Bromine basics: bromine is a popular choice when it comes to hot water sanitization. Here are some tips on working with chlorine's halogen cousin.
When bromine is added to water, it forms the sanitizer and oxidizer hypobromous acid (HOBr). Like hypochlorous acid, hypobromous acid reacts with contaminants in water resulting in combined bromine (bromamines). Compared to chloramines, bromamines are less irritating to skin and eyes and create less odor. There's no need to eliminate bromamines with a "breakpoint" procedure; they rapidly decompose.
After its sanitizing and oxidizing power is depleted, hypobromous acid ultimately reverts to bromide ions (Br-). The concentration of these ions in water is called the bromide "bank," and it has no further sanitizing potential.
However, a bromide ion can be reactivated to hypobromous acid by an oxidizer like chlorine or potassium monopersulfate. If chlorine is added to a spa previously sanitized with bromine, it will only regenerate the established bromide bank. Thus, the spa must be completely drained and refilled with fresh water in order to convert from bromine to chlorine sanitizer.
Spas differ from pools in two respects: higher temperatures and smaller volumes. Bromine remains effective at the increased temperatures found in spas, and its efficiency is practically independent of pH (a definite benefit in spas, where pH can fluctuate due to the smaller volume).
For example, at a pH of 7.5, 94 percent of bromine versus 50 percent of chlorine is in the killing form. While at a pH of 8.0, bromine is at 83 percent efficiency and chlorine is only at 22 percent.
Bromine is destroyed by sunlight at a slower rate than unstabilized chlorine, but faster than with stabilized chlorine. Therefore, bromine is most commonly used in covered or indoor spas.
Various bromine products are available commercially for spa use. Each has unique properties, but all of them produce hypobromous acid when added to water. In most cases, bromine is added to a spa using an erosion feeding system to ensure that a steady stream of sanitizer enters the water. The following outlines the three most commonly used forms of bromine:
* BCDMH (1-bromo-3-chloro-5,5-dimethylhydantoin) is commonly found in bromine tablets. When immersed in water, this chemical hydrolyzes into hypobromous acid and an equal amount of hypochlorous acid, which automatically regenerates the bromide bank. BCDMH has a pH of 4.8 in a 1 percent solution, a strength of 92.5 percent and an available chlorine content of 56 percent.
Bromine (BCDMH) + Water (H2O) [right arrow] Hypobromous Acid (HOBr) + Hypochlorous Acid (HOCl)+ Dimethylhydantoin (DMH)
* DBDMH (1,3-dibromo-5,5-dimethlyhydantoin), sometimes inaccurately referred to as "pure bromine," undergoes a reaction similar to that of BCDMH when added to water. However, this substance does not contain chlorine and therefore requires the use of a separate oxidizer (chlorine or potassium monopersulfate) to regenerate the bromide ions. It has a pH of 3.6-4.6 in a 1 percent solution and a strength of 54 percent.
Bromine (DBDMH) + Water (H20) [right arrow] Hypobromous Acid (HOBr) + Dimethylhydantoin (DMH)
* Bromide Salt/Oxidizer Systems are a two-part approach to sanitization in which a bromide salt such as sodium bromide is added to spa water to establish a bromide bank. An oxidizer (usually potassium monopersulfate, buffered to neutralize its acidity) is added to convert the bromide ions to hypobromous acid. The pH of sodium bromide is 6.5-8.0.
Sodium Bromide (NaBr) + Potassium Monopersulfate (KHSO5) + Hydrogen Ion (H+) [right arrow] Hypobromous Acid (HOBr) + Potassium Bisulfate (KHSO4)
One important thing to remember is that bromine is a slightly acidic sanitizer and lowers total alkalinity. Spa equipment can suffer damage due to corrosive water if an operator allows the total alkalinity of the water to become depleted. Regular testing is a must as is treatment to replenish total alkalinity with sodium bicarbonate as necessary.
While not as strong of an oxidizer as chlorine, bromamines are still good sanitizers and oxidizers. There's no need to test for both free and combined bromine, only the total bromine residual. Bromine can be analyzed with test strips using the syringaldezine method or with wet chemistry kits employing DPD, FAS-DPD or OT chemistries. You can use a chlorine comparator to test a bromine-sanitized pool and vice versa.
If a chlorine comparator is used, simply multiply the result by 2.25 to determine ppm bromine. To convert from bromine to chlorine, divide the bromine value by 2.25. Premium test strips and comparators include dual sanitizer values to measure bromine or chlorine without conversion.
Combination ozone/bromine systems have become increasingly popular, particularly for spas. Ozone's powerful oxidizing ability allows the use of less bromine than with bromine alone.
If you're responsible for a spa using one of these systems, don't forget that ozone breaks down in minutes--too quickly to provide full-time protection for bathers. For this reason, an adequate bromine residual must always be maintained.
Commercial spas should be tested according to applicable health codes. Water chemistry parameters for all spas should be maintained within accepted industry standards.
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|Title Annotation:||Tech Talk|
|Date:||Mar 1, 2005|
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