Scrubber-washed wastewater of Sludge drying process in sludge melting system contains both ammonium nitrogen and dissolved organic carbon (DOC) in high concentrations, and is also found to contain compounds which show inhibition to nitrification. In batch experiments, the inhibitory compounds are found to be biodegradable and also absorbable to activated carbon. Nitrification activity can be recovered immediately after the inhibition compounds are removed.<br>Therefore in this study, biological treatment process using a expanded-bed activated carbon reactor is applied to accomplish nitrification as well as removal of organic compounds from the wastewater. Under the condition where DO is more than 1mg&middot;l^-1, TKN loading rate can be raised till 5mgN&middot;(gGAC)^-1&middot;d^-1 to attain more than 90% nitrification of influent nitrogen. DOC concentration in the bio-reactor should be maintained less than 40mgC&middot;l^-1 for avoiding inhibition and assuring nitrification.