November 2015

Anion Exchange for Drinking Water TreatmentMichael Poulios, Aqua North Carolina

William Dowbiggin, CDM Smith

2015 Annual Conference Raleigh, NC

• Use a substitution reaction to remove ions

• DefinitionDescription:• Undesirable ions are captured on reactive sites of resin• Ions initially attached to resin are released into treated

water• Reversible reaction is most useful (recharge the resin)• Cation exchange uses H+ or Na+

• Anion exchange uses OH- or Cl-

• Water treatment applicationsExamples: • Softening(Ca2+, Mg2+) or other cation exchange

Ion Exchange Description and Examples

• Organics removal (Anion Exchange)• Anion Removal (Nitrate, Perchlorate, Arsenic,

Selenium, Chromium)• Wastewater/Industrial applications

• Other uses include chemical recovery• Contaminant (i.e. heavy metals) removal

Inside of the Ion Exchange Bed • Typical arrangement

• Freeboard for bed expansion during a backwash

• Gravel and underdrain or other media support system

AIR RELEASE LINE

BAFFLE

FREEBOARD

GRAVEL BED

UNDERDRAIN

VERTICAL SOFTENER TANK

" DIAMETER

" FILTER SAND, SIZE TO MM.

STANDARD SOFTENER

" GRADED GRAVEL, SIZE 1/4" x 10" GRADED GRAVEL, SIZE 1/2" x 1/4"" GRADED GRAVEL, SIZE 3/4" x 1/2"" GRADED GRAVEL, SIZE 1 1/2 x 3/4"

" SIDE SHELL HEIGHT

P.S.I. W.P.

"ZEOLITE = CU.FT.

• Specified cubic feet of ion exchange resin (e.g. zeolite for softening)

Raw Water NaCl to Regenerate

Low Organic MatterTreated WaterBackwash

Water Spent BrineTo Waste

DOCChromatePhosphatePerchlorateSulfateCarbonateBromideIodideArsenateNitrateChlorateHydroxideBromateNitriteChlorideBicarbonateFluoride

SpentBackwash

Water

Anion Exchange Process

Anion Exchange

Resin

Anions in decreasing order of selectivity:

Example Order of Anion Elution from another CDM Smith Project

0

50

100

150

200

0 200 400 600 800 1000 1200Bed Volumes

Con

centr

atio

n (m

g/L o

r mg/

L)

ChlorideBicarbonateNitrateArsenicSulfate

8

The Aqua Castle Bay Subdivision Water System is a 150 gpm Groundwater System near Hampstead NC just north of Wilmington

9

Castle Bay Anion Exchange Project Drivers

• High concentrations of disinfection byproducts

• A desire to avoid chloramines and associated nitrification control issues given the system has high residence time

10

Castle Bay Anion Exchange Project Phases• Bench study and testing of resin isotherms to

screen resins and obtain data for planning pilot testing

• Pilot testing of two short-listed resins to confirm suitability and determine guarantees for bidding

• Design• Construction and Start-up

Bench Test Results - TOC mg/L vs. mL Resin Added

0 0.2 0.4 0.6 0.8 1 1.2 1.40

0.5

1

1.5

2

2.5

3

3.5

R.Tech SIR-22R.Tech SBACRThermax A-72Thermax A-30Purolite A-860

mL of Resin Added

TOC(mg/L)

Bench Test Results - UV-254 Absorbance vs. mL Resin Added

UV-254 Abs. (cm-1)

mL of Resin Added

0 0.2 0.4 0.6 0.8 1 1.2 1.40.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

0.160

R.Tech SIR-22R.Tech SBACRThermax A-72Thermax A-30Purolite A-860

0 0.2 0.4 0.6 0.8 1 1.2 1.40.000

5.000

10.000

15.000

20.000

25.000

30.000

35.000

40.000

45.000

R. Tech SIR-22R.Tech SBACRThermax A-72Thermax A-30Purolite A-860

Bench Test Results - Color vs. mL Resin Added

Color (PCU)

mL of Resin Added

14

Bench Isotherm Preliminary Calculated Values

Resin K 1/N R2

Ld DR VR

(mg/g) (g/mL) (L/L)

R.Tech SIR-22P-HP 10.28 0.98 0.76 39.85 1.200 3288

R.Tech SBACR-HP 3.42 1.28 0.85 20.19 1.200 3029

Thermax A-72 3.26 0.93 0.64 11.84 1.100 1254

Thermax A-30 10.62 1.35 0.87 68.86 1.100 7291

Purolite A-860 9.39 1.45 0.79 70.00 1.065 6710

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0 100 200 300 400 500 600 700 800 9000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

f(x) = 0.00178212670051135 x + 0.215922981555568R² = 0.843446434497524

f(x) = 0.00191764319258326 x + 0.260362589266843R² = 0.718620356613872

Pilot Test - Raw Water Feed TOC vs Run Time

TOC Purolite Linear (TOC Purolite)TOC Tonka Linear (TOC Tonka)

