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Arsenic Removal by Ion Exchange

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

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Arsenic Removal by Ion Exchange

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  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. Softening Processes BACKWASH TO WASTE RAW WATER Ion Exchange System RINSE TO WASTE BRINE TANK (NaCI) TREATED WATER RAW WATER FOR BACKWASH IX

  6. Point of Entry Softening IX

  7. Cation and Anion Exchange System IX

  8. Acid-Base Chemistry of As(V) IX

  9. Acid-Base Chemistry of As(III) IX

  10. Resin Selectivity Sequence • Strong Base Type II Anion Resin selectivity sequence UO2(CO3)34- > SO42- > 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 HAsO42- from resin • Effluent As concentrations are much higher than influent concentrations 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 IX

  17. Bed Capacity & SO42- Sulfate Removal Technology! 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) • SO42- ≈ 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 SO42- causes breakthrough • down flow service & regeneration • single or multiple beds • single or multiple brine use IX

  23. 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 Process Design IX

  24. 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 Regeneration 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 BaCl2 IX Brine Tank Precip. Tank Brine Reuse BaSO4 IX Regeneration After 3 Cycles IX

  27. IX

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  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. IX

  31. 10 gpm water loss IX

  32. Floor Drain To POTW 10 gpm Water loss IX

  33. IX

  34. IX

  35. IX

  36. Plan Ah e a d IX

  37. IX

  38. 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 Floor Drain To POTW IX

  39. Rimrock, Arizona Basin Water IX IX

  40. $ per acre-foot IX

  41. IX

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  48. Ten in parallel • Seven in production • pH • Alkalinity • Chromatographic peaking IX

  49. IX

  50. IX

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