The most commonly used disinfectant agents are Bromine and Chlorine. They have common advantages as follows:
· being highly lethal to the vast majority of organisms
· being available in reasonably easy to handle forms
· being relatively inexpensive
· having a persistent residual disinfectant action, preventing growth of organisms throughout the system
Disinfection by means of bromine is favoured over chlorine, mainly because it is simpler to control, by virtue of its wider effective pH spectrum.
A side effect of the use of bromine is oxidation of organic contaminants and removal of ammonia from the system.
Bromine dosing is usually based on systems dissolving bromine containing solid tablets(such as BCDMH).
Manufacturers will be responsible for sizing the systems, but to allow for adequate feed pump capacity, one manufacturer recommends the provision of a flow to the brominator of 1 l.min-1 per 10,000 litres of system capacity. Brominator capacities of approximately 1 Kg of tablets per 7.5 m3 of capacity are usual, to give reasonable filling intervals.
Ultraviolet light is also used as a disinfection method. High rates of disinfection are possible with UV, but it leaves no residual disinfectant in the water, unlike chlorine or bromine.
Ozone is a highly reactive form of Oxygen that is gaining in popularity for water treatment.
Like UV, it leaves no residual disinfectant in the water, and therefore the possibility of growth of organisms within the body of the system is a concern. This is often overcome by being used in tandem with Chlorine dosing. Ozone is very toxic to humans, stringent and costly provision for avoidance of Ozone poisoning must therefore be incorporated within the design.
The above is an excerpt from an article on disinfection of water features which may be found on my website. If there are considerations in cooling tower applications which make the choices different, I would be happy to be informed of them.
Seán Moran