Intro to Iron and Manganese Control
for Small Groundwater Systems
Reid Campbell, PE, AECOM
NC AWWA-WEA
November 17, 2015
Iron and Manganese
•
•
•
•
Introduction
Sources
Regulations
Current Best Practices for Control for Groundwater WTPs
• New Source;
• Sequestration; or
• Removal
• Summary
INTRODUCTION
INTRODUCTION
• Iron, FE, ferric what does it look like?
NC AWWA-WEA
November 17, 2015
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INTRODUCTION
• Manganese, Mn, what does it like?
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November 17, 2015
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SOURCES
• Iron and manganese comprise
about 5% and 0.1% of the
Earth’s crust, respectively.
• Widely distributed in all
geographic areas.
• Found particularly in:
– Shale;
– Sandstones, and
– Alluvial deposits.
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November 17, 2015
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SOURCES
• Beneath the ground:
– Environment is lacking in oxygen;
– Low pH conditions;
– Iron (Fe) and manganese (Mn)
are typically in the divalent (2+)
soluble forms.
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November 17, 2015
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SOURCES
What does this mean?
In groundwater, iron (Fe2+)
and manganese (Mn2+) are…
• In solution
• Colorless until oxidized by
– Air
– Chemical oxidant (like chlorine,
or potassium permanganate)
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November 17, 2015
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SOURCES
• Iron-Reducing Bacteria (IRB)
– Form slimes that bioaccumulate FE and Mn
– Foul bedrock fractures, pumps, plumbing, & filters
– Often cohabiting with Sulfate-Reducing Bacteria (SRB)
• Taste and Odor;
• Corrosion;
• Reacts with iron to make black sulfide deposits.
NC AWWA-WEA
November 17, 2015
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REGULATIONS
REGULATIONS
• The United States Environmental Protection Agency (EPA)
indicates:
Secondary Contaminants are not health threatening, but
that these contaminants can cause aesthetic issues in
drinking water: cloudy or colored, taste or odor. In turn,
this could discourage people to drink water that is
actually safe.
http://water.epa.gov/drink/contaminants/secondarystandards.cfm
NC AWWA-WEA
November 17, 2015
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REGULATIONS
NC Public Water Supply Section:
NC AWWA-WEA
November 17, 2015
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Current Best Practices for Control for
Groundwater WTPs
- New source;
- Sequestration; or
- Removal.
SEQUESTRATION
• Use of Phosphates:
– Blends of polyphosphates and orthophosphates;
• Polyphosphates do the Fe / Mn sequestration;
• Orthophosphates are for addressing Pb / Cu issues;
– Generally acceptable practice if Fe + Mn < 1.0 mg/l, but…
• Better for Fe, than for Mn;
– Do not remove the Fe / Mn, just help keep it dissolved;
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November 17, 2015
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PHOSPHATES
0
• Orthophosphate
– Contains one PO4 unit
0
P
0
0
0
0
P
0
P
0
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November 17, 2015
Page 15
0
0
• Condensed (poly) phosphate
0
– Contains several PO4 units “chained” together
P
0
0
PHOSPHATES
High
Fe/Mn
Polyphosphates
2.0mg/L/0.3mg/L
SMCL
0.3 mg/L Fe
0.05 mg/l Mn
Low
Fe/Mn
Blended
Phosphates
Orthophosphates
0.1mg/L/0.02mg/L
Corrosive
water
NC AWWA-WEA
November 17, 2015
Scale forming
water
Page 16
SEQUESTRATION
• Use of Phosphates:
– Temporary measure:
• Stronger solution in the day tank is better;
• Breakdown / Conversion from poly to ortho; and
• Short shelf life in the distribution system (days).
– Make changes slowly / incrementally; and
– Several different products on the market, so talk
with your vendor.
NC AWWA-WEA
November 17, 2015
Page 17
REMOVAL
• Filter Operations:
– General Rule: Focus on the manganese removal, if you have
knocked the manganese below 0.05 mg/l, you will likely have
dropped the iron below 0.3 mg/l.
