awwa/amta© 1 strategic practices and lessons learned for integrating desalinated seawater into...
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AWWA/AMTA© 1
Strategic Practices and Lessons Learned for Integrating Desalinated Seawater
Into Existing Systems
Brent AlspachMalcolm Pirnie / ARCADIS
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AWWA/AMTA© 2
Acknowledgements• Co-Authors:
– Warren Teitz, Metropolitan Water District of Southern California– Bob Harding, Metropolitan Water District of Southern California– Ed Means, Malcolm Pirnie / ARCADIS
• Key Project Partners:– Dennis Cho, SKM– Paul Choules, Water Standard Co. (formerly of Veolia)
• Special Thanks to…– Christine Owen, Tampa Bay Water– Manuel Lattore, Independent Consultant (Spain)– Gary Crisp, GHD– Chee Hoe Woo, Singapore Public Utilities Board
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AWWA/AMTA© 3
Project Background
• Proposed regional seawater desalination projects could request to feed into the Metropolitan system
• Few comprehensive resources on integration issues and practices in the literature
Water Quality Operations
Corrosion Storage
Disinfection Stability Flexibility
Aesthetics Hydraulics
Regulatory Compliance Peaking
Key Areas of Interest
Critical Element:
Experiences from operatingSWRO plants
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AWWA/AMTA© 4
Purpose and Goal
Evaluate water utility practices for integrating large-scale
seawater desalination plants into existing distribution systems.
Purpose
Bibliography of applicable references
Survey sample of major global seawater desalination plants
Project Components
Understand major considerations associated
with integrating desalinated seawater.
Project Goal
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AWWA/AMTA© 5
Purpose and Goal
Evaluate water utility practices for integrating large-scale
seawater desalination plants into existing distribution systems.
Purpose
Bibliography of applicable references
Survey sample of major global seawater desalination plants
Project Components
Understand major considerations associated
with integrating desalinated seawater.
Project Goal
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AWWA/AMTA© 6
Purpose and Goal
Evaluate water utility practices for integrating large-scale
seawater desalination plants into existing distribution systems.
Purpose
Bibliography of applicable references
Survey sample of major global seawater desalination plants
Project Components
Summarize some of the most interesting survey results
relative to major integration considerations.
Presentation Goal
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AWWA/AMTA© 7
Disclaimer
The survey results and subsequent analysis
summarized in this presentation and
the associated paper in the conference proceedings
do not represent endorsement by,
nor representation of,
Metropolitan policies.
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AWWA/AMTA© 8
Presentation Overview Project Background
Purpose and Goal
• Facility Information Collection– Selection Criteria– Comparative Facility Summary
• Summary of Key Results– Boron– Bromide– Corrosion– Advance Planning Studies– Blending– Intertie Location– Operations
• Lessons Learned
Select information identified as
being generally significant to the
survey respondents and/or
important to convey
to the industry
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AWWA/AMTA© 9
Presentation Overview Project Background
Purpose and Goal
• Facility Information Collection– Selection Criteria– Comparative Facility Summary
• Summary of Key Results– Boron– Bromide– Corrosion– Advance Planning Studies– Blending– Intertie Location– Operations
• Lessons Learned
Select information identified as
being generally significant to the
survey respondents and/or
important to convey
to the industry
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AWWA/AMTA© 10
Diverse Characteristics
Geography
On-Line Date
Intake Mechanism
Production Capacity
CommonCharacteristics
Use of RO Technology
Significant Size
Ten (10) prominent seawater desalination plants were selected.
All ten plants have some key features in common with proposed facilities that may feed into the Metropolitan system.
