The influence of kinetic and hydrodynamic factors in electrochemical reactors used in the removal of pollutants from industrial wastewater is shown, distinguishing between the two main types of reactions, namely direct and mediated electro-oxidation. The effect of stirring during treatment of four different types of wastewater is reported. Whilst for direct electro-oxidation of pollutants, the influence of agitation on the performance of the reactor can be easily predicted from a mass transfer correlation, its effect during electro-oxidation mediated in the homogeneous phase by a redox couple is not straightforward. The Hatta number can be a useful criterion to apply to electrochemical reactors performing mediated oxidation of compounds (in analogy to gas-liquid reactions), so as to define whether the reaction occurs in the bulk of the reactor or near the electrode, and thus can be affected differently by stirring. The hydrodynamic conditions in the reactor for treatment of industrial wastewater can affect the differential selectivity of the removal of pollutants and this can be used for optimising the performance of the reactor with respect to a target pollutant. (c) 2006 Society of Chemical Industry.