The formation potentials of five haloacetic acids (HAA5FP) in 13 surface water samples taken from eight cities from northeast to south China were evaluated using the simulated distribution system (SDS) chlorination method. These samples showed a wide range of HAA5FP levels (20 to 443 μg L−1). Four pre-oxidation methods were evaluated for their performance in enhancing HAA5FP removal from six water samples by coagulation. Pre-Cl2 and pre-KMnO4 were not effective. While pre-ClO2 showed some enhancing effects for all samples, pre-O3 exhibited markedly higher effects without producing perceptible oxidation by-products such as bromate and formaldehyde. An enhancement factor (EF) value of 13–17% was achieved at an ozone dose of 0.5 mg L−1 and the maximum EF values were 16–25% at an ozone dose of 1.5–2.0 mg O3 L−1 (0.3–0.7 mg O3/mg dissolved organic carbon (DOC)). A 3D contour plot was applied to interpret the effects of two independent variables (DOC and specific ultraviolet absorbance (SUVA254)) on the formation potential of HAA5 using a quadratic smoothing technique, and it was found that the enhancing effect on the removal of HAA5FP by pre-ozonation was attributed to the destruction of reactive sites of organic compound, which could be expressed by the changes of SUVA254.

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