Introduction
to
Chlorine Dioxide
Technology
Chlorine Dioxide is …
• Oxidizer and Disinfecting Biocide
• Molecular Formula – ClO2
• 2/3 the oxidation potential of Chlorine
• 2 ½ X the oxidizing capacity of Chlorine
• Highly soluble in water (ClO2 is a gas)
• Does not dissociate like chlorine or bromine
Pros and Cons of Chlorine Dioxide
• Advantages:
~ Effective for bacteria, viruses, fungi,
algae, biofilm etc.
~ Very fast acting
~ Breaks down rapidly
~ No AOX formation
~ Not pH dependent
~ No reaction with ammonia
~ Effective at < 1 ppm concentrations
• Disadvantages:
~ Volatile
~ On-site generation required
~ Complicated methods of
generation
Chlorine Dioxide Useful Reactions
Nitrogen compounds
Unreactive with Ammonia, but reacts to eliminate odor-causing
secondary and tertiary amines (advantage compared to
chlorine). Cyanide is also reacted.
Sulfur Compounds
Hydrogen sulfide (H2S), Hydrosulfide (HS-) and Sulfite ions are
readily oxidized to simple sulfates
Transition metals
Oxidation of manganese Mn(II) ferrous Fe(II) (drinking water
applications)
Chlorine Dioxide is Volatile: A Gas in Solution
High volatility means:
1.
High concentrations partition into the air
2.
Can kill organisms on non-wetted surfaces
EFFICACIOUS – Broadest Spectrum
worst ---------------------------- best
COMPARISON OF OXIDIZING BIOCIDES
Hypochloriite Hypobromite
Chlorine
Bromine
Chlorine
Dioxide
PAA
Ozone
PERFORMANCE
High pH
Speed of Kill
Selectivity
Biofilm Removal / Prevention
Organic Contamination
Removal of phenols without halogenation
Presence of reduced Mn or Fe
Residual Activity
Application Versatility
C
B
C
B
C
C
C
B
B
B
B
B
B
C
C
C
B
C
A
A
A
A
A
A
A
A
A
C
B
B
B
B
B
B
B
C
A
A
D
C
D
B
B
D
C
THM Formation
Toxicity of by products
C
C
C
C
A
B
A
B
B
B
Ease of Use
Handling Safety
Odor
A
B
C
B
B
C
A
B
B
A
B
C
B
B
A
A
C
B
C
A
A
C
B
C
C
ENVIRONMENTAL
SAFETY
ECONOMICS
Clean System
Contaminated System
Effective Biocide
• More Tolerant of Organic Material
• Works at Lower Concentrations than other biocides
• Not affected by Water Hardness
• Will not Interfere with operation
of Waste Treatment plants
Environmental Fate
• Cl02 does not produce THM’s e.g.: chloroform
• Cl02 decays quickly – UV Degrades
• Reacts with soluble iron to produce chloride
• Can be deactivated using bisulfite:
H20 + 5Na2SO3 + 2Cl02 -> 5Na2S04 + 2HCl
4.67 ppm of Na2SO3 neutralizes 1 ppm Cl02
Chlorine Dioxide Test Methods
Use Concentration
• Use the HACH DPD test for free chlorine, with the preaddition of glycine.
• Glycine (aminoacetic acid) ties-up chlorine and leaves only
the chlorine dioxide to react and produce pink color with DPD.
High concentration (Generator Product Stream)
• Use HACH direct method (no reagent)
• Concentrated chlorine dioxide solutions are yellow color measured by spectrophotometer.
Best for Confirmation of Delivery
•ORP Devices – Can be calibrated to ppm and operate online
Note; other oxidizers present in treated water will also be read using ORP
“Secondary Disinfection”
• Primary Disinfection
– Occurs in municipal treatment plants
– Mostly uses forms of chlorine (hypochlorite, monochloramine)
• Secondary disinfection
–
–
–
–
Indicated where nosocomial illnesses have occurred
Can be added locally to water supplies to
Overcomes variation in the primary water treatment
Warranted where water pressures fluctuate, where distribution
systems are old and pipeline failures occur.
• Chlorine Dioxide is superior in preventing growth of
biofilms and pathogens on surfaces and within
distribution system
Why ClO2
•
•
•
•
•
•
•
•
•
•
Weak oxidizer
Dissolved gas in water
Non-ionic
5 electrons oxidation capability
Will pass through membrane to
both up and downstream surfaces
Rapid and free rinsing
Ease of detection of trace amounts
Can be used for continuous
protection and treatment
Proven biofilm removal and
prevents build-up
No Cl2 produced
Experience has proven that chlorine free chlorine dioxide
does not attack TFC membranes – “Purity of Solution”
Oxidizer
Oxidation
potential
E0
Oxidation
electrons
OH (Free radicals)
2.8
1
O3 (Ozone)
2.08
2
HOCl
(Hypochlorite)
1.49
1
HOBr
(hypobromite)
1.07
1
ClO2
(chlorine dioxide)
1.27
5
H2O2
(hydrogen
peroxide)
1.78
1
.
Benefits
• ClO2 attacks biofilms that re-inoculate systems
• Attractive economics and efficacy vs. Kathon,
DBNPA
• Reduced odor from sulfur decomposition
products
• Worker Health and Safety improved