Facility Selection Criteria
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AWWA/AMTA© 11
Plant ID / Location Country
Capacity(MGD)
On-LineDate
IntakeContribution toSupply Portfolio
Tampa USA 25 2003 Open Intake (C) ≤ 10%
Gold Coast Australia 33 2009 Open Intake (D) variable
Melbourne Australia 108 2012 Open Intake (D) 33%
Perth 1 Australia 33 2006 Open Intake (D) 15-20%
Sydney Australia 66 2010 Open Intake (D) 15%
Ashkelon Israel 98 2005 Open Intake (D) 15%
Fujairah 2 UAE 36 2010 Open Intake (C) 95%
Sur Oman 21 2009 Beach Wells 100%
Tuas 1 Singapore 36 2005 Open Intake (D) 10%
Valdelentisco Spain 36 2007 Open Intake (D) 35-45%
Surveyed Plant Summary
C: Co-locatedD: Dedicated
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AWWA/AMTA© 12
Surveyed Plant Locations
Perth (33 MGD)
Tuas 1 (36 MGD)
Tampa(25 MGD)
Valdelentisco(36 MGD)
Melbourne(108 MGD)
Sydney(66 MGD)
Gold Coast(34 MGD)
Ashkelon(98 MGD)
Sur(21 MGD)
Fujairah 2(36 MGD)
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AWWA/AMTA© 13
Summary of Key Results
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AWWA/AMTA© 14
Boron
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AWWA/AMTA© 15
Why is Boron an Issue?
Additional treatment drives up project costs
Not efficiently rejected by RO membranes (in general)
Impacts on both human health and irrigated plants
Not widely regulated
Present in seawater (~4.5 mg/L), but few other sources
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AWWA/AMTA© 16
Why is Boron an Issue?
Additional treatment drives up project costs
Not efficiently rejected by RO membranes (in general)
Impacts on both human health and irrigated plants
Not widely regulated
Present in seawater (~4.5 mg/L), but few other sources
For systems without desalinated seawater,
the addition of SWRO introduces a new
water quality concern:
Boron
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AWWA/AMTA© 17
ContaminantCharacteristic
Generally Higher Rejection With…
Charge Higher charge (+ or –)
Size Larger size
Shape More branched structure
Mass Higher mass
Boron Rejection
Important RO Rejection Trends
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AWWA/AMTA© 18
ContaminantCharacteristic
Generally Higher Rejection With…
Charge Higher charge (+ or –)
Size Larger size
Shape More branched structure
Mass Higher mass
Boron Rejection
Important RO Rejection Trends
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AWWA/AMTA© 19
ContaminantCharacteristic
Generally Higher Rejection With…
Charge Higher charge (+ or –)
Size Larger size
Shape More branched structure
Mass Higher mass
Boron Rejection
Important RO Rejection Trends
Boron in Seawater
Boron equilibrium: H3BO3 ↔ H+ + H2BO3- (pKa = 9.2)
Seawater system: (pH ≈ 7.5 to 8.5) < (pKa = 9.2) H3BO3 (no charge)
Result: Boron is poorly rejected
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AWWA/AMTA© 20
Boron Feed Concentration
(mg/L)
FinishedWater Goal
(mg/L)
RejectionRequired
GoalSignificance
4.5
2.4 47% WHO guideline (current)
2.0 56% Max. among surveyed plants
1 78% California standard
0.5 89% WHO guideline (historic)
0.4 91% Min. among surveyed plants
Boron Standards and Goals
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AWWA/AMTA© 21
Boron Feed Concentration
(mg/L)
FinishedWater Goal
(mg/L)
RejectionRequired
GoalSignificance
4.5
2.4 47% WHO guideline (current)
2.0 56% Max. among surveyed plants
1 78% California standard
0.5 89% WHO guideline (historic)
0.4 91% Min. among surveyed plants
Boron Standards and Goals
Primary historic boron removal driver
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AWWA/AMTA© 22
Boron Feed Concentration
(mg/L)
FinishedWater Goal
(mg/L)
RejectionRequired
GoalSignificance
4.5
2.4 47% WHO guideline (current)
2.0 56% Max. among surveyed plants
1 78% California standard
0.5 89% WHO guideline (historic)
0.4 91% Min. among surveyed plants
Boron Standards and Goals
• Rejection dependent on pH, temp., flux, recovery, membrane type, etc.• Typical best-case RO rejection: 80-90%
