Evaluating Coagulants
for Water Treatment
Kari Duncan – City of Lake Oswego
&
Doug Wise – Eugene Water & Electric Board
PNWS-AWWA Section Conference
May 2, 2008
Overview
 Varieties of Coagulants:
Inorganic – Organic
 Common
Uses
 Case Studies:
EWEB – City of Lake Oswego
Entrance Strategy
1.
2.
3.
4.
Jar Test
Pilot Filter Evaluation
Cost Evaluation
½ Plant Scale Test
Entrance Strategy cont….
5. Plant Scale Trial
6. Calculate “Real” Cost
7. Evaluation Step


Operational Effectiveness
Look for Unintended Consequences
Aluminum Sulfate
(Al2(SO4)3 · 14 H2O
coagulants  aluminum sulfate,
aluminum chloride and ferric compounds
 Inorganic
 React
with alkalinity to form positive ions
which remove contaminants by adsorption.
turbidity  higher (sometimes
dramatically higher) feed rates.
 Increasing
PACL (Polymeric Inorganic
Coagulants)
 “Generic”
name that encompasses
ACH, Sumaclear, Pass-C and others
 Product



variables:
Basicity 50%  80+%
Al:Cl ratio
Al2O3 content
PACL
 A highly
charged species that require
little or no alkalinity to precipitate floc.
 Due
to the high charge of the PACL’s
dose may not increase as much
during increasing contaminant loading
PACL : ACH
 PACL
formula: Al2(OH)(X)Cl(6-x)
 Al:Cl
ratio increases as basicity
increases
 ACH



‘special type of PACL’
Al:Cl ratio of 2:1
Basicity of 83%
Al2O3 content of 23%
Molecular Weight Comparison
 Alum
: max MW of 1,000
 PACL:
 ACH:
MW of 500 – 2,500
4,000 – 5,000 (some up to 10,000)
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
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.
Coagulation Control
 Jar
Mix
 Pilot
Filters
 Stream
 Zeta
Current Monitors
Potentiometers
Coagulant Control: Jar Test
Coagulant Control: Control Filters
Coagulant Control: Current Monitor
Coagulant Control
 Jar
Test:
 Control
Remember to look for smaller
denser floc due to high basicity
when using high molecular
weight products
Filters
 Streaming
Current Monitor
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
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
Cautions
What is in the “magic” elixir?
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.
Case Study #1
Eugene Water & Electric Board’s
Hayden Bridge Filtration Plant
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
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.
EWEB Poly Alum vs. Alum
12.00
Alum
8.00
P/A
6.00
Linear
(P/A)
4.00
Linear
(Alum )
2.00
0.00
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
Dose (mg/L)
10.00
Raw Turbidity
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%.
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)
EWEB Finds Fault
A: We changed coagulant.
B: Our system water quality changed.
Therefore: the coagulant change made
the system water quality
change.
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.”
PACL : ACH
 PACL
formula: Al2(OH)(X)Cl(6-x)
 Al:Cl
ratio increases as basicity
increases
 ACH



‘special type of PACL’
Al:Cl ratio of 2:1
Basicity of 83%
Al2O3 content of 23%
EWEB
Not so fast….
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)
EWEB – Next Steps
 Continue
 Special
Monitoring.
Monitoring.
 Make
Gradual Treatment
Changes.
 Wait
and Measure.
Case Study #2
City of Lake Oswego
Water Treatment Plant
City of Lake Oswego
Water Treatment Plant
 16
MGD
 Clackamas
 Direct
 Alum
River Source
Filtration Plant
(Coagulant)
 Pre-chlorinate
 Lime:
with Hypochlorite
corrosion control
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%
Alum and Pass-C vs. Raw NTU
100
80
ALUM,
mg/L
70
Pass-c
mg/l dry
60
Raw NTU
Avg
50
40
30
20
10
1/
26
1/
19
1/
12
1/
5
/2
9
12
/2
2
12
/1
5
12
/8
12
/1
0
12
Alum/Pass-C mg/L, Raw NTU
90
18
180
16
160
14
140
12
120
10
100
8
80
6
60
4
40
2
20
0
0
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
ALUM,
mg/L
Pass-c
mg/l dry
Raw NTU
Avg
Raw NTU
Alum and PassC (mg/L)
Alum and PassC vs. Raw NTU (2 axes)
Alum mg/L vs. Raw NTU (without Pass-C)
50
ALUM,
mg/L
40
ntu avg
35
30
25
20
15
10
5
1/13
1/6
12/30
12/23
12/16
12/9
12/2
11/25
11/18
0
11/11
Alum mg/L and Raw NTU
45
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
City of Lake Oswego Summary
 Wide
 Trial
variety of products available.
runs are very important.
 Control
your variables.
 Perform
a cost analysis.
 Shop
around and do your research.
Lessons Learned From
Coagulant Trials
Intuitive expectations
may be erroneous.
Lessons Learned
Changes in the distribution system
may result from changes in
treatment at the plant.
Lessons Learned
Unknown, unreported and / or
undocumented consequences
may be common.
Lessons Learned
Change only ONE thing at a time.
Lessons Learned
 Wait
 Measure
 Interpret
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.
Questions?