Iron-based advanced oxidation technologies, such as the Fenton process, are widely used for industrial wastewater treatment. However, wastewater sometimes contains chelating agents such as detergents, stabilizers, and masking agents for metallic ions, which have a potential to inhibit the iron-based advanced oxidation process through the masking of iron. In this research, we investigated the influence of chelating agents on Fenton-type reaction using ferrous ion (Fe 2+ ) and hypochlorous acid

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... OCl). Chelating agents tested were oxalic acid, ethylenediaminetetraacetic acid (EDTA) and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP). Hydroxyl radicals generated were determined by 1,4-dioxane degradation. When HOCl was reacted with Fe 2+ at pH 6.0, oxalic acid and EDTA strongly inhibited the 1,4-dioxane degradation. However, the inhibition effect declined at acidic pH because of the protonation of carboxyl groups in the chelating agents. The HEDP differed from the other chelating agents in the inhibition effect. It showed the inhibition effect only under the low dose at pH 6.0. On the contrary, the higher dose and acidic pH enhanced the 1,4-dioxane degradation efficiency. The regeneration of Fe 2+ from ferric ion (Fe 3+ ) by the degradation of Fe 3+ -HEDP complex was inferred to be responsible for the enhancement effect.