Fulvic acid (FA) is known to be present at high concentration in leachates from "mature" and "old" landfills. In this work, the catalytic wet air oxidation (CWAO) of FA as a model of refractory organics of stabilized leachate was studied with activated carbon (AC) as catalyst and potassium persulfate (K2S2O8) as promoter. The effect of temperature and the amount of AC and K2S2O8 on the degradation of FA were investigated. Results revealed that FA could be efficiently degraded in the K2S2O8/AC system. At 150 degrees C and 0.5 MPa oxygen pressure, almost complete FA conversion and 77.8% COD removal were achieved after 4 h of treatment. The biodegradability of BOD5/COD ratio increased from 0.13 of raw FA solution to 0.95 after CWAO. AC exhibited good stability in the catalytic wet oxidation of FA. When AC was used for the fourth time, the FA conversion was still over 60%. Additionally, radical mechanism was studied and three radical scavengers (methanol, tert-butyl alcohol, sodium bromide) were used to determine the kind of major active species taking part in the degradation of FA. It was assumed that hydroxyl radical ((OH)-O-center dot) and sulfate radical (SO4 center dot-) played a major role in the FA degradation. (C) 2012 Elsevier B.V. All rights reserved.