Iron and Manganese Removal Processes

Presentation Agenda• Arsenic Background: chemistry

and treatment options• Treatment selection

considerations • Treatment options

– Iron removal• Case studies• Conclusions

Arsenic Chemistry• Arsenic has two primary valence states:

• Arsenic Occurrence by valence state– Surface waters - predominately As (V)– Ground waters – usually found as As (III),

however, concentrations of As (V) or a combination of As (III) and As (V) can be found

As (III) As +3 Arsenite

As (V) As +5 Arsenate

Iron-based Arsenic Removal Processes

• Adsorptive properties of iron mineral toward arsenic are well known

• That knowledge is the basis for many arsenic treatment processes– Coagulation with iron coagulant– Iron-based adsorption media– Iron removal processes

Arsenic Removal by IronAs(III) vs As(V)

As(III) is removed during iron removal and other iron-based processes, but just not as well as As(V)

As (III) OxidationAs (III) OxidationEffective!

Free ChlorinePotassium PermanganateOzoneSolid Oxidizing Media (MnO2 solids)

IneffectiveChloramineChlorine Dioxide UV Radiation + SulfideOxygen

Arsenic Treatment Issues• Treatment complexity/cost• Pre- and Post-treatment needs• Residuals –Disposal Issues

– Ion exchange & RO produce liquid wastes– Adsorbent media produce wasted solids– Coagulation/filtration and iron removal

processes produce solids• Filter backwash waste• Sediment in contactor (pass TCLP test)

Arsenic Treatment Simplified Process Selection Guide

Iron - mg/L0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Ars

enic

- ug

/L

0

5

10

15

20

25

30

35

40

45

50

As MCL

Fe -

SMC

L

AIron Removal Process

(Optimized for Maximium As Removal)

BModified Iron Removal Process

C

Media AdsorptionIron Coag/FiltIon ExchangeIron Removal(M)RO / NF

20 - 1 Fe/As ra

tio

or above

Removal of 1 mg/L of iron

achieves

removal of 50 ug/L arsenic(0ptimized conditions and As[V])

Arsenic Removal by Iron Removal Processes

Arsenic Removal During Iron Removal Considerations

Iron in water (>20/1 Fe/As ratio)? • Form of arsenic, III or V?

Oxidation:– Type of oxidant: oxygen, chlorine, KMnO4…?– Point of application?

• Contact time?– Iron and As oxidation– Arsenic adsorption

• How can arsenic removal be predicted?• Ways to improve arsenic removal during iron

removal?

Iron (and Mn) RemovalBasics

Filtrationparticle removal

Oxidation Contact Basin

AerationCl2,

KMnO4, other

Oxidation, Particle Development

15 – 30 minutes

Fe(OH)3 (S)MnO2 (S)

Fe IIMn II

Fe IIIMn IV

Iron and Arsenic (and Mn) Removal

AerationCl2,

KMnO4,other

Fe IIAs III

Oxidation

Fe IIIAs V

Note: Aeration will not oxidize As III to As V

Iron and Arsenic (and Mn) Removal

Contact Basin

Oxidation, particle

development

Fe(III)/As particles+

arsenic

Iron and Arsenic (and Mn) Removal

FiltrationFe III/ As Particle Removal

Oxidant Selection

• Depends on As, Fe (and Mn)• Aeration

– Will not oxidize Mn II and As III (-) – May need contact basin (-)– Iron particles have less surface area (-)– Longer filter run lengths (+)

• Strong oxidants (chlorine, permanganate, etc)– Address Mn and As oxidation (+)– More particle surface area (+)– Probably no contactor needed (+)– Difficult to feed (-)– Shorter filter run lengths (-)

Assessment ToolJar Test

OxidationOxidation-- Point of ApplicationPoint of ApplicationCase Study Case Study -- MichiganMichigan

Parameter ConcentrationArsenic – ug/L 19 - 24

As III 95 %As V 5 %

Calcium – mg/L 74 - 84Magnesium – mg/L 30 - 33Iron – mg/L 0.5 - 0.6Manganese –mg/L 0.02Sulfate – mg/L 50 - 60Silica – mg/L 12 - 13pH - units 7.1 - 7.3

OxidationOxidation-- Point of ApplicationPoint of ApplicationCase Study Case Study -- MichiganMichigan

20 min CT

WellsWells

Aeration towerAeration towerPressure filtersPressure filters

Cl2

50 % removal

As = 19-24 ug/LFe = 0.5 -0.6 mg/L

Oxidation- Point of ApplicationCase Study - Michigan

20 min CT

Wells

Aeration towerPressure filtersCl2

50 % removal

As = 19-24 ug/LFe = 0.5 -0.6 mg/L

Oxidation- Point of ApplicationCase Study - Michigan

20 min CT

Wells

Aeration towerPressure filters

Cl2

75 % removalAs = 19-24 ug/LFe = 0.5 -0.6 mg/L

Oxidant Selection• Depends on As, Fe (and Mn)• Aeration

– Will not oxidize Mn II and As III (-) – May need contact basin (-)– Iron particles have less surface area (-)– Longer filter run lengths (+)

