205 Webster Street Bethlehem, PA 18015 888-610-2562 Application of Chlorine Dioxide in Drinking Water

205 Webster Street Bethlehem, PA 18015 888-610-2562 www.cdgenvironmental.com

Application of Chlorine Dioxide in Drinking

Water

http://www.cdgenvironmental.com/


Introduction

• Chlorine dioxide (ClO2)

• Powerful, selective oxidant

• Drinking water treatment > 50 years

• Must be produced on site

• A leading alternative to chlorine for oxidation and disinfection



Chlorine Dioxide

• Very volatile and reactive

• Unstable at high concentrations

• Gas highly soluble in water

• Oxidizes, does not chlorinate

• Selective, one-electron transfer

• Does not react with ammona



Chlorine Dioxide

• Potable water• Odor and taste control• Metals removal• THM reduction/elimination• Removal of chlorine-

resistant pathogens

• Mollusk control• Zebra mussels

• Process-water• Biocide• Metals removal

• Wastewater• Oxidation of waste products• Color removal

• Gas sterilization of medical products

• Decontamination



Drinking Water Issues

• Health effects• Chlorinated organics (THM, HAA)• Chlorine-resistant pathogens

(Cryptosporidium, Gardia lamblia)

• Water quality• Taste, odor & color• Dissolved metals

• Regulations• EPA-M/DBP Rule (Phase 1) requires

compliance by December 15, 2001



ClO2 Benefits

• Does not form chlorinated DBPs (THM, HAA)

• Does not oxidize bromide ion to bromate ion

• Broad spectrum microbiocide

• Inactivates Giardia & Cryptosporidium

• Improves sedimentation and filtration

• Lowers turbidity



ClO2 vs. Chlorine

• No cancer-causing by-products formed

• Kills chlorine-resistant pathogens

• Superior manganese oxidation

• Typical ClO2 dose ~ 0.25 - 1.5 ppm

• Typical Cl2 dose ~ 2.0 - 5.0 ppm



ClO2 vs. Ozone

• Fewer by-products (e.g., bromate)

• Lower cost (capital, power)

• Superior manganese oxidation

• Minimal power requirements



• Inefficient and unreliable generators

• Difficult and complicated analytical methods

• Odor problems “at the tap”

• Toxicology “data gaps”

• Unclear regulatory prospects

Chlorine DioxideHistorical Limitations


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Drinking Water Regulations

• Cryptosporidium: 99% removal

• Giardia lamblia: 99.9% removal

• Bromate: 0.01 PPM• Chlorite: 1 PPM• TTHM: 0.08 PPM• HAA: 0.06 PPM

Toxicology Data

PathogenRegulations

DBPRegulations


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Chlorine DioxideGeneration Methods

• Sodium chlorate (NaClO3)• Paper pulp bleaching• Very large-scale production

• Sodium Chlorite (NaClO2)• Drinking water treatment, since 1944• Wastewater treatment• Industrial process water treatment• Medical device sterilization• Decontamination


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Chlorine DioxideSodium Chlorite-based Generation

Methods• Acid : Chlorite Solution

• Chlorine Solution : Chlorite Solution

• Chlorine Gas : Atomized Chlorite Solution

• Chlorine Gas:SolidTM Chlorite Process


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Chlorine DioxideChlorite Solution Generation Method

• Oldest sodium chlorite generation method

• Maximum yield limited to 80%

• Chlorine dioxide concentration in product variable based on:

• Sodium chlorite solution concentration• Acid concentration• pH of reaction• Presence of chloride ion

• Highly inefficient and unreliable


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Chlorine DioxideChlorine Solution : Chlorite Solution

• Excess chlorine is needed to neutralize NaOH in product

• High conversion, but yield limited to 80% to 90%

• Very corrosive effluent due to low pH

• Multiple feed chemical systems required (chlorine gas, chlorine solution or hypochlorite and chlorite solution)

• Slow mixing of reagents increases chlorite and chlorate production while decreasing yield


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Chlorine DioxideChlorine Gas : Vaporized Chlorite Solution

• State of the art technology prior to Gas:SolidTM system introduction

• Rapid mixing of reagents improves purity and yield

• Frequent adjustment, re-calibration and cleaning required to minimize chlorite and chlorate production

• Liquid chemical feed system

• Difficult to apply in small applications

• Chlorite and chlorate in product make analysis difficult


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Chlorine DioxideGenerator Historic Limitations

• Poor turndown capabilities

• Re-calibration required when shut down and restarted

• Unsuited for small plants

• Generators operated with excess chlorine to create the appearance of high yield


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• Feedstock/chlorites deteriorate, requiring constant analysis

• Accurate yield/efficiency/purity analysis required-5-step titration of product

• By-product concerns


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• Yield calculation must account for ALL Oxy-chlorine species

Chlorine Dioxide + Chlorite + Chlorate + Chlorine

Chlorine Dioxide


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Chlorine DioxideChlorine Gas:SolidTM Chlorite Process

• Developed by CDG Technology, Inc.

