IX 1

Arsenic Removal by Ion Exchange

Joe Chwirka - Camp Dresser & McKee (chwirkajd@cdm.com)

Bruce Thomson - University of New Mexico (bthomson@unm.edu)

with contributions from Jerry Lowry and Steve Reiber

IX 2

Introduction

• Arsenic removal by Ion Exchange (IX) is effective for many applications

• Presentation will discuss:

• Chemistry of the process

• Variables affecting process performance

• Especially competing ions and resin selectivity

• Salt use & brine production and disposal

• Design considerations

• Two example systems

IX 3

Arsenic Treatment Technologies

Likely Technologies• Coagulation/ Microfiltration• Fixed Bed Adsorption Technologies• Coagulation/ Filtration• POU or POE

Unlikely Technologies• Ion Exchange• Activated Alumina or Regenerable Media• NF or RO or EDR• Enhanced Softening

IX 4

Ion Exchange Reactions

• Cation Exchange (water softening)

2 (R-Na) + Ca2+ = R2-Ca + 2 Na+

• Anion Exchange (arsenic removal)

R-Cl + H2AsO4- = R-H2AsO4 + Cl-

• Will only remove ionic species

• Regenerate resin with concentrated NaCl brine

R = Resin site

IX 5

BACKWASHTO WASTE

RAW WATER

RINSE TOWASTE

TREATED WATERRAW WATERFOR BACKWASH

BRINE TANK(NaCI)

Softening Processes

Ion Exchange System

IX 6

Point of Entry Softening

IX 7

Cation and Anion Exchange System

IX 8

Acid-Base Chemistry of As(V)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 2 4 6 8 10 12 14

pH

Fra

ctio

n

H3AsO4 H2AsO4- HAsO4

2-AsO4

3-

IX 9

Acid-Base Chemistry of As(III)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 2 4 6 8 10 12 14

pH

Fra

ctio

n

H3AsO3

H2AsO3-

HAsO32-

AsO33-

IX 10

Resin Selectivity Sequence

• Strong Base Type II Anion Resin selectivity sequence

UO2(CO3)34- > SO4

2- > HAsO42- > NO3

- > H2AsO4- > Cl- > HCO3

-

• All SO42- must be removed before As is removed

• Other anions may also have higher selectivity than As (i.e. VO43-)

IX 11

Concentration Profiles in IX Column

• All SO42- is removed before

HAsO42- is removed

• Can result in chromatographic peaking:

• SO42- elutes HAsO4

2- from resin

• Effluent As concentrations are much higher than influent concentrations

Re sin Sa tura te dwith SO 4

2 -

S Re m o va lZo ne

O 42 -

Re sin Sa tura te dwith HAsO 4

2-

Virg in Re sin

C o nc e ntra tio n

Sulfate

Arse

nic

Influe nt

Efflue nt

IX 12

Chromatographic Peaking

IX 13

Chromatographic Peaking

IX 14

Chromatographic Peaking

IX 15

SEPARATION & BREAKTHROUGH

•Kinetics & EBCT

•Bed Capacity & SO42-

•Leakage

•As & N03- Peaking

•Alkalinity, pH/Corrosivity

IX 16

Kinetics & Empty Bed Contact Time

• Exchange kinetics are rapid and internal mass transport limitations are small

• Empty Bed Contact Time (EBCT)

• EBCTmin = 1.5 min

• Breakthrough is sharp & leakage is low

Q

V

RateFlow

BedEmpty of .VolEBCT

Be d Vo lum e s o f Wa te r Tre a te d

Dim

ens

ionl

ess

Co

nce

ntra

tion

(C/C

)o

Arse nic

Su lfa te

IX 17

Bed Capacity & SO42-

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 50 100 150 200 250 300 350

SULFATE, mg/L

BV T

O A

s BR

EAKT

HRO

UGH

Sulfate RemovalTechnology!

IX 18

IX System - Unity, ME

• 11 Years Old

• As(III) at ≈100 µg/L

• Trace of Sulfide & Fe

• 65 gpm Design Flow

• Filox Oxidizing Filter

• SB II Anion Resin

IX 19

FJ School IX System

• Filox + IX• 1200 gpd• As ≈ 25-60 µg/L (sol)• SO4

2- ≈ 25 mg/L• pH = 7.6• Capable of < 1.0 µg/L

treated water

IX 20

EPA Study at Medical Facility - Arsenic

IX 21

EPA Study at Medical Facility - pH & Alkalinity

IX 22

Design

• EBCT = 1.5 min

• operated to regen. BEFORE SO4

2- causes breakthrough

• down flow service & regeneration

• single or multiple beds

• single or multiple brine use

IX 23

Process Design

Small Systems• single or double vessels

• EBCT > 1.5 min and long service cycle

• intermittent flow

• single use of brine

• may not be feasible w/o POTW for brine disposal

Large Systems• multiple parallel vessels

• staged regeneration

• possible reuse of brine

• may not be cost effective w/o POTW for brine disposal

IX 24

Regeneration

Small Systems• use a standard softener

control & small brine tank

• 8-15 lb salt used/cf of resin

• backwash, brine, slow rinse, & fast rinse

Large Systems• parallel vessels and staged

regeneration with salt storage & brine maker

• 5.4 lb salt used/cf of resin

• backwash, brine, & rinse steps

IX 25

Brine Disposal Options

• Municipal sewer

• Likely only for very small systems

• Systems near coast where salinity isn’t problem

• Evaporation ponds

• Deep well injection

IX 26

IX Brine Recycling

Brine TankPrecip.Tank

IX

BaSO4 IX Regeneration

Brine Reuse

BaCl2

After 3 Cycles

IX 27

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IX 29

Fruitland, Idaho

• Water Chemistry

• As – 34 micrograms/L

• Nitrate - 14.6 mg/L

• Sulfate - 51 mg/L

• pH - 7.3

1,500 X sulfate 429 X nitrate 1,929

IX 30

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10 gpm waterloss

IX 32

Floor DrainTo POTW

10 gpmWater loss

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Plan Ahe

a d

IX 37

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Floor DrainTo POTW

•Sequentially regenerated•pH •Alkalinity

•6 – 8,000 lb salt/week @ $0.10/lb•50% production loss for 5 hours (~85 gpm)

•Regenerate 1/30 hours

IX 39

Rimrock, Arizona

Basin Water IX

IX 40

$ per acre-foot

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Ten in parallelSeven in production•pH•Alkalinity•Chromatographic peaking

IX 49

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Truck fill

IX 52