The process kinetics of the mesophilic (35 degreesC) anaerobic digestion of ice-cream wastewater was investigated. The Monod equation and the Contois equation were used to develop two basic steady-state models. The kinetic parameters required for the application for the steady-state models were determined using a laboratory-scale continuously stirred tank reactor (5 1) fed with a synthetic ice-cream wastewater at a range of hydraulic retention times (2.99-7.45 days). Both models were evaluated with a set of routine analytical data obtained from a pilot-scale (5 m(3)) anaerobic contact digester treating the ice-cream wastewater at a commercial site, The steady-state model obtained with the Contois equation was more suitable than that obtained with the Monod equation for describing the process kinetics of the pilot-scale anaerobic contact process. The main reason for this is that the kinetic model based on the Contois equation considers the effect of any changes in influent substrate concentration in its prediction. (C) 2002 Elsevier Science Ltd. All rights reserved.