The paper presents an overview and discussion on the link between natural organic matter (NOM) character and its treatability by coagulation. Trials were conducted on a series of bench scale and pilot plant trials on three source waters: two from UK moorland catchments and one from a US snow melt source. Overall the work demonstrates the importance of the polarity balance and the charge density of the NOM contained within the source water. The hydrophobic content controls the coagulant demand such that variation in the demand between sources or sampling periods can be accounted for by changes in the hydrophobic content and its charge density. The raw water hydrophilic content, and specifically the nonacid fraction, provides a useful indicator of the achievable residual. Analysis of coagulation performance revealed a clear relationship between zeta potential and residual DOC. For each source an operational zeta potential range exists within which the residual concentration is optimal. Comparison of the ranges achieved during each trial demonstrated that a communal range between −10 and +3 mV exist for all waters thus providing a useful guide range for operational control.

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