Clarifier Evaluation and Upgrading Techniques

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Clarifier EvaluationandUpgrading Techniques

• Presented ByJohn K. Esler, P.E. CPE Services,
  Inc., Enfield, NH WWW.CLARIFIERS.COM

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Outline

• Typical Operating Conditions
• Problems with Clarifiers
• Some Simple Solutions
• Field Evaluation Techniques
• Case Study

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Some of the Basic Problems

• Higher solids loadings (Q R)
• Higher SVIs
• More scum
• De-nitrification ?
• P-release
• Drug dependency
• Flow measurement / distribution
• Short-circuiting currents !!!

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Q R
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(Typical?) Flow Pattern
in a TF or RBC Circular Clarifier
.. due to temperature differentials.
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Typical Flow Pattern in a
Simple Rectangular Clarifier
Q R
Q
R
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Typical Flow Pattern in a
Gould Type I Rectangular Clarifier
Q R
Q
R
(LA County Burbank San Diego North, etc.)
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Typical Flow Pattern in a
Gould Type II Rectangular Clarifier
Q R
Q
R
(All NYC plants Philadelphia Blue Plains, etc)
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Internal Clarifier Problems(Focus on Clarifier
Hydraulics!)

• Density Currents .. due to ..
• inlet / centerwell
• MLSS mass? Yes!
• to temperature differentials? Not usually!
• Secondary Currents .. due to ..
• influent/effluent configurations
• collector rotation

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Some Solutions That Work

• Equalization .. Equalization
• Inlet Modifications .. esp. w/ RSR clarifiers
• Effluent Launder Modifications
• Vertical Slotted Baffles in rect. clarifiers
• Density Current Baffles in circular clarifiers
• - Crosby peripheral (Stamford) baffle
• - Crosby cylindrical baffle
• - Horizontal peripheral baffle (DNU)

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NE WWTF Clarifier 3 Detention Time Comparison
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Operating D.T. _at_ 10 mgd 66 minutes
10 mgd
Theoretical D.T. _at_ 10 mgd 250 minutes
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Operating D.T. _at_ 14 mgd 89 minutes
Theoretical D.T. _at_ 14 mgd 180 minutes
Operating D.T. _at_ 18 mgd 73 minutes
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Theoretical D.T. _at_ 18 mgd 140 minutes
Dye Reading
18 mgd
60
40
14 mgd
20
0
0
50
100
150
200
250
Time (minutes)
10 mgd
14 mgd
18 mgd
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RSR / draft tube Clarifier Currents
RAS box
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The first Crosby (Stamford) peripheral baffle
The late Bob Crosby
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Q R
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8-sided Crosby Cylindrical Baffle
(Franklin, NH New Haven, CT Atlanta, GA
Jamaica, NYC)
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Q R
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Q R
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Some Other Solutions That Work

• Flow Measurement Weirs
• Scum anti-rotation Baffles
• Blocking Effluent Weirs
• Training in
• - Process Control
• - Filament ID and Control

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A simple Scum Baffle made by suspending PVC pipes
or a curtain from a cable ..
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Scum flusher
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Some problems are harder to resolve than others
..
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A Lack of Motivation??
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Try to avoid the really bad days !!!
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A heavy metals problem ??
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A Case History ..(from the L.A.-Hyperion WWTP)

• Brand-new 150 ft. circular clarifiers were not
  meeting their design expectations at 1400
  gal/sf/d (at 25 mgd flow rate)

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9 Hi-Purity oxygen aeration modules .. each
feeding four -150diam x 12 SWD clarifiers per
aeration module .. with 55 diam x 7 deep
feedwells .. and standard scraper-type sludge
collectors.
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The center inlet feed column with four
rectangular feed ports
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Anti-rotation baffles
In-turned lip
55 diam. centerwell
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Algae Cover
Horizontal Shelf Baffle
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McKinney / K.U. Horizontal Shelf Baffle
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Typical Operating Conditions

• Influent Flow 45 to 52 mgd per 4-clarifier
  module (12.5 mgd/clarifier _at_ aver. flow)
• RAS Rate Approx. 15 of flow
• MLSS 1,000 1,200 mg/l
• SVI Ranges from 110 to 150 ml/l
• Scraper Collector Speed 48 min/revolution

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OK .. lets do a field evaluation of the
clarifiers to see whats happening
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A good field evaluation should include .

• Dye Testing Flow curves and tracer studies to
  determine basic hydraulic characteristics.
• Visual Observations
• Drogue Testing To locate/measure currents.
• Extensive Solids Profiling (VSPs) .. includes
  full water column blanket.
• Monitoring of Effluent TSS (ETSS)
• SPA? DSS/FSS? ......... Other tests ???

