Elimination of trichloroanisoles by UV/H2O2: Kinetics, degradation mechanism, water matrix effects and toxicity assessment

Abstract

The elimination of 2,3,6-trichloroanisole (2,3,6-TCA), which produces a musty-earthy off-odor in water, by an ultraviolet (UV)/H₂O₂ process was assessed. The removal of 88.1% of 2,3,6-TCA in ultrapure water (UPW) was achieved using an initial 2,3,6-TCA concentration of 1 μg L^-1 (4.73 nM), a H₂O₂ concentration of 20 mg L^-1 (0.588 mM), a UV intensity of 1.44 mW cm^-2 and a pH of 8.2. The reaction was found to be pseudo first order with a rate constant (k_obs) of 0.0340 min^-1. Both the removal efficiency and k_obs increased significantly upon increasing the H₂O₂ concentration from 10 to 50 mg L^-1. The second order rate constant (k_{HO·,2,3,6-TCA}) in competition kinetic trials was determined to be 8.17 × 10⁷ M^-1s^-1. Degradation products generated during both the UV photolysis and UV/H₂O₂ treatment of 2,3,6-TCA solutions were analyzed using ultrahigh resolution gas chromatography/mass spectrometry, and the degradation mechanism was proposed. The toxicities of water solutions during both processes were assessed via a luminescence method in conjunction with Vibrio fischeri. The pH and Cl^-, HCO₃^- and natural organic matter concentrations of the aqueous medium were all found to significantly affect the removal of 2,3,6-TCA. The degradation rates of trichloroanisoles (TCAs) in real-world water samples demonstrated that UV/H₂O₂ has significant potential with regard to controlling TCAs as pollutants in water.

Keywords: Advanced oxidation process; Degradation mechanism; Kinetics; Toxicity assessment; Trichloroanisoles; Water matrix effects.