Bromine (Br) in Water Treatment
Quick Answer
Bromine (Br) is a halogen with atomic number 35. PubChem lists its standard state as liquid and its relative atomic mass as 79.90.
Bromide is important even at low concentration because oxidation during ozonation or chlorination can form brominated disinfection by-products. Source control, precursor removal and disinfectant-process optimization are often more useful than particle filtration.
Interesting Facts
- Bromine and mercury are the only elements that are liquid under ordinary room conditions.
- In water analysis, the practical species is usually bromide—not elemental bromine.
- During ozonation, bromide can be oxidised to bromate; treatment design therefore considers precursor control and operating conditions, not just bromide removal.
Water-treatment Design Implications
An element name alone is not enough to select treatment equipment. Confirm chemical form or speciation, total and dissolved concentration, pH, alkalinity, competing ions and the product-water target. Send the water-analysis results to Watermart to identify additional testing and shortlist processes before equipment is specified.
Summary Data Sources
Bromine (Br)
1. Basic Information
| Atomic Number | 35 |
| Symbol | Br |
| Atomic Mass | 79.904 g/mol |
| Electron Configuration | [Ar] 3d10 4s2 4p5 |
| Electronegativity | 2.8 (Pauling Scale) |
2. Physical and Chemical Properties
Bromine is the only non-metallic element that is liquid at room temperature. Bromine liquid is reddish brown in color and evaporates easily to form a red vapor with a pungent odor. Bromine is highly reactive and belongs to the halogen group. Its solubility in water is quite high (3.41 g/100 mL at 20°C), forming hypobromous acid (HBrO). Bromine has a melting point of -7.2°C and a boiling point of 58.8°C. Its density is 3.1 g/cm3 at 20°C. Bromine is less reactive than chlorine and fluorine, but more reactive than iodine. Bromine compounds have similarities with other halogens.
3. Presence in Water and Health Effects
Bromine can be found naturally in seawater at a concentration of about 65 mg/L. In freshwater, the concentration is usually lower. Inorganic bromine in water is generally in the form of bromide ion (Br-). Exposure to large amounts of bromine can cause irritation to the eyes, skin and respiratory tract. Direct contact with liquid bromine can result in serious burns. Chronic exposure to organic bromine compounds may impair the function of the nervous system and thyroid gland. Some organic bromine compounds are also potentially carcinogenic.
4. Water Treatment Applications and Removal Methods
Bromine is used in water treatment primarily as an alternative disinfectant to chlorine. Some methods of removing bromine and its compounds from water include:
- Ion exchange: Strong anion exchange resins can remove bromide ions from water.
- Adsorption: Activated carbon is effective in adsorbing organic bromine compounds.
- Advanced oxidation: Processes such as ozonation can oxidize bromide to bromate which can then be removed.
- Membrane filtration: Reverse osmosis and nanofiltration can remove most bromine compounds.
- Aeration: Effective for removing volatile free bromine from water.
- Chemical reduction: Addition of sodium thiosulfate or other reducing agents can convert bromine to bromide.
5. Industrial Uses in Water Treatment
Bromine and its compounds have several applications in industrial water treatment:
- Swimming pool and spa water disinfection as an alternative to chlorine.
- Microbial growth control in industrial cooling systems.
- Prevention of biological fouling in desalination membranes.
- Industrial wastewater treatment to remove certain organic compounds.
- Water purification for the pharmaceutical and electronics industries.
8. Environmental Impact and Sustainability Considerations
The use of bromine in water treatment can produce potentially harmful by-products, such as brominated trihalomethanes and haloacetic acid. These compounds can be toxic to aquatic organisms and potentially carcinogenic to humans. Inorganic bromine in the environment tends not to be persistent and can be converted to bromide. However, some organic bromine compounds can persist for long periods in the environment and are potentially bioaccumulative. The bromine industry has been working to improve sustainability by increasing extraction efficiency and recycling bromine from used products.