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November 17, 2015
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REMOVAL
Common approaches:
• Oxidation filters;
• Ion exchange;
• Lime-soda ash softening; or
• Biological treatment.
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November 17, 2015
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REMOVAL
• Ion Exchange (Softener):
– Useful for low levels of Fe / Mn on
a case by case basis;
– For every 10 mg/L of hardness
and iron and manganese
removed, approximately 5 mg/L of
sodium will be added to the
treated water;
www.mrwpca.org
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November 17, 2015
Page 20
REMOVAL
• Ion Exchange (Softener):
– Brine waste discharge;
– Avoid if:
• Fe / Mn is already oxidized;
• Positive IRB / SRB test result; or
• Organics are an issue.
www.mrwpca.org
NC AWWA-WEA
November 17, 2015
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FILTRATION - OXIDATION
Depending upon pH,
temperature, detention time,
and organic interference,
oxidized iron forms iron
hydroxides which group to
make large heavy flow
particles which can then be
removed.
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November 17, 2015
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FILTRATION - OXIDATION
• Aeration:
– Forced-Air Cascading Tower;
– Cascading Steps; or
– Porous Tube.
– Also removes hydrogen sulfide
– With aeration alone, the rate of
Mn oxidation is very slow if the
pH is < 9.5.
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November 17, 2015
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FILTRATION
• Chemical Addition:
– Chlorination
• Start with 0.64 mg/l per mg/l of iron;
• Most effective with Fe when 6.5 < pH < 7.5; and
• Slow with Mn when pH < 9.5.
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November 17, 2015
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FILTRATION
• Chemical Addition:
– Potassium Permanganate (KMnO4)
• Starting dose:1 mg/l KMnO4 per mg/l of iron and 2 mg/l of manganese;
• pH should be greater than 7, but over 7.5 is better for both Fe and Mn
(especially with organics); and
• With high Mn, pH > 8 is faster.
– “The rate of Mn oxidation induced by KMnO4 is influenced by pH
and temperature.
• Mn oxidation at pH values between 5.5 and 9.0 generally occurs within
10 seconds at a water temperature of 25 C (95 F).
• At 2 C (36 F), oxidation could take 2 minutes or more…”
Iron and Manganese Removal Handbook, Sommerfeld.
NC AWWA-WEA
November 17, 2015
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FILTRATION
Filters:
– Either open (gravity) or closed
(pressure) vessels;
– Multi-layer media;
– Collection manifold at the
bottom;
– Require regular backwash
(water and air); and
– Disposal of the backwash
waste.
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November 17, 2015
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FILTRATION - BACKWASH
• Most filters require routine backwashing to maintain their
ability to remove contaminants.
• The State can be reluctant
to issue new NPDES
permits for the discharge of
water treatment plant filter
backwash waste flows to
local streams.
• The waste stream may be
recyclable back to the head
of the plant at 10% of flows.
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November 17, 2015
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INFORMATION SOURCES
• Iron and Manganese Removal Handbook
– Elmer O. Sommerfeld
– AWWA, 1999
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November 17, 2015
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INFORMATION SOURCES
• Tech Brief: Iron and Manganese Removal
– National Drinking Water Clearinghouse Fact Sheet
– http://www.nesc.wvu.edu/pdf/dw/publications/ontap/2009_tb/iron_D
WFSOM42.pdf
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November 17, 2015
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CONCLUSIONS
CONCLUSIONS
• Iron (Fe) and manganese (Mn) are typically in the divalent
(2+) dissolved soluble forms;
• Polyphosphates are for Fe / Mn sequestration;
– Generally acceptable practice if Fe + Mn < 1.0 mg/l
• Ion Exchange;
– Useful for small scale and low concentrations of Fe / Mn, on a case
by case basis;
• Filtration
– Depending upon pH, temperature, detention time, and organic
interference, oxidized iron forms iron hydroxides which group to
make large heavy flow particles which are removed by media filter.