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AWWA/AMTA© 23
Boron Feed Concentration
(mg/L)
FinishedWater Goal
(mg/L)
RejectionRequired
GoalSignificance
4.5
2.4 47% WHO guideline (current)
2.0 56% Max. among surveyed plants
1 78% California standard
0.5 89% WHO guideline (historic)
0.4 91% Min. among surveyed plants
Boron Standards and Goals
• 8 of 10 surveyed facilities reported boron goals and/or standards• Range of target boron concentrations: 0.4 - 2.0 mg/L
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AWWA/AMTA© 24
Boron Treatment & Mitigation
Treatment MethodNumber of
Surveyed Facilities
Full or partial 2-pass RO(some with pH adjustment between passes)
9 of 10
Blending* 8 of 10
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AWWA/AMTA© 25
Boron Treatment & Mitigation
Treatment MethodNumber of
Surveyed Facilities
Full or partial 2-pass RO(some with pH adjustment between passes)
9 of 10
Blending* 8 of 10
Can be used intentionally as a strategic means of
reducing boron levels in water delivered to customers...
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AWWA/AMTA© 26
Boron Treatment & Mitigation
Treatment MethodNumber of
Surveyed Facilities
Full or partial 2-pass RO(some with pH adjustment between passes)
9 of 10
Blending* 8 of 10
… OR a de facto treatment method benefitting all systems using
less than approximately 95-100% desalinated seawater
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AWWA/AMTA© 27
Boron Treatment & Mitigation
Treatment MethodNumber of
Surveyed Facilities
Full or partial 2-pass RO(some with pH adjustment between passes)
9 of 10
Blending* 8 of 10
Level of benefit may vary depending
on the blending location
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AWWA/AMTA© 28
Boron: Considerations for California
• Regulatory limit = 1 mg/L– Based on human health effects…– …however, California is a “regulation by permit” state
• Key California crops are sensitive to boron concentrations– Citrus fruit– Avocado Both of these crops are affected at level < 1 mg/L
• Sensitivity of horticulture plants
Plan ahead…!
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AWWA/AMTA© 29
Boron: Considerations for California
Key Planning Considerations
Are there customers with boron-sensitive plants?
How will the customer base change in the future?
Is full or partial two-pass RO necessary?
Is full or partial two-pass RO affordable?
Can blending be used as a reliable boron mitigation strategy?
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AWWA/AMTA© 30
Boron: Considerations for California
Key Planning Considerations
Are there customers with boron-sensitive plants?
How will the customer base change in the future?
Is full or partial two-pass RO necessary?
Is full or partial two-pass RO affordable?
Can blending be used as a reliable boron mitigation strategy?
Potentially yes… for now.
Blending becomes less effective as % contribution of desalinated seawater increases.
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AWWA/AMTA© 31
Boron: Considerations for California
Key Planning Considerations
Are there customers with boron-sensitive plants?
How will the customer base change in the future?
Is full or partial two-pass RO necessary?
Is full or partial two-pass RO affordable?
Can blending be used as a reliable boron mitigation strategy?
Is this ever going to be a
realistic issue in California?
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AWWA/AMTA© 32
Boron: Considerations for California
Key Planning Considerations
Are there customers with boron-sensitive plants?
How will the customer base change in the future?
Is full or partial two-pass RO necessary?
Is full or partial two-pass RO affordable?
Can blending be used as a reliable boron mitigation strategy?
Perth Area in 2005: 0% desalinated seawater
Perth Area in 2015: 50% desalinated seawater
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AWWA/AMTA© 33
Bromide
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AWWA/AMTA© 34
Why is Bromide an Issue?
