Laboratory experiments were undertaken to investigate the treatment performances of ozonation alone and/or its combination with granular activated carbon (GAC) adsorption for raw leachate from the NENT landfill (in Hong Kong). To improve its removal of recalcitrant contaminants from the leachate, the surface of GAC was oxidized with ozone prior to treatment. With respect to ozone dose and pH, the removal of COD and/or NH3-N from ozonation alone and combined ozone-GAC adsorption were evaluated and compared to those of other physico-chemical treatments in some reported studies. The removal mechanism of recalcitrant compounds by ozone-GAC adsorption treatment was presented. Among the various treatments studied, the combination of ozone-GAC adsorption using ozone-modified GAC had the highest removal for COD (86%) and/or NH3N (92%) compared to ozonation alone (COD: 35%; NH3-N: 50%) at the same initial COD and/or NH3-N concentrations of 8000 and 2620mg/L, respectively. Although the integrated treatment was more effective than ozonation alone for treating stabilized leachate, the results suggested that it could not generate treated effluent that complied with the COD limit of lower than 200 mg/L and the NH3-N discharge standard of less than 5 mg/L. Therefore, further biological treatments to complement the degradation of the leachate are still required to meet the environmental legislation. (c) 2006 Elsevier B.V. All rights reserved.