Assessment of trihalomethane and haloacetic acid formation potential reduction by drinking water treatment processes: Application on iodide and bromide impacted waters

par Henry Mackeown

Disinfectants react with natural organic matter (NOM) to produce undesired disinfection by-products (DBPs). Drinking water resources in coastal areas can be impacted by higher concentrations of iodide leading to iodinated DBP formation which are more toxic than their brominated and chlorinated analogues. Two analytical methods to analyse DBPs by headspace-trap gas chromatography were developed at Lille University: one for the trihalomethanes – with a focus on iodinated species (I-THMs) – and one for the haloacetic acids (HAAs). Those methods were implemented in a collaboration with De Watergroep to look at the removal of these DBP precursors in a full-scale drinking water treatment plant as well as in the assessment of ion exchange resins, as part of an ambitious project to modernize the plant. As well as formation potential tests on real waters, different scenarios of increasing iodide and bromide concentrations were tested. The results were also related to the characterization of the natural organic matter, with the removal of humic substances and building blocks leading to the greatest abatement of THM formation potential during coagulation-decantation and ion exchange treatment. Preformed I-THMs and HAAs were greatly removed by the granular activated carbon filters in the full scale plant, reducing the overall relative cytotoxicity. Amberlite IRA410 had the best performance amongst 4 resins on NOM removal and DBP formation potential reduction.

Key-words: DBPs, chlorination, trihalomethanes, haloacetic acids, natural organic matter, iodide, bromide, ion exchange resins.