Bromine will Sanitize and Oxidize
Bromine Compounds
Bromine products are required by law to display on the label, their
chemical name and concentration. When Bromine in its various forms is
added to the water it produces Hypobromous acid (HOBr). Hypobromous
acid controls bacteria and algae and oxidizes organics. Hypobromous
acid is a weak acid and therefore not harmful to people. Bromine is not a
strong enough oxidizer to oxidize or destroy ammonia and nitrogen
compounds in the water.
Hypobromous acid in pools and spas
- HOBr dissociates (breaks up) HOBr <===> H+ + OBr-
(hypobromite
ion).
- HOBr reacts with bacteria and organics. HOBr is a very effective
sanitizer
- OBr- reacts with ammonia (NH3). OBr-
is an oxidizer.
- HOBr reacts with sunlight.
Liquid bromine when added to water readily forms hypobromous acid
(chemical formula HOBr) and hypobromite ions (chemical formula OBr-).
Hypobromous acid is the killing form of bromine. Unlike chlorine, bromine
cannot be protected from ultra violet light.
Bromine is 2.25 times heavier than chlorine, and at a pH
of 7.5 the killing form of bromine (hypobromous acid HOBr) is at 94% and
the oxidizing form (hypobromite ion OBr-) is at 6%. You need
twice the amount by weight of bromine as chlorine. 2 hours of bright
sunlight will reduce pool bromine levels by 65%. The equivalent
unprotected chlorine loss is 90%.
Once hypobromous acid destroys bacteria, algae or other organisms, or
is destroyed itself by sunlight it ends up as bromide ions. A strong
oxidiser can "recharge" the bromide by oxidising it back into
hypobromous acid. Chlorine does not have this ability, once chlorine is
spent it cannot be reactivated like bromine.
The hypobromous acid combines with ammonia and nitrogen compounds in
the water to form bromamines. Bromamines are active sanitizers, and they
do not have the foul-smell of chloramines.
Bromine is not a strong enough oxidizer to oxidize or destroy ammonia
and nitrogen compounds in the water. It is therefore necessary to oxidize
these swimmers wastes and reactivate the bromide ions by adding a stronger
oxidizer - usually any form of chlorine or a non-bromine shock (eg.
potassium peroxymonosulfate).
There are two basic bromine systems: 1 part and 2 part systems.
1 Part Bromine
One-part bromine or bromine tablets are actually a compound of
bromine and chlorine (1-bromo-3-chloro-5,5-dimethylhydantoin also called
BCDMH), (chemical formula BrClC5H6O2N2,).
The chlorine in the tabs is used to oxidize
the bromine to produce hypobromous acid and hypobromite ions. Bromine tabs
provide an available bromine level of 61-65 % and an available chlorine
level of about 27-31%.
One-part bromine (BCDMH) is mostly available as tablets, cartridges or
packets. It has a long shelf life, and it is very slow dissolving, so it
works extremely well in floaters and erosion-type feeders.
Bromine tablets are acidic. Bromine tablets can harm equipment or pool
plaster if improperly used. Placing bromine tablets in a skimmer rather
than in a feeder can corrode metal pipes and fittings. The corroded metal,
usually copper, will deposit on the pool walls as a turquoise discolouration.
To prevent the pool becoming acidic it is necessary to add about 200gms of
sodium hydroxide for each kg of bromine tabs used.
70kg of bromine tablets sanitize a pool of 5 x 10 meters in a year.
A "typical" 5 x10 meter bromine sanitized pool requires about
30 kg of calcium hypochlorite or peroxymonosulfate to oxidize away the
bromamines formed from the swimmer waste.
2 Part Bromine
The 2 part bromine system consists of bromide salt (sodium bromide,
chemical formula NaBr) and an oxidizer (potassium peroxymonosulfate or a
chlorine compound).
The salt is added to the water, and then the oxidizer
is added to activate the bromide into hypobromous acid. After the
hypobromous acid destroys bacteria, algae or other organisms, it returns
to being bromide ions (or bromide salts), which can again be reactivated
2 part bromine has a relatively neutral pH,
but varies with different manufacturers from 6.5 to 8 and usually averages
around 7.
Copyright © 1996, 1997, 2002 TPS Pty Ltd
