Degradation of the earthy and musty odorant 2,4,6-tricholoroanisole by persulfate activated with iron of different valences

Abstract

2,4,6-Trichloroanisole (TCA) is an odorous compound that is often detected in tap water and is difficult to be removed via water treatment. In this study, the transformation efficiency of TCA in the presence of persulfate (PS) activated by iron (Fe²⁺, Fe⁰, and Fe³⁺) was investigated for the first time. The effects of the activator dosage, oxidant dosage, pH, dosing method, chelating agents, humic acid, and temperature were evaluated. The degradation rate of TCA increased with increasing PS dosages (0.12–0.48 mM) and initial Fe²⁺ concentrations (0.12–0.96 mM), while it decreased with higher Fe²⁺ concentrations. Fe²⁺/PS and Fe⁰/PS systems achieved their best TCA removal efficiency at pH 7 and 2.5, respectively. According to the results of electron paramagnetic resonance (EPR), the contribution of SO₄⁻• to TCA degradation was much higher than that of •OH. Gradual addition of Fe²⁺ improved TCA degradation compared to single addition. Citric acid (CA) promoted TCA degradation under Fe²⁺/PS at the beginning of the reaction, but inhibited it after 10 min. Ethylenediaminetetraacetic acid (EDTA) improved the TCA removal rate with an EDTA/Fe²⁺ molar ratio of 0.5:1, while it decreased it at higher EDTA/Fe²⁺ molar ratios. Oxalic acid (OA) negatively affected TCA degradation with increasing OA/Fe²⁺ molar ratios. Among all of the chelating agents, only CA increased TCA degradation by Fe⁰/PS. Humic acid promoted TCA degradation by Fe²⁺/PS at the proper dosage (1 mg/L). Under our specific conditions and over the temperature ranging from 10 to 25 °C, no change was observed in the reaction kinetics. It was found that 2,4,6-trichlorophenol (TCP) was the only detected oxidation product. The presence of an Fe²⁺-Fe³⁺ redox cycle in iron-activated PS systems was confirmed by TCA degradation under the Fe³⁺/PS system.