BOOK OF ABSTRACTS 263 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Hall A Poster Session / Technologies and Applications P5.5 What Matters: Anthropogenic or Natural Organic Matter? Insights from Three Diverse Drinking Water Treatments in the Czech Republic Sidika Sakalli1, Christoph Steinbach1, Katerina Novotna1, Martin Dusek2, Lenka Cermakova1, Katerina Sichrova1, Martin Pivokonsky*1 1 Institute of Hydrology of the Czech Academy of Sciences, Pod Patankou 30/5, 160 00 Prague 6, Czech Republic, rozankova@ih.cas.cz. 2 Research Institute of Brewing and Malting, 120 00 Prague 2, Czech Republic In the present study[1]hence plenty of compounds are frequently determined in drinking waters, leading to unknown risks for human health. Nontarget analysis (NTA, nontargeted analysis (NTA) using UHPLC-HRMS system was applied to raw and treated water samples from three different drinking water treatment plants (DWTPs) located within the Czech Republic. DWTP1 is supplied by a small reservoir with algae laden source water, it uses granulated activated carbon (GAC) filter as an advanced technology and applies chlorination as a disinfectant. DWTP2 has relatively “clean” water source that is supplied by the Nyrsko Reservoir from protected landscape area, the treatment plan does not use any advanced technology and applies chlorine dioxide as a disinfection process. DWTP3 has humic source water that is supplied by Uhlava River, the treatment plant uses GAC filter and UV radiation as advanced technology and applies chlorination as final disinfection. The specific aims of this study were to (a) compare both the raw and treated water qualities between the distinct DWTPs, (b) assess the performance of the applied treatment process by comparing the NTA results for the raw and treated waters at DWTPs, (c) tentatively identify specific features and compounds based on confidence levels[2] and selected criteria. As expected, the results of this study showed distinct profiles of natural and anthropogenic organic matter among the studied DWTPs and identified differences in the quality of raw and treated waters. In total, 4760 features were determined. After application of background filters, features were reduced to 1173 (25%), and after following manual data cleaning, a total of 829 (17%) features remained. In raw and treated drinking waters, the total number of features was 716 (86%) and 301 (36%), respectively. In raw water, the highest number of features was present in DWTP3 (499), followed by DWTP1 (272) and DWTP2 (118). By contrast, in treated water, the highest number of features was present in DWTP1 (165), followed by DWTP2 (127) and DWTP3 (93). The features were also assigned to the following categories: (i) natural compounds/metabolites; (ii) pharmaceuticals and their respective
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