A kinetic model of the anaerobic digestion of wastewater derived from the pressing of orange peel is proposed. The process was conducted in a laboratory-scale, completely stirred tank reactor operating in batch mode at mesophilic temperature. The anaerobic biodegradability of the physical chemical pretreated wastewater was found to be 84%, while methane yield coefficient was 297 NmL CH(4)/g COD removed. The mathematical model based on six segregated differential equations simulated the evolution of the concentration of carbon in different forms from biodegradable and non-biodegradable substrate. The transformation steps followed first or second-order kinetics. The kinetic constants corresponding to these stages were found to decrease markedly with the load added to the reactor, showing the occurrence of an inhibition process. The small deviations obtained between the experimental and simulated values demonstrated the suitability of the mathematical model in predicting the behaviour of the microorganisms involved in the anaerobic digestion of this wastewater. (C) 2010 Elsevier Ltd. All rights reserved.