BOOK OF ABSTRACTS 157 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Friday, 28 August 2026 / Hall C NOM and Aquatic Systems SL80 THMFP-Based Evaluation of DOM Reactivity Across VF–HF–GDM Treatment Stages Liza Saharani Hamzah1 and Jongkwan Park2 1 Changwon National University, Department of Environmental Engineering, 20 Changwondaehak-ro, Uichang-gu, Changwon-si, Gyeongsangnam-do 51140, Republic of Korea 2 Changwon National University, Department of Environmental Engineering, 20 Changwondaehak-ro, Uichang-gu, Changwon-si, Gyeongsangnam-do 51140, Republic of Korea, email: jkpark2019@changwon.ac.kr To provide a more practically relevant assessment of low-energy water treatment systems, evaluation has increasingly shifted from bulk organic matter removal toward disinfection by-product (DBP) precursor reactivity, as DBP formation potential is governed by NOM characteristics rather than bulk organic concentration alone, highlighting the critical role of NOM composition in DBP control [1–2]. In this study, a labscale treatment train consisting of a vertical-flow wetland (VF), a horizontalflow wetland (HF), and a gravity-driven membrane (GDM) was evaluated using trihalomethane formation potential (THMFP) to assess dissolved organic matter (DOM) reactivity. The VF stage achieved substantial dissolved organic carbon (DOC) removal of almost 80%, yet specific THMFP increased from 0.0030 to 0.0037–0.0062 µg/mg-DOC. This increase corresponded to higher SUVA, enhanced humic-like fluorescence, and the persistence of intermediate-molecular-weight fractions, indicating enrichment in more reactive DOM despite bulk removal, consistent with previous studies showing that microbial transformation preferentially enriches aromatic and humified DOM fractions [3]. In contrast, the HF stage reduced specific THMFP to 0.0007– 0.0024 µg/mg-DOC, accompanied by decreased SUVA, lower fluorescence intensity, and a shift toward lower molecular weight fractions, reflecting transformation to less reactive DOM. Across the GDM unit, specific THMFP further decreased from 0.0113 to 0.0064 µg/mg-DOC, despite minimal changes in DOC (~3.5 to ~4.6 mg/L). This reduction was associated with decreased SUVA, attenuation of humic-like components, and removal of high-molecular-weight fractions, indicating selective retention of reactive DOM within the fouling layer. These results demonstrate a clear decoupling between DOC concentration and DBP formation potential. While the VF stage increased DOM reactivity through compositional enrichment, the HF and GDM stages progressively reduced reactivity via transformation and selective removal mechanisms. Overall, the findings confirm that DBP
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