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Technologies for Arsenic Removal

Technologies for Arsenic Removal. Tom Sorg U. S. Environmental Protection Agency. Arsenic Chemistry. Two primary valence states As (III) As (V). Arsenic III. H 3 AsO 3 0 H 2 AsO 3 -1 HAsO 3 -2. Arsenic V. H 3 AsO 4 0 H 2 AsO 4 -1 HAsO 4 -2 AsO 4 -3.

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Technologies for Arsenic Removal

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  1. Technologies for Arsenic Removal Tom Sorg U. S. Environmental Protection Agency

  2. Arsenic Chemistry • Two primary valence states • As (III) • As (V)

  3. Arsenic III H3AsO30 H2AsO3-1 HAsO3-2

  4. Arsenic V H3AsO40 H2AsO4-1 HAsO4-2 AsO4-3

  5. Why is arsenic form important? • Final Answer! • As V more effectively removed • by • ALL technologies

  6. Example! Treatment Process Percent Removal As IIIAs V Iron Coag/Filt - pH 7 55 97 Alum Coag/Filt - pH 7 18 95

  7. Example! • Ion exchange treatment • As III - 0 percent removal • As V - 98+ percent removal

  8. Arsenic Occurrence • Surface waters predominantly As(V) • Ground waters generally As(III), but not always

  9. Arsenic Speciation Method On site anion exchange separation As III, As V As V As V retained on resin column As III passes through column As III

  10. Arsenic Speciation - Anion separation of AsIII/AsV

  11. Good News! As III easily oxidized to As V by several oxidants

  12. As III Oxidation Study Dr. Dennis Clifford Univ. of Houston • Oxidants Studied 1. Free Chlorine 2. Chloramine 3. Ozone 4. Chlorine Dioxide 5. UV Radiation 6. Potassium Permanganate 7. Oxidizing Media

  13. Arsenic Removal Processes • Precipitative processes • Adsorption processes • Ion Exchange process • Iron Removal processes • Membrane processes • POU/POE devices

  14. Arsenic Removal Processes • Emerging processes • Iron coagulation with microfiltration • Iron based adsorption media

  15. Precipitative Processes ProcessRemoval Coagulation/ 95 % Filtration Lime softening 85+ %

  16. Adsorption Processes ProcessesRemoval Activated Alumina 90+ % Iron Media 90+ %

  17. Ion Exchange 95 + % removal

  18. Iron Removal Processes ProcessRemoval Oxidation/filtration 80+ % Manganese greensand 80+ % (Dependent on amount of Fe)

  19. Membrane Processes ProcessRemoval Reverse osmosis (RO) 90+ % Nanofiltration (NF) 65-90 % Ultrafiltration (UF) 35-75 %

  20. Arsenic Removal Processes • Large Systems Using Surface Waters • Coagulation/filtration • Direct filtration • Lime softening

  21. Arsenic Removal Processes • Large Systems Using Ground Waters • Lime softening • Membrane Separation Processes • -reverse osmosis (RO) • -ultrafiltration (UF • -electrodialysis reversal (EDR) • Iron Removal processes - oxidation/filtration

  22. Arsenic Removal Processes • Small Systems Using Surface Waters • Coagulation/filtration package plants • Iron Removal processes - oxidation/filtration • Lime softening package plants

  23. Arsenic Removal Processes • Small Systems Using Ground Waters • Anion Exchange • Activated Alumina adsorption • Iron Removal processes - oxid/filt. • Membrane Separation Processes • -reverse osmosis (RO) • -ultrafiltration (UF) • -electrodialysis reversal (EDR)

  24. Arsenic Removal Processes • Very Small Community Option • Point-of-use systems • -RO, AA • Point-of-entry systems • -RO, Ion Exchange

  25. Evaluation of Treatment Plant Performance Investigator - Battelle, Columbus, OH Processes - 5 • Conventional Coag. -- 2 Systems • Lime Softening ------- 1 System • Iron Removal ----------2 Systems • Anion Exchange -------2 Systems • Activated Alumina ----2 Systems

  26. AA System - Source Water Quality (Avg) Analysis - ug/LCS (30) Total As 63 Particulate As 2 Soluble As 66 As III <1 As V 66 (100%) pH - Units 8.4 Hardness – mg/L 37 Sulfate – mg/L 14 Alkalinity - mg/L 57

  27. Activated Alumina System - New Hampshire Non regeneration system A A Roughing filter Polishing filter B B

  28. Activated Alumina System, 20 gpm - NH

  29. Activated Alumina System, NH

  30. IE System - Source Water Quality (Avg) Analysis - ug/LMMA (45) Total As 57 Particulate As <1 Soluble As 57 As III <1 As V 57 (100%) pH - Units 8.3 Hardness – mg/L 38 Sulfate – mg/L 45 Alkalinity - mg/L 64

  31. Ion Exchange System, ME Oxidizing filter media KMnO4 regeneration A B Mixed bed resin

  32. Ion Exchange System with Oxidizing Filter, ME 2 gpm

  33. Ion Exchange System, ME

  34. Iron Media System, MI Source Water Quality ParameterConcentration - mg/L Arsenic 0.025 - 0.041 As III 85 % As V 15 % Calcium 80 - 90 Magnesium 34 - 35 Iron 1.06 - 1.35 Manganese 0.02 - 0.03 Sulfate 21 - 30 Silica 19 - 20 pH 7.1 - 7.2

  35. Iron Media System, MI Well Tank 1A Tank 2A Tank 3A Cl2 Acid Tank 1B Tank 2B Tank 3B Softener Distribution system

  36. Iron Media System, MI

  37. Iron Media System, MI

  38. SUMMARY • Soluble arsenic occurs in natural water in the As III and As V oxidation states. • As V is dominant in oxygenated waters • As III is dominant in anoxic water

  39. SUMMARY • Treatment processes remove As V more effectively than As III • As III can be converted to As V with strong oxidants

  40. SUMMARY • Most conventional treatment processes have capability to reduce arsenic to less than 10 ug/L, many to to 5 ug/L or less.

  41. Tom Sorg USEPA Cincinnati, OH 45268 513-569-7370 sorg.thomas@epa.gov

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