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This study elucidated the mechanism and kinetics of ozone decolorization and dechlorination of composite wastewaters obtained from various pulp mill effluents by means of ultrafiltration and freeze drying. These raw samples had similar initial true color but varied color intensity (C.I.) and biodegradability. Both raw and ozone-treated samples were separated into four components to assess the effects of ozonation on individual components. Analytical HPSEC was employed to determine the changes induced by ozonation in molecular weight distribution of lignins and their derivatives.This study revealed that (1) the color intensity, which is an intrinsic property of pulp mill effluents, was a determining factor on the efficiency of ozone decolorization; (2) the kinetics of ozone decolorization appeared to be 3/2 orders with respect to C.I., and the new kinetic model satisfactorily predicted the ozone decolorization of pulp mill effluents; (3) ozone treatment induced varied blue shifts in the UV spectra of various pulp mill effluents; (4) the chromophoric components of lignins and their derivatives preferentially competed for ozone with other organics, but ozone treatment had little effect on the TOC of pulp mill effluents when the dose level was lower than 200 mg/L; (5) ozone treatment seemed to dechlorinate the organics non-selectively and inefficiently compared with other processes; (6) ozone decolorization converted a large amount of high-molecular-weight components (MWCO > 1000) into low-molecular-weight components (MWCO < 1000) which was more biodegradable, although the pattern of the molecular weight distribution of the organics detected at 280 nm showed little effect. Downloaded by [Monash University Library] at

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