Application of Breakpoint Chlorination for Removal of Nitrogen

Complete removal of the 25-40 mg per liter ammonium-N is far too costly by this method. Chlorine costs about 38-45 US cents per kg, which means that the chlorine consumption alone will cost about 14 US cents per m3 waste. When the capital cost and the other operational costs are added the total treatment cost will be as high as 30-45 US cents per m3, which is considerably more expensive than other nitrogen removal methods.

It is possible to use chlorine to oxidize ammonium compounds to free nitrogen, but this process involves even higher chlorine consumption and, is therefore, even more expensive.

The formation of organic chlorine compounds is another crucial disadvantage of this process, because discharge of these compounds should be avoided due to their high toxicity.

The method has, however, two advantages:

1) By using sufficient chlorine it is possible to obtain a very high efficiency.

2) The low spatial requirement makes it particularly suitable for certain applications, including addition to an existing facility, where nitrogen removal Is required, but space constraints exist.

This means that the method has found application mainly after other ammonium removal methods, where high efficiencies are required. This is the case when the waste water is reclaimed, for example in the two plants shown in Figs, 7.19 and 8.2. As can be seen, it is necessary to use several treatment processes to achieve a sufficient water quality after the treatment. Chlorination and treatment on activated carbon are used as the last treatment to assure good ammonium removal and sufficient disinfection of the water. An additional chlorination is even used after the treatment on activated carbon to ensure a chlorine residue in the water supply system. Note that the solution in Fig. 7.19, where the major portion of ammonium-nitrogen is removed by stripping before the residue of ammonium-N is removed by breakpoint-chlorination, is preferable, because the operating costs become more limited due to the pronounced lower consumption of chlorine.

It should be mentioned in this context that ozonation, which is a disinfection process widely used for treatment of water and related to chlorination, is able to oxidize amines. It is possible by ozonation to oxidize amines completely to nitrite and nitrate, provided that ozone is used in a ratio to the concentration of amines slightly above the stoichiometric ratio; see Elmghari-Tabib et al., 1982.

Ozone is also able to oxidize ammonia to nitrate. This process is catalyzed by the presence of bromide ions; see Haag et al., 1984.

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