Integration of ozone and aranular activated carbon (GAC) was applied to treat highly concentrated real wastewater from chemical industry. The results revealed that the integrated process had more advantages than the individual ozonation and GAC adsorption. The integrated process enhanced COD removal, increased ozone utilization and avoided frequent GAC regeneration. The pH value was found to exert a great effect on COD removal: a positive effect on COD removal was more pronounced at basic conditions than at acidic conditions. Furthermore, there were some differences in reaction mechanisms at different pH conditions, as confirmed by FTIR and SEM analysis. At the acidic conditions, the primary reaction mechanism was adsorption-ozonation regeneration, while at the basic conditions, GAC adsorption ability was restrained, and the primary mechanism was catalytic oxidation. (c) 2007 Elsevier B.V. All rights reserved.