Finding a Solution for Challenging Manganese and TOC Removal

Russell Ford PhD, PE, BCEE

Global Service Leader – Drinking Water and Reuse

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Presentation Overview

• Project Goals and Objectives

• Manganese Removal Options

• TOC Removal Options

• Recommended Solution

• Proof of Concept

• Summary of Pilot Testing Results

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Project Water Quality Goals and Objectives

• To improve manganese removal at Oswestry WTW in order to improve iron compliance and reduce customer contacts for discoloured water in the zones supplied by Oswestry WTW

• To improve bacteriological compliance at the WTW;

• To restore maximum treated water output capacity of 210Ml/day, while maintaining gravity flow through the treatment works;

• To enable the treatment of all raw water, within the specified raw water parameters as stipulated by the Employer;

• To minimise operational manpower, chemicals, electricity consumption and maintenance costs (OPEX)

• Total Project Budget approximate $70,000,000

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Water Quality Goals

TABLE A Final water Manganese Concentration Limits

Samples Manganese Concentration Limit

80%ile < 0.40 µg/l

90%ile < 0.91 µg/l

95%ile < 1.20 µg/l

99%ile < 2.50 µg/l

Max 12.5 µg/l

TABLE B

TOC Concentration Limits at “TOC Compliance Sample Point

Samples Total Organic Carbon Concentration

Average < 1.17 mg/l

70%ile < 1.30 mg/l

80%ile < 1.38 mg/l

95%ile < 1.55 mg/l

99%ile < 1.75 mg/l

Max 2 mg/l

Raw Water Maximum Design Mn Concentration is 463 ug/L

Raw Water Maximum Design TOC Concentration is 6.1 mg/L

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Overview of Manganese and TOC Removal

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Iron or Manganese SMCL’s

• Found in both groundwater and surface water supplies

• Surface Waters

– Dissolved oxygen depleted in reservoirs

– Hypolimnion

• Iron <20 mg/l

• Mn <2 mg/l

• Groundwater

– Carbon dioxide (CO2) works to dissolve iron (Fe) and manganese (Mn)

– FeCO3+ CO2 + H2O -----> Fe(HCO3)2

– MnCO3+ CO2 + H2O ------> Mn(HCO3)2

– Potential solubility of iron is 150 mg/L

– Usually iron <10 mg/L, manganese < 2 mg/L

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Forms of Iron and Manganese

• Reduced iron – ferrous iron (Fe2+)

• Oxidized iron – ferric iron (Fe3+)

• Reduced manganese – Manganous (Mn2+)

• Oxidized manganese – Manganic (Mn3+) or (Mn4+)

• Iron and Manganese can complex with organic compounds

– Typically makes oxidation harder, specifically for Manganese

– Mostly observed in surface water

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Why do we care about iron and manganese?

• No known health effects

• Aesthetic problems can be serious

• When oxidized, precipitation occurs

• Manganese

– Black stains on laundry

– Black stains on fixtures

• Iron

– Red stains on fixtures

– Reaction with tannic acid in tea and coffee

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Iron and Manganese Removal Alternatives

• Oxidation> Precipitation

– Aeration > precipitation >filtration

– Oxidant > precipitation> filtration

• Adsorption

– Ion exchange (zeolite) softening

– Manganese - zeolite (greensand) filtration

– Oxide coated sand filtration

– Pyrolusite media adsorption

• Biological removal

• Membrane filtration

• Lime softening

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Oxidation & Precipitation

Per mg/L of Mn Per mg/L of Fe

Oxygen (from aeration) 0.29 0.14

Ozone 0.67 0.43

Chlorine 1.28 0.63

Potassium permanganate 1.92 0.94

Chlorine Dioxide 2.4 1.2

How Much Chemical is Needed ?

Other Oxidant Demands Include Hydrogen Sulfide & Organic Material

Oxidant (mg/L)

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< 5 min.< 5 min.Chlorine Dioxide

< 7 min.< 5 min.Potassium permanganate

15 min. to 12 hrs. *< 1 hr. *Chlorine

< 5 min.< 5 min.Ozone

80 min. to Days *<10 min. to hrs. *Oxygen (from aeration)

ManganeseIron

How long does it take ?

* pH dependent - oxidation rate quicker at high pH

Oxidant

Oxidation & Precipitation

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Dissolved

manganese

(Mn+2)

Filter

Oxidante.g. O3

KMnO4

ClO2

Settling Basin

Reacts with dissolvedMn to form solid MnO2

Larger MnO2

particles settle out

Smaller MnO2

particles pass throughsettling basin and should

be removed in filters

Finished Water

MANGANESE REMOVAL

OXIDATION / SOLID-LIQUID SEPARATION

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Dissolved

manganese

(Mn+2)

Mn+2

Mn+2

Sticks to negatively

charged surface

Mn+2

MnO2 Coating

(negatively charged)

Chlorine

Mn+2

MnO2

Mn+2

MnO2

MnO2

Mn+2

Mn+2

MnO2

MnO2

MnO2 Coating Grows as Cl2oxidizes Mn+2 on surface

Filter Filter Media

Grain

Chlorine(Cl2)

Finished Water

MANGANESE REMOVAL

Filter Adsorption / Oxidation

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WHAT WAS AND IS DONE TO CHOOSE THE COAGULANT DOSE

Tests and Measurements

– Floc Formation and Size Observations

– Jar Tests

– Floc particle charge

• Zeta Potential or EPM measurements

• Streaming Current Monitor

• Coagulant Charge Analyzer

• Our Method is to base coagulant dose on treated water monitoring of UV and setting coagulant dose to achieve a goal

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COAGULANT DOSES RELATED TO TOC(From Edzwald’s Research and Experience with Water Plants)

Waters of low SUVA (~ 2-2.5 or less)

– NOM has a nature such it is low in humic matter so NOM does not react much with coagulant (low coagulant demand).

