Selective Salt Recovery from Reverse Osmosis Brine Using Inter-Stage Ion Exchange

SELECTIVE SALT RECOVERY FROM REVERSE OSMOSIS BRINE USING INTER-STAGE ION EXCHANGE

Joshua E. Goldman Kerry J. Howe Bruce M. Thomson PhD Candidate Associate Professor Regents Professor University of New University of New University of New Mexico Mexico Mexico

ACKNOWLEDGMENTS

• WateReuse • Kerry Howe • Bruce Thomson • CDM • Mehdi Ali • Steve Cabannis • Purolite • Angela Montoya • Lana Mitchell • ResinTech

2 of 38 PRESENTATION OUTLINE

• Background • Project Overview • Bench Test Conclusions • Pilot Testing Objectives • Pilot Testing Results • Conclusions

3 of 38 CONCENTRATE PRODUCTION

RO Fresh Water (Typically 70%-90%)

Concentrate Brackish (Typically 10%-30%) Well

Concentrate disposal is a big problem in inland areas • Expensive • Complicated state and EPA regulations depending on constituents in water

4 of 38 CONCENTRATE REDUCTION

Inter-stage sequential ion exchange • Remove ions that form sparingly soluble salts from concentrate • Calcium, magnesium, sulfate • Replace them with sodium and chloride • 2nd RO stage to treat sodium chloride solution without worrying about scaling • 2nd stage RO concentrate used a regeneration solution for cation and anion exchange columns

5 of 38 SALT RECOVERY

• Calcium carbonate • Pulp and paper • Building construction (marble floors, roof materials, and roads) • Glass (improves chemical durability) • Rubber and plastic • Paint (extend resin and polymers and control texture) • Dietary supplement (antacids) • Water treatment (pH control, softening) • Calcium sulfate • Drywall

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PROPOSED PROCESS TRAIN

Concentrate

Reverse Osmosis Stage 1

Stage 1 Permeate

7 of 38 PROPOSED PROCESS TRAIN

Ca Mg CO3 SO4 Concentrate Anion Exchange Reverse Cation Osmosis Exchange Stage 1 Na CO3 SO4

Stage 1 Na Cl Permeate

8 of 38 PROPOSED PROCESS TRAIN

Concentrate Anion Exchange Reverse Cation Osmosis Exchange Stage 1

Stage 1 Permeate Reverse Osmosis Stage 2 Stage 2 Permeate

9 of 38 PROPOSED PROCESS TRAIN Regeneration Concentrate Anion Exchange Reverse Cation Osmosis Brine Exchange Stage 1 Reservoir

Stage 1 Waste Permeate Reverse Osmosis Stage 2 Stage 2 Permeate

10 of 38 PROPOSED PROCESS TRAIN Regeneration Concentrate Anion Exchange Reverse Cation Osmosis Brine Exchange Stage 1 Reservoir

Stage 1 Waste Permeate Reverse Osmosis Stage 2 Stage 2 Permeate

Precipitation Basin 11 of 38 PILOT TESTING OBJECTIVES

• Determine the consistency of the mass and purity of the recovered salt products. • Determine the “best” fraction of the regenerant solution to use for salt recovery. • Optimize the operation cycle length to maximize ion concentrations in regeneration solutions and minimize unused cation exchange capacity. • Determine if pilot effluent recycle affects the performance of the 2nd stage RO system. • Determine the effect of anti-scalant addition on the resin capacity.

12 of 38 PILOT SCALE • Outside of Brighton, CO TESTING • In conjunction with CDM • June 6th – July 14th • Continuous operation

Average Pilot Feed RO Concentrate mg/L Ca 456 Mg 191 K 17 Na 570 Cl 613

SO4 957 TDS 4450 M

CO3 0.274 13 of 38 PILOT SCALE TESTING Service Cycle 1-4 20 BV

Service Cycle 5-6 28 BV

Service Flow Rate 10 BV/hr

Regeneration Cycle 0.75 BV

Rinse Cycle 1 BV

Rinse and 2 BV/hr Regeneration Flow Rate

14 of 38 15 of 38 16 of 38 MASS ANALYSIS AND QUANTIFICATION METHODS

• Tare Erlenmeyer flask • Mixed 100 mL of each regeneration solution in flask • For low pH prepetition, adjust pH of anion regeneration solution to 4 • Allow precipitates to form and settle for 36 hours. • Separate liquid and solid by centrifuge • Dry in the lab oven at 104°C for 24 hours • Mass of flask - tared mass = precipitate mass • Analyze precipitated solid by SEM, EDS, XRD

17 of 38 1 M Ca VISUAL MINTEQ 1 M SO4 1 M CO MODELING 3

4 Calcite 3 Gypsum 2 1 0 0 2 4 6 8

-1 pH -2 -3 -4 -5 -6 Saturation Index

18 of 38 PURE CALCIUM 70 60 CARBONATE 50

70 40 30

60 20

50 10 % (Atomic) Composition % 0 40 C O Na Mg P S Cl Ca Sr

30 % (Atomic) Composition % 20

0 C O Ca

19 of 38 80 PURE CALCIUM 60 1 SULFATE 40 70 20

60 0 O Na Mg Si S Cl Ca

80 50 60

40 40 2

20 30 0 O Na Mg P S Cl Ca Sr

% (Atomic) Composition % 20

1 2 10

0 O S Ca 20 of 38 MASS ANALYSIS Representative Sample RESULTS Ambient pH Low pH

21 of 38 MASS ANALYSIS RESULTS - XRD

• Spectra Identified as CaCO3 • Ambient pH precipitate from Weeks 2-4

• Spectra Identified as CaSO4 • Low pH precipitate from Weeks 3,4,6 • Ambient pH precipitate from Week 6 • Other Spectra Identified • Halite (NaCl) • Week 2 Ambient pH • Week 4 Low pH

