1. An Overview of Chlorine Dioxide Usage in Water
Dean Gregory
CDG Environmental, LLC
205 Webster Street Bethlehem, PA

2. Agenda Background Chlorine dioxide (ClO2 characteristics)
Regulatory concerns
ClO2 vs. free chlorine
ClO2 applications in water treatment
Bench/full-scale data
Analytical requirements (chlorite)
ClO2 generating systems 2
205 Webster Street Bethlehem, PA

3. Background Chlorine dioxide (ClO2)
Used in drinking water treatment > 50 years
First used in U.S. for T&O control (Niagara Falls, NY)
A primary alternative to free chlorine for oxidation and disinfection
Generally not used for secondary disinfection 3
205 Webster Street Bethlehem, PA
205 Webster Street Bethlehem, PA

4. Background 1st ClO2 application point 2nd ClO2 application point 4
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5. General Characteristics
Background
General Characteristics
Highly soluble in water (10x more than Cl2)
Volatile & subject to photo-decomposition
Unstable at high concentrations (>15%) and under pressure ~ must be generated onsite
Oxidizes, does not chlorinate, using selective one-electron transfer
Does not react with ammonia
Unaffected by pH over broad range (4-8) 5
205 Webster Street Bethlehem, PA

6. Demand/Decay Characteristics
Background
Demand/Decay Characteristics
TOC = 5.1 mg/L
pH = 6.6
Mn2+< 10 μg/L
TOC = 1.2 mgl/L 6
205 Webster Street Bethlehem, PA

7. Demand/Decay Characteristics
Background
Demand/Decay Characteristics
TOC = 5.6 mg/L
Mn2+ = 250 μg/L
TOC = 1.4 mgl/L
Mn2+ = 0 μg/L
205 Webster Street Bethlehem, PA

8. Regulations of Concern
Ct Disinfection Targets (20°C)
2-log Giardia lamblia: 10mg/L*min
2-log virus: 2.1mg/L*min
0.5-log Crypto (20°C): 58mg/L*min
0.5-log Crypto (10°C): 138mg/L*min
D/DBP Rule (MCL)
TTHM: 0.08 ppm
HAA: 0.06 ppm
Chlorite: 1.0 ppm 8
205 Webster Street Bethlehem, PA

9. Regulations of Concern
Chlorite ion (ClO2)
Must be measured daily at POE
Monthly samples from distribution system
Amp. titration ≈ 30 min. with experience
LGB method
Requires laboratory technician
Colorimetric
Provides ClO2 and ClO2 residuals 9
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10. Chlorine Dioxide vs. Chlorine
No THM/HAA formation
Giardia Ct requirements significantly lower
Superior manganese oxidation
Typical ClO2 dose ~ ppm
Typical Cl2 dose ~ ppm 10
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11. Chlorine Dioxide vs. Chlorine
Reactions with Natural Organic Matter
HOCl + NOM
TTHM, HAA
ClO2 + NOM
ClO2 + Low MW
organic compounds
ClO2 reacts ONLY through a one-electron oxidative pathway 11
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12. Water Treatment Applications
TTHM/HAA Precursor Destruction
Greater impact on TTHM precursors
Manganese Oxidation
Taste & Odor Control (algae, diatoms)
Inactivates Giardia and viruses
CT for 2-log Giardia inactivation: 10mg/L-min at 20°C
CT for 2-log virus inactivation: 2.1mg/L-min
Pre-ox. 12
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13. Water Treatment Applications
Impact on TTHM/HAA-5 Formation
Raw TOC = 4.3 mg/L 13
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14. Water Treatment Applications
Impact on TTHM/HAA-5 Formation
Raw TOC = 5.1 mg/L 14
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15. Water Treatment Applications
Impact on TTHM/HAA-5 Formation
Raw TOC = 6.2 mg/L 15
205 Webster Street Bethlehem, PA

16. Water Treatment Applications
Impact on TTHM/HAA-5 Formation
Raw TOC = 7.8 mg/L 16
205 Webster Street Bethlehem, PA

17. Water Treatment Applications
Mn2+ Oxidation
Raw TOC = 6.3 mg/L
pH = 6.8 mg/L
Contact time = 5 min. 17
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18. Water Treatment Applications
Impact of ClO2 on Chlorophyll-a
Pilot Results (presented at ’05 WQTC)
Date
Raw Water Chlor-a
Post-ClO2 Chlor-a
Reduction
μg/L %
August 20 21
100
August 24 31 95
September 2 9
September 14 22
September 24 5
September 30 18
October 5 71
October 7 17 92
October 12
October 22 30
October 26 20
November 8 11
November 16 8
November 18 6
November 22 18
205 Webster Street Bethlehem, PA

