Technologies

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

• Two primary valence states
• As (III)
• As (V)

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Arsenic III
H3AsO30 H2AsO3-1 HAsO3-2
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Arsenic V
H3AsO40 H2AsO4-1 HAsO4-2 AsO4-3
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Why is arsenic form important?
Final Answer! As V more effectively
removed by ALL technologies
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Example!
Treatment Process Percent Removal
As III
As V Iron Coag/Filt - pH 7 55
97 Alum Coag/Filt - pH 7 18
95
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Example!
Ion exchange treatment As III - 0 percent
removal As V - 98 percent removal
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Arsenic Occurrence
Surface waters predominantly As(V) Ground waters
generally As(III), but not always
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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
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Arsenic Speciation - Anion separation of AsIII/AsV
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Good News!
As III easily oxidized to As V by several
oxidants
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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

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Arsenic Removal Processes

• Precipitative processes
• Adsorption processes
• Ion Exchange process
• Iron Removal processes
• Membrane processes
• POU/POE devices

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Arsenic Removal Processes

• Emerging processes
• Iron coagulation with microfiltration
• Iron based adsorption media

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Precipitative Processes
Process Removal Coagulation/
95 Filtration Lime softening 85
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Adsorption Processes
Processes Removal Activated
Alumina 90 Iron Media 90
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Ion Exchange
95 removal
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Iron Removal Processes
Process
Removal Oxidation/filtration 80 Manganese
greensand 80 (Dependent on amount of Fe)
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Membrane Processes
Process
Removal Reverse osmosis (RO) 90
Nanofiltration (NF) 65-90 Ultrafiltration
(UF) 35-75
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Arsenic Removal Processes

• Large Systems Using Surface Waters
• Coagulation/filtration
• Direct filtration
• Lime softening

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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

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Arsenic Removal Processes

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

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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)

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Arsenic Removal Processes

• Very Small Community Option
• Point-of-use systems
• -RO, AA
• Point-of-entry systems
• -RO, Ion Exchange

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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
  

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AA System - Source Water Quality (Avg)
Analysis - ug/L CS (30) Total As
63 Particulate As
2 Soluble As
66 As III
lt1 As V 66 (100) pH -
Units 8.4
Hardness mg/L 37
Sulfate mg/L 14
Alkalinity - mg/L 57
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Activated Alumina System - New Hampshire
Non regeneration system
A
A
Roughing filter Polishing filter
B
B
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Activated Alumina System, 20 gpm - NH
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Activated Alumina System, NH
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IE System - Source Water Quality (Avg)
Analysis - ug/L MMA (45) Total As
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Particulate As lt1
Soluble As 57
As III lt1 As V
57 (100) pH - Units
8.3 Hardness mg/L
38 Sulfate mg/L 45
Alkalinity - mg/L 64
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Ion Exchange System, ME
Oxidizing filter media KMnO4 regeneration
A
B
Mixed bed resin
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Ion Exchange System with Oxidizing Filter, ME
2 gpm
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Ion Exchange System, ME
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Iron Media System, MI Source Water Quality
Parameter Concentration - 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
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Iron Media System, MI
Well
Tank 1A
Tank 2A
Tank 3A
Cl2
Acid
Tank 1B
Tank 2B
Tank 3B
Softener
Distribution system
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Iron Media System, MI
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Iron Media System, MI
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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

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SUMMARY

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

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SUMMARY

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

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Tom Sorg USEPA Cincinnati, OH 45268 513-569-7370
sorg.thomas_at_epa.gov