The aim of this work is to study the viability of the H2O2 Promoted Catalytic Wet Air Oxidation (PP-CWAO) process, using activated carbon (AC) as catalyst, to increase the biodegradability of phenolic aqueous solutions. Seventy-two hours experiments were performed in a trickle bed reactor at 140 degrees C and 2 bar of oxygen partial pressure. Feed concentrations, in terms of theoretical chemical oxygen demand (ThCOD), were 11.8 g COD1(-1) for phenol, 12.6 g COD1(-1) for o-cresol and 8.0 g COD1(-1) for p-nitrophenol. Air was used as main oxidant and 20% of the stoichiometric amount of H2O2 needed for pollutant complete mineralisation was added as oxidation promoter. Adding H2O2 to the CWAO process not only increases pollutant removal but also leads to higher mineralisation of the remaining oxidation products. For instance, removal of phenol, o-cresol and p-nitrophenol increase from 45, 33 and 15% in the CWAO process to 64, 64 and 49% in the PP-CWAO process. In addition, the PP-CWAO process leads to better biodegradability enhancements, when compared to CWAO, as demonstrated by the respirometric tests. However, it is still necessary to improve the oxidation step in order to assure more biodegradable effluents that could be combined with a subsequent biological wastewater plant. (C) 2007 Elsevier B.V. All rights reserved.