• Source Waters*– Typical: [Br-] ≈ 63 μg/L = 0.063 mg/L– Max: [Br-] ≈ 1,000 μg/L = 1 mg/L
• Treatment– Minimal impact on bromide removal Bromide is roughly conserved in the treatment process
• Issues– THM / HAA formation (with Cl2 disinfection)
– Bromate (BrO3-) formation (with O3 disinfection)
• Variability– DBP formation = f(precursor conc. & character, pH, temp., etc.)
Conventional Source & Treatment
* Water Research Foundation (2011)
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AWWA/AMTA© 35
Why is Bromide an Issue?
• Source Waters– Typical: [Br-] ≈ 65,000 μg/L = 65 mg/L
Seawater Source & Desalination
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AWWA/AMTA© 36
Why is Bromide an Issue?
• Source Waters– Typical: [Br-] ≈ 65,000 μg/L = 65 mg/L
Seawater Source & Desalination
Three orders of magnitude higher than conventional sources
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AWWA/AMTA© 37
Why is Bromide an Issue?
• Source Waters– Typical: [Br-] ≈ 65,000 μg/L = 65 mg/L
• Treatment– @ 99.8% rejection, permeate [Br-] ≈ 0.13 mg/L…– …for NaCl under standard conditions– Field conditions are not standard rejection is lower– Br- salt passage ≈ 15% higher than Cl-
Seawater Source & Desalination
Three orders of magnitude higher than conventional sources
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AWWA/AMTA© 38
Why is Bromide an Issue?
• Source Waters– Typical: [Br-] ≈ 65,000 μg/L = 65 mg/L
• Treatment– @ 99.8% rejection, permeate [Br-] ≈ 0.13 mg/L…– …for NaCl under standard conditions– Field conditions are not standard rejection is lower– Br- salt passage ≈ 15% higher than Cl-
Seawater Source & Desalination
Three orders of magnitude higher than conventional sources
Double the concentration over conventional treatment applied to conventional sources (at a minimum)
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AWWA/AMTA© 39
Why is Bromide an Issue?
• Issues– THM / HAA formation (with Cl2 disinfection)
– Bromate (BrO3-) formation (with O3 disinfection)
– Bromamine formation (with chloramine residual disinfection)
Seawater Source & Desalination
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AWWA/AMTA© 40
Why is Bromide an Issue?
• Issues– THM / HAA formation (with Cl2 disinfection)
– Bromate (BrO3-) formation (with O3 disinfection)
– Bromamine formation (with chloramine residual disinfection)
Seawater Source & Desalination
Characteristic Implication
Preferential formation over chloramines in the presence of ammonia
Reduces measured chloramine residual
Oxidant strength ~90% that of free chlorine
Increases THM / HAA formation
What You Need to Know About Bromamines
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AWWA/AMTA© 41
Why is Bromide an Issue?
• Issues– THM / HAA formation (with Cl2 disinfection)
– Bromate (BrO3-) formation (with O3 disinfection)
– Bromamine formation (with chloramine residual disinfection)
Seawater Source & Desalination
An issue by virtue of higher bromide concentrationsin desalinated seawater supplies
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AWWA/AMTA© 42
Why is Bromide an Issue?
• Issues– THM / HAA formation (with Cl2 disinfection)
– Bromate (BrO3-) formation (with O3 disinfection)
– Bromamine formation (with chloramine residual disinfection)
• Variability– DBP formation = f(precursor conc. & character, pH, temp., etc.)– DBP precursor material is largely rejected by RO membranes
Seawater Source & Desalination
An issue by virtue of higher bromide concentrationsin desalinated seawater supplies
Net impact on THM / HAA formation…?
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AWWA/AMTA© 43
Net impact on THM / HAA formation…?
Why is Bromide an Issue?
