Wet oxidation was investigated for its process performance on methane fermentation of newspaper waste. The mechanisms of solubilization of newspaper waste were investigated using the following criteria: destruction of total COD (TCOD), production of soluble COD (SCOD), production of volatile fatty acids, production of soluble carbohydrates, production of soluble lignin derivatives (SLD), production of furan (F) and destruction of lignin and cellulose. Wet oxidation was carried out at 170, 190, and 210degreesC, with a retention time of 1 h. The highest removal efficiencies of TCOD and cellulose were achieved at 210degreesC, approximately 40% and 69% were destroyed, respectively. On the other hand, highest lignin removal efficiency was achieved at 190degreesC in which approximately 65% was removed. Batch methane fermentation tests were performed in 2-1 glass bottles filled with the wet oxidized newspaper samples. Methane fermentation of newspaper pretreated,at 190degreesC, gave the highest CH4 conversion efficiency (59% of the initial TCOD was recovered as CH4 gas). Anaerobic cellulose removals varied from 74% to 88%. (C) 2003 Elsevier Ltd. All rights reserved.