Advanced oxidation processes (AOPs), such as hydroxyl radical (HO)- and sulfate radical (SO)-mediated oxidation, are alternatives for the attenuation of pharmaceuticals and personal care products (PPCPs) in wastewater effluents. However, the kinetics of these reactions needs to be investigated. In this study, kinetic models for 15 PPCPs were built to predict the degradation of PPCPs in both HO- and SO-mediated oxidation. In the UV/HO process, a simplified kinetic model involving only steady state concentrations of HO and its biomolecular reaction rate constants is suitable for predicting the removal of PPCPs, indicating the dominant role of HO in the removal of PPCPs. In the UV/KSO process, the calculated steady state concentrations of CO and bromine radicals (Br, Br and BrCl) were 600-fold and 1-2 orders of magnitude higher than the concentrations of SO, respectively. The kinetic model, involving both SO and CO as reactive species, was more accurate for predicting the removal of the 9 PPCPs, except for salbutamol and nitroimidazoles. The steric and ionic effects of organic matter toward SO could lead to overestimations of the removal efficiencies of the SO-mediated oxidation of nitroimidazoles in wastewater effluents.

Excited triplet states of chromophoric dissolved organic matter (3CDOM*) are highly reactive species in sunlit surface waters and play a critical role in reactive oxygen species (ROS) formation and pollutant attenuation. In the present study, a series of chemical probes, including sorbic acid, sorbic alcohol, sorbic amine, trimethylphenol, and furfuryl alcohol, were employed to quantitatively determine 3CDOM* and 1O2 in various organic matters. Using a high concentration of sorbic alcohol as high-energy triplet states quencher, 3CDOM* can be first distinguished as high-energy triplet states (>250 kJ mol–1) and low-energy triplet states (<250 kJ mol–1). The terrestrial-origin natural organic matter (NOM) was found to mainly consist of low-energy triplet states, while high-energy triplet states were predominant in autochthonous-origin NOM and effluent/wastewater organic matter (EfOM/WWOM). The 1O2 quantum yields and electron transfer quantum yield coefficients (f TMP) generated from low-energy triplet states remained constant in all tested organic matters. External phenolic compound showed quenching effects on triplet-state formation and tended to have a higher quenching efficiency for aromatic ketone triplet states, which are the main high-energy triplet states. In comparison with terrestrial-origin NOM, autochthonous-origin NOM and EfOM/WWOM presented lower reaction rate constants for sorbic amines and higher reaction rate constants for sorbic acid, and these differences are likely due to dissimilar surface electric charge conditions. Understanding the triplet-state photochemistry of CDOM is essential for providing useful insights into their photochemical effects in aquatic systems.

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The photochemical formation and decay rates of superoxide radical ions (O 2•− ) in irradiated dissolved organic matter (DOM) solutions were directly determined by the chemiluminescent method. Under irradiation, uncatalyzed and catalyzed O 2dismutation account for ∼25% of the total O 2•− degradation in air-saturated DOM solutions. Light-induced O 2•− loss, which does not produce H 2 O 2 , was observed. Both the O 2•− photochemical formation and light-induced loss rates are positively correlated with the electron-donating capacities of the DOM, suggesting that phenolic moieties play a dual role in the photochemical behavior of O 2•− . In air-saturated conditions, the O 2 •− quantum yields of 12 DOM solutions varied in a narrow range, from 1.8 to 3.3‰, and the average was (2.4 ± 0.5)‰. The quantum yield of O 2•− nonlinearly increased with increasing dissolved oxygen concentration. Therefore, the quantum yield of one-electron reducing intermediates, the precursor of O 2•− , was calculated as (5.0 ± 0.4)‰. High-energy triplets ( 3 DOM*, E T > 200 kJ mol −1 ) and 1 O 2 quenching experiments indicate that 3 DOM* and 1 O 2 play minor roles in O 2•− production. These results are useful for predicting the photochemical formation and decay of O 2•− in sunlit surface waters.

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