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.

Tom SorgUSEPA

Cincinnati, OH 45268

513-569-7370

sorg.thomas@epa.gov