Intro to Iron and Manganese Control for Small Groundwater Systems Reid Campbell, PE, AECOM November...

Intro to Iron and Manganese Control for Small Groundwater Systems

Reid Campbell, PE, AECOM

November 17, 2015NC AWWA-WEA

Iron and Manganese

• Introduction• Sources• Regulations • Current Best Practices for Control for Groundwater WTPs

• New Source;• Sequestration; or• Removal

• Summary

INTRODUCTION

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INTRODUCTION

• Iron, FE, ferric what does it look like?

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INTRODUCTION

• Manganese, Mn, what does it like?

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SOURCES

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• 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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SOURCES

November 17, 2015

• 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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SOURCES

November 17, 2015

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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SOURCES

November 17, 2015

• 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.

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


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REGULATIONS

November 17, 2015

NC Public Water Supply Section:

Current Best Practices for Control for Groundwater WTPs

- New source; - Sequestration; or- Removal.

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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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PHOSPHATES

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• Orthophosphate

– Contains one PO4 unit

• Condensed (poly) phosphate

– Contains several PO4 units “chained” together

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PHOSPHATES

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LowFe/Mn0.1mg/L/0.02mg/L

HighFe/Mn2.0mg/L/0.3mg/L

Corrosivewater

Scale formingwater

SMCL0.3 mg/L Fe0.05 mg/l Mn

Orthophosphates

BlendedPhosphates

Polyphosphates

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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.

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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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REMOVAL

Common approaches:

• Oxidation filters;

• Ion exchange;

• Lime-soda ash softening; or

• Biological treatment.

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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;

November 17, 2015

www.mrwpca.org

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REMOVAL

• Ion Exchange (Softener):

– Brine waste discharge;

– Avoid if:

• Fe / Mn is already oxidized;

• Positive IRB / SRB test result; or

• Organics are an issue.

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www.mrwpca.org

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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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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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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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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.

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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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FILTRATION - BACKWASH

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• 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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INFORMATION SOURCES

• Iron and Manganese Removal Handbook– Elmer O. Sommerfeld– AWWA, 1999

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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_DWFSOM42.pdf

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CONCLUSIONS

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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.

November 17, 2015

NC AWWA-WEA

Reid Campbell, PE 919.854.7749 | [email protected]

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FILTRATION

• Filter Operations:

November 17, 2015

- 2011 AWWA Journal: New Filtration Process Improves Iron and Manganese Removal, by David Manz

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Well / Treatment Decision Tree

November 17, 2015

Choose new well lot (Rules Governing

Public Water Systems NC 15A 18C)

How much water is needed?

Drill WellTest Production and

Water Quality

Is Yield Adequate

?

No?

Yes?

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Well Treatment Decision Tree

November 17, 2015

No? Yes?No?

Design Oxidation Treatment

No?Yes?Yes?

Sequester Fe/Mn with

PO4

Pursue permitting the

well

Drill Well

Is WQ Adequate

?

Insolubles < SMCL?

Is re-drilling an option?

Well Treatment Decision Tree


Is BW recycling required

or desired?

No?Design

Oxidation Treatment

Yes?

Pursue permitting of

well

Pursue Pump & Haul

Approval

Pursue NPDES Permit

Yes?

Design Recycling System

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Design Summary

November 17, 2015

Design Parameter Site #1 Site #2 Notes

Design Flow Rate, gpm 48 120 Average annual well productionNo. of Filters 2 4 Parallel operationNormal Flow Rate / filter, gpm 24 30 Well production only

Design + Recycle Flow Rate, gpm 48 132Design Flow with recycled contribution

Design + Recycle Flow Rate per filter, gpm 24 44 Normal operation mode

Diameter of Bed, inches 30 36 Depth of Bed, inches 32 30 Bed Volume / filter, cu ft 13 17.7 Area of Each Filter, sq ft 4.91 7.06 Filter Rate, gpm/sq ft 4.9 4.24 Normal operation mode

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Design Summary

November 17, 2015

Design Parameter Site #1 Site #2 NotesFilter Rate during BW Event,

gpm/sq ft NA 6.23 During a BW event.Backwash Source Water Finished Finished Backwash Rate, gpm sq ft 20 10 Backwash Flow/filter, gpm 98 71 Backwash Time, min 12 2.0 Backwash Vol./filter, gal 1,176 330 Air Assist Flow Rate, cfm/sq ft NA 5.0 Air Assist Time, min NA 1.0 Backwash Design Frequency, gal 35,000 43,000 Per VesselBackwash Design Frequency, BV 360 325 Per VesselBackwash Design Frequency, hrs 24 24 Per Vessel

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Design Summary

November 17, 2015

Design Parameter Site #1 Site #2 NotesBackwash Operational

Frequency, gal25,000 – 38,000

31,000-35,000 Per Vessel

BW Filter Tank Drain Time, hr 8 6 Backwash Settling Time, hr 3 NA BW Holding Tank Volume, gal 3,000 575

Recycle Efficiency, % 3.4 0.77Design Recycled Gal / Filtered Gal

Recycle Efficiency, % 2.8 0.67Operational Recycle Gal / Filtered Gal

Recycle Pumping Rate, GPM 4.8 10Duty Point on pump curve, controlled with throttling valve

Sludge Discharge Frequency/yr 4 0.66 Sludge State of Matter liquid solid Date Filters Placed into Service 3/19/10 1/3/11 Filter Cost $87,188 $124,010 Filters only

Intro to Iron and Manganese Control for Small Groundwater Systems Reid Campbell, PE, AECOM November...

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