IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 BOOK OF ABSTRACTS 108 NOM and Aquatic Systems Thursday, 27 August 2026 / Hall C overall treatment efficiency. Moreover, DOM components were categorised by non-target analysis into remained and eliminated features by UV/chlorine. Eliminated components were more reactive than remained ones during UV/ chlorine, affecting degradation of the target micropollutants. For the molecules consisting of C, H, O, and N, unsaturation of carbon skeleton — determined as double bond equivalent subtracted by oxygen number — was a significant factor to interfere reactions between the oxidants and micropollutants (p < 0.05). Molecules including phosphorous or sulphur also consumed oxidants; however, electron-withdrawing functions such as sulfonic acid did not interrupt degradation of the micropollutants. Consequently, results showed that the origin and character of NOM play a significant role on the performance of UV/chlorine treatment for micropollutants degradation. Optimisation of the removal of competitive moieties from the environmental NOM in treatment facilities is a prerequisite for efficient contaminant removal by UV/chlorine. Furthermore, this study revealed that P and S containing organic moieties — except sulfonic acids, and unsaturated carbon are the prioritised structures to be removed by pre-treatments. References 1. U. von Gunten, Water Res. 253 (2024) 121148. 2. Y. Murata, H. Sakai, Chemosphere 374 (2025) 144206. 3. D.B. Miklos, W.L. Wang, K.G. Linden, et al. Chem. Eng. J. 362 (2019) 537. 4. Polar NOM: Characterization, DBPs, treatment, C.J. Hwang, S.W. Krasner, M.J. Sclimenti, et al., Denver, AWWA Research Foundation, 2001. Acknowledgement This study was partially supported by JSPS KAKENHI (Grant number 24KJ1853 and 25H00759).
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