Catalytic ozonation is a promising treatment method for both water and wastewater. In this study, in order to increase the biodegradability of bleaching wastewater from an integrated pulp- and -paper production plant, granulated activated carbon-(GAC), iron-(Fe2+) and manganese-(Mn2+) ion-catalyzed ozonation processes were used as a pre-treatment process. The effects of the catalyst concentration and the initial pH (pH(i)) of wastewater on the treatment efficiency of processes were investigated. Although metal-ion-catalyzed ozonation at pH(i)=7 led to an increase in the biodegradability of wastewater a similar treatment performance was obtained by mere ozonation process at natural pH of wastewater (pH=10). The integration of ozone with GAC resulted in both higher treatment efficiency and the regeneration of GAC. The BOD5/COD ratio of bleaching wastewater increased from 0.11 to 0.29 by the application of O-3/GAC (10 g.L-1)/pH(i)=10 process within a 60-minute treatment period. While 50% overall COD removal rate was obtained by the O-3/GAC (10 g.L-1)/pH(i)=10 process overall COD removal was increased to 63% by decreasing the initial pH of wastewater to 7.