Formation of iodinated trihalomethanes after ferrate pre-oxidation during chlorination and chloramination of iodide-containing water

• Ferrate pre-oxidation is very effective in minimizing I-DBPs formation.
• pH effects the transformation of iodide to iodate during ferrate oxidation.
• Bromide could restrain the transformation of iodide during ferrate oxidation.

Iodinated disinfection by-products (I-DBPs) are responsible for taste and odor issues, and more toxic than their brominated and chlorinated analogs. Ferrate salt (Fe(VI)) is green, efficient and multifunctional in drinking water treatment. Iodinated trihalomethanes (I-THMs) formation of iodide containing water pretreated by ferrate during chlorination/chloramination was investigated in this paper. The results indicated that I-THMs can be reduced significantly by ferrate pre-oxidation due to the oxidation of iodide to iodate. During chlorination, no detectable I-THMs were found at pH < 8 after ferrate pre-oxidation. However, I-THMs formation increased significantly at pH 8–9. I-THMs formation decreased drastically with increasing ferrate dosage and no detectable I-THMs were found at high ferrate dosage (>2 mg/L). The presence of high bromide concentration could restrain the transformation from iodide to iodate during ferrate pre-oxidation. However, no obvious changes in the amount and speciation of I-THMs were observed with increasing bromide addition. The yield of I-THMs was within 15 ± 2 µg/L when bromide addition varied. During chloramination, compared to the samples without bromide, the formation of I-THMs was restrained too. However, increasing bromide concentration in chloraminated solutions would lead to significant increase in the I-THMs formation and could contribute to the changes in speciation. The yield of I-THMs increased from 16.11 µg/L to 33.28 µg/L when bromide concentration is 25 µM and 100 µM, respectively. Ferrate pre-oxidation can be employed to reduce the I-THMs formation in drinking water treatment for iodide-containing water.

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