Cumulative Run Time, hr

TOC

(mg/

L)

16

0 50 100 150 200 250 300 350 400 4500

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

f(x) = 0.00324905261850034 x − 0.0570065229545879R² = 0.922705538377324

f(x) = 0.00385393122241286 x + 0.545993602920621R² = 0.816982341212327

Pilot Test - Filtered Water Feed to Resin TOC vs. Run Time

TOC Purolite Linear (TOC Purolite)TOC Tonka Linear (TOC Tonka)

Cumulative Run Time, hr

TOC

(mg/

L)

Regenerated at 163 hours

17

600 650 700 750 800 8500

0.02

0.04

0.06

0.08

0.1

0.12

Pilot Test - Raw Water Fed to Resin Iron Removed vs Run Time

Iron Purolite Iron Tonka

Cumulative Run Time, hr

Iron

Rem

oved

by

the

Resi

n, m

g/L

18

0 50 100 150 200 250 3000

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.360.34

Filtered Water Fed to Resin Iron Removed vs. Run Time

Iron Purolite Iron Tonka

Cumulative Run Time, hr

Iron

Rem

oved

by

the

Resi

n (m

g/L)

19

The Resin is Piped for Raw Water or Filtered Water Feed-Initially to use Raw Water because:• Purolite ended up the selected media supplier, and they

recommended treating the raw water with the resin based on prior experiences, concern over the chlorine residuals, and the pilot data for this project.

• Chlorine degrades the anion exchange resin and chlorine residuals coming out of the iron filters have been highly variable and up to 1.63 mg/L reaching the pilot units which is far above Purolite’s recommended 0.2 mg/L max chlorine reaching the anion exchange resin.

• Even Tonka, who recommended trying downstream on filtered water, concurred that it should be on raw water after the pilot test on filtered water.

• After the iron removal filters, the Tonka unit had clogging (pressure increases) quickly dropping flows and requiring regeneration then had clogging again.

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The Resin is Piped for Raw Water or Filtered Water Feed-Initially to use Raw Water because (continued):

• Iron removal in the anion exchange resin was found to be low when operated on the raw water, but up to 0.44 mg/L in the Tonka unit and up to 0.34 mg/L in the Purolite unit when operated after the iron removal filter. These levels of iron removal in the AER resin indicate quick iron fouling potential and correspond to the observed clogging (pressure increases and flow decreases).

• Total run time on the log sheet is 817 hours for raw water. The run time for post iron filters was 588 hours. The Tonka unit reportedly also had a regen/wash before even reaching the 588 hours due to the clogging.

• Anion resin on the raw water helps DBPs by removing the organics before the first chlorine dose.

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Planning for the Anion Exchange Resin Operations

• Based on the pilot testing and prior projects, the vendors suggested planning on regenerating the media once a week typically. The necessary regeneration frequency will increase with age and fouling.

• The salt required for regeneration was reported to be 8 to 10 lb/cubic foot of media. The final installation is to have 87 cubic feet of media including all three vessels. Consequently, the amount of salt used per regeneration of all three vessels was estimated to be about 700 to 870 lb of salt per regeneration of all three vessels. Salt cost is about $ 0.12/lb, and the vendor indicated about 3,200 gallons of water would be used in each regeneration.

• The resin is guaranteed to last at least a week between regenerations.

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Design, Construction and Costs

• The design included plan and profiles and a detailed technical specification with performance requirements

• The purchase cost of the anion exchange system was approximately $ 140,000 with all items included.

• Potential cost saving measures could include strategies such as operating just one or 2 beds at a time pending DBP levels.

• In conclusion, the anion exchange resin should do an excellent job of removing the organic precursors of disinfection byproducts. Cost control for the resin will be influenced by careful operations to prevent fouling while still being frugal with respect to labor and chemical costs.

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Design - Anion Exchange Vessels

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The Anion Exchange Vessels at Castle Bay Water System

25

Water Softening System at Castle Bay Water System

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42217 42125 42036 41944 41852 41760 41671 415790

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

Quarterly TTHM vs. TimeCastle Bay Water System

Date

TTHM

(mg/

L)

AER Started

27

Conclusions

• The anion exchange resin should do an excellent job of removing the organic precursors of disinfection byproducts. Cost control for the resin will be influenced by careful operations to prevent fouling while still being frugal with respect to labor and chemical costs.

• Potential cost saving measures could include strategies such as operating just one or 2 beds at a time pending DBP levels.

Questions?

Michael Poulios, PE LEEDAqua North Carolina

(919) 653-6965

William B. Dowbiggin, PE BCEECDM Smith

(919) 623-7964 dowbigginwb@cdmsmith.com