As a result, many chlorine alternatives are receiving renewed interest. These include bromine, bromine-chloride, iodine and chlorine dioxide. As complimentary agents for chlorine in water disinfection, ozone is showing the greatest promise, and ultra-violet irradiation limited usefulness.
Ozonation Ozone is a relatively unstable gas. It is a powerful oxidising agent. It eliminates undesirable odour, taste and colour, and removes all chlorine demand from the water. Most importantly, ozone has a strong virucidal effect. It inactivates viruses in a matter of seconds, whereas minutes are required to inactivate them with either chlorine or iodine. The drawback of ozone is that after it has done its job, it decomposes and disappears. There is no residual germicidal effect. The current thinking is that ozone should be used in the pre-treatment of water to destroy not only viruses and bacteria but also organic compounds that are precursors for undesirable chloro-organic compounds that form when chlorine is added. Thus ozonation is usually employed in combination with chlorination. The ozone required for potable water treatment varies between 0.2 and 1.5 mg/l.
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