Controlling the Formation of Chlorate Ion in Liquid Hypochlorite Feedstocks

Experiments were carried out to confirm the presence of chlorate ion (ClO3−) in the treated water of utilities that use hypochlorination. Sixteen commercially produced, concentrated liquid hypochlorite feedstocks were analyzed for ClO3−, and levels as high as 158 g percent ClO3− relative to hypochlorite ion were measured. Finished‐water samples from the utilities surveyed contained as much as 0.30 mg ClO3−/L, primarily the result of decomposition of the liquid hypochlorite feedstocks. Although both dilution and lower temperatures can be effective in minimizing ClO3− formation, it was observed that diluting the initial liquid hypochlorite concentration by a factor of 2 is more effective than decreasing the temperature from 24 to 10°C. A methodology is proposed that predicts the dilution or temperature reduction (or both) required to avoid significant ClO3− formation in the feedstock solutions.