The fate of the azo dye Direct Yellow 12 (DY 12) were investigated with partially granulated anaerobic mixed culture using glucose (3000 mg l(-1) COD) as carbon source and electron donor during batch incubation. Monod's zerro-, first-, and second-order reaction kinetics were tested to determine the most suitable substrate removal kinetic. COD was removed according to the first-order reaction kinetic. Since increasing dye concentrations significantly inhibited substrate degradation, different kinetics were tested in order to detect the type and the level of inhibition. Aromatic amine and volatile fatty acid accumulation was observed proportionally at a higher DY 12 concentration. A competitive kinetic model that describes the anaerobic co-metabolism of increasing DY 12 dye concentrations with glucose as co-substrate was developed based on the experimental data. The inhibition constants (KID) were between 1055 and 255 mg l(-1) for batch reactors containing between 400 and 3200 mg l(-1) of DY 12 dye. In a sample containing 200 mg l(-1) of DY 12, no inhibition was observed. The slope of the inhibited reaction was K-s/R-max (1 + IIKID) and the R-max values did not vary significantly. The rate of substrate removal was competitively inhibited by 90%. in reactors containing 3200 mg l(-1) of DY 12 compared to dye-free reactors for 1000 mg l(-1) of glucose-COD. In this type of inhibition, the substrate removal rates was 1.33 mg l(-1) h and the K-s value was 14301 mg l(-1) in batch reactors containing for 3200 mg l(-1) of DY 12 dye, and 1000 mg l(-1) of glucose-COD. (C) 2004 Elsevier Ltd. All rights reserved.