Owing to the strong oxidation potential, ozone has been used widely in advanced water treatment. However, degradation and oxidation efficiencies of NOM (Natural Organic Matter) by the traditional ozone contact system are normally believed to be low. Oxidation efficiency of NOM by the PHOC (Pressurized High Ozone Contact) method was compared with that by the MOC (Mechanical Ozone Contact, the traditional system) method for the drinking water treatment. Sand filtered water of the drinking water treatment plant was used for experimental samples. Removal rates of UV254 absorbance, KMnO4 consumption and DOC by the MOC system were 18.4%, 2.39%, and 2.72% respectively with 1 mg-O3/L. On the other hand, removal rates of KMnO4 consumption, TOC, DOC, UV254 absorbance and SUVA by the PHOC system were 8–20%, 7.52–34.4%, 6.65–18.2%, 37.4–60.8% and 33.8–60% with 1–3 mg/L of ozone concentrations. Concentration of BDOC after ozone application was 0.003–0.044 mg/L by the MOC method, while 0.084–0.044 mg/L by the PHOC method with 1–3 mg/L of ozone concentrations. Concerning molecular weight distribution, fractions of NOM below 1 kDa were increased by the PHOC method of ozone application. Analysis shows that the reason for overall enhancement of the treatment efficiencies by the PHOC system is because contacting surface area of numerous micro ozone bubbles was increased dramatically in the PHOC system, and oxidation potential was enhanced by increased ozone concentrations in the ozone contact tank. Thus, it is understood that the PHOC method is a more efficient system for ozone application than the traditional MOC system in drinking water treatment process.

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