Evaluating Coagulants for Water Treatment Kari Duncan – City of Lake Oswego & Doug Wise – Eugene...
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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
Evaluating Coagulants for Water Treatment Kari Duncan City of
Lake Oswego & Doug Wise Eugene Water & Electric Board
PNWS-AWWA Section Conference May 2, 2008
Slide 2
Overview Varieties of Coagulants: Inorganic Organic Common Uses
Case Studies: EWEB City of Lake Oswego
Slide 3
Entrance Strategy 1.Jar Test 2.Pilot Filter Evaluation 3.Cost
Evaluation 4. Plant Scale Test
Slide 4
Entrance Strategy cont. 5.Plant Scale Trial 6.Calculate Real
Cost 7.Evaluation Step Operational Effectiveness Operational
Effectiveness Look for Unintended Consequences Look for Unintended
Consequences
Slide 5
Aluminum Sulfate (Al 2 (SO 4 ) 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.
Slide 6
PACL (Polymeric Inorganic Coagulants) Generic name that
encompasses ACH, Sumaclear, Pass-C and others Product variables:
Basicity 50% 80 + % Basicity 50% 80 + % Al:Cl ratio Al:Cl ratio Al
2 O 3 content Al 2 O 3 content
Slide 7
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
Slide 8
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 Al:Cl ratio of 2:1 Basicity of 83% Basicity of 83% Al
2 O 3 content of 23% Al 2 O 3 content of 23%
Slide 9
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)
Slide 10
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
Slide 11
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.
Slide 12
Coagulation Control Jar Mix Pilot Filters Stream Current
Monitors Zeta Potentiometers
Slide 13
Coagulant Control: Jar Test
Slide 14
Coagulant Control: Control Filters
Slide 15
Coagulant Control: Current Monitor
Slide 16
Coagulant Control Jar Test: Remember to look for smaller denser
floc due to high basicity denser floc due to high basicity when
using high molecular when using high molecular weight products
weight products Control Filters Streaming Current Monitor
Slide 17
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
Slide 18
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
Slide 19
Cautions What is in the magic elixir?
Slide 20
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.
Slide 21
Case Study #1 Eugene Water & Electric Boards Hayden Bridge
Filtration Plant
Slide 22
Slide 23
EWEB 72 MGD Raw Water Flow (108 MGD in 2009) McKenzie River
Source Direct Filtration (summer) Conventional Filtration (winter)
Alum coagulant Pre-chlorinate Cl 2 gas 50% Caustic: corrosion
control
Slide 24
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.
Slide 25
Slide 26
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%.
Slide 27
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)
Slide 28
EWEB Finds Fault A: We changed coagulant. B: Our system water
quality changed. Therefore: the coagulant change made the system
water quality change.
Slide 29
EWEB Review of JAWWA Article on Cl - / SO 4 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 90 th -percentile lead concentration.
Slide 30
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 Al:Cl ratio of 2:1 Basicity of 83% Basicity of 83% Al
2 O 3 content of 23% Al 2 O 3 content of 23%
Slide 31
EWEB Not so fast.
Slide 32
There Are Other Considerations (EWEB) Multiple changes in
treatment variables at the time of test: Added 15 MG Clearwell (May
2003) Added 15 MG Clearwell (May 2003) Changed chlorination
practice (May 2004) Changed chlorination practice (May 2004)
Switched from Lime to Caustic (July 2004) Switched from Lime to
Caustic (July 2004) Switched from Alum to Sumaclear 1000
(2005-2006) Switched from Alum to Sumaclear 1000 (2005-2006)
Slide 33
EWEB Next Steps Continue Monitoring. Special Monitoring. Make
Gradual Treatment Changes. Wait and Measure.
Slide 34
Case Study #2 City of Lake Oswego Water Treatment Plant
Slide 35
City of Lake Oswego Water Treatment Plant 16 MGD Clackamas
River Source Direct Filtration Plant Alum (Coagulant)
Pre-chlorinate with Hypochlorite Lime: corrosion control
Slide 36
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 % ?? Al = 5/4 % ?? Al2O3:
10.3% Al2O3: 10.3% Basicity: 55% Basicity: 55%
Slide 37
Slide 38
Slide 39
Slide 40
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
Slide 41
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.
Slide 42
Lessons Learned From Coagulant Trials Intuitive expectations
may be erroneous.
Slide 43
Lessons Learned Changes in the distribution system may result
from changes in treatment at the plant.
Slide 44
Lessons Learned Unknown, unreported and / or undocumented
consequences may be common.
Slide 45
Lessons Learned Change only ONE thing at a time.
Slide 46
Lessons Learned Wait Measure Interpret
Slide 47
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.