Temperature is an important environmental variable that can strongly affect the performance of anaerobic reactors working at ambient temperatures. This study presents a mechanistic mathematical model which depends in an explicit way on the operating temperature. The cardinal temperature model function is proposed to describe the temperature dependence of the kinetic parameters and the experimental data from an UASB-degasification system was used to calibrate and validate the model. The performance of the model is compared with the classic Arrhenius approach. The results showed that the temperature-based model of the anaerobic digestion is able to reproduce a long-term reactor operation in terms of biogas production and the concentration of organic matter at fluctuating ambient temperature. (C) 2013 Elsevier Ltd. All rights reserved.