• Most advanced generation technology available

• Product is pure chlorine dioxide gas

• No chlorite or chlorate ions produced by generator

• Infinite turndown capability without need for re-calibration

• Effluent analysis need account only for chlorine dioxide and chlorine


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“...this [Gas:Solid] process resolves essentially all of the

problems associated historically with chlorine dioxide

generation...”

—George Clifford White, Handbook of Chlorination and Alternative Disinfectants, 4th Edition, 1999


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Gas:SolidTM Plant-ScaleChlorine Dioxide Generators

SAF-T-CHLORSOLID

SODIUMCHLORITE

CHLORINE

AIRAIR

FILTER

EJE

CT

OR

RAW WATER IN

SOLUTION OUT CHLORINE

SAF-T-CHLORSOLID

SODIUMCHLORITE

CHLORINE DIOXIDE + AIR

SCALESCALE

Cl2 + 2NaClO2 2ClO2 + 2NaClChlorine Sodium Chlorite Chlorine Dioxide Sodium Chloride


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Model No. GS 8 GS 20 GS 50 GS 100 GS 200 GS 400

ClO2 Output (lbs./day) 8 20 50 100 200 400

Cl2 Feed (lbs./day) 4 10 25 50 100 200

Panel blend / control / air flow b / c / af b / c / af b / c / af b / c / af b / c / af

Width (in) 24 / 17 / 12 24 / 17 / 12 24 / 17 / 12 24 / 17 / 12 24 / 17 / 12 30 / 17 / 12

Height (in) 31 / 18 / 48 31 / 18 / 48 31 / 18 / 48 31 / 18 / 48 31 / 18 / 48 36 / 18 / 48

Depth (in) 14 / 11 / 9 14 / 11 / 9 14 / 11 / 9 14 / 11 / 9 14 / 11 / 9 18 / 11 / 9

Weight (lbs) 65 / 25 / 28 65 / 25 / 28 65 / 25 / 28 65 / 25 / 28 65 / 25 / 28 100 / 25 / 28

Power Requirement 115V - 5 amps

Mounting Wall

Ejector Included

Manual Cl2 Rate Valve Included

Options Multiple Cartridge Configuration, Cl2 Gas Breakthrough Detector



Chlorine DioxideGeneration Method Considerations

• Chlorine dioxide by-products• Chlorite ion: ClO2

• Chlorate ion: ClO3

• Two sources of by-products• Inherent with chlorine dioxide use• Un-reacted sodium chlorite feedstock


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Chlorine DioxideGeneration Method Considerations

• Chlorite/Chlorate ion avoidance and removal

• Generator maintenance and calibration: All except Gas:SolidTM process

• Generator selection: type, size, etc.• Reducing agents - ferrous salts, sulfite• Limit amount of contaminants in

feedstock (liquid systems)• Limit chlorine over-feed (liquid systems)


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• Unstable under pressure and in high concentrations (>15%)

• Never stored or shipped

• Strong aqueous solutions will release chlorine dioxide gas

• OSHA maximum exposure limit over 8 hrs. in 0.1 ppm-also odor threshold

Chlorine DioxideSafety Considerations


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Chlorine DioxideConventional GeneratorSafety Considerations

• Chemical feed systems • Materials of construction (storage tanks,

pumps, piping)• Containment and spill protection• Personnel protective equipment• Contact with chemicals

• Generator Operation• Proper calibration and adjustment of feed

chemicals• Personnel protective equipment• Contact with chemicals


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Chlorine DioxideGas:SolidTM GeneratorSafety Considerations

• Chemical handling • Process designed to eliminate contact with chemical• Sodium chlorite shipped in sealed cartridges• Maximum worker safety

• Safety interlocks• Low vacuum• Low air flow• Excessive chlorine gas flow• Low ambient temperature• Combustible gas presence

• Solid sodium chlorite formulation


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Sodium ChloriteSafety Considerations

Fuel

FireIgnition Source OxidantTriangle

• Sodium chlorite is a strong oxidizer


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Sodium ChloriteGas:SolidTM GeneratorSafety Considerations

• Fuel exclusion• Sealed chemical cartridges• Ceramic internal cartridge components• No external handling after production• Air and chlorine gas pass through ultra

filtration• Combustible gas detector

• Sodium chlorite formulation


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Sodium ChloriteGas:SolidTM GeneratorSafety Considerations

• CDG Saf-T-ChlorTM sodium chlorite• Specially formulated• Minimizes possibility of ignition source• Absorbs and dissipates heat• Does not propagate and ignite


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Gas:SolidTM GeneratorSafety Review

• Vacuum feed• System shuts down with loss of vacuum

• Saf-T-ChlorTM does not auto-degrade under excessive heat conditions

• No direct contact with chemical• Closed system

• No chemical mixing

• No chemical leaks


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Chlorine DioxideSummary Guidelines

• Set clear ClO2 treatment goal• THM & HAA avoidance• Taste, odor & color control• Disinfection CT• Oxidation (iron & manganese)

• Define use conditions• pH• Temperature• Contact time

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chlorine dioxide, pure and simple

Documents

205 Webster Street Bethlehem, PA 18015 888-610-2562 Application of Chlorine Dioxide in Drinking Water