• Issues– THM / HAA formation (with Cl2 disinfection)
– Bromate (BrO3-) formation (with O3 disinfection)
– Bromamine formation (with chloramine residual disinfection)
• Variability– DBP formation = f(precursor conc. & character, pH, temp., etc.)– DBP precursor material is largely rejected by RO membranes
Seawater Source & Desalination
An issue by virtue of higher bromide concentrationsin desalinated seawater supplies
Bromide issues assume heightened
significance in systems with
SWRO treatment
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AWWA/AMTA© 44
Bromide Feed Concentration
(mg/L)
FinishedWater Goal
(mg/L)
RejectionRequired
GoalSignificance
65
0.45 99.3% Max. among surveyed plants
0.2 99.7% Recommended max by one plant
0.1 99.8% Min. among surveyed plants
Bromide Standards and Goals
• 5 of 10 plants reported having a goal or standard for bromide• 4 of 5 plants with a bromide goal or standard reported a value of 0.1 mg/L• 5th plant (of the five) reported a standard of 0.45 mg/L…• …However, respondent recommended a standard of 0.1 to 0.2 mg/L for
minimizing THM / HAA formation and chloramine residual decay
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AWWA/AMTA© 45
Bromide Feed Concentration
(mg/L)
FinishedWater Goal
(mg/L)
RejectionRequired
GoalSignificance
65
0.45 99.3% Max. among surveyed plants
0.2 99.7% Recommended max by one plant
0.1 99.8% Min. among surveyed plants
Bromide Standards and Goals
Even the highest reported bromide goal / standard
is difficult to achieve in a single pass of SWRO
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AWWA/AMTA© 46
Bromide Treatment & Mitigation
Treatment MethodNumber of
Surveyed Facilities
Full or partial 2-pass RO 9 of 10
Blending* 8 of 10
(Same options as for boron treatment…)
• 3 of 10 plants utilized chloramines for residual disinfection…• All three utilize full or partial two-pass RO• All three blend desalinated seawater with other supplies
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AWWA/AMTA© 47
Bromide Treatment & Mitigation
Treatment MethodNumber of
Surveyed Facilities
Full or partial 2-pass RO 9 of 10
Blending* 8 of 10
Blend chlorinated supplies of groundwater, surface water, and
desalinated seawater prior to applying ammonia
1 of 10
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AWWA/AMTA© 48
Bromide Treatment & Mitigation
Treatment MethodNumber of
Surveyed Facilities
Full or partial 2-pass RO 9 of 10
Blending* 8 of 10
Blend chlorinated supplies of groundwater, surface water, and
desalinated seawater prior to applying ammonia
1 of 10
Novel strategy of blending with low-bromide supplies prior to NH3 addition
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AWWA/AMTA© 49
Bromide Treatment & Mitigation
Treatment MethodNumber of
Surveyed Facilities
Full or partial 2-pass RO 9 of 10
Blending* 8 of 10
Blend chlorinated supplies of groundwater, surface water, and
desalinated seawater prior to applying ammonia
1 of 10
May not be practical and/or feasible in all cases
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AWWA/AMTA© 50
Bromide: Considerations for California
Key Planning Considerations
Is full or partial two-pass RO necessary?
Is full or partial two-pass RO affordable?
Can blending be used as a reliable bromide mitigation strategy?
Is blending chlorinated supplies prior to NH3 addition an option?
Most Southern California systems utilize chloramines
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AWWA/AMTA© 51
Bromide: Considerations for California
Key Planning Considerations
Is full or partial two-pass RO necessary?
Is full or partial two-pass RO affordable?
Can blending be used as a reliable bromide mitigation strategy?
Is blending chlorinated supplies prior to NH3 addition an option?
Most Southern California systems utilize chloramines
Same caveat…
Blending becomes less effective as % contribution of desalinated seawater increases.
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AWWA/AMTA© 52
Corrosion
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AWWA/AMTA© 53
Why is Corrosion an Issue?
