The application of a new control strategy to optimize the degradation rate of organic toxic compounds is presented. An optimal control strategy called event-driven time optimal control was applied to biodegrade, in a discontinuous reactor, wastewater containing 4-chlorophenol as an inhibitory compound model. The strategy estimates the oxygen mass uptake rate, which is linearly related to the substrate uptake rate, by measuring only the dissolved oxygen concentration and the volume of the reactor. Using this estimation, the optimal strategy sets the influent flow rate such that the substrate degradation rate is maintained around its maximal value as long as possible, thus minimizing the reaction time. The strategy was tested for the degradation of different influent concentrations of 4-chlorophenol between 175 and 625 mg L-1. Also, the robustness of the strategy under different airflow rates was studied. It was concluded that the practical implementation of the optimal strategy was possible and very successful. (c) 2006 Society of Chemical Industry.