Optimizing%20Clarifiers:%20What%20Have%20We%20Learned?

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Optimizing Clarifiers What Have We Learned?

• Presented by
• John K. Esler, P.E.
• CPE Services, Inc.
• Enfield, NH
• www.clarifiers.com

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(Alternate Title) Optimizing Clarifiers What
Do We Think We Learned?

• Presented by
• John K. Esler, P.E.
• CPE Services, Inc.
• Enfield, NH
• www.clarifiers.com

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(Alternate Title) Optimizing Clarifiers What
Do We Still Have to Learn?

• Presented by
• John K. Esler, P.E.
• CPE Services, Inc.
• Enfield, NH
• www.clarifiers.com

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To Learn to gain knowledge or understanding
of .. by study, instruction or experience.
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A Basic Understanding

• What do their currents look like?

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with a Stamford/Crosby baffle.
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More Basics

• How do we analyze clarifiers? . How do we get an
  initial handle on their performance?

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Daigger-Roper Curves
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Focus on field testing!!
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RSR / draft tube Clarifier Currents
RAS box
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Begin with best shape It all depends on ..

• Your professor circular!
• Your state of mind .. Square?
• Your location
• NYC, LA, DC, Boston .. Rectangular
• The rest of the universe? .. Circular
• Your data ASCE CRTC
• NYC Rockaway Gould Type 2 .. 1800 g/sf/d
• LACSD San Jose Gould Type 1 .. 2200 g/sf/d

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Typical LA County San. Dist. Clarifier Layout
150 long x 20 wide x 9.5 deep
2 parallel effluent launders
3 opposing jet inlet nozzles
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150-ft x 20-ft x 9.5-ft SWD
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3 Opposing Jet Nozzle Inlets
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Two parallel launders 1/3 clarifier length
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Circular Clarifier Centerwells

• What diameter?
• How deep?
• Anything else?

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What diameter?

• No one knows!
• JE Too big (gt 20) reduces mixing
• JE Too small (10 /-) increases turmoil
• Depends on MLSS concentration SVI

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What centerwell depth?

• No one knows .. With or without EDI?
• JE too deep (gt1/2 center depth)
• LA-Hyp. 0.25 center depth was OK
• LA-Hyp. 0.4 center depth was OK
• Design for downward velocity?
• Depends on blanket depth

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Any special centerwell details?

• In-turned lip? (NG)
• Baffles?.. With mixers.
• Submerged? .. It depends .
• Structural supports?

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In-turned Lip
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Centerwell Scum!!!
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Flow is inward!
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Sheet Flow Inward!
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Submerged Centerwells?
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Now we have Q R .. R1 .. ..flowing
downward in the centerwell.
.. which leads to faster density currents!
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What about the rest of the scum ???
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What about the launders?

• Weir length is not as important as ..
• Location! Location! Location!

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The absolute WORST configuration .
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This is what happens !!!!!
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A simple solution ..
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MAJOR Causes of failure in circular clarifiers

• poor flocculation
• High SVIs
• High solids loadings
• Solids leaving the central portion!!!! WHY???

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9/15 _at_ 0700 hrs 3FC _at_ 10 mgd
LOCATION 7 12 15 45 70
-1 .92 .85 .04 .03 .03
-2 .85 .84 .04 .03 .03
-3 .80 .84 .04 .03 .03
-4 .80 .85 .04 .03 .03
-5 .80 .85 .04 .03 .03
-6 .78 .84 .04 .03 .04
-7 .69 .82 .04 .03 .04
-8 .69 .80 .04 .03 .05
-9 .68 .76 .04 .03 .05
-10 .65 .71 .03 .04 .05
-11 .63 .67 .03 .04 .05
-12 .62 .65 .47 1.20 5.10
-13 .61 .55 .58 3.40
-14 .64 .65 .59
-15 .66 .65
TOTALS 12 13 2 5 5 37
?
?
?
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Not due to the downward velocity.

• Texas Standard not to exceed 9 fpm
• Metro Syracuse .. 4.8 fpm
• Erie Co. Southtowns .. 6 fpm
• Joint Meeting (NJ) .. 4.7 fpm
• Houston 69th Street .. 3.3 fpm
• Manchester (NH) .. 3 fpm
• LA-Hyperion .. 1 fpm!!!

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Eslers Baffle Hypothesis

• One baffle is good (Oak Orchard)
• Two baffles are better (Herkimer)
• Three baffles even better (Branford, CT)
• Four baffles better yet! (Waterford)
• Five baffles ????? Six baffles ?????
• The wrong baffle will mess it up (Moravia, Salt
  Lake City, Edgewood (NJ))

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Edmonton Gold Bar WWTP
Baffled Clarifier
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Crosby Cylindrical Baffle
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McKinney Baffle

• Crosby Baffle

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Sludge Collection in circular clarifiers

• Do we suction it .. or scrape it?
• A suction manifold . or draft tubes?
• plow blade scrapers .. or spiral blade?

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Sludge Collection in circular clarifiers

• Floor slope? 1 per ft for scrapers
• Tip speed? Very little data ..
• JE 7 to 10 fpm .. Not 15 to 30 fpm

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CFD Modeling what do we know?

• Its now used on many major projects.
• Remember G.I.G.O?
• I have had too much negative experience.
• Why has it never shown the excessive turbulence
  in the central area of a circular clarifier??
• We need a concerted effort to demonstrate the
  predicted performance with actual field tests!

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In summary, what have we learned?

• The right operator can make almost anything work
  !
• Almost every clarifier can be optimized.
• (Occasionally, one should be nuked.)

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