ISIA reactors and the Chlorate issue


One of the most undesirable byproducts in generators is the chlorate ion (ClO3-). 

In some generators that operate with relatively low initial reactant concentrations, a significant amount of chlorate is formed by reactions with {Cl2O2}, as shown in reaction:

{Cl2O2} + H2O = ClO3- + Cl- + 2H+ 

{Cl2O2} + HOCl = ClO3- + Cl- + H+ 

{Cl2O2} + 3HOCl + H2O = 2ClO3- + 5H+ + 3Cl- 

Highly acidic (pH <3) reaction mixtures force the degradation of {Cl2O2} to chlorate rather than chlorine dioxide, as well as the direct oxidation of chlorite to chlorate.

The overall reactions that describe chlorate ion formation are:

ClO2- + HOCl = ClO3- + Cl- + H+ 


ClO2- + Cl2 + H2O = ClO3- + 2Cl- + H+

The following conditions may also produce the chlorate ion:

1.Excessively high ratios of Cl2 gas: ClO2-.

2.Presence of high concentrations of free chlorine at low pH in aqueous solutions.

3.Dilute chlorite solutions held at low pH.

4.Base-catalyzed disproportionation of chlorine dioxide at high pH values (pH >11).

5.Reaction mixtures that are highly acidic (pH <3).

6.An excess of hypochlorous acid will directly oxidize chlorite ions to chlorate ions rather than to chlorine dioxide (independent of the rapid formation of the {Cl2O2} intermediate).

ISIA underwater reactors achieve a very high purity chlorine dioxide solution that is the most important feature in case of drinkable water. In fact, to comply with international regulations (WHO, EPA), residual chlorate and chlorite must be kept below 0.7 mg/l. The formation of chlorate takes place in the generators during the reaction and also chlorite formation, in case of desalinated water, is mainly linked to the yield of the reaction. 

According to many years of experience in desalinated water disinfection all over the Middle East (please have a look at the references) and recently in Qatar (certified by Kahramaa), with ISIA submerged generators we can guarantee a negligible formation of chlorate and the highest possible yield of conversion of chlorite into chlorine dioxide. 

Therefore, ISIA always guarantees to comply with international regulations.