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matte rinatio ganic entials elope f ozon to the refore g wate tion; O The dominant organic precursors of THM formation in the cluding direct ozone and indirect hydroxyl radical ozone reac-water environment would be aquatic NOMs, mainly consist of humic substance Boyce and Hornig 1983; Rook 1976. However, aquatic humic substances are complicated by its uncertain chemi-cal structure. Many studies have focused on the reaction of chlo-rine with simple organic species in humic substance. It had been reported that aliphatic carboxylic, hydroxybenzoic acid, phenol, and pyrrole nitrogen derivatives were the main functional groups observed in the model compounds such as resorcinol, phloroglu-cinol, and p-hydroxybenzoic acid Richardson et al. 1999; Boyce and Hornig 1983. Moreover, these simple organic matters are tions, which are affected by different pH levels Westerhoff et al. 1998; Daniel et al. 1999; von Gunten 2003. At high pH, ozone reacts with hydroxyl ions OH− as a catalyst and yields many kinds of free radical such as ·OH, O2−·, and HO2−·, etc., which is also called the indirect ozonation. However, there are inhibitors including tert-butanol, p-chlorobenzoate, carbonate, and bicar-bonate ions, which would limit and inhibit the hydroxyl radical formation resulted in reducing the performance of ozonation Jan