Intro to Iron and Manganese Control for Small Groundwater Systems Reid Campbell, PE, AECOM November 17, 2015 NC AWWA-WEA

Iron and Manganese Introduction Sources Regulations Current Best Practices for Control for Groundwater WTPs New Source; Sequestration; or Removal Summary

INTRODUCTION

Iron, FE, ferric what does it look like? November 17, 2015NC AWWA-WEAPage 4

INTRODUCTION Manganese, Mn, what does it like? November 17, 2015NC AWWA-WEAPage 5

SOURCES November 17, 2015NC AWWA-WEAPage 6 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.

SOURCES November 17, 2015NC AWWA-WEAPage 7 Beneath the ground: –Environment is lacking in oxygen; –Low pH conditions; –Iron (Fe) and manganese (Mn) are typically in the divalent (2+) soluble forms.

SOURCES November 17, 2015NC AWWA-WEAPage 8 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)

SOURCES November 17, 2015NC AWWA-WEAPage 9 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

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. Page 11 November 17, 2015 NC AWWA-WEA

REGULATIONS November 17, 2015NC AWWA-WEAPage 12 NC Public Water Supply Section:

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; November 17, 2015NC AWWA-WEAPage 14

PHOSPHATES November 17, 2015NC AWWA-WEAPage 15 Orthophosphate –Contains one PO 4 unit Condensed (poly) phosphate –Contains several PO 4 units “chained” together P P P P 0

PHOSPHATES November 17, 2015NC AWWA-WEAPage 16 Low Fe/Mn 0.1mg/L/0.02mg/ L High Fe/Mn 2.0mg/L/0.3mg/L Corrosive water Scale forming water SMCL 0.3 mg/L Fe 0.05 mg/l Mn Orthophosphates Blended Phosphates Polyphosphates

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. November 17, 2015NC AWWA-WEAPage 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. November 17, 2015NC AWWA-WEAPage 18

REMOVAL Common approaches: Oxidation filters; Ion exchange; Lime-soda ash softening; or Biological treatment. November 17, 2015NC AWWA-WEAPage 19

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, 2015NC AWWA-WEAPage 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. November 17, 2015NC AWWA-WEAPage 21

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. November 17, 2015NC AWWA-WEAPage 22

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. November 17, 2015NC AWWA-WEAPage 23

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. November 17, 2015NC AWWA-WEAPage 24

FILTRATION Chemical Addition: –Potassium Permanganate (KMnO 4 ) Starting dose:1 mg/l KMnO 4 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. November 17, 2015NC AWWA-WEAPage 25

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. November 17, 2015NC AWWA-WEAPage 26

FILTRATION - BACKWASH November 17, 2015NC AWWA-WEAPage 27 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.

INFORMATION SOURCES Iron and Manganese Removal Handbook –Elmer O. Sommerfeld –AWWA, 1999 November 17, 2015 NC AWWA-WEAPage 28

INFORMATION SOURCES Tech Brief: Iron and Manganese Removal –National Drinking Water Clearinghouse Fact Sheet – WFSOM42.pdf November 17, 2015 NC AWWA-WEAPage 29

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-WEAPage 31

NC AWWA-WEA Reid Campbell, PE | P Questions or Comments

FILTRATION Filter Operations: November 17, 2015NC AWWA-WEAPage AWWA Journal: New Filtration Process Improves Iron and Manganese Removal, by David Manz

Well / Treatment Decision Tree November 17, 2015NC AWWA-WEAPage 34 Choose new well lot (Rules Governing Public Water Systems NC 15A 18C) How much water is needed? Drill Well Test Production and Water Quality Is Yield Adequate ? No? Yes?

Well Treatment Decision Tree November 17, 2015 NC AWWA-WEAPage 35 No? Yes? No? Design Oxidation Treatment No?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 November 17, 2015 NC AWWA-WEA Page 36 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

Design Summary November 17, 2015 NC AWWA-WEAPage 37 Design ParameterSite #1Site #2Notes Design Flow Rate, gpm48120Average annual well production No. of Filters24Parallel operation Normal Flow Rate / filter, gpm2430Well production only Design + Recycle Flow Rate, gpm48132 Design Flow with recycled contribution Design + Recycle Flow Rate per filter, gpm2444Normal operation mode Diameter of Bed, inches3036 Depth of Bed, inches3230 Bed Volume / filter, cu ft Area of Each Filter, sq ft Filter Rate, gpm/sq ft Normal operation mode

Design Summary November 17, 2015 NC AWWA-WEAPage 38 Design ParameterSite #1Site #2Notes Filter Rate during BW Event, gpm/sq ftNA6.23During a BW event. Backwash Source WaterFinished Backwash Rate, gpm sq ft2010 Backwash Flow/filter, gpm9871 Backwash Time, min122.0 Backwash Vol./filter, gal1, Air Assist Flow Rate, cfm/sq ftNA5.0 Air Assist Time, minNA1.0 Backwash Design Frequency, gal35,00043,000Per Vessel Backwash Design Frequency, BV360325Per Vessel Backwash Design Frequency, hrs24 Per Vessel

Design Summary November 17, 2015 NC AWWA-WEAPage 39 Design ParameterSite #1Site #2Notes Backwash Operational Frequency, gal 25,000 – 38,000 31, ,000Per Vessel BW Filter Tank Drain Time, hr86 Backwash Settling Time, hr3NA BW Holding Tank Volume, gal3, Recycle Efficiency, % Design Recycled Gal / Filtered Gal Recycle Efficiency, % Operational Recycle Gal / Filtered Gal Recycle Pumping Rate, GPM4.810 Duty Point on pump curve, controlled with throttling valve Sludge Discharge Frequency/yr40.66 Sludge State of Matterliquidsolid Date Filters Placed into Service3/19/101/3/11 Filter Cost$87,188$124,010 Filters only