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Phenolic aldehydes are widespread pollutants in water and soil, originating from lignin-based agro-industries. With increasing wastewater pollution, improved treatment systems are necessary to degrade phenolic aldehydes into less hazardous compounds. Over the past two decades, ozonolysis wastewater treatment has been implemented in the United States, Japan, and South Korea. However, the mechanistic understanding of phenolic aldehyde ozonolysis in water remains incomplete. This study investigates the ozonolysis of three model phenolic aldehydes (syringaldehyde, vanillin, 4-hydroxybenzaldehyde) in representative concentrations for wastewater of 0.5–1.5 mM and pH 4–8. Each compound solution was sparged for 30 min at a fixed O3(g) flow (0.20 to 1.00 L min−1), providing steady-state dissolved concentrations of 5.4 to 16.2 μM. Reactant loss and product generation were monitored using UV–visible (UV–vis) spectroscopy, ultra-high pressure liquid chromatography (UHPLC) with UV–vis and mass spectrometry (MS) detection, and ion chromatography with conductivity and MS detection of anions. Identified products based on their mass-to-charge ratio (m/z−) included oxalic acid (89), glycolic acid (75), formic acid (45), and maleic acid (115). Additional intermediate products were identified under various reaction conditions, revealing competing mechanisms in the degradative oxidation of aqueous phenolic aldehydes exposed to O3(g). A unifying mechanism is proposed to explain the production of smaller, less toxic molecules during phenolic aldehyde ozonolysis, enhancing water quality. This mechanism serves as a basis for evaluating the implementation of ozonolysis in scaled-up water treatment processes. 

Iodinated disinfection by-products (I-DBPs) are of growing concern due to their elevated toxicity compared to their chlorinated counterparts, with links to adverse health effects such as bladder cancer and miscarriages. Medical imaging agents like iohexol, commonly used in healthcare facilities, introduce iodine into wastewater systems. This study investigates the photodegradation of iohexol and the subsequent formation of products, including I-DBPs, during simulated final wastewater treatment under chlorination and sunlight exposure. Experiments were conducted with solutions containing 30 μM iohexol, 3 mg L−1 humic acids, and 5.5 mg L−1 hypochlorite. Samples were irradiated at λ ≥ 295 nm and subject to ion chromatography monitoring of I−, IO3−, Cl−, and ClO3−, providing mechanistic insight into the fate of iodide released from iohexol. UV-visible spectroscopy was employed to monitor the degradation profile of iohexol and the concurrent release of iodide. Electrospray ionization mass spectrometry (ESI-MS) identified a range of anionic products based on their mass-to-charge ratios (m/z), including low molecular weight carboxylic acids, their carcinogenic haloacetic derivatives (chloroacetic acid (m/z 93), iodoacetic acid (IAA, m/z 185), and hydroxyiodoacetic acid (m/z 201)) as well as phenolic halides. Notably, IAA was present at a concentration of 0.16 μM at the conclusion of the reaction. These findings elucidate photodeiodination-coupled radical attack, photooxidative cleavage, and halogenation transformation pathways of iodinated compounds during disinfection and underscore the potential risks associated with their presence in wastewater. The results provide valuable insights for medical facilities and wastewater treatment plants aiming to mitigate the formation of hazardous I-DBPs.