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of its oxidizing properties, chlorine dioxide reacts with
iron, manganese and nitrates, but does not react with
ammonia. The oxidizing properties and the radical nature
of chlorine dioxide makes it an excellent disinfectant
against virus and bacteria, as well as many fungi and
protozoa. In an alkaline media, the permeability of living
cell walls to chlorine dioxide radicals seems to increase,
allowing easier access to molecules. It is efficient against
Giardia and has excellent biocidal activity against Cryptosporidia,
which are resistant to chlorine and chloromines.
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Biofilm
Chlorine Dioxide disinfects bacteria by penetrating
the cell wall. Organic substances within cells and on
the surface of cell membranes react with Chlorine Dioxide,
disrupting cell metabolism. Chlorine Dioxide also reacts
directly with amino acids and the RNA in the cell. This
reaction is not dependent on reaction time or concentration.
Unlike non-oxidizing disinfectants, Chlorine Dioxide
kills microorganisms even when they are inactive. Microorganisms
are unable to build up resistance to Chlorine Dioxide.
In practical terms however, few bacteria live alone,
and they are most often found in water and on surfaces
in the form of a "biofilm" which is a close
association of many millions of bacteria. Many biocides
have particular problems in penetrating this biofilm,
due to the polysaccharide "glue" that is secreted
by the bacteria to hold the biofilm together. Unlike
most biocides, Chlorine Dioxide can effectively penetrate
biofilm to provide complete protection.
Chlorine Dioxide kills viruses by preventing protein
formation. ClO2 reacts
with peptone, a water-soluble substance that originates
from hydrolysis of proteins to amino acids.
Chlorine Dioxide is one of a number of disinfectants
that are effective against Giardia Lambia and Cryptosporidium
oocysts, which cause cryptosporidiosis in public drinking
water supplies.
FAQs: Frequently Asked Questions
Can Chlorine Dioxide Be Used In Combination With Other
Disinfectants?
Answer: Yes.
Chlorine Dioxide is often used in combination with chlorine
in municipal drinking water plants in order to reduce
the amount of trihalomethanes and HAAs that would be
formed if chlorine was used alone. Chlorine Dioxide
is added as the primary disinfectant in order to remove
a number of oxidizable compounds without forming chlorinated
byproducts. While chlorine is added after coagulation,
settling and filtration at low levels in order to provide
a residual biocide for use in the disinfection system.
Recent
research indicates that applying Chlorine Dioxide and
chlorine within the same mixing zone can exhibit some
synergistic effects (The combined effect being greater
than the sum of the two parts).
What Makes Chlorine Dioxide Different
from Chlorine?
Answer: While Chlorine Dioxide has “chlorine”
in its name, its chemistry is radically different from
that of chlorine. As we all learned in high school chemistry,
we can mix two compounds and create a third compound
that bears little resemblance to its parents. For instance,
by mixing two parts of hydrogen gas with one of oxygen
- liquid water forms. We should not be misled by the
fact that chlorine and Chlorine Dioxide share a word
in common. The chemistries of the two compounds are
completely different.
Chlorine Dioxide is generally more powerful, easier
to use, and more environmentally friendly than equivalent
chlorine treatments. Chlorine Dioxide is a more expensive
treatment, but its superior environmental performance
means that it is rapidly replacing chlorine in a number
of applications.
Chlorine and Chlorine Dioxide are both oxidizing agents
(electron receivers). However, chlorine has the capacity
to take up two electrons, whereas Chlorine Dioxide can
absorb five. This means that, mole for mole, ClO2 is
2.5 times more effective than chlorine.
It is of greater importance that Chlorine Dioxide will
not react with many organic compounds and, as a result,
ClO2 does not produce environmentally dangerous chlorinated
organics. For example: aromatic compounds have carbon
atoms arranged in rings and they may have other atoms,
such as chlorine, attached to these rings to form a
chlorinated aromatic - a highly toxic compound that
persists in the environment long after it is produced.
Chlorine Dioxide's behavior as an oxidizing agent is
quite dissimilar. Instead of combining with the aromatic
rings, Chlorine Dioxide breaks the aromatic rings apart.
In addition, as the use of Chlorine Dioxide increases,
the generation of chlorinated organics falls dramatically.
How Does Chlorine Dioxide React
When it Oxidizes?
Answer: The predominant oxidation reaction mechanism
for Chlorine Dioxide (and for ozone as well) proceeds
through a process called free radical electrophilic
(electron-attracting) abstraction, rather than by oxidative
substitution or addition (as in chlorinating agents
such as chlorine or hypochlorite).
It has this ability due to its unique one-electron exchange
mechanism. One electron is transferred and Chlorine
Dioxide is reduced to chlorite (ClO2-).
The term "oxidation strength" is used to describe
how strongly an oxidizer reacts with an oxidizable substance.
Ozone is generally regarded as having the highest oxidation
strength and reacts with every substance that can be
oxidized. In practical terms, this is often undesirable
since a number of side reactions can take place causing
undesirable
disinfection byproducts.
Chlorine Dioxide has lower oxidation strength than ozone,
but is more powerful than chlorine. Less Chlorine Dioxide
is normally required to obtain an active residual disinfectant.
Unlike ozone, ClO2 can also be used when a large amount
of organic matter is present.
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