awwa/amta© 1 strategic practices and lessons learned for integrating desalinated seawater into...

AWWA/AMTA© 1

Strategic Practices and Lessons Learned for Integrating Desalinated Seawater

Into Existing Systems

Brent AlspachMalcolm Pirnie / ARCADIS

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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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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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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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Purpose and Goal



Purpose



Project Components

Understand major considerations associated

with integrating desalinated seawater.

Project Goal

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Purpose and Goal



Purpose



Project Components

Summarize some of the most interesting survey results

relative to major integration considerations.

Presentation Goal

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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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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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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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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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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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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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Summary of Key Results

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Boron

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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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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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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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Size Larger size


Mass Higher mass

Boron Rejection


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Size Larger size


Mass Higher mass

Boron Rejection


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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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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(mg/L)

FinishedWater Goal

(mg/L)

RejectionRequired

GoalSignificance

4.5







Primary historic boron removal driver

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(mg/L)

FinishedWater Goal

(mg/L)

RejectionRequired

GoalSignificance

4.5







• Rejection dependent on pH, temp., flux, recovery, membrane type, etc.• Typical best-case RO rejection: 80-90%

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(mg/L)

FinishedWater Goal

(mg/L)

RejectionRequired

GoalSignificance

4.5







• 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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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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Surveyed Facilities


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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Surveyed Facilities


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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Surveyed Facilities


9 of 10

Blending* 8 of 10

Level of benefit may vary depending

on the blending location

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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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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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Potentially yes… for now.

Blending becomes less effective as % contribution of desalinated seawater increases.

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Is this ever going to be a

realistic issue in California?

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Perth Area in 2005: 0% desalinated seawater

Perth Area in 2015: 50% desalinated seawater

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Bromide

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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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• Source Waters– Typical: [Br-] ≈ 65,000 μg/L = 65 mg/L

Seawater Source & Desalination

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Three orders of magnitude higher than conventional sources

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• 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-



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• 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-



Double the concentration over conventional treatment applied to conventional sources (at a minimum)

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– Bromamine formation (with chloramine residual disinfection)


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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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An issue by virtue of higher bromide concentrationsin desalinated seawater supplies

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• Variability– DBP formation = f(precursor conc. & character, pH, temp., etc.)– DBP precursor material is largely rejected by RO membranes



Net impact on THM / HAA formation…?

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Net impact on THM / HAA formation…?





• Variability– DBP formation = f(precursor conc. & character, pH, temp., etc.)– DBP precursor material is largely rejected by RO membranes



Bromide issues assume heightened

significance in systems with

SWRO treatment

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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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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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Bromide Treatment & Mitigation


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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Surveyed Facilities


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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Surveyed Facilities


Blending* 8 of 10



1 of 10

Novel strategy of blending with low-bromide supplies prior to NH3 addition

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Surveyed Facilities


Blending* 8 of 10



1 of 10

May not be practical and/or feasible in all cases

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Bromide: Considerations for California




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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Bromide: Considerations for California




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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Corrosion

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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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Corrosion Treatment & Mitigation


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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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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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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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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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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• Planning stage corrosion studies are importantAre corrosion studies critical?

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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

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Pipe-loop testing

Water Quality

Blending / mixing




Hydraulics Modeling



Evaluated the introduction of a pressurized supply of desalinatedseawater into an existing gravity-fed regional pipeline

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Pipe-loop testing

Water Quality

Blending / mixing




Hydraulics Modeling



Very similar to several proposed

SWRO projects in California

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Pipe-loop testing

Water Quality

Blending / mixing




Hydraulics Modeling



For discharge of desalinated seawater into auntreated water reservoir

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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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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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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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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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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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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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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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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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in System


Mode(Capacity)

Rationale




system demand

Desalinated seawater is typically

the most expensive source of supply.

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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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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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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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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.

awwa/amta© 1 strategic practices and lessons learned for integrating desalinated seawater into...

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