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
/26
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?
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