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CONCLUSIONS FROM MASS ANALYSIS

• Calcium sulfate and calcium carbonate can be precipitated separately • Low pH mixing conditions - calcium sulfate • Ambient pH mixing conditions – calcium carbonate • Except for Week 6

23 of 38 MASS QUANTIFICATION RESULTS

0.40 Ambient pH Low pH

0.35

0.30

0.25

0.20

0.15

0.10

kg Precipitate per m3 RO Concentrate Concentrate RO m3 per Precipitatekg 0.05

0.00 Week 1 Week 2 Week 3 Week 4 Week 5 Week 6

-0.05 24 of 38 MASS QUANTIFICATION CONCLUSIONS

• Salts precipitate spontaneously when the regeneration solutions are mixed • Possible to precipitate approximately 12 kg of gypsum per cubic meter of regeneration solution • Approximately 45% of the calcium is recovered • Approximately 28% of the sulfate is recovered

25 of 38 METHOD TO DETERMINE BEST PORTION OF REGENERATION SOLUTION

• Regeneration and rinse cycles total 1.75 BV • Results from column tests showed sharp regeneration curves • Effluent samples taken every 5 minutes (0.17 BV) • Anion column - conductivity and total carbonate • Cation column - conductivity and calcium

1.20

1.00

0.80 0.60 0.40 (C/Cmax) 0.20 Concentration Concentration 0.00 0.00 1.00 2.00 3.00 BV 26 of 38 PILOT ELUTION CURVES SBA SAC

Conductivity TotCO3 Conductivity Ca

1.2 1.2

1 1

0.8 0.8

0.6 0.6

C/Cmax C/Cmax 0.4 0.4

0.2 0.2

0 0 0.0 0.5 1.0 1.5 2.0 0 0.5 1 1.5 2 Bed Volumes Bed Volumes

27 of 38 RESULTS – ION CONCENTRATION

AND SALT YIELD 0.35

0.3 Ambient • Significant increase in ion Low concentrations 0.25 • 5.8x increase in salt yield 0.2

per unit treated RO 0.15 concentrate 0.1 • Increased total recovery of

total Ca and SO4 in system 0.05

from 5% to 20% RO Concentrate m3 per Precipitate kg 0 Week 5 Week 6 Ca Mg SO4 NO3 CO3 Week mg/L mg/L mg/L mg/L M 5 5798 1708 17673 799 0.13 6 12546 3703 48167 1023 0.25 CF 2.2 2.2 2.7 1.3 1.9

28 of 38 OPTIMIZATION OF OPERATION CYCLE • Constructed breakthrough curve • Started at end of standard operation cycle (20 BV) • Grabbed samples of SBA and SAC effluent • Sample taken every 2 BV (12 minutes)

29 of 38 BREAKTHROUGH CURVE

1.8 CO3 Ca Mg SO4 1.6 1.4 1.2

1.0

0.8 C/Cin 0.6 0.4 0.2 0.0 20 25 30 35 40 Bed Volumes • Started taking samples at end of standard regeneration and rinse cycle • Extended cycle to point just before magnesium breakthrough (28 BV) 30 of 38 OPTIMIZED OPERATION CYCLE Increase 25

Week 2 in Ratio

20 Week 5 Ca:Mg 1.3x

15 SO4:CO3 2.7x 10 SO4:NO3 2.4x 5

Resin Phase Ionic Ratio Ionic Phase Resin 0 Ca:Mg SO4:CO3 SO4:NO3

Ca Mg NO3 SO4 CO3 mg/L mg/L mg/L mg/L M

Week 2 5096 1919 1090 10236 0.20

Week 5 5798 1708 799 17673 0.13 31 of 38 OVERALL CONCLUSIONS

• Separation factors can be predicted based on solution characteristics

Ca/Na α α 30

20 Predicted Predicted

0 0 10 20 30 40 50 60 Measured α Ca/Na 32 of 38 OVERALL CONCLUSIONS

• Column performance well predicted by separation factor regressions and modeling

Number of BV to to BV of Number 15

Breakthrough 10

5 Calculated Calculated 0 0 5 10 15 20 25 30 35 40 Measured Number of BV to Breakthrough

33 of 38 OVERALL CONCLUSIONS

• Gypsum can be spontaneously precipitated from mixed cation and anion regeneration solutions • Lab and pilot tests • Requires pH adjustment when system not optimized for sulfate recovery • Can recover 45% of calcium and 28% of sulfate from the mixed solution • 15% of total possible gypsum recovered from RO concentrate stream • For a 5 MGD plant • 6 tons/day of gypsum could be recovered

34 of 38 OVERALL CONCLUSIONS

• Process has potential to improve RO recovery and to generate to gypsum

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Letterman, R.D. and American Water Works Association., Water quality and treatment : a handbook of community water supplies. 5th ed. 1999, New York: McGraw-Hill. 1 v. (various pagings).2010. 44(9): p. 2957-2969.

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37 of 38 QUESTIONS???

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