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U. S. Environmental Protection Agency
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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As V more effectively removed
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 Alum Coag/Filt - pH
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Example! Ion exchange treatment As III - 0 percent removal
As V 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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As III easily oxidized to As V
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 Free Chlorine Chloramine Ozone Chlorine Dioxide UV Radiation Potassium Permanganate 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/ % Filtration Lime softening %
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Adsorption Processes Processes Removal Activated Alumina 90+ %
Iron Media %
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Ion Exchange 95 + % removal
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Iron Removal Processes
Process Removal Oxidation/filtration 80+ % Manganese greensand % (Dependent on amount of Fe)
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Membrane Processes Process Removal Reverse osmosis (RO) 90+ %
Nanofiltration (NF) % Ultrafiltration (UF) %
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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 Systems Lime Softening System Iron Removal Systems Anion Exchange Systems Activated Alumina Systems
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AA System - Source Water Quality (Avg)
Analysis - ug/L CS (30) Total As Particulate As Soluble As As III <1 As V (100%) pH - Units Hardness – mg/L Sulfate – mg/L Alkalinity - mg/L
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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 Particulate As <1 Soluble As As III <1 As V (100%) pH - Units Hardness – mg/L Sulfate – mg/L Alkalinity - mg/L
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Ion Exchange System, ME A B Mixed bed resin 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 As III % As V % Calcium Magnesium Iron Manganese Sulfate Silica pH
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Iron Media System, MI Distribution system 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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As V is dominant in oxygenated waters
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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Treatment processes remove As V more effectively than As III
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
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