Fresh water from three western reservoirs of Singapore was assessed for the formation of trihalomethanes and the removal of precursors in a pilot-scale study. Raw water was processed through flocculation-sedimentation modules in a pilot plant with a capacity of 45 m3/day. Alum was the primary coagulant. Normal coagulation removed 10–60% of THM precursors. Kranji Reservoir, which has a watershed with thick vegetation, had relatively higher levels of dissolved organic matter with correspondingly higher potential for the formation of THM than Pandan Reservoir; Pandan is largely an urban catchment. Land-use pattern and proximity to seashore seem to influence THM formation. UV254 and SUVA were found to be better surrogates than DOC for THM. A benchmark criterion (UV254<0.08 cm−1) for on-line monitoring of THM was deduced from SDS-THM data and this criterion would vary slightly among the water works.

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