Coagulants for Water Treatment

8/3/2019 Coagulants for Water Treatment

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Evaluating Coagulantsfor 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. 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 (sometimesdramatically 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+%

Al:Cl 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)

Al:Cl ratio increases as basicityincreases

ACH special type of PACL Al:Cl ratio of 2:1 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 lowbasicity PACL form more voluminous,fragile floc.

With increasing charge, PACL tend

to form smaller floc with greaterdensity

ACH forms a very tight, dense floc


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Typical dosages

Product sales advisors often quote anAluminum percentage ratio

For example, if the Al in the PACL is 4x that ofAlum, they will cite an expected 25% of alumdosage.

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 smallerdenser 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 generationSludge 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) extensivelybefore committing to their use.

Some products are sensitive to chlorine.

Products which form a suspension orgenerate sludge after only six months ofstorage 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 fromSummit Research Lab

Used Sumaclear predominantly through2006.

Trial examined cost and filter run timeswhile maintaining existing filtered waterturbidity goal of 0.035 NTU.


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EWEB Poly Alum vs. Alum

0.00

2.00

4.00

6.00

8.00

10.00

12.00

0.90

1.04

1.34

1.35

1.41

1.50

1.50

1.60

1.70

1.77

2.40

2.50

4.40

7.74

Raw Turbidity

Dose(m

g/L)

Alum

P/A

Linear

(P/A)

Linear

(Alum )


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EWEB Field Results

Sumaclear 1000 dose was approximately 1/3 ofAlum with low raw water turbidity.

With raw water turbidity above 4 ntu, Sumaclear1000 was approximately 1/2 of Alum dose.

Experienced longer filter runs with Sumaclear.

Sumaclear resulted in an overall economicbenefit (chemicals, wash water, sludgemanagement) of approximately 20%.


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EWEB Concerns

Some changes in distribution

water quality coincided withSummaclear 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 qualitychange.


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EWEB

Review of JAWWA Article

on Cl-

/ SO4 Ratio Edwards & Triantafyllidou July 2007

as the relative concentration ofchloride to sulfate increased in awater supply, a utility was more likelyto have a higher 90th-percentile leadconcentration.


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PACL : ACH

PACL formula: Al2(OH)(X)Cl(6-x)

Al:Cl ratio increases as basicityincreases

ACH special type of PACL Al:Cl ratio of 2:1 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 treatmentvariables 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 GradualTreatment

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 SourceDirect 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 turbidityevents.

Pass-C: Al = 5/4 % ??

Al2O3: 10.3%

Basicity: 55%


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Alum and Pass-C vs. Raw NTU

0

10

20

30

40

50

60

70

80

90

100

1

2/1

1

2/8

12

/15

12

/22

12

/29

1/5

1

/12

1

/19

1

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Alum/Pass-Cm

g/L,RawNTU ALUM,

mg/L

Pass-c

mg/l dry

Raw NTUAvg

Al d P C R NTU (2 )


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Alum and PassC vs. Raw NTU (2 axes)

0

2

4

6

8

10

12

14

16

18

DATE 12/5 12/10 12/15 12/20 12/25 12/30 1/4 1/9 1/14 1/19 1/24 1/29

AlumandPas

sC(mg/L)

0

20

40

60

80

100

120

140

160

180

RawNTU

ALUM,mg/L

Pass-c

mg/l dry

Raw NTUAvg


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Alum mg/L vs. Raw NTU (without Pass-C)

0

5

10

15

20

25

30

35

40

45

50

11

/11

11

/18

11

/25

1

2/2

1

2/9

12

/16

12

/23

12

/30

1/6

1

/13

A

lummg/Land

Raw

NTU

ALUM,

mg/L

ntu avg

Ci f L k O


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City of Lake OswegoField Results

The use of Pass-C at 3 to 11 mg/L decreasesAlum use by up to (75%)* during periods of high

raw water turbidity.

The use of Pass-C at high turbidity prevents theneed 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 systemmay result from changes in

treatment at the plant.


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Lessons Learned

Unknown, unreported and / orundocumented 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 atHayden Bridge.

The Operators at both plants for theirpatience and persistence.


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Questions?

Documents

Coagulants for Water Treatment