• Desalinated seawater is very corrosive– Very low TDS…– Very low alkalinity…– …but relatively high in chloride concentrations
• Corrosion-related problems:– Exceedance of lead and copper regulatory standards– Aesthetic concerns– Long-term pipeline integrity decay
Mitigation of corrosion potential
is a well-known desalination issue
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AWWA/AMTA© 54
Corrosion Treatment & Mitigation
Treatment MethodNumber of
Surveyed Facilities
Post-Treatment Conditioning Routine Practice
Blending* 8 of 10
Many respondents reported that corrosion studies
were conducted in the project planning phase
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AWWA/AMTA© 55
Corrosion Treatment & Mitigation
Treatment MethodNumber of
Surveyed Facilities
Post-Treatment Conditioning Routine Practice
Blending* 8 of 10
Many respondents reported that corrosion studies
were conducted in the project planning phase
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AWWA/AMTA© 56
Corrosion Treatment & Mitigation
1. Match water quality to existing supplies as closely as possible
2. Develop water quality targets designed to preclude corrosion
Corrosion-Related Water Quality Parameter Typical Range
pH 8.0 - 8.5
Alkalinity > 50 mg/L as CaCO3
LSI 0 - 1
CCPP 0 - 10 mg/L
Two Approaches Cited for Post-Treatment Conditioning
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AWWA/AMTA© 57
Corrosion Treatment & Mitigation
1. Match water quality to existing supplies as closely as possible
2. Develop water quality targets designed to preclude corrosion
Two Approaches Cited for Post-Treatment Conditioning
No plant cited any corrosion-related
issues using either approach
However...– Are contract plant operators fully aware of distribution system issues?– How long does it take corrosion issues to manifest?
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AWWA/AMTA© 58
Corrosion: Considerations
• Corrosion is a universal consideration with seawater desalination…
• …but it does not have to be a problematic issue
• Post-treatment can be effective to mitigate corrosion
• Multiple post-treatment strategies can be successful
• Planning stage corrosion studies are important
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AWWA/AMTA© 59
Corrosion: Considerations
• Corrosion is a universal consideration with seawater desalination…
• …but it does not have to be a problematic issue
• Post-treatment can be effective to mitigate corrosion
• Multiple post-treatment strategies can be successful
• Planning stage corrosion studies are importantAre corrosion studies critical?
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AWWA/AMTA© 60
Corrosion: Considerations
• Corrosion is a universal consideration with seawater desalination…
• …but it does not have to be a problematic issue
• Post-treatment can be effective to mitigate corrosion
• Multiple post-treatment strategies can be successful
• Planning stage corrosion studies are importantWhy risk not conducting a study?
![Page 61: AWWA/AMTA© 1 Strategic Practices and Lessons Learned for Integrating Desalinated Seawater Into Existing Systems Brent Alspach Malcolm Pirnie / ARCADIS](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bff31a28abf838cbc589/html5/thumbnails/61.jpg)
AWWA/AMTA© 61
AdvancePlanningStudies
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AWWA/AMTA© 62
Category Integration-Related Studies Reported by Survey Respondents
CorrosionPost-treatment testing
Pipe-loop testing
Water Quality
Blending / mixing
Disinfectant stability assessment
DBP formation evaluation
Treatment process pilot testing
Hydraulics Modeling
Miscellany Reservoir soil dispersion model
Summary of Studies Reported
![Page 63: AWWA/AMTA© 1 Strategic Practices and Lessons Learned for Integrating Desalinated Seawater Into Existing Systems Brent Alspach Malcolm Pirnie / ARCADIS](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bff31a28abf838cbc589/html5/thumbnails/63.jpg)
AWWA/AMTA© 63
Category Integration-Related Studies Reported by Survey Respondents
CorrosionPost-treatment testing
Pipe-loop testing
Water Quality
Blending / mixing
Disinfectant stability assessment
DBP formation evaluation
Treatment process pilot testing
Hydraulics Modeling
Miscellany Reservoir soil dispersion model
Summary of Studies Reported
