BOOK OF ABSTRACTS 95 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Thursday, 27 August 2026 / Hall C NOM and Aquatic Systems SL44 Chlorination vs Chloramination: HRMS-Based Insights into DOM Transformations and Halogenated Byproduct Formation during Disinfection Francisco Zafra-Navarro1,2, Guillem Fernandez-Carrillo2, Saida Marti1, Mira Petrovic1,3 and María José Farré1 1 Catalan Institute for Water Research (ICRA), Carrer Emili Gahit, 101, 17003 Girona, Spain. fazafra@icra.cat 2 University of Girona (UdG), Plaça de Sant Domènec, 3, 1704 Girona, Spain. 3 Catalan Institution for Research and Advanced Studies (ICREA), Passeig Lluís Companys, 23, 08010 Barcelona, Spain. Disinfection is a critical step in drinking water treatment. Chlorination remains the most widely used method due to its simplicity and costeffectiveness; however, its reaction with dissolved organic matter (DOM) leads to the formation of disinfection byproducts (DBPs). As an alternative, chloramination is frequently applied to reduce the formation of regulated DBPs, although it promotes the formation of a broader range of nitrogen-containing DBPs (N-DBPs), many of which remain poorly characterized and unregulated. Despite their relevance, a systematic molecular-level comparison of how these disinfection strategies transform DOM remains limited. In this study, we compare the molecular-level transformations of DOM induced by chlorination and chloramination using high-resolution mass spectrometry (HRMS). Controlled disinfection experiments were performed on the same water matrix to enable direct comparison of halogenated DOM (X-DOM) formation and to identify compositional shifts across van Krevelen space. This approach allows the identification of specific molecular regions preferentially affected by each disinfectant and provides a detailed assessment of halogenation pathways. Current HRMS data processing reveals consistent differences in DOM reactivity depending on the disinfectant applied. Distinct halogenation patterns are observed, with chloramination leading to a higher diversity of nitrogencontaining molecular formulas, indicating distinct reaction pathways under each disinfection strategy. To further evaluate the influence of DOM origin, seasonal variability, and disinfectant selection, multiple sampling campaigns were conducted throughout two years. Raw water samples from reservoirs and rivers across Europe were analyzed before and after disinfection. Ongoing data treatment enables crosscomparison of DOM compositional features and halogenated signals across case studies, providing insights into
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