• Strong oxidants (chlorine, permanganate, etc)– Address Mn and As oxidation (+)– More particle surface area (+)– Probably no contactor needed (+)– Difficult to feed (-)– Shorter filter run lengths (-)

The Effect of Oxidant on Visual Properties of Iron Particles

pH

7.0 7.5 8.0 8.5 9.0 9.5 10.0

Colo

r, P

tCo

unit

s

0

50

100

150

200

250

300PO2= 0.122 atm

PO2=saturated

0.122 atm PO2+5 mg Cl2/L

ClO2 (2 mg/L)

Fe[III] Linear regression

The effect of oxidant type on colorFetot= 5 mg/L, DIC= 5 mg C/L, 0.122 atm O2, 23oC.

The effect of oxidant type on the color of iron particles collected from filter backwash.

Process ModificationsIncreasing As RemovalIncreasing As Removal

Utility with iron removal in place or willbe in place but can not meet MCL:

•Change point of oxidant addition•Increase iron concentration•Adjust pH•Replace media w/ As adsorption media

Climax, MN Iron Removal System

Climax, MN Iron Removal Process

Date - 2004/2005

Aug Sep Oct Nov Dec Jan Feb Mar

Ars

enic

con

cent

ratio

n - u

g/L

0

5

10

15

20

25

30

35

40

45

50

55

Iron

conc

entra

tion

- mg/

L

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Raw Water ArsenicTreated Water Arsenic Raw Water Iron

2004 2005

MCL

0.8 mg/L Fe added

Climax, MN Iron Removal System

The Effect of Initial Arsenic(V) Concentration on the Capacity of Iron to

Remove Arsenic(Fe(II)init=1 mg/L, DIC=10 mg C/L, pH=8, 24oC)

Initial As, μg/L

0 50 100 150 200 250

μg A

s/m

g Fe

0

20

40

60

80

100

120

140

160

180

200

1 mg Fe/L reduces 150 ug As/L by 115 ug As/L to 35 ug As/L

1 mg Fe/L reduces 35 ug As/L by 23 ug As/L to 12 ug As/L

The Effect of pH, Iron and Free Chlorine on Arsenic Removal

1 mg Fe/L, 100 mg As(V)/L, 5 mg C/L DIC, PO2= 0.122

atm, 24 OC

pH

6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5

Ars

enic r

emov

ed, %

0

20

40

60

80

100

No chlorine1 mg Cl2/L

RegressionFe(III), no chlorine

Effect of Water Quality1 mg Fe/L, 100 ug As(V)/L, 5 mg C/L DIC, pH=8, 24 OC

Phosphate, mg/L

0.0 0.5 1.0 1.5 2.0 2.5 3.0

% A

rsen

ic R

emov

al

0

20

40

60

80

1001 mg/L Chlorine0 mg/L Chlorine

Lidgerwood, NDTwo Wells:

•100 feet deep

•As Raw 135 – 150 ug/L (mostly As III)

•As Finished 35 ug/L

•Fe Raw 1.3 – 1.6 mg/L (9/11:1)

•Superfund site – arsenic for grasshopper control

Lidgerwood, NDExisting Treatment:

•Pre-chlorination

•Aeration

•Oxidation – KMnO4

•Filtration Aid – polymer

•Filtration – Antrasand (2 gpm/ft2)

•Post chlorination and fluoridation

Lidgerwood, ND

Mixing Tank

Detention Tank

Aeration Tower

Well 1

Well 2

Filters

Clearwell

Backwash tank Sludge Tank

KMn04

Filter AidChlorine

Chlorine

Lidgerwood, ND

EPA Demonstration Project:

•Turbidmeters

•Additional polymer feed

•FeCl3 Coagulation (~1 mg/L)

•As Finished 7-8 ug/L

•Cost - $55,740

Lidgerwood, ND

Mixing Tank

Detention Tank

Aeration Tower

Well 1

Well 2

Filters

Clearwell

Backwash tank Sludge Tank

KMn04

Filter Aid (2)Ferric chloride

Chlorine

Chlorine

Sabin, MN

Two Wells:

•As Raw 45 ug/L

•As Finished 40 ug/L (20-25 ug/L

Plant is falling apart!!

Sabin, MNExisting Treatment:

•Chlorination

•Aeration

•Sand filtration

•Fluoridation

Sabin, MNMajor Capital Improvement:

•Population 400

•$1,200,000 Total cost

•$800,000 low interest loan

•$160,000 grant

•EPA Demonstration Project

Conclusions• Iron removal = arsenic removal• Arsenic speciation is important• Oxidant type is important• Point of oxidant application is

important– Arsenic removal impacted – Plant operation impacted

Thank-you

QUESTIONS TO DARREN LYTLE

EPA/ORD