Evaluated the introduction of a pressurized supply of desalinatedseawater into an existing gravity-fed regional pipeline
![Page 64: AWWA/AMTA© 1 Strategic Practices and Lessons Learned for Integrating Desalinated Seawater Into Existing Systems Brent Alspach Malcolm Pirnie / ARCADIS](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bff31a28abf838cbc589/html5/thumbnails/64.jpg)
AWWA/AMTA© 64
Category Integration-Related Studies Reported by Survey Respondents
CorrosionPost-treatment testing
Pipe-loop testing
Water Quality
Blending / mixing
Disinfectant stability assessment
DBP formation evaluation
Treatment process pilot testing
Hydraulics Modeling
Miscellany Reservoir soil dispersion model
Summary of Studies Reported
Very similar to several proposed
SWRO projects in California
![Page 65: AWWA/AMTA© 1 Strategic Practices and Lessons Learned for Integrating Desalinated Seawater Into Existing Systems Brent Alspach Malcolm Pirnie / ARCADIS](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bff31a28abf838cbc589/html5/thumbnails/65.jpg)
AWWA/AMTA© 65
Category Integration-Related Studies Reported by Survey Respondents
CorrosionPost-treatment testing
Pipe-loop testing
Water Quality
Blending / mixing
Disinfectant stability assessment
DBP formation evaluation
Treatment process pilot testing
Hydraulics Modeling
Miscellany Reservoir soil dispersion model
Summary of Studies Reported
For discharge of desalinated seawater into auntreated water reservoir
![Page 66: AWWA/AMTA© 1 Strategic Practices and Lessons Learned for Integrating Desalinated Seawater Into Existing Systems Brent Alspach Malcolm Pirnie / ARCADIS](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bff31a28abf838cbc589/html5/thumbnails/66.jpg)
AWWA/AMTA© 66
Planning Studies: Considerations
1. There are many different types of integration planning studies that are conducted in conjunction with SWRO projects.
2. Project proponents consider “due diligence” integration studies an important component of successful SWRO project development.
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AWWA/AMTA© 67
Blending
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AWWA/AMTA© 68
Blending
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AWWA/AMTA© 69
Summary of Reported Strategies
None of the survey respondents reported specific
blending ratios of desalinated water with existing supplies.
Blending Strategy
No. of SurveyedSWRO Plants Notes
Direct Pipe-to-Pipe Connections 5 of 10
StorageFacilities 4 of 10 Use of both tanks
and reservoirs reported
No Blending 1 of 10 New distribution system
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AWWA/AMTA© 70
Summary of Reported Strategies
Blending Strategy
No. of SurveyedSWRO Plants Notes
Direct Pipe-to-Pipe Connections 5 of 10
StorageFacilities 4 of 10 Use of both tanks
and reservoirs reported
No Blending 1 of 10 New distribution system
Many respondents acknowledged the usefulness of
blending for meeting water quality goals.
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AWWA/AMTA© 71
Blending: Considerations• Blending can potentially serve as a low-cost means of achieving
finished water quality goals…
• …but cost of piping and storage facilities needs to be considered
• Blending ratio target is not necessary for successful integration…
• …but the blending ratio can be actively managed to reduce costs
• Is strategic blending feasible?– Cost?– Distribution system configuration?– Availability of existing supplies?
• Does blending cause customer water quality to vary by location?– Customer complaints?– Public perception issues?
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AWWA/AMTA© 72
Blending: Considerations• Blending can potentially serve as a low-cost means of achieving
finished water quality goals…
• …but cost of piping and storage facilities needs to be considered
• Blending ratio target is not necessary for successful integration…
• …but the blending ratio can be actively managed to reduce costs
• Is strategic blending feasible?– Cost?– Distribution system configuration?– Availability of existing supplies?
• Does blending cause customer water quality to vary by location?– Customer complaints?– Public perception issues?
Remember:
The effectiveness of blending diminishes
with increasing percentage of
desalination seawater.
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AWWA/AMTA© 73
IntertieLocation
“Intertie Location” images…
Bah!
