Catalytic wet oxidation of different organic pollutant in an industrial process water treatment increases its importance with respect to sustainable chemical technologies R&D. Trickle-bed reactor can enable capacity demands, high pressure and temperature operation conditions using sufficiently active catalyst with a long term stability. The paper deals with phenol removal by wet oxidation on an active carbon extruded catalyst using high-pressure laboratory trickle-bed reactor. To suppress external mass transfer resistance both a diluted catalytic bed by inert fines and liquid feed rate modulation were applied. The forced pulsing flow regime was created by ON-OFF liquid feed flow modulation. Feed period length and split can influence both reactor throughput and its hydrodynamics, e.g., liquid holdup, wetting efficiency and pressure drop. If the period length was comparable with an effective liquid residence time, mean dynamic liquid holdup at periodic operation mode was found to be lower than the steady state one and thus phenol conversion was found to be 10% higher than that measured at steady state conditions. (C) 2003 Elsevier Science B.V. All rights reserved.