Leachate from a landfill site of old landfill-age are containing refractory organics and high concentration of ammonium nitrogen. It is not very clear how refractory organics from advanced treatment of landfill leachate behaves in natural environment. In this study, four treatment processes were employed, including biological activated carbon fluidized bed (BACFB) process, pre-ozone Ireatuent-BACFB process (ozone-BACFB), internediate ozone treatment-BACFB process (BACFB-ozone-BACFB) and post-ozone treatment-BACFB process (BACFB-ozone).Then landfill leachate and process treated water from the treatment processes were evaluated for assessment of the performance of the above processes from biological oxygen consumption point of view. The intermediate ozone treatment-BACFB process removed 77% of dissolved organic carbon (DOC). The biological oxygen consumption over a period of 5 days of a landfill leachate was 20 mg·l^-1, but the value of that a period of 100 days was over 300 mg·l^-1. Therefore, refractory organics in landfill Ieacate can become source of organic pollution. On the other hand, the biological oxygen consumption over a period of 100 days of effluent from intermediate ozone treatment-BACFB process was 15 mg·L^-1, much lower than that of the landfill leacate. Intermediate ozone treatment-BACFB process was thus efficient advanced treatment system from biological oxygen consumption point of view.