Technologies for Arsenic Removal Tom Sorg . S. Environmental Protection Agenc
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Technologies for
Arsenic Removal
Tom SorgU. S. Environmental Protection Agency
Two primary valence states
• As (III)
• As (V)
Arsenic Chemistry
H3AsO30
H2AsO3-1
HAsO3-2
Arsenic III
H3AsO40
H2AsO4-1
HAsO4-2
AsO4-3
Arsenic V
Why is arsenic form important?
Final Answer!
As V more effectively removed
by
ALL technologies
Treatment Process Percent Removal As III As VIron Coag/Filt - pH 7 55 97
Alum Coag/Filt - pH 7 18 95
Example!
Ion exchange treatment
As III - 0 percent removal
As V - 98+ percent removal
Example!
Arsenic Occurrence
Surface waters predominantly As(V)
Ground waters generally As(III), but not always
Arsenic Speciation Method
On site anion exchange separation
AsV
As III, As V
As III
As V retained on resin column
As III passes through column
Arsenic Speciation - Anion separation of AsIII/AsV
Good News!
As III easily oxidized to As V
by
several oxidants
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
As III Oxidation Study
Arsenic Removal Processes
•Precipitative processes•Adsorption processes•Ion Exchange process•Iron Removal processes•Membrane processes•POU/POE devices
Emerging processes
Iron coagulation with microfiltration
Iron based adsorption media
Arsenic Removal Processes
Precipitative Processes
Process Removal
Coagulation/ 95 %Filtration Lime softening 85+ %
Adsorption Processes
Processes Removal
Activated Alumina 90+ %
Iron Media 90+ %
Ion Exchange
95 + % removal
Iron Removal ProcessesProcess Removal
Oxidation/filtration 80+ % Manganese greensand 80+ %
(Dependent on amount of Fe)
Membrane Processes
Process Removal
Reverse osmosis (RO) 90+ %Nanofiltration (NF) 65-90 %Ultrafiltration (UF) 35-75 %
Large Systems Using Surface Waters
•Coagulation/filtration
•Direct filtration
•Lime softening
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
Arsenic Removal Processes
Small Systems Using Surface Waters
•Coagulation/filtration package plants
•Iron Removal processes - oxidation/filtration
•Lime softening package plants
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)
Arsenic Removal Processes
Very Small Community Option•Point-of-use systems -RO, AA
•Point-of-entry systems -RO, Ion Exchange
Arsenic Removal Processes
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
AA System - Source Water Quality (Avg)
Analysis - ug/L CS (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
A
BB
A
Activated Alumina System - New Hampshire
Roughing filter
Polishing filter
Non regenerationsystem
Activated Alumina System, 20 gpm - NH
Week
0 5 10 15 20 25 30 35 40 45 50
Ars
enic
con
cent
ratio
n -
ug/L
0
10
20
30
40
50
60
70
80
Influent water After 1st AA tank After 2nd AA tank
System effluent
Influent water: pH 8.2, alk 58 mg/L (CaCO3), Fe <0.03 mg/L
Activated Alumina System, NH
IE System - Source Water Quality (Avg)
Analysis - ug/L MMA (45)Total As 57 Particulate As <1 Soluble As 57 As III <1 As V 57 (100%)pH - Units 8.3 Hardness – mg/L 38Sulfate – mg/L 45 Alkalinity - mg/L 64
A
B
Ion Exchange System, ME
Oxidizingfilter media
KMnO4
regenerationMixed bed resin
Ion Exchange System with Oxidizing Filter, ME
2 gpm
Week
0 5 10 15 20 25 30 35 40 45 50
Ars
enic
con
cent
ratio
n -
ug/L
5
10
15
20
25
30
35
40
45
50
55
60
65
70
Influent water: pH 8.2, alk 63 mg/L (CaCO3), Fe 0.1 mg/LRaw water sulfate - 45 mg/LTreated water sulfate - <5 mg/L
Influent Water
Effluent Water
Ion Exchange System, ME
Iron Media System, MISource Water Quality
Parameter Concentration - mg/LArsenic 0.025 - 0.041 As III 85 % As V 15 %Calcium 80 - 90Magnesium 34 - 35Iron 1.06 - 1.35Manganese 0.02 - 0.03Sulfate 21 - 30Silica 19 - 20pH 7.1 - 7.2
Distribution system
Tank 1B Tank 2B Tank 3B
Tank 1A Tank 2A Tank 3A
Softener
Well
Acid
Cl2
Iron Media System, MI
Iron Media System, MI
Date
2/22/99
3/4/99
3/26/99
4/9/99
4/29/99
5/5/99
6/9/99
7/8/99
7/26/99
8/4/99
9/7/99
10/7/99
11/3/99
11/18/99
12/7/99
12/9/99
3/7/00
Ars
enic
con
cent
ratio
n -
ug/L
0
5
10
15
20
25
30
35
40
45
50
Well Water
Treated Water
Iron Media System, MI
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
SUMMARY
•Treatment processes remove As V more effectively than As III
•As III can be converted to As V with strong oxidants
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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