![Page 74: AWWA/AMTA© 1 Strategic Practices and Lessons Learned for Integrating Desalinated Seawater Into Existing Systems Brent Alspach Malcolm Pirnie / ARCADIS](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bff31a28abf838cbc589/html5/thumbnails/74.jpg)
AWWA/AMTA© 74
IntertieLocation
Typical Advantages
TypicalDisadvantages
Regional
• Strategic integration• Increased blending potential• Greater operational flexibility• Greater water quality consistency More operational advantages
• Long transmission lines• Alignments through existing development• Significant hydraulic gradient for pumping Higher capital and operating costs
Local• Convenient integration• Minimizes conveyance issues Lower capital and operating costs
• Less blending potential• Less operational flexibility• Less water quality consistency Fewer operational advantages
Summary of Intertie StrategiesBoth regional and local intertie approaches
were reported by respondents
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AWWA/AMTA© 75
Intertie Location: Considerations
Is a regional intertie feasible?
Are there clear project-specific benefits for a regional intertie?
Do the benefits of a regional intertie justify the project costs?
(capital & operating)
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AWWA/AMTA© 76
Operations
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AWWA/AMTA© 77
Operations Trends Observed
Why?
Percentage ofDesalinated Seawater
in System
PredominantOperational
Mode(Capacity)
Rationale
Higher Base-loaded SWRO is more criticalfor meeting demand
Lower More variable production
Conventional water sources are sufficient for a greater portion of
system demand
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AWWA/AMTA© 78
Operations Trends Observed
Cost
Percentage ofDesalinated Seawater
in System
PredominantOperational
Mode(Capacity)
Rationale
Higher Base-loaded SWRO is more criticalfor meeting demand
Lower More variable production
Conventional water sources are sufficient for a greater portion of
system demand
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AWWA/AMTA© 79
Operations Trends Observed
Percentage ofDesalinated Seawater
in System
PredominantOperational
Mode(Capacity)
Rationale
Higher Base-loaded SWRO is more criticalfor meeting demand
Lower More variable production
Conventional water sources are sufficient for a greater portion of
system demand
Desalinated seawater is typically
the most expensive source of supply.
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AWWA/AMTA© 80
Operations Trends Observed
Fairly intuitive
Percentage ofDesalinated Seawater
in System
PredominantOperational
Mode(Capacity)
Rationale
Higher Base-loaded SWRO is more criticalfor meeting demand
Lower More variable production
Conventional water sources are sufficient for a greater portion of
system demand
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AWWA/AMTA© 81
Counterintuitive Operation
Gold Coast SWRO Plant
• Built for emergency supply to offset declining reservoir levels
• Currently routine use includes only as-needed operation when reservoirs levels are low…
• …or during extreme wet weather conditions!
Provided critical water supplies when record storm events renderedsurface water supplies too turbid for conventional treatment
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AWWA/AMTA© 82
Operations: Considerations
Consider a SWRO plant as a strategic assetrather than simply another source of supply.
Conduct advance planning to anticipatelong-term SWRO plant operating scenarios.
Cost is not always the singular driving factorfor SWRO plant operations.
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AWWA/AMTA© 83
Lessons Learned
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AWWA/AMTA© 84
Lessons Learned
Lessons Learned
Conduct advance planning studies to help ensure successful integration
Consider end uses in the development of water quality goals
Evaluate the potential for blending desalinated seawater with existing supplies in storage tanks to increase treatment and operational flexibility
Establish an intra-plant water goal for bromide at the RO permeate to minimize DBP formation and chloramine residual decay
Conduct a cost-benefit analysis on the appropriate treatment level for boron
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AWWA/AMTA© 85
Lessons Learned
Plan pretreatment processes carefully to accommodate a range of anticipated feed water quality (e.g., algae blooms)
Consider the water quality and operational flexibility afforded by a two-pass SWRO system vs. the additional capital and operating cost
A knowledgeable owner’s agent and a carefully planned water quality performance specification can be essential to control project cost, maximize efficiency, and facilitate successful implementation
A seawater desalination plant can serve as a valuable emergency asset, providing backup treatment reliability in both dry- and wet-weather conditions
Lessons Learned…cont.