NC AWWA-WEA
November 17, 2015
Page 31
Questions or
Comments
Reid Campbell, PE
919.854.7749 | Reid.Campbell@AECOM.com
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P
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NC AWWA-WEA
FILTRATION
• Filter Operations:
- 2011 AWWA Journal: New Filtration Process Improves Iron and Manganese Removal, by David Manz
NC AWWA-WEA
November 17, 2015
Page 33
Well / Treatment Decision Tree
How much
water is
needed?
Choose new well lot
(Rules Governing
Public Water Systems
NC 15A 18C)
Yes?
Test Production and
Water Quality
Drill Well
Is Yield
Adequate
?
No?
NC AWWA-WEA
November 17, 2015
Page 34
Well Treatment Decision Tree
No?
No?
Is WQ
Adequate
?
Yes?
Pursue
permitting the
well
NC AWWA-WEA
Yes?
Is redrilling an
option?
Insolubles
< SMCL?
Yes?
No?
Sequester
Fe/Mn with
PO4
November 17, 2015
Design
Oxidation
Treatment
Page 35
Drill Well
Well Treatment Decision Tree
No?
Yes?
Is BW
recycling
required
or
desired?
Design
Oxidation
Treatment
Pursue
NPDES
Permit
Yes?
Design
Recycling
System
Pursue Pump
& Haul
Approval
NC AWWA-WEA
Pursue
permitting of
well
November 17, 2015
Page 36
Design Summary
Design Parameter
Site #1
Site #2
Design Flow Rate, gpm
No. of Filters
Normal Flow Rate / filter, gpm
48
2
24
120
4
30
Design + Recycle Flow Rate, gpm
Design + Recycle Flow Rate per
filter, gpm
Diameter of Bed, inches
Depth of Bed, inches
Bed Volume / filter, cu ft
Area of Each Filter, sq ft
Filter Rate, gpm/sq ft
48
132
24
30
32
13
4.91
4.9
44
36
30
17.7
7.06
4.24
NC AWWA-WEA
November 17, 2015
Page 37
Notes
Average annual well production
Parallel operation
Well production only
Design Flow with recycled
contribution
Normal operation mode
Normal operation mode
Design Summary
Design Parameter
Filter Rate during BW Event,
gpm/sq ft
Backwash Source Water
Backwash Rate, gpm sq ft
Backwash Flow/filter, gpm
Backwash Time, min
Backwash Vol./filter, gal
Air Assist Flow Rate, cfm/sq ft
Air Assist Time, min
Backwash Design Frequency, gal
Backwash Design Frequency, BV
Backwash Design Frequency, hrs
NC AWWA-WEA
November 17, 2015
Site #1
Site #2
NA
Finished
20
98
12
1,176
NA
NA
35,000
360
24
Page 38
6.23
Finished
10
71
2.0
330
5.0
1.0
43,000
325
24
Notes
During a BW event.
Per Vessel
Per Vessel
Per Vessel
Design Summary
Design Parameter
Backwash Operational
Frequency, gal
BW Filter Tank Drain Time, hr
Backwash Settling Time, hr
BW Holding Tank Volume, gal
Site #1
25,000 –
38,000
8
3
3,000
Site #2
31,00035,000
6
NA
575
Recycle Efficiency, %
3.4
0.77
Recycle Efficiency, %
2.8
0.67
Recycle Pumping Rate, GPM
Sludge Discharge Frequency/yr
Sludge State of Matter
Date Filters Placed into Service
Filter Cost
NC AWWA-WEA
November 17, 2015
4.8
4
liquid
3/19/10
$87,188
Notes
Per Vessel
Design Recycled Gal /
Filtered Gal
Operational Recycle Gal /
Filtered Gal
Duty Point on pump curve,
controlled with throttling valve
10
0.66
solid
1/3/11
$124,010 Filters only
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