BOOK OF ABSTRACTS 121 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Thursday, 27 August 2026 / Hall C NOM and Aquatic Systems mass ratio was kept constant. Measures of floc strength indicated that these IEX pre-treated flocs could also maintain a larger size on exposure to increased shear rates. In relation to water character, IEX pre-treated had a much reduced sulphate and phosphate content, while chloride ions were significantly increased. Addition of aluminium and ferric sulphate coagulants into IEX pre-treated water did somewhat increase the sulphate concentration again, but to much lower levels than were seen in the original source water. Further experiments were then undertaken in a controlled manner using a model NOM surrogate (humic acid), where sulphate and phosphate ions were incrementally added to the water and subsequent floc analysis was carried out. Significant differences in floc size and strength were identified with changing ion concentration. In addition changes in floc structure were also observed to occur as a result of different interactions between natural organic matter and coagulant depending on the nature of the DOC. Coagulation of different model organic compound solutions was shown to form a range of floc sizes and strength depending on the character of the organic molecule, with molecular weight and hydrophobicity being important controlling factors. The results from these experiments have shown that both inorganic ions (sulphate and phosphate) and organic matter play a critical role in controlling the floc formation process during NOM coagulation. These results provide an explanation for why improvements in clarification occurs following ionexchange pre-treatment of NOM-laden water sources, as well as providing a potential way of manipulating the background ion-balance for water sources that do not currently plan to install ion-exchange for DOC removal. References 1. Jarvis, P., Mergen, M., Banks, J., McIntosh, B., Parsons, S. A., Jefferson, B. (2008). Pilot scale comparison of enhanced coagulation with magnetic resin and coagulation systems. Environmental Science and Technology, 42 (4), 1276-1282. X. Author, Y. Author, Z. Author, Nature 20 (2001) 537. 2. Liu, M., Liu, X., Graham, N.J. and Yu, W., 2024. Uncovering the neglected role of anions in trivalent cation-based coagulation processes. Water Research, 254, p.121352. Acknowledgement The authors greatly appreciate and acknowledge the funding of the project from Anglian Water and the Sue White Fund for Africa
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