• Removals of TOC and UV (254 nm) are poor

– Particles Control and Dosages Can be Low at optimum pH for all coagulants

Waters with SUVA > 2.5

– NOM controls coagulant dosing.

– Coagulant dose depends on TOC and UV (254 nm)

– Removals depend on SUVA and NOM Concentration

• Vary from ~ 30-70 % for TOC and ~ 40-80 % for UV (254 nm)

Selecting Coagulant Dose by J.K. Edzwald

• Alum

– pH 6-7: 0.6 to 0.65 mg Al/mg TOC (6.6 – 7.2 mg alum per mg TOC)

– pH 7-7.5: 1 mg Al/mg TOC (11 mg alum per mg TOC)

– (pH 5-5.5) 0.5 mg as Al/mg TOC (Do not recommend except high TOC waters)

• PACls:

– pH 6-7: 0.4 to 0.6 mg Al/mg TOC

– pH 7-7.5: 0.7 to 1 mg Al/mg TOC

• Ferric Coagulants

– Optimum pH for removing NOM is 5 to low 6s. Need much more Fe even at higher pH

– pH 5 to 6: 1.3-1.8 mg Fe/mg TOC

– pH 6 to 7: 2-3 mg Fe/mg TOC

– pH 7 - 7.5: 3-4 mg as Fe per mg TOC

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Alternatives Analysis

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Clarification Process Evaluation

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Manganese Control Options Evaluated

Technology Considered for Manganese Control

Concerns Regarding Performance Guarantee Impact on Existing Oswestry WTW

2nd Stage Filtration Piloting work is being done by UU, limited data is available. Need to either review pilot testing data or conduct independent testing

Needs to be downstream of RGF’s

Still need to upgrade RGF’s

Chlorine Dioxide One of the most effective oxidants for manganese control. Confident that the plant can reliably be below 20 ug/L under all water quality conditions.

Would be added upstream of coagulation, no impact on hydraulics

Intermediate Ozonation Confident that ozone would sufficiently oxidize the manganese to below 20 ug/L. Would also get an added benefit of TOC reduction

Would require hydraulic improvements because the ozone system needs to be prior to the RGFs

Leave Slow Sand Filters Process is currently working and removing manganese in a biological mode.

SSFs need to be upgraded. Currently a maintenance and reliability issue.

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TOC Control Options EvaluatedTechnology Considered for TOC

Control Concerns Regarding Performance

Guarantee Impact on Existing Oswestry WTW

Enhanced Coagulation Attempting to achieve 60 to 70% removal of TOC with just coagulation will be a challenge. Can most likely guarantee less than 2 mg/L, but not sure if we can routinely be below 1.75 mg/L without more historical water quality data

This will most likely double the sludge production at the plant. We need to verify the loadings of the existing solids handling processes.

Will need to use either soda ash or CO2 to add alkalinity to water for coagulation.

MIEX Limited MIEX testing showed that the TOC levels could be met.

Would be added upstream of coagulation, and will need about 2m of hydraulic head

Ozone/BAC Enhanced coagulation along with Ozone coupled with BAC will reliability get the TOC down below 2 mg/L.

Would require hydraulic improvements because the ozone system needs to be prior to the RGF. New deeper bed filters would need to be designed.

Leave Slow Sand Filters Process is currently working and removing manganese and organics in a biological mode.

SSFs need to be upgraded and provide a maintenance issue for current plant operations.

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Comparison of Proposed Alternatives

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Proof of Concept Testing

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Proof of Concept Mn Bench-Scale Testing

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Proof of Concept TOC Bench-Scale Testing

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Proof of Concept DBP Formation

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Brief Summary of Testing Results

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Raw Water Pilot Testing Temperatures

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Manganese Removal Optimized Runs

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Manganese Optimized Runs in Cold Water

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Pilot Testing TOC Results

Clarifier Compliance Filter 1 Filter 2 Filter 3 Filter 4 Compliance

Average 1.73 <1.17 mg/L 1.18 1.16 1.20 1.18 <1.17 mg/L

70%ile 1.78 N/A 1.20 1.20 1.19 1.19 <1.3 mg/L

80%ile 1.91 N/A 1.25 1.24 1.24 1.28 <1.38 mg/L

95%ile 2.14 <1.55 mg/L 1.34 1.34 1.47 1.34 <1.55 mg/L

99%ile 2.79 N/A 1.71 1.37 1.72 1.67 <1.75 mg/L

Max 2.98 <2 mg/L 1.90 1.38 1.82 1.82 <2 mg/L

Min 1.37 N/A 1.01 1.00 1.00 0.93 N/A

All Data

Anticipate that full-scale plate settlers will remove particulate TOC prior to filtration.

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Project Summary

• First Project in UK to utilize chlorine dioxide for drinking water application

• Retrofit of existing filters and removal of slow sand filters while keeping plant in service

• Optimum solution demonstrated under extreme cold water conditions

• Optimum saved approximately 25 feet of hydraulic head that is used for energy recovery

• Plant is currently on schedule to be in full operation Spring 2017

Thank You

Russell Ford, PhD, PE, BCEE

Global Service Leader – Drinking Water and Reuse

Email: Russell.ford@ch2m.com

Phone: 973-316-3555