CHLORINE DIOXIDEJonathan Beresford BSc (Hons)

MScAKVO Ltd

www.akvo.co.uk

History of Chlorine DioxideDiscovered in 1811 by Sir Humphrey Davy

No progressed as no means of compressing or controlling such a volatile and potentially explosive material.

First commercial user was the City of Niagra Falls Public Water Authority in 1944.High levels of natural phenols in the water

made the use of chlorine unacceptable.By 1977 over 100 US utility companies were

using the material along with several thousand utilities in Europe.

Physical propertiesPure ClO2 is a dark brown oily liquid.Explosive in air at concentrations above 10%.Highly soluble gas that does not react with

waterEg chlorine produces hypochlorous acid in

water.Very stable when dissolved in water at <3g/lIn aqueous state it is a non polar free radical

oxidising agent.Solutions are yellow/greenish yellow and

smell of chlorine.

Benefits of ClO2Effective against all micro organisms at

very low concentrationsDWi limit in drinking water 0.5mg/l total

oxidant Total oxidant = chlorite + chlorate + chlorine

dioxideRapid Killing actionEffective against LegionellaExcellent Biofilm control.Excellent Biofilm Disruption / Removal

But not at DWI limitsDiffuses into biofilm to kill from within,

Cl2/Br2 burn the surface.

Benefits of ClO2

Does not react with organics to form ecotoxic and bioaccumulative byproducts

Maintains biocidal activity to pH 10Not corrosive to pipes and metals at

normal use concentrationsNo reaction with amines or phenolics

No taint potential compared to Cl2 or Br2Better tolerance to organics than Cl2 or

Br2

Chlorine Dioxide - OptionsAcid Chlorite generators

AKVO preferred option, safest & most efficient dosing method

Electrolytic generators, feedstock chlorite solution Nalco Halox Clearwater also have similar system,

CLOX CAT R self regenerating units, uses sulphuric acid CLOX CAT X non regenerating units, cartridge sent back

for regen. Both these show poor conversion rate of chlorite to

Chlorine dioxide, approx 50%.Dilute Chlorine Dioxide solution

3% chlorite solution requires activation with weak acid.“Stabilised” Chlorine Dioxide -

Solutions of approx. 2g/l - short shelf life, chlorite often is active biocide, not chlorine dioxide

Chlorine Dioxide Tablets Available from AKVO

Acid/Chlorite GeneratorsProminent & LMI the most common.Can use hydrochloric acid/sodium chlorite in

a range of concentrations.5NaClO2 + 4HCl = 4ClO2 + 5NaCl + 2H2OIn practice this typically means 7.5 % solution of

chlorite reacted with a weak 10% solution of HCl

The various PartsControl PanelReceives water meter

pulses and doses set amounts of the precursor chemicals to match the water flow.

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The dosing pumpsThese draw the two

precursor chemicals from their tanks, across flow sensors to the mixing chamber.

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Chemical mixing chamberThe precursor

chemical mixing chamber is contained inside an air tight housing that it is evacuated using water and air every 5 mins.

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Water flowA magnet on the back

of the flow gauge will shut down the generator if the water flow ever drops to low level

The generator will automatically re-commence dosing once flow is detected again.

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Chlorine Dioxide MonitorThis samples water

and constantly monitors the chlorine dioxide level.

Below the probe is a sample tap.

Checks that are requiredUse a digital tester to check the chlorine

dioxide level in the water (random sample point at a use location).

Check the digital readout from the continuous sampler

Check the main control panel display for fault messages

Check the water flow gauge shows a flowCheck the chemical levels in the tanks

Chlorine dioxide summaryClO2 is an effective means of controlling the

growth of Legionella and other contaminating micro-organisms in engineered water systems.

Used extensively in the food and beverage industries – safe for direct food contact.

Used for potable water suppliesDWi approvedPrime recommendation via HTM04 for NHS sites

FOR FURTHER INFORMATIONon our bespoke chlorine

dioxide products

Contact AKVO Ltd

Tel 0844 244 8726

Or visit www.akvo.co.uk