A pre-ozonation step to oxidise iodide to iodate is an efficient process to mitigate the formation of iodinated disinfection by-products (I-DBPs) and bromate in drinking water treatment.
The presence of iodinated disinfection by-products (I-DBPs) in drinking water poses a potential health concern, since it has been shown that I-DBPs are generally more genotoxic and cytotoxic than their chlorinated and brominated analogues.
I-DBPs are formed during oxidation/disinfection of iodide-containing waters, by reaction of transient hypoiodous acid (HOI) with natural organic matter (NOM).
This Australian–Swiss study demonstrates that ozone pre-treatment selectively oxidises iodide to iodate and avoids the formation of I-DBPs. Iodate is non-toxic, and is therefore a desired sink of iodine in drinking water.
Complete conversion of iodide to iodate while minimising bromate formation to below the guideline value of 10 μg/l was achieved for a wide range of ozone doses in five raw waters with dissolved organic carbon (DOC) and bromide concentrations of 1.1–20 mg/l and 170–940 μg/l, respectively.
Lowering the pH effectively further reduced bromate formation, but had no impact on the extent of iodate and bromoform formation – the main trihalomethane (THM) formed during ozonation.
Experiments carried out with pre-chlorinated/post-clarified samples already containing I-DBPs, showed that ozonation effectively oxidised I-THMs.
Therefore, in iodide-containing waters, in which I-DBPs can be produced on chlorination or especially chloramination, a pre-ozonation step to oxidise iodide to iodate is an efficient process to mitigate I-DBP formation.
Water Research, Volume 47, Issue 6, 15 April 2013, Pages 1953–1960.
