Introduction to Chlorine Dioxide Technology

Chlorine Dioxide is …

• Oxidizer and Disinfecting Biocide • Molecular Formula – ClO 2 • 2/3 the oxidation potential of Chlorine • 2 ½ X the oxidizing capacity of Chlorine • Highly soluble in water (ClO 2 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 (H 2 S), 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 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

Hypochloriite Hypobromite Chlorine Chlorine Bromine Dioxide 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 ENVIRONMENTAL

THM Formation Toxicity of by products

SAFETY

Ease of Use Handling Safety Odor

ECONOMICS

Clean System Contaminated System

C C A B C A C C C B B C B C A B A B B A A PAA A B A B C C B C B B B B B B B C Ozone A A D C D B B D C B B B B A C C

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

• Cl0 2 does not produce THM’s e.g.: chloroform • Cl0 2 decays quickly – UV Degrades • Reacts with soluble iron to produce chloride • Can be deactivated using bisulfite

:

H 2 0 + 5Na 2 SO 3 + 2Cl0 2 4.67 ppm of Na 2 SO 3 -> 5Na 2 S0 4 + 2HCl neutralizes 1 ppm Cl0 2

Chlorine Dioxide Test Methods

Use Concentration

• Use the HACH DPD test for free chlorine, with the pre addition 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 ClO

2

• 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 Cl 2 produced Experience has proven that chlorine free chlorine dioxide does not attack TFC membranes – “Purity of Solution” Oxidizer OH .

(Free radicals) Oxidation potential E 0 2.8

Oxidation electrons 1 O 3 (Ozone) HOCl (Hypochlorite) 2.08

1.49

2 1 HOBr (hypobromite) ClO 2 (chlorine dioxide) H 2 O 2 (hydrogen peroxide) 1.07

1.27

1.78

1 5 1

Benefits

• ClO 2 attacks biofilms that re-inoculate systems • Attractive economics and efficacy vs. Kathon, DBNPA • Reduced odor from sulfur decomposition products • Worker Health and Safety improved