What is Bromine?

By swimmingpoolchemicals.co.uk

What is bromine?

Bromine is the most widely used sanitiser for domestic hot tubs and spas. Bromine destroys bacteria, algae, and water-born diseases in much the same way that chlorine sanitises water.

What is the difference between bromine and chlorine?

• Bromine does not form the corrosive by products which cause corrosion of metals in indoor pools

  • Bromine is less volatile than chlorine so it does not evaporate as quickly at the high temperatures which spas operate.
  • Bromine does not form smelly by products, so indoor pools using bromine do not have that typical swimming pool smell. When you have used a bromine hot tub your skin will not smell of chlorine.
  • Bromine does not form the corrosive by products which cause corrosion of metals (including stainless steel) in indoor pools.
  • Bromine does not lose its ability to kill bacteria and viruses at pH values up to 8.2. This is useful on hot tubs in hard water areas where it is difficult to keep the pH down.
  • Bromine cannot be stabilised against breakdown by sunlight, so it is not often used in outdoor pools.
  • Bromine is two and a quarter times as heavy a molecule as chlorine so it is used at a concentration 2.25 times as high as chlorine.

How is bromine dosed?

  • Bromine is normally supplied as white tablets, bromo-chloro-dimethyl hydantoin (BCDMH).
  • In hot tubs these are usually placed in a floating dispenser. The dispenser is adjusted to give a bromine level between 3 and 6 ppm.
  • Bromine tablets are very slow dissolving making them very useful in domestic hot tubs. On a hot tub that is used by two people twice a week two tablets in the floating dispenser will keep the water clear and fresh. One extra tablet will need to be added every 7 to 10 days.
  • Indoor swimming pools usually use an erosion feeder known as a brominator to dose bromine tablets. Because bromine is so slow dissolving it is essential that brominators on busy pools and spas are large enough to meet the bather load.

How much bromine should be kept in bathing water?

  • Spas and hot tubs 3 to 6ppm
  • Swimming pools 2 to 4 ppm

How do we test bromine?

  • Bromine is tested using exactly the same test as chlorine using DPD 1 tablets.
  • This is read against color standards in a visual comparator.
  • Since Free Bromine and Combined Bromine are similar in sanitising strength, they both react with a DPD 1 tablet. This reading represents the level of Total Bromine.
  • If a bromine comparator is not available, operators can use a chlorine comparator and multiply the reading by 2.25 to calculate ppm bromine.
  • Bromine can also be tested using bromine test strips.

What pH should a bromine bathing water use?

As mentioned before bromine does not lose its ability to kill micro organisms as pH rises. This means that hot tubs and pools using bromine can use a pH up to 8.2. This is particularly useful on hot tubs and leisure pools where the pH tends to rise if an adequate alkalinity level is maintained.

The Chemistry (if you are interested)

Bromine and ammonia

In common with free chlorine, free bromine also reacts with the ammonia (NH3) which is continually added to the water through the decomposition of the urea in the nitrogenous products (urine, sweat etc.) introduced by bathers.  However, there are significant differences between the two sets of reactions.

The first bromine reaction is:

HOBr (hypobromous acid)NH3 (ammonia)NH2Br (monobromamine) H2O (water)

This reaction is normal and acceptable. Monobromamine is not an irritating compound and has disinfecting properties as powerful as free chlorine or free bromine. Consequently, when the pollution level increases the product of its reaction with the free bromine is still effective against micro organisms.

The second reaction, analogous to the production of dichloramine, is:

HOBr (hypobromous acid)NH2Br (monobromamine) <> NHBr2 (dibromamine) + H2O (water)

It should be noticed that this is an equilibrium reaction with the equilibrium strongly to the left. It is not possible to drive the equilibrium to the right under pool conditions, therefore the concentration of dibromamine is minimal. This is analogous to the breakpoint condition in a chlorine pool.

Brominous disinfection is, therefore, effectively always at breakpoint. The absence of dibromamine ensures that nitrogen tribromide – the bromine equivalent of the atmospheric irritant nitrogen trichloride – cannot form. Consequently the irritating conditions for bathers and the corrosive conditions for bathers cannot occur in an indoor bromine pool.

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