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[Display omitted] • Iohexol degradation in Fe 3 O 4 /O 3 system was higher than in O 3 only system. • Trace HBT could enhance iohexol degradation efficiency in Fe 3 O 4 /O 3 system. • 1O 2 and radicals of O H ∙ , and O 2 - ∙ were identified in the Fe 3 O 4 /O 3 /HBT system. • Iohexol degradation mechanisms and pathways in the Fe 3 O 4 /O 3 /HBT system were proposed. This study explored the degradation of an iodine X-ray contrast media, iohexol, under heterogeneous ozone-catalyzed oxidation by adding Fe 3 O 4 and 1-hydroxybenzotriazole (HBT). Results show that increasing the dosages of Fe 3 O 4 catalyst and ozone as well as solution pH were beneficial to the degradation of iohexol. The presence of low background humic acid (HA) concentration (≤10 mg/L) promoted iohexol degradation, but high HA concentration (≥20 mg/L) inhibited it. Adding HBT exhibited a similar effect on iohexol degradation as HA. The degradation rate constant of iohexol was calculated as 0.07108 min−1 in the Fe 3 O 4 /O 3 /HBT process ([HBT] = 5 μM) at pH 7.0, which was approximately 1.5 times higher than that in the Fe 3 O 4 /O 3 process (0.04533 min−1), and 4 times higher than that in the O 3 process (0.01742 min−1). Fe 3 O 4 /O 3 /HBT process was pH-dependent with high degradation efficiency of iohexol at pH 5 or 7. Singlet oxygen (1O 2), hydroxyl radical (OH ∙), and superoxide radical (O 2 - ∙) have been identified in the Fe 3 O 4 /O 3 /HBT process, and the conversion of Fe2+ to Fe3+ was more obvious on the surface of Fe 3 O 4 compared to that in the Fe 3 O 4 /O 3 process. Transformation intermediates were identified, and the degradation pathways of iohexol were proposed. Overall, Fe 3 O 4 /O 3 could enhance iohexol degradation compared with ozone-only system, and adding trace HBT in Fe 3 O 4 /O 3 system can further enhance heterogeneous ozone-catalyzed process for rapid organic matter degradation. [ABSTRACT FROM AUTHOR]

Prometryn is a herbicide that is widely used and frequently detected in aqueous environment and soil. Prometryn is chemically stable, biologically toxic, and easily to accumulate in living bodies, which can cause accumulate in the environment and acute and chronic toxicity to living creatures. In this study, factors affecting the degradation kinetics of prometryn chlorination were studied, including solution pH, bromide and ammonium concentrations, and temperature. Prometryn reacted quickly with aqueous chlorine following the pseudo-first-order kinetics. The maximum pseudo-first-order rate constant (k app) appeared at pH 5 with the observed rate constant (k obs) as 190. 08 h−1; the minimum value of k app reached at pH 9 with k obs as 5.26 h−1. The presence of Br− and increase of temperature both accelerated the degradation rate of prometryn during chlorination. The activation energy was calculated as 31.80 kJ/mol. Meanwhile 6 disinfection by-products (DBPs) were detected, namely: chloroform (CF), trichloroacetonitrile (TCAN), dichloroacetonitrile (DCAN), dichloroacetone, trichloronitromethane (TCNM), and trichloroacetone. Solution pH significantly affected the formation and distribution of DBPs. CF was the most formed carbonated DBP (C-DBP) with the maximum of 217.9 μg/L at pH 8, and its formation was significantly higher in alkaline conditions. For nitrogenated DBPs (N-DBPs), the yields of DCAN and TCAN were significantly higher in acidic conditions, while the maximum of TCNM achieved in neutral conditions. Because the toxicity of N-DBPs is higher than that of C-DBPs, the pH should be controlled in neutral or slight alkaline conditions during prometryn chlorination to effectively control DBP formation and reduce the related toxicity. [Display omitted] • Prometryn chlorination followed pseudo-first-order kinetics. • The highest prometryn degradation rate happened at pH 5. • Br− promote prometryn degradation during chlorination, while NH 4 + inhibited it. • The degradation rate of prometryn increased with increasing temperature. • Solution pH should be controlled at around 7 to reduce the toxicity of DBPs. [ABSTRACT FROM AUTHOR]