A comparative study of the oxidative degradation of trans-3,4-dihydroxycinnamic acid was carried out using three different methods, two of which have in common the use of electrogenerated ozone as a potential oxidant: (i) direct electrolysis; (ii) external cell chemical reactions with O-3; and (iii) a 'cathodic oxidation' in which an O-2/O-3 mixture is fed into the cathodic compartment containing the organic substrate; H2O2 produced reacts with ozone to yield radicals that bring about the demolition of the organic compound. The nature products formed by the direct electrochemical oxidation depends on potential. The degradation of dihydroxy-acid is observed only at relatively high potentials, where radical oxygen species are formed ill a high amount by the oxidation of water. At relatively lower potentials the process shows stirring dependence and leads essentially to one oxidation product which is adsorbed on the electrode. A comparative examination of the results, considering also the requested amount of ozone as a parameter, shows that the external cell and cathodic oxidation are the most efficient methods. This confirms our previous data on the oxidation of phenolic compounds, and the cathodic oxidation with ozone emerges as a promising approach in the abatement of pollutants. (C) 2000 Elsevier Science Ltd. All rights reserved.