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We begin with a four-clarifier test on Module 3

A
C
B
D
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Typical Clarifier Flow Curves
Dye Concentration
Time (in minutes)
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Clarifier Flow Curves
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Tracer Studies Using Full-Depth Core Samplers
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Drogue Testing

• A drogue is a simple device used to measure the
  current in a bay or a stream .. or in a
  clarifier.

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The operator prepares the drogue for a test
run..
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The drogue will move with the current ..
regardless of the direction of the flights or the
skimmer.
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For this test _at_ LA-Hyperion, well do drogue
measurements at two locations along the access
bridge .. 30 ft. and 50 ft. from the center.
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Drogue Data for Clarifier 3A at 13.3 mgd
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Drogue Data for Clarifier 3A at 20 mgd
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Collect full-column, vertical solids profile data
at multiple locations, using a Royce Model 711
TSS meter.
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Clarifier 3A _at_ 13.3 mgd
RAS 7,000 mg/l
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Clarifier 3A _at_ 20 mgd
RAS 4,000 mg/l !!!
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Solids boiling at 20 mgd ..
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Additional Information

• A State Point Analysis (SPA) was done during the
  testing by one of the clarifier manufacturers.
• The SPA indicated that the 15 RAS rate was too
  low.
• The SPA also indicated that, if the RAS rate was
  increased to 30, the clarifier would be able to
  handle the design flow of 25 mgd.

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At this point, the client is looking for .

• Simple solutions ..
• that are inexpensive ..
• and dont take long to implement.

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Now its your turn Solutions, please ?
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And this is what the panel came up with .
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Status .

• The time is now three months after the original
  investigation. Stress testing was undertaken once
  more .. beginning at 12.5 mgd per clarifier,
  increasing to 15 mgd, then 17.5 mgd.
• Still good performance at 17.5 mgd.
• At 20 mgd ..

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Oooooops! They all failed just like before!!!
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Conditions at Failure

• The conditions at failure this time were similar
  to the original observations
• Plumes of solids around the clarifier.
• The solids in the bottom of the clarifier again
  left the central portion and migrated to the
  outer portion!
• The RAS concentration again decreased to about
  4,000 mg/l as the clarifiers reached failure!

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Conditions at Failure

• The drogues showed similar flow patterns in all
  clarifiers.
• The dye tracer studies showed that the currents
  were similar in all clarifiers.
• The density current at failure showed that it
  still moved upward and outward, over the solids
  in the outer portion of the clarifier.

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Now what do we do???
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Status

• There are now 10 months left before the court
  order . with substantial (100,000/day!!!!)
  penalties . kicks in.
• What could you recommend to correct the
  problem(s) and improve clarifier performance?

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Added a peripheral baffle to 3C
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This kind of an EDI was installed in Clarifier 3B.
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This is the standard scooped EDI in action in
Clarifier 3B
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We added a new EDI with opposing jet nozzles
to Clarifier 3A
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Typical EDI tub
Eight 24 diam. Opposing Jet Nozzles ..
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Detention Time Comparison
Dye Concentration
3B with standard scooped EDI
Time (Minutes)
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Clarifier Effluent Suspended Solids
Comparison March 31st
Effluent TSS mg/l
Scooped EDI
High ETSS!!!
AM
PM
Time
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Clarifier 3A _at_ 12.5 mgd
Drogue Data with Opposing Jets
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Drogue Data with scooped EDI
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Drogue Data with Opposing Jets
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Drogue Data with scooped EDI
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Drogue Data with Opposing Jets
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Drogue Data with Scooped EDI
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Summary of Final Evaluations

• Clarifier 3B (with scooped EDI) failed at 12.5
  mgd.
• Tried it again at 20 and 22.5 mgd it still
  didnt work.
• Clarifiers 3C and 3D (Control) failed at 22.5
  mgd.
• Clarifier 3A held at 22.5 mgd . 25 mgd .. 27.5
  mgd .. and 30 mgd (1800 gal/sf/d)
• Testing was ended in 3A, without reaching
  failure, at 30 mgd.
• Note The MLSS in Reactor 4 was raised to 2300
  mg/l it still failed .. just like all the
  others!

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Question 1 Why didnt the tangential port EDI
work??Question 2 Why did the opposing-jet EDI
work??
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Lessons?

• Take advantage of the full range of exploratory
  field tests.
• Allow the test data and visual observations to
  dictate the solutions.
• Dont be afraid to try something different if
  its supported by peer-reviewed test data.
• Optimize .. Optimize .. Optimize !

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