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