AbstractThe performance of a packed‐bed biological reactor has been analysed under sinusoidal variations of substrate concentration and temperature for zero‐order, first‐order and Michaelis‐Menten kinetics. The model equations were solved by the method of orthogonal collocation. The results show that the cyclic steady‐state conversion is not affected by cyclic variations in the feed concentration. However, cyclic temperature variations with an amplitude of 20°C significantly decrease the mean exit concentration for zero‐order and Michaelis‐Menten kinetics compared to the constant‐temperature case. The approach to cyclic steady‐state conditions is estimated to be somewhat flower for zero‐order kinetics than for the other kinetics models investigated. We conclude that temperature variations during the day or changes in the performance of upstream plant will not adversely affect the performance of a packed‐