Managing Salt in Southern Arizona Water

Department of Chemical and

Environmental Engineering

University of Arizona

04/18/2009

By Justin Nixon, Dr. Robert Arnold

and Dr. Wendell Ela

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1984 1989 1994 1999 2004 2009 2014 2019 2024Year

Su

pp

ly (

1000

s o

f A

F)

Incidental Reuse

CAP Delivery

Renewable Groundwater

Water Reuse

Total Demand

Water Supply/Demand Projections

Tucson Active Management Area

Tucson Primary Water SourcesConversion to CAP

Water Quality Constituent

Mean Well Water

CAP Water

Total Dissolved Solids (mg/L) 179 806 Hardness (mg/L CaCO3) 96 322

Sodium (mg/L) 24 102 Calcium (mg/L) 31 75

Magnesium (mg/L) 5 31 Barium (mg/L) < 0.01 0.15

Strontium (mg/L) < 0.1 1 Chloride (mg/L) 13 94 Sulfate (mg/L) 26 256

Alkalinity (mg/L HCO 3̄ ) 103 119 Total Organic Carbon (mg/L C) < 1 3.1

Salinity Impact in TAMA

275

300

325

350

1993 1997 2001 2005 2009

Year

TD

S L

ev

els

Projected TDS levels in TAMA ground waters

5-8 mg/L annual increase

Arizona (all sources) : 1.0M-1.3M tons/yrTAMA (all sources) : 140,000-233,000 tons/yrTAMA (CAP only) : 85,000-190,000 tons/yr

Research Objective: Find cost effective

ways to manage salt in inland water supplies.

Reverse Osmosis ForSalt Separation

Single RO Element

RO TreatmentSchematic

ConcentratedSalts

FEEDFLOW

H2OH2O

H2O

H2O Mg

Cl

Fe++

HCO3 Ca

SO4

++

++

H2O H2OH2O

H2O H2OH2O

Permeate

Na+ ConcentratedSalts

FEEDFLOW

H2OH2O

H2O

H2O Mg

Cl

Fe++

HCO3 Ca

SO4

++

++

H2O H2OH2O

H2O H2OH2O

H2O H2OH2O

H2O H2OH2O

Permeate

Na+

Sources of Membrane ScalingPrecipitate Ion

Concentrationlog (ion prod) log KS0 Degree of Over

Saturation

BaSO4 -8.48 -10.0 827.83

CaSO4-5.25 -4.85 9.95

CaCO3 -7.7 -8.48 150.64

[Ba+2] = 1.17 x 10-6 M

[SO4-2] = 2.81 x 10-3 M

[Ca+2] = 2.0 x 10-3 M

[CO3-2] = 1.0 x 10-5 M

Precipitate IonConcentration

log (ion prod) log KS0 Degree of OverSaturation

BaSO4 -8.48 -10.0 827.83

CaSO4-5.25 -4.85 9.95

CaCO3 -7.7 -8.48 150.64

[Ba+2] = 1.17 x 10-6 M

[SO4-2] = 2.81 x 10-3 M

[Ca+2] = 2.0 x 10-3 M

[CO3-2] = 1.0 x 10-5 M

CAP Sample Point - 713

Barium versus RO Recovery

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0.02

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0.12

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0.16

0.18

0.20

Time

Ba+

2 Co

ncen

trati

on

(m

g/l

)

65%

70%

75%

80%

85%

90%

Barium RO Recovery*Courtesy of Kevin Alexander, SPI

Amount of Water Loss:163 Billion Gallons

per year

Value of Water Loss: $160M/year

Cross-flow Filtration

• High velocity fluid flow

• Plate & frame; tubular; spiral-wound cartridge assembly

Unknown

• Causes of membrane scaling during RO treatment of CAP water

*(images from eco-tec.com and vsep.com)

Unknown

• Sustainability of brine minimization at 95-99 % water recovery

*(images from vsep.com)

V-SEP System

• Intense shear waves on the face of a membrane

• Solids and foulants to be lifted off the membrane surface

Principles of RO vs VSEP

Qconc

Qfeed

QpermSemi-permeable

membrane

During open valve

period

closed/open

How VSEP WorksSeries LP (in P Mode):

Membrane Area: 16.44 ft2 (1.58 m2)

Hold-Up Volume: 0.8 gal (3 L)

Qfeed

Qperm

Qconc = 0

Semi-permeable membrane

During closed valve

period

VSEP Results

Relationship of closed valve time with water recovery and permeate flux.

• Permeate flow rate decreases as closed valve time increases

• Water recovery increases as closed valve time increases

VSEP ResultsPermeate Flow vs. Water Recovery

• Tradeoff Between Recovery and Membrane Flux

• Increased recovery reduces amount of permeate flow rate

• Must purchase additional V-SEP Machines

• Optimization: MF/Ion Exchange / RO / V-SEP in series

Permeate 0.9 MGD110 mg/l

0.002 MGDTS ~ 10%

Concentrate

Permeate 0.098 MGDTDS = TBD

0.1 MGD6000 mg/l

90% Recovery

Brine

98% Recovery

RO Unit

V-SEP Unit

Influent

1 MGD700 mg/l

IX Unit

Removal ofBarium &Calcium

Future Experimental Work

Desalination Research Facility

Participating Water UtilitiesParticipating Water Utilities

Slow Sand Filtration Reverse Osmosis Concentrate Management

Questions?Acknowledgements

Chris Hill (MDWID)Mike Dew, Jeff Biggs (City of Tucson)Martin Yoklic (ERL, U of A)Dr. Chuck Moody, Eric Holler (BOR)Dongxu Yan, Bob Seaman, Andrea Corral, James

Lykins, Dane Whitmer, Brian McNerney (UA)Special Thanks to Dr. Wendell Ela, Dr. Robert

Arnold, and Dr. Umur Yenal (U of A)

AcknowledgementBureau of ReclamationTucson WaterMetropolitan Domestic Water Improvement

DistrictOro Valley Water UtilityMarana Municipal Water DepartmentFlowing Wells Water DistrictTRIF/WSP