Chemical-biological: formation of
chloramine
• Volatility: The most dangerous chlorine disin-
fection by-products are those that are volatile
because they will escape the water as a gas. The
chlorine smell in swimming pools is not chlorine
but a volatile gas called trichloramine (NCl 3 ). This
gas causes skin and eye irritation and is most
hazardous to the lungs. The human lung is very
efficient for gas exchange with over 70 m 2 surface
area. Trichloramine causes irritation and strips the
protective mucous lining from the lung.
Trichloramine will cause skin, eye and lung irritati-
on but it does not enter the blood stream. Other
by-products produced by chlorine and short wave
UVC light will pass through skin and lung tissue
to enter the blood stream. These chemicals inclu-
de chloroform (CHCl 3 ) and cyanogen chloride
(ClCN). Both are much more toxic than trichlora-
mine. That is why we are against the use of medi-
um pressure UVC irradiation to reduce combined
chlorine from public and private pool water. It is well
know that UVC will convert organo-chlorine into
chloroform and cyanide. For existing installations
we recommend the use of ACO (see page 11).
• Mono-, di- and trichloramine: When ammonia
and chlorine mix in water, inorganic chloramines
are formed by a chlorine substitution oxidation
reaction. The first stage is the formation of mono-
chloramine, then dichloramine followed by tri-
chloramine; especially under acidic conditions.
Trichloramine is very volatile.
Chlorine substitution oxidation reactions
+
+
Hypochlorous + ammonia
=
monochloramine + water
Formation o f mono-, di- und trichloramine
(1) HOCl + NH 3 NH 2 Cl + H 2 O
(2) HOCl + NH 2 Cl NHCl 2 + H 2 O
(3) HOCl + NHCl 2 NH 3 + H 2 O
monochloramine
dichloramine
trichloramine
Biochemical relationships
pH
Chloramines formed
1 monochloramine
2 dichloramine
3 trichloramine
ideal
pH-range
• Ammonia and chlorine forms inor-
ganic chloramines (mono- > di-
> trichloramine). Converts at low
pH values, monochloramine to
di-and trichloramine.
• Trichloramine are responsible for
the characteristic smell of chlorine.
They cause eye irritation and may
cause damage to the protective
film of the lungs.
• The formation of Trichloramine
occurs mainly at pH values below
5.5.
• Biological conversion: Humans excrete nitrogen
through sweat and urine. About 10 % of urine will
be ammonia but the majority of the nitrogen (ap-
proximately 85 %) will be in the form of urea. Urea
reacts with chlorine to form the organic chloramine,
chlorourea. This is a non-hazardous substance
because it is a stable, non-volatile molecule.
Bacteria growing on the sand convert urea into
ammonia; the ammonia then reacts with chlorine to
form inorganic chloramines. AFM ® does not sup-
port the growth of bacteria and with no bacteria
present, urea cannot be converted into ammoni-
um and no inorganic combined chorine is formed.
For example sand filters work well for a few weeks
but once the biofilm develops they start to pro-
duce combined chlorine. This can be avoided by
using AFM ® .
No biofilm = no bacteria = much less inorganic
chloramine
(NH 2 ) 2 CO + H 2 O CO 2 + 2NH 3
• No acidic environment: Even without bacteriolo-
gical activity, sweat and urin are still responsible for
the formation of some inorganic chloramines in an
AFM ® system because 10 % of urine is ammonia.
Monochloramine will always form but it is non-toxic
and non-volatile. Monochlormamine will then form
dichloramine and harmful trichloramine. However,
the reaction is time dependent upon concentration
of monochloramine and pH of the water. The key
driver for pushing the formation of trichloramine
is a low pH: The more acidic the conditions the
higher the concentration of trichloramine.
Pools are always maintained at a pH close to 7.0.
So how is it possible to have a low pH? The expla-
nation is the low pH of the biofilm because bacte-
ria produce acids. The greatest surface area in the
pool is the sand in the filter. Every m 3 of sand has
an area of 3‘000 m 2 for biofilm to grow and this is
where monochloramine is converted
to harmful trichloramine.
New sand filters work well for a few weeks until
the acidic biofilm becomes established, then
they start to produce trichloramine. AFM ® rejects
biofilm growth so there is never an acidic surface,
trichloarmines are not formed and AFM ® pools do
not smell of trichloramine. Dryden Aqua AFM ®
pools are therefore much cleaner and safer, espe-
cially for the sensitive lungs of young children.
No biofilm = no acidic environment = no tri-
chloramine = no chlorine smell
• The primary environment in a
swimming pool where we have
acidic conditions, the biofilm.
DRYDEN AQUA
5