The removal of Odours and Flavours


The presence of odours and flavours in water is due to numerous compounds, both from natural origin and resulting from pollution phenomena, namely:

1) Metabolites of organisms (algae, actinomycetes, and the likes) present in surface waters;
2) Phenolics, originating from industrial pollution, or the decay of algae, or, together with chloramines, formed in cases where the water has been pre-oxidized with chlorine;
3) Chlorides and bromides present in ground waters affected by sea water contamination;
4) Hydrocarbons, derived from pollution. The oxidizing, bactericidal, fungicidal, algaecidal actions of ClO2 makes it used to improve the organoleptic characteristics of the water with the advantage of avoiding the formation of chlorophenols and chloramines. However, its non-reactivity with some hydrocarbons may render it ineffectual for the removal of odours related to them.

A common application of chlorine dioxide in drinking water in the United States is the control of tastes and odours associated with algae and decaying vegetation. Chlorine dioxide is also effective in destroying taste and odour producing phenolic compounds. The recommended location for application of chlorine dioxide for this purpose will depend on raw water quality, the type of treatment plant and any other purposes for chlorine dioxide addition. In conventional treatment plants, it is recommended that chlorine dioxide be added near the end of or following, the sedimentation basin. If the raw water turbidity is low (for example, less than 10 NTU), chlorine dioxide can be added at the beginning of the plant. Some utilities follow this practice because chlorine dioxide is effective in controlling algae growth in flocculation and sedimentation basins that are exposed to sunlight (DeMers and Renner, 1992). Such application during periods of darkness may be more successful for nuisance algae control.