Download - Akvo - chlorine dioxide
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