launder, weir, and baffle
Can be connect to odor control
Limit algae growth
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Alternative Evaluation
Launder cover on final clarifier
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Alternative Evaluation
Individual access hatches
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Alternative Evaluation
Accessible for routine OM checks
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Alternative Evaluation
Alternative 1
Remove cover
Coated steel mechanism
Install launder covers with odor control
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Alternative Evaluation
Alternative 2
316SS above water line
Coated steel below waterline
Isolate steel bridge from corrosive environment
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Alternative 2 Bridge Design
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Alternative Evaluation
Bid Results
Elected to proceed with Alternate 2
Alternative Cost
Alternate 1:
Launder Covers
Coated mechanism
$2.24M
Alternate 2:
Exist Aluminum Cover
SS/Coated Mechanism
$2.04M
Prices from July 2018
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Construction Update
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Construction Update
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Construction Update
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Construction Update
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Construction Update
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Construction Update
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Construction Update
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Construction Update
4343
Construction Update
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Lessons Learned
Varying outlet conditions require a variable plan
Dedicated effluent box
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Lessons Learned
Junction structure effluent box
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Lessons Learned
Be selective with approving you’re coatings!
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Lessons Learned
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Lessons Learned
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Lessons Learned
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My Advice
Be aware of “simple” projects
When spending millions of $$
Tailor every solution to the problem
Bidding markets are complex
Alternatives can be helpful
51
Thank You!
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