19. ClO2 for Pre-ox. and Disinfection
Full-Scale Case Study
ClO2 for Pre-ox. and Disinfection
Raw water
Water Quality (TX Utility)
Raw TOC = 4.3 mgl/L (lower Rio Grande)
pH = 7.2, T = 23°
Pre-ox ClO2: 0.85 mg/L
Clearwell
Post-filt. ClO2: 0.85 mg/L 19
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20. Full-Scale Results Texas Utility (6 mgd)
Total ClO2 dose = mg/L 20
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21. Water Treatment Issues
Chemical sequencing
Avoid NaOH/High-pH conditions
pH > 9 = instant destruction
Avoid simultaneous application with NH2Cl
mg/L decrease in ClO2 residual
Interference from coagulant possible
Pre-ox. DT > 5 min. is optimum 21
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22. Analytical Methods Amperometric titration
Manual and semi-automatic systems
Ion chromatography
Expensive, requires highly-trained technician, turnaround time
Colorimetric (forming or removing a color)
205 Webster Street Bethlehem, PA

23. Amperometric Titration
Hach™ AutoCat 9000 Amperometric Titrator 23
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24. ClO2 Generation Systems
Solution-based systems
Chlorine Gas/25% Sodium Chlorite (NaClO2) Solution
Most common
Sulfuric Acid: Chlorate/Hydrogen Peroxide Solution (Purate)
Electrochemical (small systems)
Acid-chlorite (less efficient)
Solid-based systems (CDG Gas: Solid™) 24
205 Webster Street Bethlehem, PA

25. Generation Systems 2ClO2 + Cl2 2ClO2 + 2Cl
NaClO2(aq) : Cl2(gas)
2ClO2 + Cl2
2ClO2 + 2Cl
Efficient mixing of reagents improves purity and yield (95% attainable)
High-concentration solution can be batched and fed from day tank
Most efficient with chlorine overdose 25
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26. Generation Systems 2ClO2 + Cl2 2ClO2 + 2Cl
NaClO2(aq) : Cl2(gas)
2ClO2 + Cl2
2ClO2 + 2Cl
Effluent must be analyzed regularly to ensure efficiency
i.e. addition amp. titration required
frequent re-calibration possible
Disruption in Cl2(g) feed may cause ClO2 spike
Sodium chlorite storage/leaks are biggest safety concern 26
205 Webster Street Bethlehem, PA

27. Sulfuric Acid: NaClO3(aq)
Generation Systems
Sulfuric Acid: NaClO3(aq)
2NaClO3 + H2O2 + H2SO4
2ClO2 + Na2SO4 + O2
Purate®
Effluent must be analyzed regularly to ensure efficiency
Bulk storage of sodium chlorate and 73% sulfuric acid required 27
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28. CDG Gas:Solid™ Process
Cl NaClO ClO NaCl
Chlorine Gas
Solid Sodium Chlorite
SAF-T-CHLOR™
Chlorine Dioxide Gas
Solid Sodium Chloride 28
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29. CDG Gas:Solid™ Plant-Scale ClO2(g) Generators
SAF-T-CHLOR
SOLID
SODIUM
CHLORITE
CHLORINE
AIR
FILTER
EJECTOR
RAW WATER IN
SOLUTION
OUT
CHLORINE DIOXIDE + AIR
SCALE
Cl2 + 2NaClO ClO2 + 2NaCl 29
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30. 30
205 Webster Street Bethlehem, PA

31. CDG Gas:Solid™ Process
Produces pure ClO2 gas, minimizes chlorite ion
Relatively simple operation: Cl2(g) feed only
Flow-paced: Generator production changes with plant capacity w/o need for re-calibration
No need for additional titrations of generator effluent
Safety 31
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32. CDG Gas:Solid™ System Safety Considerations
Chemical handling
Sodium chlorite shipped in sealed cartridges w/ quick disconnects
Maximum operator safety ~ no contact with the chemical
No liquid chemical storage & handling
Safety interlocks
Low vacuum
Low air flow
Excessive chlorine gas flow
Combustible gas presence 32
205 Webster Street Bethlehem, PA

33. CDG Gas:Solid™ System Safety Considerations
Saf-T-Chlor™ Thermally Stable Sodium Chloride
Specially formulated
Minimizes possibility of ignition source
Absorbs and dissipates heat
Does not propagate and ignite
Sealed cartridges with ceramic internal components 33
205 Webster Street Bethlehem, PA

34. New Option for ClO2 Applications
CDG Solution 3000®
Stabilized ClO2 solution mg/L
Ideal for small systems, pilot plants
Available in 55g drums, 275g totes 34
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35. CDG Consultative Programs
Water Treatability Studies
Protocols dependent on program objectives
Testing done on actual raw water
Trial programs
Production unit installed at water plant
Limited financial exposure 35
205 Webster Street Bethlehem, PA

36. Questions? CDG Environmental, LLC. 205 Webster Street
Bethlehem, PA 18015 36
205 Webster Street Bethlehem, PA