1. Complex bromine preparation
In water, complex bromine preparation (such as BCDMH, BCCA) is hydrolyzed into hypobrous (HBrO) and hypochlorous (HClO) acid, rate of releasing HBrO is very fast, while releasing HClO is slow. The positive bromine ion Br＋ from HBrO can further react with HClO or ClO- (hypochlorous radical) to from more active HBrO. HBrO is a complex bromine preparation and is the primary component for Killing microorganisms. Compared with some simple chlorine preparations, such as SDIC and TCCA, brorochlorohydantoin (BCDMH) and rich bromin (BCCA) has the following advantages:
The following chemical equations illustrate the reactions which take place when BCDMH is dissolved in water.
BrClR + 2H2O → HOBr + HOCl + R
bromochlorodimethyl- water hypobromous hypochlorous dimethyl-hydantoin acid acid hydantoin Hypobromous acid partly dissociates to give hydrogen ions and hypobromite ions.
HOBr ® H+ + OBr-
hypobromous hydrogen ion hypobromite ion Therefore, pool water that is disinfected with bromine will contain both hypobromous acid and hypobromite ions.
When acting as a disinfectant hypobromous acid produces bromide ions.
HOBr + Live . → Br- + Dead
hypobromous acid micro-organisms bromide ion micro-organisms
The bromide ions react with the hypochlorous acid which was formed when BCDMH dissolved in water to produce hypobromous acid.
Br- + HOCl → HOBr + Cl-
bromide ion hypochlorous acid hypobromous acid chloride ion.

2. Bromamine formation
Hypobromous acid reacts with ammonia and organic nitrogen compounds to form bromamines.
The following chemical equations illustrate the reactions of hypobromous acid with ammonia.
NH3 + HOBr → NH2Br + H2O
ammonia hypobromous mono- water Acid bromamine
NH3Br + HOBr → NHBr2 + H2O
mono- hypobromous dibromamine water bromamine acid
NHBr2 + HOBr - → NBr3 + H2O
Dibromamine hypobromous tribromamine water acid

3. Properties of bromine and chlorine preparations in comparison 
Under the long period of practice and study, it has been found that the organic chlorine -containing disinfectants can nearly kill all species of microorganisms. They are widely used in various areas, with low cost and easy operation. Yet, the conventional preparations are unstable, easily lose their available chlorine and sensitive to the presence of organic compounds as well as pH value, they have bleaching and corrosive effects on many metals. From the current reports, it is known that they have carcinogenic trends and are more harmful than those inorganic chlorine, bromine and ozone. Hence, to search and develop for a new product with higher disinfecting power, low harmfulness and residuals becomes the point.
At present, the chlorine preparations used as the primary disinfectants are still widely applied in the world. But, recently the tendency of bromine preparations to replace chlorine preparations used as disinfectants have been received more and more attention or eventually the bromine preparations will occupy the market. The main differences between bromine preparations and chlorine preparations for disinfection and killing algae are as follows:

(1). Higher disinfecting activity of bromine preparations than that of chlorine preparations in high pH value water solution and in the presence of ammonia. 
The primary function of disinfect ion is based on the fact that chlorine and bromine preparations are hydrolyzed in water solution to produce corresponding hypochlorous and hypobromous acid which are the key components responsible for disinfections. Yet, the pH values of the solution influence greatly on the activity of chlorine preparation and as the increasing of the pH value, its activity decreases rapidly and approaches zero at around pH value of 8.5. On the contrary, even the pH value is high up to 9.0, hypobromous acid remains in high activity. So in the most water systems with high pH value, the disinfecting power of bromine preparations is greater than that of chlorine preparations.
In the ammonia containing water systems, chlorine preparations will produce monochloramine, which is very stable, although it also has some disinfecting activity, yet lower then that of hypochlorous acid and far lower than that of hypobromous acid. Whereas, bromine preparations will produce a mixture of mono-, di- and tribromo amines. They decompose quickly and give high disinfecting activity, also a little bit higher than that of bromochlorodimethylhydratoin（BCDMH）, and hence far more higher than that of chloramine, as the following curves (in terms of the concentration of hypochlorous and hypobromous acid vs pH value) show.

(2). Lower volatility of bromine than that of chlorine and less evaporation loss. 
From the related curve of the solubility of bromine and chlorine in water, it gives the volatility of bromine in water is about tenfold less than that of chlorine, when they are in the form of hypobromous and hypochorus acid, their volatilities with respect to that of their corresponding gaseous state elements are lowered some what, but the volatility of hypobromous acid is still about tenfold less than that of hypochlorous acid. So bromine preparation is more stable than chlorine preparation, the loss of erective component is likewise less.

(3). Lower oxidizability of bromine than that of chlorine and lower corrosiveness to metals. 
When the corrosion of metals is caused by the action of oxidation, the seriousness of it is comparatively less by bromine preparation than by chlorine preparation, if their boscages in application are same, such fact is still existing in basic water solution or in the presence of ammonia. In the case of requiring a minimum amount of active chlorine in water the corrosion of metal can also be lowered by cooperation with bromine preparation.

(4). Higher rate of degradation of bromine and its compounds and less pollution to surroundings. 
In some conditions, especially in the presence of humus acid, the halogen containing the preparations can be transformed into, such as, chloroform (trichloromethane) and bromoform (tribromomethane ).They are affirmed as a carcinogen. In many countries, their contents in drinking water are strictly controlled, particularly chloroform. Under the given conditions of the formation of chloroform, bromoform can be also formed. But there exists a great difference between them, bromoform is quickly decomposed in water, while chloroform is not, so the harmfulness of the former is far less than that of the later.
The field tests give, the half-life of bromoform is 15 days, and that of chloroform is 50 days. In presence of microorganisms the decomposing rate of bromoform will be faster. When the concentrations of bromine and chlorine water solutions are same, the test of living period of fish shows that after 96 hours fishes in bromine containing water grow well, those in chlorine containing water are dead completely.