IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 BOOK OF ABSTRACTS 74 Research Frontiers Tuesday, 25 August 2026 / Hall B+C Fe(III) flocs create a reactive matrix that enhances subsequent Fe(VI) oxidation efficiency, broadening the NOM removal spectrum beyond what either coagulant achieves alone. FEEM-PARAFAC analysis resolved three fluorescent components: C1 (protein/aromatic-like), C2 (fulviclike), and C3 (humic-like). While Fe(III) provided broader, more uniform removal across all three components, sequential Fe(III) → Fe(VI) at pH 5.5 achieved 59% total fluorescence intensity reduction, which was the highest among all combined strategies, confirming the complementary targeting of fluorophoric NOM fractions under this approach. Post-coagulation impacts: settleability, disinfection, and biostability Three post-coagulation effects merit consideration when transitioning from Fe(III) to Fe(VI). First, Fe(VI)-generated flocs settled 62% more slowly than Fe(III) flocs, necessitating extended sedimentation retention times or enhanced flocculation design. Second, Fe(VI) demonstrated outstanding disinfection performance, achieving >7-log E. coli inactivation, which was double the efficiency of equivalent chlorine, representing a genuine multibarrier benefit at the pretreatment stage. Third, and critically from a NOM perspective, Fe(VI) coagulation elevated NOX-AOC approximately 10-fold relative to Fe(III), reflecting the accumulation of short-chain carboxylates from oxidative NOM scission. This fundamental shift in the NOM substrate profile increases downstream biofilm risk and necessitates a polishing step to restore biostability prior to distribution. Acknowledgement We appreciate the substantial support from NV PWN Water Supply Company North-Holland, a public water utility, for providing access to the treatment facility, natural raw water samples, and instrumental assistance in conducting LC-OCD-UVD and AOC analyses.
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