Water treatment processes produce water with low turbidity and colour. It is also now becoming necessary to reduce DOC (Dissolved Organic Carbon) so that less chlorine is lost in a distribution system and less THMs (trihalomethanes) are formed. Enhanced coagulation (exceeding other requirements) at pH of about 5-6 is known to significantly reduce DOC so that acceptable water quality can be achieved at the tap. In this paper, models are integrated to project the impact of water treatment on water quality through the entire distribution system. A DOC removal model, which predicts DOC resulting from a given coagulant, its dose and the coagulation pH, is used to simulate the treatment. By linking this model of DOC removal with models of chlorine decay and THM formation, the impact of treatment on chlorine and THM concentrations in a distribution system can be simulated. This method was applied in a case study with relatively high initial DOC. It was shown that more DOC can be removed by using ferric coagulant than the current practice achieves. This would result in an improved chlorine profile and a substantial reduction in THM concentrations.

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