Evaluating Coagulants for Water Treatment

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Evaluating Coagulants for Water Treatment

• Kari Duncan City of Lake Oswego
• Doug Wise Eugene Water Electric Board
• PNWS-AWWA Section Conference
• May 2, 2008

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Overview

• Varieties of Coagulants
• Inorganic Organic
• Common Uses
• Case Studies
• EWEB City of Lake Oswego

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Entrance Strategy

• 1. Jar Test
• 2. Pilot Filter Evaluation
• 3. Cost Evaluation
• 4. ½ Plant Scale Test

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Entrance Strategy cont.

• 5. Plant Scale Trial
• 6. Calculate Real Cost
• 7. Evaluation Step
• Operational Effectiveness
• Look for Unintended Consequences

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Aluminum Sulfate(Al2(SO4)3 14 H2O

• Inorganic coagulants ? aluminum sulfate, aluminum
  chloride and ferric compounds
• React with alkalinity to form positive ions which
  remove contaminants by adsorption.
• Increasing turbidity ? higher (sometimes
  dramatically higher) feed rates.

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PACL (Polymeric Inorganic Coagulants)

• Generic name that encompasses ACH, Sumaclear,
  Pass-C and others
• Product variables
• Basicity 50 ? 80
• AlCl ratio
• Al2O3 content

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PACL

• A highly charged species that require little or
  no alkalinity to precipitate floc.
• Due to the high charge of the PACLs dose may not
  increase as much during increasing contaminant
  loading

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PACL ACH

• PACL formula Al2(OH)(X)Cl(6-x)
• AlCl ratio increases as basicity increases
• ACH special type of PACL
• AlCl ratio of 21
• Basicity of 83
• Al2O3 content of 23

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Molecular Weight Comparison

• Alum max MW of 1,000
• PACL MW of 500 2,500
• ACH 4,000 5,000 (some up to 10,000)

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Floc Size

• Inorganic coagulants (Alum), and low basicity
  PACL form more voluminous, fragile floc.
• With increasing charge, PACL tend
• to form smaller floc with greater density
• ACH forms a very tight, dense floc

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Typical dosages

• Product sales advisors often quote an Aluminum
  percentage ratio
• For example, if the Al in the PACL is 4x that of
  Alum, they will cite an expected 25 of alum
  dosage.
• 50 basicity PACL approx 80 of alum dosage
• ACH approx 33 of alum dosage.

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Coagulation Control

• Jar Mix
• Pilot Filters
• Stream Current Monitors
• Zeta Potentiometers

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Coagulant Control Jar Test
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Coagulant Control Control Filters
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Coagulant Control Current Monitor
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Coagulant Control

• Jar Test Remember to look for smaller
• denser floc due to high basicity
• when using high molecular
• weight products
• Control Filters
• Streaming Current Monitor

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Benefits

• Increased filter runs
• Reduced sludge generation
• Sludge compacts / dewaters better
• Greater turbidity removal capacity
• Effective in low water temperatures
• PACL does not lower pH

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Check With Friends

• Drinking Water Program
• Bay Hills Water Association
• City of Creswell
• Garden Valley Water District
• City of Lowell
• City of Myrtle Point
• City of Waldport
• City of Yachats

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Cautions

• What is in the magic elixir?

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More Cautions!

• PACL products range in grade and composition
  test product(s) extensively before committing to
  their use.
• Some products are sensitive to chlorine.
• Products which form a suspension or generate
  sludge after only six months of storage are very
  low grade.

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Case Study 1

• Eugene Water Electric Boards
• Hayden Bridge Filtration Plant

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EWEB

• 72 MGD Raw Water Flow (108 MGD in 2009)
• McKenzie River Source
• Direct Filtration (summer)
• Conventional Filtration (winter)
• Alum coagulant
• Pre-chlorinate Cl2 gas
• 50 Caustic corrosion control

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EWEB

• 7 month trial of Sumaclear 1000 from Summit
  Research Lab
• Used Sumaclear predominantly through 2006.
• Trial examined cost and filter run times while
  maintaining existing filtered water turbidity
  goal of 0.035 NTU.

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EWEB Field Results

• Sumaclear 1000 dose was approximately 1/3 of Alum
  with low raw water turbidity.
• With raw water turbidity above 4 ntu, Sumaclear
  1000 was approximately 1/2 of Alum dose.
• Experienced longer filter runs with Sumaclear.
• Sumaclear resulted in an overall economic benefit
  (chemicals, wash water, sludge management) of
  approximately 20.

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EWEB Concerns

• Some changes in distribution water quality
  coincided with Summaclear 1000 trials.
• Apparent DBP increase
• Small Lead and Copper increase (may no
  longer be optimized)

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EWEB Finds Fault

• A We changed coagulant.
• B Our system water quality changed.
• Therefore the coagulant change made the
  system water quality change.

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EWEB

• Review of JAWWA Article
• on Cl- / SO4 Ratio Edwards Triantafyllidou
  July 2007
• as the relative concentration of chloride to
  sulfate increased in a water supply, a utility
  was more likely to have a higher 90th-percentile
  lead concentration.

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PACL ACH

• PACL formula Al2(OH)(X)Cl(6-x)
• AlCl ratio increases as basicity increases
• ACH special type of PACL
• AlCl ratio of 21
• Basicity of 83
• Al2O3 content of 23

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EWEB

• Not so fast.

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There Are Other Considerations (EWEB)

• Multiple changes in treatment variables at the
  time of test
• Added 15 MG Clearwell (May 2003)
• Changed chlorination practice (May 2004)
• Switched from Lime to Caustic (July 2004)
• Switched from Alum to Sumaclear 1000 (2005-2006)

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EWEB Next Steps

• Continue Monitoring.
• Special Monitoring.
• Make Gradual Treatment Changes.
• Wait and Measure.

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Case Study 2

• City of Lake Oswego
• Water Treatment Plant

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City of Lake OswegoWater Treatment Plant

• 16 MGD
• Clackamas River Source
• Direct Filtration Plant
• Alum (Coagulant)
• Pre-chlorinate with Hypochlorite
• Lime corrosion control

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City of Lake Oswego

• Feeds Alum alone during low turbidity.
• Feeds a combination of Alum and Pass-C (Hydortech
  product) during high turbidity events.
• Pass-C
• Al 5/4 ??
• Al2O3 10.3
• Basicity 55

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City of Lake Oswego Field Results

• The use of Pass-C at 3 to 11 mg/L decreases Alum
  use by up to (75) during periods of high raw
  water turbidity.
• The use of Pass-C at high turbidity prevents the
  need for Operators to add additional alkalinity.
• Improves ease of operation
• Cost differences appear to be nominal

Rough number
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City of Lake Oswego Summary

• Wide variety of products available.
• Trial runs are very important.
• Control your variables.
• Perform a cost analysis.
• Shop around and do your research.

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Lessons Learned From Coagulant Trials

• Intuitive expectations
• may be erroneous.

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Lessons Learned

• Changes in the distribution system may result
  from changes in treatment at the plant.

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Lessons Learned

• Unknown, unreported and / or undocumented
  consequences may be common.

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Lessons Learned

• Change only ONE thing at a time.

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Lessons Learned

• Wait
• Measure
• Interpret

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Acknowledgements

• Kari Duncan for her work in documenting these
  results.
• Randy Prock for developing the data at Hayden
  Bridge.
• The Operators at both plants for their patience
  and persistence.

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Questions?