The disinfectant of bromine

Scopes of bromine use
Bromine can be used for the disinfection of swimming pool and cooling tower water. Bromine is not used for the disinfection of drinking water.

Characteristics
Bromine is the only liquid nonmetallic element at room temperature, and one of only two elements on the periodic table that are liquid at room temperature. The melting point of bromine is 7.2 °C and the boiling point 58.8 °C (138 °F). The pure chemical element has the physical form of a diatomic molecule, Br2. It is a dense, mobile, reddish-brown liquid, that evaporates easily at standard temperature and pressures to give a red vapor (its color resembles nitrogen dioxide) that has a strong disagreeable odor resembling that of chlorine. Bromine is a halogen, and is less reactive than chlorine and more reactive than iodine. Bromine is slightly soluble in water, and highly soluble in carbon disulfide, aliphatic alcohols (such as methanol), and acetic acid. It bonds easily with many elements and has a strong bleaching action. Bromine, like chlorine, is also used in maintenance of swimming pools.

Bromine is a bleach. It is poisonous in fluid form and bromine vapor is destructive for the human skin, eyes and respirational tract. It causes serious burns. A concentration of 1 ppm can cause eye watering and when inhalation of concentrations below 10 ppm occurs, one starts to cough and the respirational tracts are irritated.

Bromine is a powerful oxidizing agent. It reacts vigorously with metals, especially in the presence of water, as well as most organic compounds, especially upon illumination.

Bromine can easily be dissolved in water (35 g per L water), carbon disulfide and other organic solutions. When added to water, bromine forms hypobromous acid. Hyprobromous acid is a weak acid. It partly dissociates to form hydrogen ions and hypobromite ions. The rate of hypobromous acid and hypobromite ions is determined by the pH value of the water. When the pH value is between 6.5 and 9 both hypobromous acid and hypobromite ions can be found in water.

If water contains ammonia nitrogen, bromamines will be formed (NH2Br, NHBr2 and NHBr3). For disinfection bromamines are as effective as hypobromous acid. Changing the pH value influences the amount of mono-, di- and tribromamine that is formed.

Applications of bromine?
A wide variety of organobromine compounds are used in industry. Some are prepared from bromine and others are prepared from hydrogen bromide, which is obtained by burning hydrogen in bromine.

The first known application of a bromine-containing product is the color purple. This substance is produced by purple snails and was used by the Romans to paint their clothes purple. This is a very demanding activity and only the richest Romans could buy these clothes.

Nowadays bromine has many applications. In industry and agriculture it is used on a large scale to produce bromine-containing substances. Bromine was used mainly to produce ethyleen dibromide; a constituent of lead-containing fuel. Because of its damaging effects on the environment, this product is no longer used. Bromine is applied in brominated flame retardants, in medicines, in photography, in oil production, in paints and in pesticides. In water treatment bromine is used as an alternative for swimming pool disinfection, and for cooling tower disinfection by chlorine.

Can bromine be used for the disinfection of swimming pools?
Bromine substances are disinfectants and can be used as an alternative for chlorine. In swimming pools, bromine is used against the formation and growth of algae, bacteria and odors in swimming water.

Bromine-chlorine-dimethylhydantoine (BCDMH) is an organic substance, after disinfection and oxidation free bromine remains. When BCDMH is dissolved in water, hypobromous acid and hypochlorous acid are released. Those substances react with bromides (Br–), causing additional hypobromous acid to be produced. This is why bromine can be used both as a disinfectant and as an oxidizing agent. The concentration of BCDMH in water should not reach 200 mg/L or higher, otherwise the equilibrium between the residual disinfectant and the organic matter is disturbed. An advantage of BCDMH is that it is harmless when it is stored. It is easy to apply. Occasionally, the pH value has to be adjusted.

BCDMH is provided as tablets or cartridges. It has a long shelf life and it dissolves very slowly. Another system that can be used is dissolving bromine salt (sodium bromide) in water and activating it by the addition of an oxidator (hypochlorite or ozone). At first, salt is added to the water. Second, the oxidator is added to activate the bromine and hypobromous acid is formed.

During disinfection, hypobromous acid dissociates into bromide ions. These ions can be reactivated. Bromine reacts with other substances in the water to form bromine-containing substances. These substances are disinfectants and do not give off odors. Bromine does not oxidize ammonia or other nitrogen substances. Hypobromous acid reacts with sunlight.

When the pH value is between 7 and 8,5 dibromoamine is the most common form of bromine. Dibromoamine is almost as effective as free chlorine in killing microorganisms. Dibromoamine is very active and usually dissociates quickly into bromide ions. Because of this, no bromine remains in the water.

Can bromine be used for the disinfection of drinking water?
Free bromine (Br2) is not used in drinking water treatment. It reacts far to quickly with organic substances, and no residue will remain. Bromine gives drinking water a terrible medicine-like taste. Bromine should only be used in emergency cases

What is the efficiency of bromine?
The bromamines which are formed when bromine is added to ammonia-rich water are as effective as free chlorine in killing pathogenic microorganisms.

What are the environmental effects of bromine use?
Bromine is used as a disinfectant, because it is harmful for microorganisms. When organic bromine enters surface waters, it has negative effects on the health of water fleas, fishes, lobsters and algae.

When bromine is used to disinfect water, bromamines and hypobromous acid react with organic matter in the water to form brominated disinfection byproducts. These can be harmful to human health.

What are the health effects of bromine use?
Bromine concentrations around 0.5 mg/L in swimming pools cause eye and mucous membrane irritation and can lead to odor nuisance. In nature bromine is found in inorganic substances. During the twentieth century, humans have produced organic bromine for several applications. Organic bromine is not a natural substance and causes severe damage to the environment. Humans can obtain organic bromine through the skin, through food uptake and through inhalation. It is widely used as a spray to kill insects and other unwanted pests. Organic bromine is dangerous for humans and animals. It effects the thyroid gland, genetic material and nerve system.

Advantages of bromine use
Bromine dissolves in water three times better than chlorine. No dangerous gasses are required for bromine production. Bromine’s activity in water is short, because it does not bind strongly. The advantage is that the residual concentration is low and no separate substances are required to remove bromine.

Disadvantages of bromine use
Bromine is very reactive. To maintain an adequate disinfection, the amount of bromine that is added must be high. Bromine aggressively reacts with metals and it is a corrosive material.

Security measures should be taken when bromine is transported, stored or used.

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