Catalytic wet-air oxidation of acidic and alkaline Kraft bleach plant effluents was investigated in a batch slurry reactor over TiO2 and Ru)3 wt.%)/TiO2 solids. At 463 K and 5.5 MPa total pressure, a drastic extent of total organic carbon (TOC) removal was observed with addition of the titanium dioxide support (TOC conversions up to 87%). The rate of TOC removal was further enhanced by deposition of metallic ruthenium on the TiO2 support. In that case, the decolorized liquid effluents were produced, with very low TOC values (TOC removal >99.6%). constituted of traces of acetic acid. No leaching of Ru or Ti was detected by ICP-AES analysis to the detection limits of 0.2 and 0.1 mg l(-1), respectively. The overall kinetics of TOC removal was described by a simplified lumped kinetic model, assuming second-order kinetics for all reaction steps in a triangular reaction scheme. This model and its calculated parameters successfully predicted the time course and distribution of carbon lumps involved in the reactions. (C) 2003 Elsevier B.V. All rights reserved.