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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.
Hypbromous acid in pools and spas
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 (hypochlorite 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 nonbromine shock (potassium peroxymonosulfate).
There are two basic bromine systems: 1 part and 2 part systems.
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 (the pH of a 1-percent solution in distilled water is 3.6, and the pH of a l-percent solution in de-ionized water is 4.6). 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 discoloration. To prevent the pool becoming acid 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.
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.
Prepared by Trevor Croll,
42 Pearse Street, Keperra, Queensland Australia, 4054.
Phone 61 7 3855 1115