This paper presents the application of the ADM1 model to simulate the dynamic behaviour of an anaerobic reactor treating the condensate effluent (EC) generated in a sulphite pulp mill. The model was implemented in the simulation software AQUASIM (R) 2.1d and its predictions were compared to experimental data obtained in lab-scale semi-continuous assays treating the industrial effluent. Sensitivity analysis revealed high influence of kinetic parameters on the process behaviour, which were further estimated: maximum specific uptake rate (k(m) = 13.2 d(-1)) and half-saturation constant (K-s = 0.06 kg COD m(-3)). The accuracy of the optimised parameters was assessed against experimental data from a second lab-scale reactor treating EC effluent with an additional carbon source (molasses). It was concluded that the model predicted reasonably the dynamic behaviour of the anaerobic reactor under different loading rates. In addition, simulations successfully predicted a better stability and performance of the process (lower VIA accumulation and higher COD removal and methane production) for the EC treatment when an external carbon source is added to the reactor, specifically at high organic loads (2 kg COD m(-3) d(-1) or higher). The model was not able to describe adequately the reactor behaviour at high organic loads when molasses was not added, thus application of the model for the anaerobic treatment of EC effluent needs to be further evaluated. (C) 2008 Elsevier B.V. All rights reserved.